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The following document is from the Microsoft Programmer’s Library 1.3 CD-ROM.

Microsoft  Macro Assembler - Programmer's Guide








────────────────────────────────────────────────────────────────────────────
                Microsoft (R) Macro Assembler - Programmer's Guide

                                Version 6.0
────────────────────────────────────────────────────────────────────────────


                For MS (R) OS/2 and MS-DOS (R) Operating Systems








Microsoft Corporation

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NEC and V25 are registered trademarks and V35 is a trademark
of NEC Corporation.

Document No. LN06556-0291

10 9 8 7 6 5 4 3 2 1







Introduction
        New and Extended Features in MASM 6.0
            New MASM Language Features
            ML and MASM Command Lines
            Compatibility with Earlier Versions of MASM
        Scope and Organization of this Book
        Books for Further Reading
        Document Conventions
        Getting Assistance and Reporting Problems

Chapter 1  Understanding Global Concepts

        1.1   The Processing Environment
            1.1.1    8086-Based Processors
            1.1.2    Operating Systems
            1.1.3    Segmented Architecture
            1.1.4    Segment Protection
            1.1.5    Segmented Addressing
            1.1.6    Segment Arithmetic
        1.2   Language Components of MASM
            1.2.1    Reserved Words
            1.2.2    Identifiers
            1.2.3    Predefined Symbols
            1.2.4    Integer Constants and Constant Expressions
            1.2.5    Operators
            1.2.6    Data Types
            1.2.7    Registers
            1.2.8    Statements
        1.3   The Assembly Process
            1.3.1    Generating and Running Executable Programs
            1.3.2    Using the OPTION Directive
            1.3.3    Conditional Directives
        1.4   Related Topics in Online Help

Chapter 2  Organizing MASM Segments

        2.1   Overview of Memory Segments
        2.2   Using Simplified Segment Directives
            2.2.1    Defining Basic Attributes with .MODEL
            2.2.2    Specifying a Processor and Coprocessor
            2.2.3    Creating a Stack
            2.2.4    Creating Data Segments
            2.2.5    Creating Code Segments
            2.2.6    Starting and Ending Code with .STARTUP and .EXIT
        2.3   Using Full Segment Definitions
            2.3.1    Defining Segments with the SEGMENT Directive
            2.3.2    Controlling the Segment Order
            2.3.3    Setting the ASSUME Directive for Segment Registers
            2.3.4    Defining Segment Groups
        2.4   Related Topics in Online Help

Chapter 3  Using Addresses and Pointers

        3.1   Programming Segmented Addresses
            3.1.1    Initializing Default Segment Registers
            3.1.2    Near and Far Addresses
        3.2   Specifying Addressing Modes
            3.2.1    Register Operands
            3.2.2    Immediate Operands
            3.2.3    Direct Memory Operands
            3.2.4    Indirect Memory Operands
        3.3   Accessing Data with Pointers and Addresses
            3.3.1    Defining Pointer Types with TYPEDEF
            3.3.2    Defining Register Types with ASSUME
            3.3.3    Basic Pointer and Address Operations
        3.4   Related Topics in Online Help

Chapter 4  Defining and Using Integers

        4.1   Declaring Integer Variables
            4.1.1    Allocating Memory for Integer Variables
            4.1.2    Data Initialization
        4.2   Integer Operations
            4.2.1    Moving and Loading Integers
            4.2.2    Pushing and Popping Stack Integers
            4.2.3    Adding and Subtracting Integers
            4.2.4    Multiplying and Dividing Integers
        4.3   Manipulating Integers at the Bit Level
            4.3.1    Logical Operations
            4.3.2    Shifting and Rotating Bits
            4.3.3    Multiplying and Dividing with Shift Instructions
        4.4   Related Topics in Online Help

Chapter 5  Defining and Using Complex Data Types

        5.1   Arrays and Strings
            5.1.1    Declaring and Referencing Arrays
            5.1.2    Declaring and Initializing Strings
            5.1.3    Processing Arrays and Strings
        5.2   Structures and Unions
            5.2.1    Declaring Structure and Union Types
            5.2.2    Defining Structure and Union Variables
            5.2.3    Referencing Structures, Unions, and Fields
            5.2.4    Nested Structures and Unions
        5.3   Records
            5.3.1    Declaring Record Types
            5.3.2    Defining Record Variables
            5.3.3    Record Operators
        5.4   Related Topics in Online Help

Chapter 6  Using Floating-Point and Binary Coded Decimal Numbers

        6.1   Using Floating-Point Numbers
            6.1.1    Declaring Floating-Point Variables and Constants
            6.1.2    Storing Numbers in Floating-Point Format
        6.2   Using a Math Coprocessor
            6.2.1    Coprocessor Architecture
            6.2.2    Instruction and Operand Formats
            6.2.3    Coordinating Memory Access
            6.2.4    Using Coprocessor Instructions
        6.3   Using Emulator Libraries
        6.4   Using Binary Coded Decimal Numbers
            6.4.1    Defining BCD Constants and Variables
            6.4.2    Calculating with BCDs
        6.5   Related Topics in Online Help

Chapter 7  Controlling Program Flow

        7.1   Jumps
            7.1.1    Unconditional Jumps
            7.1.2    Conditional Jumps
        7.2   Loops
            7.2.1    Loop-Generating Directives
            7.2.2    Writing Loop Conditions
        7.3   Procedures
            7.3.1    Defining Procedures
            7.3.2    Passing Arguments on the Stack
            7.3.3    Declaring Parameters with the PROC Directive
            7.3.4    Using Local Variables
            7.3.5    Creating Local Variables Automatically
            7.3.6    Declaring Procedure Prototypes
            7.3.7    Calling Procedures with INVOKE
            7.3.8    Generating Prologue and Epilogue Code
        7.4   DOS Interrupts
            7.4.1    Calling DOS and ROM-BIOS Interrupts
            7.4.2    Replacing or Redefining Interrupt Routines
        7.5   Related Topics in Online Help

Chapter 8  Sharing Data and Procedures among Modules and Libraries

        8.1   Selecting Data-Sharing Methods
        8.2   Sharing Symbols with Include Files
            8.2.1    Organizing Modules
            8.2.2    Declaring Symbols Public and External
            8.2.3    Positioning External Declarations
        8.3   Using Alternatives to Include Files
            8.3.1    PUBLIC and EXTERN
            8.3.2    Other Alternatives
        8.4   Developing Libraries
            8.4.1    Associating Libraries with Modules
            8.4.2    Using EXTERN with Library Routines
        8.5   Related Topics in Online Help

Chapter 9  Using Macros

        9.1   Text Macros
        9.2   Macro Procedures
            9.2.1    Creating Macro Procedures
            9.2.2    Passing Arguments to Macros
            9.2.3    Specifying Required and Default Parameters
            9.2.4    Defining Local Symbols in Macros
        9.3   Assembly Time Variables and Macro Operators
            9.3.1    Text Delimiters (< >) and the Literal-Character
                        Operator (!)
            9.3.2    Expansion Operator (%)
            9.3.3    Substitution Operator (&)
        9.4   Defining Repeat Blocks with Loop Directives
            9.4.1    REPEAT Loops
            9.4.2    WHILE Loops
            9.4.3    FOR Loops and Variable-Length Parameters
            9.4.4    FORC Loops
        9.5   String Directives and Predefined Functions
        9.6   Returning Values with Macro Functions
        9.7   Advanced Macro Techniques
            9.7.1    Nesting Macro Definitions
            9.7.2    Testing for Argument Type and Environment
            9.7.3    Using Recursive Macros
        9.8   Related Topics in Online Help

Chapter 10  Managing Projects with NMAKE

        10.1  Overview of NMAKE
        10.2  Running NMAKE
        10.3  NMAKE Description Files
            10.3.1    Description Blocks
            10.3.2    Pseudotargets
            10.3.3    Comments
            10.3.4    Macros
            10.3.5    Inference Rules
            10.3.6    Directives
            10.3.7    Preprocessing Directives
            10.3.8    Extracting Filename Components
        10.4  Command-Line Options
        10.5  NMAKE Command File
        10.6  The TOOLS.INI File
        10.7  Inline Files
        10.8  Sequence of NMAKE Operations
        10.9  A Sample NMAKE Description File
        10.10 Differences between NMAKE and MAKE
        10.11 Using NMK
        10.12 Using Exit Codes with NMAKE
        10.13 Related Topics in Online Help

Chapter 11  Creating Help Files with HELPMAKE

        11.1  Structure and Contents of a Help Database
            11.1.1    Contents of a Help File
            11.1.2    Help File Formats
        11.2  Invoking HELPMAKE
        11.3  HELPMAKE Options
            11.3.1    Options for Encoding
            11.3.2    Options for Decoding
            11.3.3    Options for Help
        11.4  Creating a Help Database
        11.5  Help Text Conventions
            11.5.1    Structure of the Help Text File
            11.5.2    Local Contexts
            11.5.3    Context Prefixes
            11.5.4    Hyperlinks
        11.6  Using Help Database Formats
            11.6.1    QuickHelp Format
            11.6.2    Rich Text Format
            11.6.3    Minimally Formatted ASCII Format
        11.7  Related Topics in Online Help

Chapter 12  Linking Object Files with LINK

        12.1  Overview
        12.2  LINK Output Files
        12.3  LINK Syntax and Input
            12.3.1    The objfiles Field
            12.3.2    The exefile Field
            12.3.3    The mapfile Field
            12.3.4    The libraries Field
            12.3.5    The deffile Field
            12.3.6    Examples
        12.4  Running LINK
            12.4.1    Specifying Input with LINK Prompts
            12.4.2    Specifying Input in a Response File
        12.5  LINK Options
            12.5.1    Specifying Options
            12.5.2    The /ALIGN Option
            12.5.3    The /BATCH Option
            12.5.4    The /CO Option
            12.5.5    The /CPARM Option
            12.5.6    The /DOSSEG Option
            12.5.7    The /DSALLOC Option
            12.5.8    The /EXEPACK Option
            12.5.9    The /FARCALL Option
            12.5.10   The /HELP Option
            12.5.11   The /HIGH Option
            12.5.12   The /INCR Option
            12.5.13   The /INFO Option
            12.5.14   The /LINE Option
            12.5.15   The /MAP Option
            12.5.16   The /NOD Option
            12.5.17   The /NOE Option
            12.5.18   The /NOFARCALL Option
            12.5.19   The /NOGROUP Option
            12.5.20   The /NOI Option
            12.5.21   The /NOLOGO Option
            12.5.22   The /NONULLS Option
            12.5.23   The /NOPACKC Option
            12.5.24   The /OV Option
            12.5.25   The /PACKC Option
            12.5.26   The /PACKD Option
            12.5.27   The /PADC Option
            12.5.28   The /PADD Option
            12.5.29   The /PAUSE Option
            12.5.30   The /PM Option
            12.5.31   The /Q Option
            12.5.32   The /SEG Option
            12.5.33   The /STACK Option
            12.5.34   The /TINY Option
            12.5.35   The /W Option
            12.5.36   The /? Option
        12.6  Setting Options with the LINK Environment Variable
            12.6.1    Setting the LINK Environment Variable
            12.6.2    Behavior of the LINK Environment Variable
            12.6.3    Clearing the LINK Environment Variable
        12.7  Using Overlays under DOS
            12.7.1    Restrictions on Overlays
            12.7.2    Specifying Overlays
            12.7.3    How Overlays Work
            12.7.4    Overlay Interrupts
        12.8  Linker Operation under DOS
            12.8.1    Segment Alignment
            12.8.2    Frame Number
            12.8.3    Segment Order
            12.8.4    Combined Segments
            12.8.5    Groups
            12.8.6    Fixups
        12.9  LINK Temporary Files
        12.10 LINK Exit Codes
        12.11 Related Topics in Online Help

Chapter 13  Module-Definition Files

        13.1  Overview
        13.2  Module Statements
            13.2.1    Syntax Rules
            13.2.2    Reserved Words
        13.3  The NAME Statement
        13.4  The LIBRARY Statement
        13.5  The DESCRIPTION Statement
        13.6  The STUB Statement
        13.7  The EXETYPE Statement
        13.8  The PROTMODE Statement
        13.9  The REALMODE Statement
        13.10 The STACKSIZE Statement
        13.11 The HEAPSIZE Statement
        13.12 The CODE Statement
        13.13 The DATA Statement
        13.14 The SEGMENTS Statement
        13.15 CODE, DATA, and SEGMENTS Attributes
        13.16 The OLD Statement
        13.17 The EXPORTS Statement
        13.18 The IMPORTS Statement
        13.19 Related Topics in Online Help

Chapter 14  Customizing the Microsoft Programmer's WorkBench

        14.1  Setting Switches
            14.1.1    Changing Current Assignments and Switch Settings
            14.1.2    Editing the TOOLS.INI Initialization File
        14.2  Assigning Functions to Keystrokes
        14.3  Writing Macros
            14.3.1    Macro Syntax
            14.3.2    Macro Responses
            14.3.3    Macro Arguments
            14.3.4    Macro Conditionals
            14.3.5    Recording Macros
            14.3.6    Temporary Macros
        14.4  Related Topics in Online Help

Chapter 15  Debugging Assembly-Language Programs with CodeView

        15.1  Understanding Windows in CodeView
        15.2  Overview of Debugging Techniques
        15.3  Viewing and Modifying Program Data
            15.3.1    Displaying Variables in the Watch Window
            15.3.2    Displaying Expressions in the Watch Window
            15.3.3    Displaying Local Variables
            15.3.4    Using Pointers to Display Arrays and Strings
            15.3.5    Displaying Structures
            15.3.6    Using Quick Watch
            15.3.7    Displaying Memory
            15.3.8    Displaying the Processor Registers
            15.3.9    Modifying the Values of Variables, Memory,
                            and Registers
        15.4  Controlling Execution
            15.4.1    Continuous Execution
            15.4.2    Single-Stepping
            15.4.3    Changing the Program Display Mode
        15.5  Replaying a Debug Session
        15.6  Advanced CodeView Techniques
        15.7  CodeView Command-Line Options
        15.8  Customizing CodeView with the TOOLS.INI File
        15.9  Related Topics in Online Help

Chapter 16  Converting C Header Files to MASM Include Files

        16.1  Basic H2INC Operation
        16.2  H2INC Syntax and Options
        16.3  Converting Data and Data Structures
            16.3.1    User-Defined and Predefined Constants
            16.3.2    Variables
            16.3.3    Pointers
            16.3.4    Structures and Unions
            16.3.5    Bit Fields
            16.3.6    Enumerations
            16.3.7    Type Definitions
        16.4  Converting Function Prototypes
        16.5  Related Topics in Online Help

Chapter 17  Writing OS/2 Applications

        17.1  OS/2 Overview
        17.2  Differences between DOS and OS/2
        17.3  A Sample Program
        17.4  Building an OS/2 Application
        17.5  Binding OS/2 MASM Programs
        17.6  Register and Memory Initialization
        17.7  Other OS/2 Utilities
        17.8  Module-Definition Files
        17.9  Related Topics in Online Help

Chapter 18  Creating Dynamic-Link Libraries

        18.1  DLL Overview
        18.2  DLL Programming Requirements
            18.2.1    Separate Stack and Data Requirement
            18.2.2    Floating-Point Math Requirement
            18.2.3    Re-entrance Requirement
            18.2.4    Segment Strategy in a DLL
        18.3  Writing the DLL Code
            18.3.1    Choosing Module Attributes
            18.3.2    Defining Procedures and Data
            18.3.3    Creating Initialization and Termination Code
        18.4  Building the DLL
            18.4.1    Writing the Module-Definition File
            18.4.2    Generating an Import Library with IMPLIB
            18.4.3    Creating and Using the DLL
        18.5  Related Topics in Online Help

Chapter 19  Writing Memory-Resident Software

        19.1  Terminate-and-Stay-Resident Programs
            19.1.1    Structure of a TSR
            19.1.2    Passive TSRs
            19.1.3    Active TSRs
        19.2  Interrupt Handlers in Active TSRs
            19.2.1    Auditing Hardware Events for TSR Requests
            19.2.2    Monitoring System Status
            19.2.3    Determining Whether to Invoke the TSR
        19.3  Example of a Simple TSR: ALARM
        19.4  Using DOS in Active TSRs
            19.4.1    Understanding DOS Stacks
            19.4.2    Determining DOS Activity
            19.4.3    Interrupting DOS Functions
            19.4.4    Monitoring the Critical Error Flag
        19.5  Preventing Interference
            19.5.1    Trapping Errors
            19.5.2    Preserving an Existing Condition
            19.5.3    Preserving Existing Data
        19.6  Communicating through the Multiplex Interrupt
            19.6.1    The Multiplex Handler
            19.6.2    Using the Multiplex Interrupt Under DOS Version 2.x
        19.7  Deinstalling TSRs
        19.8  Example of an Advanced TSR: SNAP
            19.8.1    Building SNAP.EXE
            19.8.2    Outline of SNAP
        19.9  Related Topics in Online Help

Chapter 20  Mixed-Language Programming

        20.1  Naming and Calling Conventions
            20.1.1    Naming Conventions
            20.1.2    The C Calling Convention
            20.1.3    The Pascal Calling Convention
            20.1.4    The Standard Calling Convention
        20.2  Writing the Assembly-Language Procedure
        20.3  The MASM/High-Level-Language Interface
            20.3.1    The C/MASM Interface
            20.3.2    The FORTRAN/MASM Interface
            20.3.3    The Basic/MASM Interface
            20.3.4    The Pascal/MASM Interface
            20.3.5    The QuickPascal/MASM Interface
        20.4  Related Topics in Online Help

Appendix A  Differences between MASM 6.0 and 5.1

        A.1   New Features of Version 6.0
            A.1.1    The Assembler, Environment, and Utilities
            A.1.2    Segment Management
            A.1.3    Data Types
            A.1.4    Procedures, Loops, and Jumps
            A.1.5    Simplifying Multiple-Module Projects
            A.1.6    Expanded State Control
            A.1.7    New Processor Instructions
            A.1.8    Renamed Directives
            A.1.9    Macro Enhancements
            A.1.10   MASM 6.0 Programming Practices
        A.2   Compatibility between MASM 5.1 and 6.0
            A.2.1    Rewriting Code for Compatibility
            A.2.2    Using the OPTION Directive
            A.2.3    Changes to Instruction Encodings

Appendix B  BNF Grammar


Appendix C  Generating and Reading Assembly Listings

        C.1   Generating Listing Files
            C.1.1    Generating a First Pass Listing
            C.1.2    Controlling the Contents of the Listing File
            C.1.3    Controlling Listing Information on Macros
            C.1.4    Controlling the Page Format
            C.1.5    Precedence of Command-Line Options and Listing
                Directives
        C.2   Reading the Listing File
            C.2.1    Code Generated
            C.2.2    Error Messages
            C.2.3    Symbols and Abbreviations
            C.2.4    Reading Tables in a Listing File

Appendix D  MASM Reserved Words

        D.1   Operands and Symbols
            D.1.1    Special Operands for the 80386/486
            D.1.2    Predefined Symbols
        D.2   Registers
        D.3   Operators and Directives
        D.4   Processor Instructions
            D.4.1    8086/8088 Processor Instructions
            D.4.2    80186 Processor Instructions
            D.4.3    80286 Processor Instructions
            D.4.4    80286 and 80386 Privileged-Mode Instructions
            D.4.5    80386 Processor Instructions
            D.4.6    80486 Processor Instructions
            D.4.7    Instruction Prefixes
        D.5   Coprocessor Instructions
            D.5.1    8087 Coprocessor Instructions
            D.5.2    80287 Privileged-Mode Instruction
            D.5.3    80387 Instructions

Appendix E  Default Segment Names


Appendix F  Error Messages

        F.1   BIND Error Messages
        F.2   CodeView Error Messages
        F.3   EXEHDR Error Messages
        F.4   HELPMAKE Error Messages
            F.4.1    HELPMAKE Fatal Errors
            F.4.2    HELPMAKE Errors
            F.4.3    HELPMAKE Warnings
        F.5   H2INC Error Messages
            F.5.1    H2INC Fatal Errors
            F.5.2    H2INC Compilation Errors
            F.5.3    H2INC Warnings
        F.6   IMPLIB Error Messages
            F.6.1    IMPLIB Fatal Errors
            F.6.2    IMPLIB Errors
        F.7   LIB Error Messages
            F.7.1    LIB Fatal Errors
            F.7.2    LIB Errors
            F.7.3    LIB Warnings
        F.8   LINK Error Messages
            F.8.1    LINK Fatal Errors
            F.8.2    LINK Errors
            F.8.3    LINK Warnings
        F.9   ML Error Messages
            F.9.1    ML Fatal Errors
            F.9.2    ML Errors
            F.9.3    ML Warnings
        F.10  NMAKE Error Messages
            F.10.1   NMAKE Fatal Errors
            F.10.2   NMAKE Errors
            F.10.3   NMAKE Warnings
        F.11  PWB.COM Error Messages
        F.12  PWBRMAKE Error Messages
            F.12.1   PWBRMAKE Fatal Errors
            F.12.2   PWBRMAKE Warnings

Glossary


Index




Introduction
────────────────────────────────────────────────────────────────────────────

The Microsoft (R) Macro Assembler Programmer's Guide provides the
information you need to write and debug assembly-language programs with the
Microsoft Macro Assembler (MASM), version 6.0. This book documents enhanced
features of the language and the programming environment for MASM 6.0. It
also describes new features that take advantage of the capabilities of the
80386/486 processors.

The Programmer's Guide is written for experienced programmers who know
assembly language and are familiar with an assembler. The book does not
teach the basics of assembly language; it does explain Microsoft-specific
features. If you want to learn or review the basics of assembly language,
refer to "Books for Further Reading" later in this introduction.

The documentation for MASM 6.0 is an integrated set, comprehensive and
cohesive. This book emphasizes writing efficient code with the new and
advanced features of MASM. Installing and Using the Professional Development
System explains not only how to set up MASM 6.0 but also how to use the
extensive online reference system, the Microsoft Advisor.

Installing and Using also introduces the integrated environment called the
Programmer's WorkBench (PWB) and shows how to manage development projects
with it. The Microsoft Macro Assembler Reference provides a full listing of
all MASM instructions, directives, statements, and operators, and it serves
as a quick reference to utility commands.

For more information on these same topics, see the online Microsoft Advisor,
which is a complete reference to Macro Assembler language topics, to the
utilities, and to PWB. You should be able to find most of the information
you need in the Microsoft Advisor. The printed documents give more in-depth
and background information.


New and Extended Features in MASM 6.0

Version 6.0 of MASM differs from version 5.1 in many ways, from optional
extensions to features that replace or modify previous assembler behavior.

MASM 6.0 includes the Programmer's WorkBench, an integrated software
development environment, and the CodeView (R) source-level debugger. From
within PWB you can edit, build, debug, or run a program, and you can perform
most of these operations with either menu selections or keyboard commands.
You can also customize PWB to suit your individual programming and editing
requirements and preferences.


New MASM Language Features

MASM 6.0 includes a number of new features, described in the list below,
designed to make programming more efficient and intuitive and to increase
your productivity. For example, MASM's new high-level-language features mean
that you can get the speed of assembly language with the ease of high-level
languages. You can also maintain your programs more easily.


    ■   MASM 6.0 has many enhancements related to types. You can now use the
        same type specifiers in initializations as in other contexts (BYTE
        instead of DB). You can also define your own types, including pointer
        types, with the new TYPEDEF directive. See Chapter 3, "Using Addresses
        and Pointers," and Chapter 4, "Defining and Using Integers."

    ■   The syntax for defining and using structures and records has been
        enhanced. You can also define unions with the new UNION directive. See
        Chapter 5, "Defining and Using Complex Data Types."

    ■   MASM now generates complete CodeView information for all types. See
        Chapter 3, "Using Addresses and Pointers," and Chapter 4, "Defining
        and Using Integers."

    ■   New control-flow directives let you use high-level-language constructs
        such as loops and if-then-else blocks defined with .REPEAT and .UNTIL
        (or .UNTILCXZ); .WHILE and .ENDW; and .IF, .ELSE, and .ELSEIF. The
        assembler generates the appropriate code to implement the control
        structure. See Chapter 7, "Controlling Program Flow."

    ■   MASM now has more powerful features for defining and calling
        procedures. The extended PROC syntax for generating stack frames has
        been enhanced in version 6.0. You can also use the PROTO directive to
        prototype a procedure, which you can then call with the INVOKE
        directive. INVOKE automatically generates code to pass arguments
        (converting them to a related type, if appropriate) and make the call
        according to the specified calling convention. See Chapter 7,
        "Controlling Program Flow."

    ■   MASM optimizes jumps by automatically determining the most efficient
        coding for a jump and then generating the appropriate code. See
        Chapter 7, "Controlling Program Flow."

    ■   Maintaining multiple-module programs is easier in MASM 6.0. The
        EXTERNDEF and PROTO directives make it easy to maintain all global
        definitions in include files shared by all the source modules of a
        project. See Chapter 8, "Sharing Data and Procedures among Modules and
        Libraries."


The assembler has many new macro features that make complex macros clearer
and easier to write:


    ■   You can specify default values for macro arguments or mark arguments
        as required. And with the VARARG keyword, one parameter can accept a
        variable number of arguments.

    ■   You can implement loops inside of macros in various ways. For example,
        the new WHILE directive expands the statements in a macro body while
        an expression is not zero.

    ■   You can define macro functions, which return text macros. Several
        predefined text macros are also provided for processing strings. Macro
        operators and other features related to processing text macros and
        macro arguments have been enhanced. For more information on all these
        macro features, see Chapter 9, "Using Macros."


Finally, MASM 6.0 has improved customizable capabilities:


    ■   With the new .STARTUP and .EXIT directives you can automatically
        generate appropriate start-up and exit code for DOS or OS/2 modules.
        See Chapter 2, "Organizing MASM Segments."

    ■   MASM 6.0 supports flat memory model, available with OS/2 version 2.0.
        In flat model, segments can be as large as 4 gigabytes instead of 64K
        (kilobytes). Offsets are 32 bits instead of 16 bits. See Chapter 2,
        "Organizing MASM Segments."

    ■   The program H2INC.EXE converts C include files to MASM include files
        and translates data structures and declarations. See Chapter 16,
        "Converting C Header Files to MASM Include Files."


MASM 6.0 includes many other minor new features as well as extended support
for features of earlier versions of MASM. These features are listed in
Appendix A, "Differences between MASM 6.0 and 5.1," with cross-references to
the chapters where they are discussed in detail.


ML and MASM Command Lines

MASM 6.0 provides a new command-line driver, ML, which is more powerful and
flexible than the previous driver (MASM). ML assembles and links with one
command. The old MASM driver command syntax is still supported, however, to
support existing batch files and makefiles that use MASM command lines.

────────────────────────────────────────────────────────────────────────────
NOTE

The name MASM has traditionally been used to refer to the Microsoft Macro
Assembler. It is used in that context throughout this book. But MASM also
refers to MASM.EXE, which has been replaced by ML.EXE. In MASM 6.0, the
MASM.EXE file is a small utility that translates command-line options to
those accepted by ML.EXE, and then calls ML.EXE. The distinction between
ML.EXE and MASM.EXE is made whenever necessary. Otherwise, MASM refers to
the assembler and its features.
────────────────────────────────────────────────────────────────────────────


Compatibility with Earlier Versions of MASM

In many cases, MASM 5.1 code will assemble without modification under MASM
6.0. However, MASM 6.0 provides a new OPTION directive that lets you
selectively modify the assembly process. In particular, you can use the M510
argument with OPTION or the /Zm command-line option to set most features to
be compatible with version 5.1 code.

See Appendix A, "Differences between MASM 6.0 and 5.1," for information
about obsolete features that will not assemble correctly under MASM 6.0. The
appendix also discusses how to update code to use the new features.


Scope and Organization of this Book

The Programmer's Guide describes how to get the most out of the Microsoft
Macro Assembler 6.0 and the Programmer's WorkBench. The book is arranged by
topic, with each topic answering a question or solving a problem. The last
section in each chapter lists topics in the online reference system that
provide additional information.

The Programmer's Guide is divided into three parts:

Part 1, "Programming in Assembly Language," explains how to program
efficiently using both the new and old features of MASM. It reviews the
basic components of assembly language and also describes the new and
enhanced features.

Part 2, "Improving Programmer Productivity," introduces the utility programs
included with MASM 6.0. These programs can help you program more quickly and
efficiently. For example, the chapters in Part 2 show you how to
automatically update your project (Chapter 10), use program lists as input
(Chapter 11), use the Microsoft linker (LINK) (Chapter 12), write
module-definition files (Chapter 13), customize PWB to suit your programming
style (Chapter 14), use the CodeView debugger to record and play back a
debugging session (Chapter 15), and easily port data structures from C
programs to MASM programs (Chapter 16).

Part 3, "Advanced Topics," covers specialized areas. It describes how to
write programs to run under OS/2 (Chapter 17) and how to build dynamic-link
libraries (Chapter 18). Chapter 19 shows how to write a
terminate-and-stay-resident (TSR) program. Chapter 20, on mixed-language
programming, defines the calling conventions and equivalent data types that
allow MASM to call and be called by C, FORTRAN, Basic, and Pascal.

In addition, six appendixes and a glossary detail the features of MASM 6.0.
Of particular interest are Appendix A, "Differences between MASM 6.0 and
5.1," and Appendix B, "BNF Grammar." Appendix A lists the new features of
MASM 6.0 and also explains how to update MASM 5.1 code. The BNF grammar, or
Backus-Naur Form for grammar notation, lets you determine the exact syntax
for any MASM language component. It clearly defines recursive definitions
and shows all the available options for any placeholder. Other appendixes
cover assembly listings, reserved words, default segment names, and error
messages.


Books for Further Reading

The following books may help you learn to program in assembly language or
write specialized programs. These books are listed only for your
convenience. Microsoft makes no specific recommendations concerning any of
these books.


Books about Programming in Assembly Language

Abrash, Michael, Zen of Assembly Language.
    Glenview, IL: Scott, Foresman and Co., 1990.

Duntemann, Jeff, Assembly Language from Square One: For the PC AT and
Compatibles.
    Glenview, IL: Scott, Foresman and Co., 1990.

Fernandez, Judi N., and Ashley, Ruth, Assembly Language Programming for the
80386.
    New York: McGraw-Hill, 1990.

Miller, Alan R., DOS Assembly Language Programming.
    San Francisco: SYBEX, 1988.

Scanlon, Leo J., 80286 Assembly Language Programming on MS-DOS Computers.
    New York: Brady Communications, 1986.

Turley, James L., Advanced 80386 Programming Techniques.
    Berkeley, CA: Osborne McGraw-Hill, 1988.


Books about DOS and BIOS

"Article 11." MS-DOS Encyclopedia.
    Redmond, WA: Microsoft Press, 1988. Contains information about
terminate-and-stay-resident programs.

Duncan, Ray, Advanced MS-DOS.
    2nd ed. Redmond, WA: Microsoft Press, 1988.

Jourdain, Robert, Programmer's Problem Solver for the IBM PC, XT and AT.
    New York: Brady Communications, 1986.

Microsoft MS-DOS Programmer's Reference.
    Redmond, WA: Microsoft Press, 1986-87.

Norton, Peter and Wilton, Richard, The New Peter Norton Programmer's Guide
to the IBM PC and PS/2.
    Redmond, WA: Microsoft Press, 1988.

Wilton, Richard, Programmer's Guide to PC & PS/2 Video Systems.
    Redmond, WA: Microsoft Press, 1987.


Books about OS/2

Duncan, Ray, Advanced OS/2 Programming.
    Redmond, WA: Microsoft Press, 1989.

───, Essential OS/2 Functions.
    Redmond, WA: Microsoft Press, 1989.

Letwin, Gordon, Inside OS/2.
    Redmond, WA: Microsoft Press, 1989.

OS/2 Programmer's Reference.
    4 vols. Redmond, WA: Microsoft Press, 1989.


Books about Other Topics

Nelson, Ross P., The 80386 Book.
    Redmond, WA: Microsoft Press, 1988.

Startz, Richard, 8087/80287/80387 for the IBM PC and Compatibles.
    Bowie, MD: Robert J. Brady Co., 1988.

Writing ROMable Code in Microsoft C.
    Costa Mesa, CA: SSI Corporation.


Document Conventions

The following document conventions are used throughout this manual:

Example of                        Description
Convention
────────────────────────────────────────────────────────────────────────────
SAMPLE2.ASM                       Uppercase letters indicate file names,
                                    segment names, registers, and terms used
                                    at the command level.

.MODEL                            Boldface type indicates
                                    assembly-language directives,
                                    instructions, type specifiers, and
                                    predefined macros, as well as keywords
                                    in other programming languages.

placeholders                      Italic letters indicate placeholders for
                                    information you must supply, such as a
                                    file name. Italics are also occasionally
                                    used for emphasis in the text.

target                            This font is used to indicate example
                                    programs, user input, and screen output.

;                                 A semicolon in the first column of an
                                    example signals illegal code. A
                                    semicolon also marks a comment.

SHIFT                             Small capital letters signify names of
                                    keys on the keyboard. Notice that a plus
                                    (+) indicates a combination of keys. For
                                    example, CTRL+E means to hold down the
                                    CTRL key while pressing the E key.

«argument»                        Items inside double square brackets are
                                    optional.

{register|memory}                 Braces and a vertical bar indicate a
                                    choice between two or more items. You
                                    must choose one of the items unless
                                    double square brackets surround the
                                    braces.

Repeating elements...             A horizontal ellipsis (...) following an
                                    item indicates that more items having
                                    the same form may appear.

Program                           A vertical ellipsis tells you that part
.                                 of a program has been intentionally
.                                 omitted.
.
Fragment


Getting Assistance and Reporting Problems

If you need help or think you have discovered a problem in the software,
please provide the following information to help us locate the problem:


    ■   The version of DOS or OS/2 that you are running

    ■   Your system configuration: the type of machine you are using, its
        total memory, and its total free memory at assembler execution time,
        as well as any other information you think might be useful

    ■   The assembly command line used, or the link command line if the
        problem occurred during linking

    ■   Any object files or libraries you linked with if the problem occurred
        at link time


If your program is very large, please try to reduce its size to the smallest
possible program that still produces the problem.

Use the Product Assistance Request form at the back of this book to send
this information to Microsoft. If you have comments or suggestions regarding
any of the books accompanying this product, please indicate them on the
Document Feedback Card at the back of this book.

If you are not a registered Macro Assembler owner, you should fill out and
return the Registration Card. This enables Microsoft to keep you informed of
updates and other information about the assembler.






Chapter 1  Understanding Global Concepts
────────────────────────────────────────────────────────────────────────────

With the development of the Microsoft Macro Assembler (MASM) version 6.0,
you now have more options available to you for approaching a programming
task. This chapter explains the general concepts of programming in assembly
language, beginning with the environment and reviewing the components you
need to work in the assembler environment. Even if you are familiar with
previous versions of MASM, you should examine this chapter for information
on new terms and features.

The first section of the chapter takes a look at the available processors
and operating systems and how they work together. It also discusses the
relationship of segmented architecture to assembly programming and the
differences it makes for programming in OS/2 rather than in DOS.

The second section describes some of the language components of MASM that
are common to most programs, such as reserved words, constant expressions,
operators, and registers. The rest of this book assumes that you understand
the information presented in this section.

The last section summarizes the assembly process, from assembling a program
through running it. You can affect this process by the way you develop your
code. Finally, this section explores how you can change the assembly process
with the OPTION directive and conditional assembly.

────────────────────────────────────────────────────────────────────────────
NOTE

This manual does not cover information specific to programming for Microsoft
Windows(tm). For information on this, see the Microsoft Windows Software
Development Kit.
────────────────────────────────────────────────────────────────────────────


1.1  The Processing Environment

The processing environment for MASM 6.0 includes the processor on which your
programs run, the operating system your programs will use, and the aspects
of the segmented architecture that influence the choice of programming
models. This section summarizes these elements of the environment and how
they affect your programming choices.


1.1.1  8086-Based Processors

The 8086 "family" of processors uses segments to control data and code. The
later 8086-based processors have larger instruction sets and more memory
capacity, but they still use the same segmented architecture. Knowing the
differences between the various 8086-based processors can help you select
the target processor for your programs.

The instruction set of the 8086 processor is upwardly compatible with its
successors. To write code that runs on the widest number of machines, select
the 8086 instruction set. By choosing to use the instruction set of a more
advanced processor, you increase the capabilities and efficiency of your
program, but you also reduce the number of systems on which the program can
run.

Table 1.1 lists modes, memory, and segment size of processors on which your
application may need to run. Each processor is discussed in more detail
below.

Table 1.1  8086 Family of Processors

╓┌────────────┌───────────────────┌──────────────────┌───────────────────────╖
                Available           Addressable        Segment
Processor    Modes               Memory             Size
────────────────────────────────────────────────────────────────────────────
8086/8088    Real                1 megabyte         16 bit

80186/80188  Real                1 megabyte         16 bit

                Available           Addressable        Segment
Processor    Modes               Memory             Size
────────────────────────────────────────────────────────────────────────────

80286        Real and Protected  16 megabytes       16 bit

80386        Real and Protected  4 gigabytes        16 or 32 bit

80486        Real and Protected  4 gigabytes        16 or 32 bit

────────────────────────────────────────────────────────────────────────────



Processor Modes - Real mode allows only one process to run at a time. The
DOS operating system runs in real mode. The OS/2 operating system can
execute programs written for DOS, but is designed to provide capabilities
available only in protected mode. In protected mode, more than one process
can be active at any one time. Memory accessed by these different processes
is protected from access by another process.

Protected-mode addresses do not correspond directly to physical memory.
Under protected-mode operating systems, the processor allocates and manages
memory dynamically. Additional privileged instructions initialize protected
mode and control multiple processes. Section 1.1.2 provides more information
on operating systems.

8086 and 8088 - The 8086 is faster than the 8088 because of its 16-bit data
bus; the 8088 has only an 8-bit data bus. The 16-bit data bus allows you to
use EVEN and ALIGN on an 8086 processor to word-align data and thus improve
data-handling efficiency. Memory addresses on the 8086 and 8088 refer to
actual physical addresses.

80186 and 80188 - These two processors are identical to the 8086 and 8088
except that new instructions have been added and several old instructions
have been optimized. These processors run significantly faster than the
8086.

80286 - The 80286 processor adds some instructions to control protected
mode, and it runs faster. It also provides the optional protected mode that
can be used by the operating system to allow multiple processes to run at
the same time. The 80286 is the minimum for running 16-bit versions of OS/2.

80386 - Unlike its predecessors, the 80386 processor can handle both 16-bit
and 32-bit data. It is fully software-compatible with the 80286. It
implements many new hardware-level features, including virtual paged memory,
multiple virtual 8086 processes, addressing of up to four gigabytes of
memory, and specialized debugging registers.

Under DOS, the 80836 supports all the instructions of the 80286 as well as
several additional ones. It also allows limited use of 32-bit registers and
addressing modes. The 80386 operates at faster processor speeds than the
80286 and is the minimum for running 32-bit versions of OS/2 and other
32-bit operating systems.

80486 - The 80486 processor is an enhanced version of the 80386, with
instruction "pipelining" that executes many instructions two to three times
faster. It incorporates an enhanced version of the 80387 coprocessor, as
well as an 8K (kilobyte) memory cache. The 80486 includes several new
instructions and is fully compatible with 80386 software.

8087, 80287, and 80387 - These math coprocessors work concurrently with the
8086 family of processors. Performing floating-point calculations with math
coprocessors is up to 100 times faster than emulating the calculations with
integer instructions. Although there are technical and performance
differences among the three coprocessors, the main difference to the
applications programmer is that the 80287 and 80387 can operate in protected
mode. The 80387 also has several new instructions. The 80486 does not use
any of these coprocessors; its floating-point processor is built in and is
functionally equivalent to the 80387.


1.1.2  Operating Systems

With MASM, you can create programs that run under DOS, Windows, or OS/2─or
all three, in some cases. For example, ML.EXE can produce executable files
that run in any of the target environments, regardless of the programmer's
environment. For information on building programs for different
environments, see "Building and Running Programs" in PWB's online help.

DOS and OS/2 provide different processing modes. DOS uses the single-process
real mode. OS/2 uses the multiple-process protected mode. While OS/2 can
also run in real mode, this book assumes it is being used in protected mode.


DOS and OS/2 differ primarily in system access methods, size of addressable
memory, and segment selection. Table 1.2 summarizes these differences.

Table 1.2  The DOS and OS/2 Operating Systems

                        Available               Contents
Operating   System      Active      Addressabl  of Segment  Word Length
System      Access      Processes   e Memory
                                                Register
─────────────────────────────────────────────────────────────────────────────
DOS (and    Direct to   One         1 megabyte  Actual      16 bit
OS/2 1.x    hardware                            address
real mode)

OS/2 1.x    Operating   Multiple    16          Segment     16 bit
protected   system                  megabytes   selectors
mode        call

OS/2 2.x    Operating   Multiple    4           Segment     32 bit
            system                  gigabytes   selectors
            call

─────────────────────────────────────────────────────────────────────────────


DOS - In real-mode programming, you can access system functions by calling
DOS, calling the basic input/output system (BIOS), or directly addressing
hardware. Access is through DOS interrupt 21h.

Protected-mode programs cannot directly access hardware ports.

OS/2 1.x - As you can see in Table 1.2, protected mode allows for much
larger data structures than real mode, since the addressable memory is
extended to 16 megabytes. In protected mode, segment registers contain
segment selectors rather than actual segment values. These selectors cannot
be calculated by the program; they must be obtained by calling the operating
system. Programs that attempt to calculate segment values or to address
memory directly do not work.

Note that protected-mode operating systems such as XENIX (R) and OS/2
provide system functions for memory and hardware accesses that would be
prohibited with direct processor commands. This software interface permits
access without the possibility of corrupting memory or crashing the system.


Protected mode uses privilege levels to maintain system integrity and
security. Programs cannot access data or code that is in a higher privilege
level. Some instructions that directly access ports or clear interrupts
(such as CLI, STI, IN,  and OUT) are available at privilege levels normally
used only by systems programmers.

OS/2 protected mode enforces the separation of segment values. The segments
have selectors that have no relationship to the offset. The operating system
combines the segment and offset so that your programs can address up to 16
megabytes of virtual memory in a 16-bit system.

OS/2 2.x and flat model eliminate segments.

OS/2 2.x - OS/2 2.x uses an unsegmented architecture. (See Section 1.1.3.)
It creates a "flat model" in which the entire address space is within one
32-bit segment. Section 2.2.1, "Defining Basic Attributes with .MODEL,"
explains how to use the flat model. In a 32-bit system, you can access up to
four gigabytes of virtual memory. (The term "virtual memory" means that if
the programs running under OS/2 request more memory than is physically
available, part of the memory is temporarily swapped out to disk.) Since
code, data, and stack are in the same segment, the value of segment
registers never needs to change. Internal mechanisms of OS/2 2.x implement
protection at a lower level.


1.1.3  Segmented Architecture

The 8086 processors differ from many other microprocessors in that they use
a segmented architecture: that is, each address is represented in two
parts─a segment and an offset. Segmented addresses affect many aspects of
assemblylanguage programming, especially addresses and pointers.

Only 64K of data can be addressed by a 16-bit segment address.

Segmented architecture was originally designed to enable a 16-bit processor
to access an address space larger than 64K. (Section 1.1.5, "Segmented
Addressing," explains how the processor uses both the segment and offset to
create addresses larger than 64K.) DOS is an example of an operating system
that uses segmented architecture on a 16-bit processor.

With the advent of protected-mode processors such as the 80286, segmented
architecture gained a second purpose. Segments can separate different blocks
of code and data to protect them from undesirable interactions. OS/2 1.x is
an operating system that takes advantage of the protection features of the
16-bit segments on the 80286.

Segmented architecture went through another significant change with the
release of 32-bit processors, starting with the 80386. These processors are
backward compatible with the older 16-bit processors, but they also offer a
32-bit mode that minimizes the memory limitations of a 16-bit segmented
architecture. Both offer paging to maintain segment protection. XENIX 386 is
an example of a 32-bit segmented operating system using segment protection.


OS/2 2.x takes advantage of the 32-bit processors to allow a nonsegmented
memory configuration. The processor still uses 32-bit segments, but from the
user's viewpoint, there is only one segment. The flat memory model used by
OS/2 2.x places code and data in a single segment. See Section 2.2.1,
"Defining Basic Attributes with .MODEL," for more information about the flat
memory model.


1.1.4  Segment Protection

Segmented architecture is an important part of the OS/2 memory-protection
scheme. In a "multitasking" operating system where numerous programs can run
simultaneously, programs must not access the code and data of another
process without permission.

In DOS, the data and code segments are usually allocated adjacent to each
other, as shown in Figure 1.1. In OS/2, the data and code segments may be
anywhere in memory. The programmer knows nothing about their location and
has no control over it. The segments may even be moved to a new memory
location or swapped to disk while the program is running.

(This figure may be found in the printed book.)

Segment protection prevents a bug in one program from corrupting another
program.

Segment protection makes software development easier and more reliable in
OS/2 than in DOS because, in OS/2, any illegal access is detected
immediately. The operating system intercepts illegal memory accesses,
terminates the program, and displays a message. This makes the bug easier to
track down and fix.

In DOS, an illegal access is not detected and may not cause an error until
later, when another part of the program attempts to use the corrupted
memory.


1.1.5  Segmented Addressing

Segmented addressing is the internal mechanism that combines a segment value
and an offset value to create an address. The two parts of an address are
represented as

    segment:offset

The segment portion is always a 16-bit value. The offset portion is a 16-bit
value in 16-bit mode or a 32-bit value in 32-bit mode.

In real mode, the segment value is a physical address that has an arithmetic
relationship to the offset value. The segment and offset together create a
20-bit physical address (explained in the next section). Although 20-bit
addresses can access up to one megabyte of memory, the operating system on
IBM (R) PCs and compatibles uses part of this memory, leaving 640K of memory
for programs.


1.1.6  Segment Arithmetic

Manipulating segment and offset addresses directly in real-mode programming
is called "segment arithmetic." Programs that perform segment arithmetic are
not portable to protected-mode operating systems, where addresses do not
correspond to a known segment and offset.

The segment selects a region of memory; the offset selects the byte within
that region.

To perform segment arithmetic successfully, it helps to understand how the
processor combines a 16-bit segment and a 16-bit offset to form a 20-bit
linear address. In effect, the segment selects a 64K region of memory, and
the offset selects the byte within that region. Here's how it works:


    1.  The processor shifts the segment address to the left by four binary
        places, producing a 20-bit address ending in four zeros. This
        operation has the effect of multiplying the segment address by 16.

    2.  The processor adds this 20-bit segment address to the 16-bit offset
        address. The offset address is not shifted.

    3.  The processor uses the resulting 20-bit address, often called the
        "physical address," to access an actual location in the one-megabyte
        address space.


Figure 1.2 illustrates this process.

(This figure may be found in the printed book.)

A 20-bit physical address may actually be specified by 4,096 equivalent
segment:offset addresses. For example, the 20-bit physical address 0F800 is
equivalent to 0000:F800, 0F00:0800, or 0F80:0000.

You may need to convert two segmented addresses with different segments to
segmented addresses with the same segment to write TSRs (see Chapter 19), to
write code to handle huge arrays, or to determine the size of an area of
memory.


1.2  Language Components of MASM

Programming with MASM requires that you understand the MASM concepts of
reserved words, identifiers, predefined symbols, constants, expressions,
operators, data types, registers, and statements. This section defines
important terms and provides lists that summarize these topics. See online
help or the MASM Reference for detailed information.


1.2.1  Reserved Words

A reserved word has a special meaning fixed by the language. You can use it
only under certain conditions. MASM's reserved words include:


    ■   Instructions, which correspond to operations the processor can execute

    ■   Directives, which give commands to the assembler

    ■   Attributes, which provide a value for a field, such as segment
        alignment

    ■   Operators, which are used in expressions

    ■   Predefined symbols, which return information to your program


MASM reserved words are not case sensitive except for predefined symbols
(see Section 1.2.3).

Use OPTION NOKEYWORD if you want to use a reserved word in another context.


The assembler generates an error if you use a reserved word as a variable,
code label, or other identifier within your source code. However, if you
need to use a reserved word for another purpose, the OPTION NOKEYWORD
directive can selectively disable a word's status as a reserved word.

For example, to remove the STR instruction, the MASK operator, and the NAME
directive from the set of words MASM recognizes as reserved, use this
statement in the code segment of your program prior to the first reference
to STR, MASK, or NAME:

    OPTION NOKEYWORD:<STR MASK NAME>

The OPTION directive is discussed in Section 1.3.2. Appendix D provides a
complete list of MASM reserved words.


1.2.2  Identifiers

Identifiers are names of variables of a given type.

An identifier is a name that you invent and attach to a definition.
Identifiers can be symbols representing variables, constants, procedure
names, code labels, segment names, and user-defined data types such as
structures, unions, records, and types defined with TYPEDEF. Identifiers
longer than 247 characters generate an error.

Certain restrictions limit the names you can use for identifiers. Follow
these rules to define a name for an identifier:


    ■   The first character of the identifier can be an alphabetic character
        (A-Z) or any of these four characters: @  _   $  ?

    ■   The other characters in the identifier can be any of the characters
        listed above or a decimal digit (0-9)


Avoid starting an identifier with the at sign (@), because MASM 6.0
predefines some special symbols starting with @ (see Section 1.2.3).
Beginning an identifier with @ may also cause conflicts with future versions
of the Macro Assembler.

The symbol--and thus the identifier--is visible as long as it remains within
scope. (See Section 8.2, "Sharing Symbols with Include Files," for
additional information about visibility and scope.)


1.2.3  Predefined Symbols

Macros and conditionalassembly blocks often use predefined symbols.

The assembler includes a number of predefined symbols (also called
predefined equates). You can use these symbol names at any point in your
code to represent the equate value. For example, the predefined equate
@FileName represents the base name of the current file. If the current
source file is TASK.ASM, the value of @FileName is TASK. The MASM predefined
symbols are listed below according to the kinds of information they provide.
Case is important only if the /Cp option is used. (See online help on ML
command-line options for additional details.)


Predefined Symbols for Segment Information

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Symbol                            Description
────────────────────────────────────────────────────────────────────────────
@code                             Provides the name of the code segment,
                                    except in tiny model when it returns
                                    DGROUP.

@CodeSize                         Returns an integer representing the
                                    default code distance.

@CurSeg                           Returns the name of the current segment.

@data                             Expands to DGROUP except in flat model.

@DataSize                         Returns an integer representing the
                                    default data distance.

@fardata                          Represents the name of the segment
                                    defined by the .FARDATA directive.

@fardata?                         Represents the name of the segment
Symbol                            Description
────────────────────────────────────────────────────────────────────────────
@fardata?                         Represents the name of the segment
                                    defined by the .FARDATA? directive.

@Model                            Returns the selected memory model.

@stack                            Expands to DGROUP for near stacks or
                                    STACK for far stacks. (See Section 2.2.3,
                                    "Creating a Stack.")

@WordSize                         Provides the size attribute of the
                                    current segment.




Predefined Symbols for Environment Information

Symbol                            Description
────────────────────────────────────────────────────────────────────────────
@Cpu                              Contains a bit mask specifying the
                                    processor mode.

@Environ                          Returns values of environment variables.

@Interface                        Contains information about the language
                                    parameters.

@Version                          Represents the text equivalent of the
                                    MASM version number. In MASM 6.0, this
                                    expands to 600.



Predefined Symbols for Date and Time Information

Symbol            Description
────────────────────────────────────────────────────────────────────────────
@Date             Supplies the current system date.
@Time             Supplies the current system time.


Predefined Symbols for File Information

Symbol                            Description
────────────────────────────────────────────────────────────────────────────
@FileCur                          Names the current file (base and suffix).

@FileName                         Names the base name of the main file
                                    being assembled as it appears on the
                                    command line.

@Line                             Gives the source line number in the
                                    current file.



Predefined Functions for Macro String Manipulation

Symbol    Description
────────────────────────────────────────────────────────────────────────────
@CatStr   Returns concatenation of two strings.
@InStr    Returns the starting position of a string within another string.
@SizeStr  Returns the length of a given string.
@SubStr   Returns substring from a given string.


1.2.4  Integer Constants and Constant Expressions

An integer constant is a series of one or more numerals followed by an
optional radix specifier. For example, in these statements

    mov     ax, 25
            mov     ax, 0B3h

the numbers  25  and  0B3h  are integer constants. The  h  appended to  0B3
is a radix specifier. The specifiers are


    ■   y  for binary (or  b  if radix is less than or equal to 10)

    ■   o  or  q  for octal

    ■   t  for decimal (or  d  if radix is less than or equal to 10)

    ■   h  for hexadecimal


The default radix is decimal.

Radix specifiers can be either uppercase or lowercase letters; sample code
in this book uses lowercase. If no radix is specified, the assembler
interprets the integer according to the current radix. The default radix is
decimal, but it can be changed with the .RADIX directive.

Hexadecimal numbers must always start with a decimal digit (0-9). If
necessary, add a leading zero to distinguish between symbols and hexadecimal
numbers that start with a letter. For example,  ABCh  is interpreted as an
identifier. The hexadecimal digits A through F can be either uppercase or
lowercase letters. Sample code in this book uses uppercase letters.

Values of integer constants and expressions are known at assembly time.

Constant expressions contain integer constants and (optionally) operators
such as shift, logical, and arithmetic operators, and can be evaluated. The
assembler evaluates them at assembly time. (In addition to constants,
expressions can contain labels, types, registers, and their attributes.)
Constant expressions do not change value during program execution.

Symbolic Integer Constants - You can define symbolic integer constants with
either of the data assignment directives, EQU or the equal sign (=). These
directives assign values to symbols during assembly, not during program
execution. Symbols defined as integer constants can then be used in
subsequent statements as immediate operands having the assigned value.
Symbolic constants are often used to assign mnemonic names to constant
values, which makes your code more readable and easier to maintain.

The assembler does not allocate data storage when you use either EQU or =.
Instead, it replaces each occurrence of the symbol with the value of the
expression.

Symbols defined with EQU cannot be redefined.

The difference between EQU and = is that integers defined with the =
directive can be changed in your source code, but those defined with EQU
cannot. Once a symbolic integer constant has been defined with the EQU
directive, attempting to redefine it generates an error. The syntax is

    symbol EQU expression

The symbol must be a unique name. The expression can be an integer, a
constant expression, a one- or two-character string constant (four-character
on the 80386/486), or an expression that evaluates to an address. If a
constant value used in numerous places in the source code needs to be
changed, you modify the expression in one place rather than throughout the
source code.

The following example shows the correct use of EQU to define symbolic
integers.

    column  EQU    80                ; Constant -    80
    row     EQU    25                ; Constant -    25
    screen  EQU    column * row      ; Constant  - 2000
    line    EQU    row               ; Constant -    25

            .DATA

            .CODE
            .
            .
            .
            mov     cx, column
            mov     bx, line

The value of a symbol defined with the = directive can be different at
different places in the source code. However, a constant value is assigned
during assembly for each use, and that value does not change at run time.

The syntax for the = directive is

symbol = expression

Size of Constants - The default word size for MASM 6.0 expressions is 32
bits. This behavior can be modified using OPTION EXPR16 or OPTION M510. Both
of these options set the expression word size to 16 bits, but OPTION M510
affects other assembler behavior as well (see Appendix A).

It is illegal to change the expression word size once it has been set with
OPTION M510, OPTION EXPR16, or OPTION EXPR32, but you can repeat the same
directive in a file. This can be useful for putting an OPTION EXPR16 in
every include file, for example.


1.2.5  Operators

Operators are used in expressions. The value of the expression is determined
at assembly time and does not change when the program runs.

Operators should not be confused with processor instructions. The reserved
word ADD is an instruction. The plus sign (+) is an operator. For example,
Amount+2  is a valid use of the plus operator (+); it tells the assembler to
add  2 to  Amount, which might be a value or an address. This operation,
which occurs at assembly time, is different from the ADD instruction, which
tells the processor to perform addition at run time.

The assembler evaluates expressions that contain more than one operator
according to the following rules:


    ■   Operations in parentheses are always performed before any adjacent
        operations.

    ■   Binary operations of highest precedence are performed first.

    ■   Operations of equal precedence are performed from left to right.

    ■   Unary operations of equal precedence are performed right to left.


The order of precedence for all operators is listed in Table 1.3. Operators
on the same line have equal precedence.

Table 1.3  Operator Precedence

╓┌───────────────────┌───────────────────────────────────────────────────────╖
Precedence          Operators
────────────────────────────────────────────────────────────────────────────
1                   ( ), [ ]
2                   LENGTH, SIZE, WIDTH, MASK
Precedence          Operators
────────────────────────────────────────────────────────────────────────────
2                   LENGTH, SIZE, WIDTH, MASK
3                   . (structure-field-name operator)
4                   : (segment-override operator), PTR
5                   LROFFSET, OFFSET, SEG, THIS, TYPE
6                   HIGH, HIGHWORD, LOW, LOWWORD
7                   + ,- (unary)
8                   *, /, MOD, SHL, SHR
9                   +, - (binary)
10                  EQ, NE, LT, LE, GT, GE
11                  NOT
12                  AND
13                  OR, XOR
14                  OPATTR, SHORT, .TYPE
────────────────────────────────────────────────────────────────────────────



1.2.6  Data Types

A "data type" describes a set of values. A variable of a given type can have
any of a set of values within the range specified for that type.

The intrinsic types for MASM 6.0 are BYTE, SBYTE, WORD, SWORD, DWORD,
SDWORD, FWORD, QWORD, and TBYTE. These types define integers and binary
coded decimals (BCDs); they are discussed in Chapter 6. The signed data
types SBYTE, SWORD, and SDWORD are new to MASM 6.0. They are useful in
conjunction with directives such as INVOKE (for calling procedures) and .IF
(introduced in Chapter 7). The REAL4, REAL8, and REAL10 directives can be
used to define floating-point types. See Chapter 6.

Previous versions of MASM have separate directives for types and
initializers. For example, BYTE is a type and DB is the corresponding
initializer. The distinction has been eliminated for MASM 6.0. Any type
(intrinsic or user-defined) can be used as an initializer.

MASM does not have specific types for arrays and strings. However, it allows
a sequence of data units to be treated as arrays, and character (byte)
sequences to be treated as strings. (See Section 5.1, "Arrays and Strings.")


Types can also have attributes such as langtype and distance (NEAR and FAR).
See Section 7.3.3, "Declaring Parameters with the PROC Directive," for
information on these attributes.

You can also define your own types with STRUCT, UNION, and RECORD. The types
have fields that contain string or numeric data, or records that contain
bits. These data types are similar to the user-defined data types in
high-level languages such as C, Pascal, and FORTRAN. (See Chapter 5,
"Defining and Using Complex Data Types.")

The TYPEDEF directive defines aliases and pointer types.

You can define new types, including pointer types, with the TYPEDEF
directive, which is also new to MASM 6.0. TYPEDEF assigns a qualifiedtype
(explained below) to a typename.

────────────────────────────────────────────────────────────────────────────
NOTE

The concept of the qualifiedtype is essential to understanding many of the
new features in MASM 6.0, including prototypes and the .IF and INVOKE
directives. Descriptions of these topics in later chapters refer to this
section.
────────────────────────────────────────────────────────────────────────────

Once assigned, the typename can be used as a data type in your program. Use
of the qualifiedtype also allows the CodeView debugger to display
information on the type. You cannot use a qualifiedtype as an initializer,
but you can use a type defined with TYPEDEF.

The qualifiedtype is any MASM type (such as structure types, union types,
record types, or an intrinsic type) or can be a pointer to a type with the
form

    «distance» PTR «qualifiedtype»

where distance is NEAR, FAR, or any distance modifier. See Section 7.3.3,
"Declaring Parameters with the PROC Directive," for more information on
distance.

The qualifiedtype can also be any type previously defined with TYPEDEF. For
example, if you use TYPEDEF to create an alias for BYTE, as shown below,
then you can use that  CHAR  type as a qualifiedtype when defining the
pointer type  PCHAR.

    CHAR    TYPEDEF BYTE
    PCHAR   TYPEDEF PTR CHAR

Section 3.3, "Accessing Data with Pointers and Addresses," shows how to use
the TYPEDEF directive to define pointers.

Since distance and qualifiedtype are optional syntax elements, you can use
variables of type PTR or FAR PTR. You can also define procedure prototypes
with qualifiedtype. See Section 7.3.6, "Declaring Procedure Prototypes," for
more information about procedure prototypes.

Several rules govern the use of qualifiedtype:


    ■   The only component of a qualifiedtype definition that can be
        forwardreferenced is a structure or union type identifier.

    ■   If distance is not specified, the right operand and current memory
        model determine the type of the pointer. If the operand following PTR
        is not a distance or a function prototype, the operand is a pointer of
        the default data pointer type in the current mode. Otherwise, the type
        of the pointer is the distance of the right operand.

    ■   If .MODEL is not specified, SMALL model (and therefore NEAR pointers)
        is the default.


A qualifiedtype can be used in seven places:

╓┌─────────────────────────────────────┌─────────────────────────────────────╖
Use                                   Example
────────────────────────────────────────────────────────────────────────────
In procedure arguments                proc1 PROC pMsg:PTR BYTE

In prototype arguments                proc2 PROTO pMsg:FAR PTR WORD

With local variables declared inside  LOCAL pMsg:PTR
procedures

Use                                   Example
────────────────────────────────────────────────────────────────────────────

With the LABEL directive              TempMsg LABEL PTR WORD

With the EXTERN and EXTERNDEF         EXTERN pMsg:FAR PTR BYTE
directives                            EXTERN MyProc:PROTO

With the COMM directive               COMM var1:WORD:3

With the TYPEDEF directive            PPBYTE TYPEDEF PTR PBYTE PFUNC
                                        TYPEDEF PROTO MyProc



Section 3.3.1 shows ways to write a TYPEDEF type for a qualifiedtype.
Attributes such as NEAR and FAR can also be applied to a qualifiedtype.

You can also determine an accurate definition for TYPEDEF and qualifiedtype
from the BNF grammar definitions given in Appendix B. The BNF grammar
defines each component of the syntax for any directive, showing the
recursive properties of components such as qualifiedtype.


1.2.7  Registers

All the 8086 processors have the same base set of 16-bit registers. Some
registers can be accessed as two separate 8-bit registers. In the 80386/486,
most registers can also be accessed as extended 32-bit registers.

Figure 1.3 shows the registers common to all the 8086-based processors. Each
register has its own special uses and limitations.

(This figure may be found in the printed book.)

80386/486 Only - The 80386/486 processors use the same 8-bit and 16-bit
registers that the rest of the 8086 family uses. All of these registers can
be further extended to 32 bits, except segment registers, which always
occupy 16 bits. The extended register names begin with the letter "E." For
example, the 32-bit extension of AX is EAX. The 80386/486 processors have
two additional segment registers, FS and GS. Figure 1.4 shows the extended
registers of the 80386/486.

(This figure may be found in the printed book.)


1.2.7.1  Segment Registers

At run time, all addresses are relative to one of four segment registers:
CS, DS, SS, or ES. (The 80386/486 processors add two more, FS and GS.) These
registers, their segments, and their purpose are listed below:

Register and Segment              Purpose
────────────────────────────────────────────────────────────────────────────
CS (Code Segment)                 Contains processor instructions and
                                    their immediate operands.

DS (Data Segment)                 Normally contains data allocated by the
                                    program.

SS (Stack Segment)                Creates stacks for use by PUSH, POP,
                                    CALLS,
                                    and RET.

ES (Extra Segment)                References secondary data segment. Used
                                    by string instructions.

FS, GS                            Provides extra segments on the
                                    80386/486.


1.2.7.2  General-Purpose Registers

Operations on registers are usually faster than operations on memory
locations.

The AX, DX, CX, BX, BP, DI, and SI registers are 16-bit general-purpose
registers. They can be used for temporary data storage. Since the processor
accesses registers more quickly than it can access memory, you can speed up
execution by keeping the most frequently used data in registers.

The 8086 family of processors does not perform memory-to-memory operations.
Thus, operations on more than one variable often require the data to be
moved into registers.

Four of the general registers, AX, DX, CX, and BX, can be accessed either as
two 8-bit registers or as a single 16-bit register. The AH, DH, CH, and BH
registers represent the high-order 8 bits of the corresponding registers.
Similarly, AL, DL, CL, and BL represent the low-order 8 bits of the
registers. All the general registers can be extended to 32 bits on the
80386/486.


1.2.7.3  Special-Purpose Registers

The 8086 family of processors has two additional registers whose values are
changed automatically by the processor.

SP (Stack Pointer) - The SP register points to the current location within
the stack segment. Pushing a value onto the stack decreases the value of SP
by 2; popping from the stack increases the value of SP by 2. With 32-bit
operands on 80386/486 processors, SP is increased or decreased by 4 instead
of 2. Call instructions store the calling address on the stack and decrease
SP accordingly; return instructions get the stored address and increase SP.
SP can also be manipulated as a general-purpose register with instructions
such as ADD.

Only the processor can change IP.

IP (Instruction Pointer)  - The IP register always contains the address of
the next instruction to be executed. You cannot directly access or change
the instruction pointer. However, instructions that control program flow
(such as calls, jumps, loops, and interrupts) automatically change the
instruction pointer.


1.2.7.4  Flags Register

Flags reveal the status of the processor.

The 16 bits in the flags register control the execution of certain
instructions and reflect the current status of the processor. In 80386/486
processors, the flags register is extended to 32 bits. Some bits are
undefined, so there are actually 9 flags for real mode, 11 flags (including
a 2-bit flag) for 80286 protected mode, 13 for the 80386, and 14 for the
80486. The extended flags register of the 80386/486 is sometimes called
"Eflags."

Figure 1.5 shows the bits of the 32-bit flags register for the 80386/486.
Only the lower word is used for the other 8086-family processors. The
unmarked bits are reserved for processor use; do not modify them.

(This figure may be found in the printed book.)

The nine flags common to all 8086-family processors are summarized below,
starting with the low-order flags. In these descriptions, "set" means the
bit value is 1, and "cleared" means the bit value is 0.

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Flag                              Description
────────────────────────────────────────────────────────────────────────────
Carry                             Set if an operation generates a carry to
                                    or a borrow from a destination operand.

Parity                            Set if the low-order bits of the result
                                    of an operation contain an even number
                                    of set bits.
Flag                              Description
────────────────────────────────────────────────────────────────────────────
                                    of set bits.

Auxiliary Carry                   Set if an operation generates a carry to
                                    or a borrow from the low-order four bits
                                    of an operand. This flag is used for
                                    binary coded decimal (BCD) arithmetic.

Zero                              Set if the result of an operation is 0.

Sign                              Equal to the high-order bit of the
                                    result of an operation (0 is positive, 1
                                    is negative).

Trap                              If set, the processor generates a
                                    single-step interrupt after each
                                    instruction. A debugging program can use
                                    this feature to execute a program one
                                    instruction at a time.

Flag                              Description
────────────────────────────────────────────────────────────────────────────

Interrupt Enable                  If set, interrupts are recognized and
                                    acted on as they are received. The bit
                                    can be cleared to turn off interrupt
                                    processing temporarily.

Direction                         Set to make string operations process
                                    down from high addresses to low
                                    addresses; can be cleared to make string
                                    operations process up from low addresses
                                    to high addresses.

Overflow                          Set if the result of an operation is too
                                    large or small to fit in the destination
                                    operand.




1.2.8  Statements

Statements are the line-by-line components of source files. Each MASM
statement specifies an instruction or directive for the assembler.
Statements have up to four fields. The syntax is shown below:

    «name» «operation» «operands»
    «;comment»

The fields are explained below:

Field                             Purpose
────────────────────────────────────────────────────────────────────────────
name                              Defines a label that can be accessed
                                    from elsewhere in the program. For
                                    example, it can name a variable, type,
                                    segment, or code location.

operation                         States the action of the statement. This
                                    field contains either an instruction or
                                    an assembler directive.

operands                          Lists one or more items on which the
                                    instruction or directive operates.

comment                           Provides a comment for the programmer.
                                    Comments
                                    are for documentation only; they are
                                    ignored by the
                                    assembler.


The following line contains all four fields:

    mainlp: mov     ax, 7   ; Comments follow the semicolon

Here,  mainlp  is the label,  mov  is the operation, and  ax  and  7  are
the operands, separated by a comma. The comment follows the semicolon.

All fields are optional, although certain directives and instructions
require an entry in the name or operand field. Some instructions and
directives place restrictions on the choice of operands. By default, MASM is
not case sensitive.

Each field (except the comment field) must be separated from other fields by
white-space characters (spaces or tabs). MASM also requires code labels to
be followed by a colon, operands to be separated by commas, and comments to
be preceded by a semicolon.

The backslash character joins physical lines into one logical line.

A logical line can contain up to 512 characters and occupy one or more
physical lines. To extend a logical line into two or more physical lines,
put the backslash character () as the last non-whitespace character before
the comment or end of the line. You can place a comment after the backslash
as shown in this example:

    .IF     (x > 0)      ; X must be positive
            &&     (ax > x)     ; Result from function must be > x
            &&     (cx == 0)     ; Check loop counter too
            mov    dx, 20h
            .ENDIF

Multiline comments can also be specified with the COMMENT directive. The
assembler ignores all code between the delimiter character following the
directive and the line containing the next instance of the delimiter
character. This example illustrates the use of COMMENT.

    COMMENT ^               The assembler
                            ignores this text
    ^       mov     ax, 1   and this code


1.3  The Assembly Process

Creating and running an executable file involves several processes:


    ■   Assembling the source code into an object file

    ■   Linking the object file with other modules or libraries into an
        executable program

    ■   Loading that program into memory

    ■   Running the program


Once you have written your assembly-language program, MASM provides several
options for assembling it. The OPTION directive, new to MASM 6.0, has
several different arguments that let you control the way MASM assembles your
programs.

You can control assembly behavior with conditional assembly.

Conditional assembly allows you to create one source file that can generate
a variety of programs, depending on the status of various
conditional-assembly statements.


1.3.1  Generating and Running Executable Programs

This section briefly lists all the actions that take place during each of
the assembly steps. You can change the behavior of some of these actions in
various ways, for example, by using macros instead of procedures, or by
using the OPTION directive or conditional assembly. The other chapters in
this book discuss specific programming methods; this list simply gives you
an overview.


1.3.1.1  Assembling

The ML.EXE program does two things to create an executable program. First,
it assembles the source code into an intermediate object file. Second, it
calls the linker, LINK.EXE, which links the object files and libraries into
an executable program (usually with the .EXE extension).

At assembly time, the assembler


    ■   Evaluates conditional-assembly directives, assembling if the
        conditions are true.

    ■   Expands macros and macro functions.

    ■   Evaluates constant expressions such as  MYFLAG AND 80H, substituting
        the calculated value for the expression.

    ■   Encodes instructions and nonaddress operands. For example,  mov cx, 13
        can be encoded at assembly time because the instruction does not
        access memory.

    ■   Saves memory offsets as offsets from their segment.

    ■   Passes segments and segment attributes to the object file.

    ■   Saves placeholders for offsets and segments (relocatable addresses).

    ■   Outputs a listing if requested.

    ■   Passes messages (such as INCLUDELIB and .DOSSEG) directly to the
        linker.


See Section 1.3.3 for information about conditional assembly; see Chapter 9
for macros. Chapters 2 and 3 give further details about segments and
offsets, and Appendix C explains listing files.


1.3.1.2  Linking

Once your source code is assembled, the resulting object file is passed to
the linker. At this point, the linker may combine several object files into
an executable program.

At link time, the linker


    ■   Combines segments according to the instructions in the object files,
        rearranging the positions of segments that share the same class or
        group.

    ■   Fills in placeholders for offsets (relocatable addresses).

    ■   Writes relocations for segments into the header of .EXE files (but not
        .COM files).

    ■   Writes an executable image.


Section 2.3.4, "Defining Segment Groups," defines classes and groups.
Chapter 3, "Using Addresses and Pointers," explains segments and offsets.


1.3.1.3  Loading

The operating system loads the file generated by the linker into memory.
When the executable file is loaded into memory, DOS


    ■   Reads the program segment prefix (PSP) header into memory.

    ■   Allocates memory for the program, based on the values in the PSP.

    ■   Loads the program.

    ■   Calculates the correct values for absolute addresses from the
        relocation table.

    ■   Loads the segment registers SS, CS, DS, and ES with values that point
        to the proper areas of memory.

    ■   Loads the instruction pointer (IP) to point to the start address in
        the code segment and the stack pointer (SP) to point to the stack.

    ■   Begins execution of the program.


The process is similar for OS/2.

See Section 1.2.7, "Registers," for information about segment registers, the
instruction pointer (IP), and the stack pointer (SP). See MASM online help
or a DOS reference for more information on the PSP.


1.3.1.4  Running

Your program is now ready to run. Some program operations cannot be handled
until the program runs, such as resolving indirect memory operands. See
Section 7.1.1.2, "Indirect Operands."


1.3.2  Using the OPTION Directive

The OPTION directive lets you modify global aspects of the assembly process.
With OPTION, you can change command-line options and default arguments.
These changes affect only statements that follow the use of OPTION.

For example, you may have MASM code in which the first character of a
variable, macro, structure, or field name is a dot (.). Since a leading dot
causes MASM 6.0 to generate an error, you can use this statement in your
program:

    OPTION DOTNAME

This enables the use of the dot for the first character.

Changes made with OPTION override any corresponding command-line option. For
example, suppose you compile a module with this command line (which enables
M510 compatibility):

    ML /Zm TEST.ASM

but this statement is in the module:

    OPTION NOM510

From this point on in the module, the M510 compatibility options are
disabled.

The lists below explain each of the arguments for the OPTION directive. You
can put more than one OPTION statement on one line if you separate them by
commas.


Options for M510 Compatibility

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Argument                          Description
────────────────────────────────────────────────────────────────────────────
CASEMAP: maptype                  CASEMAP:NONE (or /Cx) causes internal
                                    symbol recognition to be case sensitive
Argument                          Description
────────────────────────────────────────────────────────────────────────────
                                    symbol recognition to be case sensitive
                                    and causes the case of identifiers in
                                    the .OBJ file to be the same as
                                    specified in the
                                    EXTERNDEF, PUBLIC, or COMM statement.
                                    The default is CASEMAP:NOTPUBLIC (or
                                    /Cp). It specifies case insensitivity
                                    for internal symbol recognition and the
                                    same behavior as CASEMAP:NONE for case
                                    of identifiers in .OBJ files.
                                    CASEMAP:ALL (/Cu) specifies case
                                    insensitivity for identifiers and
                                    converts all identifier names to
                                    uppercase.

DOTNAME | NODOTNAME               Enables the use of the dot (.) as the
                                    leading character in variable, macro,
                                    structure, union, and member names.
                                    NODOTNAME is the default.
Argument                          Description
────────────────────────────────────────────────────────────────────────────
                                    NODOTNAME is the default.

M510 | NOM510                     Sets all features to be compatible with
                                    MASM version 5.1, disabling the SCOPED
                                    argument and enabling OLDMACROS,
                                    DOTNAME, and, OLDSTRUCTS. OPTION M510
                                    conditionally sets other arguments for
                                    the OPTION directive. The default is
                                    NOM510. See Appendix A for more
                                    information on using OPTION M510.

OLDMACROS | NOOLDMACROS           Enables the version 5.1 treatment of
                                    macros. MASM 6.0 treats macros
                                    differently. The default is NOOLDMACROS.



OLDSTRUCTS | NOOLDSTRUCTS         Enables compatibility with MASM 5.1 for
                                    treatment of structure members. See
Argument                          Description
────────────────────────────────────────────────────────────────────────────
                                    treatment of structure members. See
                                    Section 5.2 for information on
                                    structures.

SCOPED | NOSCOPED                 Guarantees that all labels inside
                                    procedures are local to the procedure
                                    when SCOPED (the default) is enabled.




Options for Procedure Use

Argument                          Description
────────────────────────────────────────────────────────────────────────────
LANGUAGE : langtype               Specifies the default language type (C,
                                    PASCAL, FORTRAN, BASIC, SYSCALL, or
                                    STDCALL) to be used with PROC, EXTERN,
                                    and PUBLIC. This use of the OPTION
                                    directive overrides the .MODEL directive
                                    but is normally used when .MODEL is not
                                    given.

EPILOGUE: macroname               Instructs the assembler to call the
                                    macroname to generate a user-
                                    defined epilogue instead of the standard
                                    epilogue code when a RET instruction is
                                    encountered. See Section 7.3.8.

PROLOGUE: macroname               Instructs the assembler to call
                                    macroname to generate a user-
                                    defined prologue instead of generating
                                    the standard prologue code. See Section
                                    7.3.8.

PROC: visibility                  Allows the default visibility to be set
                                    explicitly. The default visibility is
                                    PUBLIC. The visibility can also be
                                    either EXPORT or PRIVATE.



Other Options

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Argument                          Description
────────────────────────────────────────────────────────────────────────────
EXPR16 | EXPR32                   Sets the expression word size to 16 or
                                    32 bits. The default is 32 bits. The
                                    M510 argument to the OPTION directive
                                    sets the word size to 16 bits. Once set
                                    with the OPTION directive, the
                                    expression word size cannot be changed.

EMULATOR | NOEMULATOR             Controls the generation of
                                    floating-point instructions. The
                                    NOEMULATOR option generates the
                                    coprocessor instructions directly. The
                                    EMULATOR option generates instructions
                                    with special fixup records for the
                                    linker so that the Microsoft
Argument                          Description
────────────────────────────────────────────────────────────────────────────
                                    linker so that the Microsoft
                                    floating-point emulator, supplied with
                                    other Microsoft languages, can be used.
                                    It produces the same result as setting
                                    the /Fpi command-line option. You can
                                    set this option only once per module.

LJMP | NOLJMP                     Enables automatic conditional-jump
                                    lengthening. The default is LJMP. See
                                    Section 7.1.2 for information about
                                    conditional-jump lengthening.

NOKEYWORD:<keywordlist>           Disables the specified reserved words.
                                    See Section 1.2.1, "Reserved Words," for
                                    an example of the syntax for this
                                    argument.

NOSIGNEXTEND                      Overrides the default sign-extended
                                    opcodes for the AND, OR, and XOR
Argument                          Description
────────────────────────────────────────────────────────────────────────────
                                    opcodes for the AND, OR, and XOR
                                    instructions and generates the larger
                                    non-sign-extended forms of these
                                    instructions. Provided for compatibility
                                    with NEC V25 (R) and NEC V35(tm)
                                    controllers.

OFFSET: offsettype                Determines the result of OFFSET operator
                                    fixups. SEGMENT sets the defaults for
                                    fixups to be segment-
                                    relative (compatible with MASM 5.1).
                                    GROUP, the default, generates fixups
                                    relative to the group (if the label is
                                    in a group). FLAT causes fixups to be
                                    relative to a flat frame. (The .386 mode
                                    must be enabled to use FLAT.) See
                                    Appendix A for more information.

READONLY | NOREADONLY             Enables checking for instructions that
Argument                          Description
────────────────────────────────────────────────────────────────────────────
READONLY | NOREADONLY             Enables checking for instructions that
                                    modify code segments, thereby
                                    guaranteeing that read-only code
                                    segments are not modified. Replaces the
                                    /p command-line option of MASM 5.1. It
                                    is useful for OS/2, where code segments
                                    are normally read-only.

SEGMENT: segSize                  Allows global default segment size to be
                                    set. Also determines the default address
                                    size for external symbols defined
                                    outside any segment. The segSize can be
                                    USE16, USE32, or FLAT.




1.3.3  Conditional Directives

MASM 6.0 provides conditional-assembly directives and conditional-error
directives. You can also use conditional-assembly directives when you want
to test for a specified condition and assemble a block of statements if the
condition is true. You can use conditional-error directives when you want to
test for a specified condition and generate an assembly error if the
condition is true.

Both kinds of conditional directives test assembly-time conditions, not
run-time conditions. Only expressions that evaluate to constants during
assembly can be compared or tested. Predefined symbols are often used in
conditional assembly. See Section 1.2.3.


Conditional-Assembly Directives

The IF and ENDIF directives enclose the statements to be considered for
conditional assembly. The optional ELSEIF and ELSE blocks follow the IF
directive. There are many forms of the IF and ELSE directives. Online help
provides a complete list.

The syntax used for the IF directives is shown below. The syntax for other
condition-assembly directives follow the same form.

    IF expression1
    ifstatements
    [[ELSEIF expression2
    elseifstatements]]
    [[ELSE
    elsestatements]]
    ENDIF



The statements following the IF directive can be any valid statements,
including other conditional blocks, which in turn can contain any number of
ELSEIF blocks. ENDIF ends the block.

The statements following the IF directive are assembled only if the
corresponding condition is true. If the condition is not true and an ELSEIF
directive is used, the assembler checks to see if the corresponding
condition is true. If so, it assembles the statements following the ELSEIF
directive. If no IF or ELSEIF conditions are satisfied, the statements
following the ELSE directive are assembled.

For example, you may want to assemble a line of code only if a particular
variable has been defined. In this example,

    IFDEF   buffer
    buff    BYTE    buffer DUP(?)
            ENDIF

buff  is allocated only if  buffer  has been previously defined.

The following list summarizes the conditional-assembly directives:

Directive                         Use
────────────────────────────────────────────────────────────────────────────
IF and IFE                        Tests the value of an expression and
                                    allows
                                    assembly based on the result.

IFDEF and IFNDEF                  Tests whether a symbol has been defined
                                    and allows assembly based on the result.

IFB and IFNB                      Tests to see if a specified argument was
                                    passed to a macro and allows assembly
                                    based on the result.

IFIDN and IFDIF                   Compares two macro arguments and allows
                                    assembly based on the result. (IFDIFI
                                    and IFIDNI perform the same action but
                                    are case insensitive.)





Conditional-Error Directives

You can use conditional-error directives to debug programs and check for
assembly-time errors. By inserting a conditional-error directive at a key
point in your code, you can test assembly-time conditions at that point. You
can also use conditional-error directives to test for boundary conditions in
macros.

Like other severe errors, those generated by conditional-error directives
cause the assembler to return a nonzero exit code. If a severe error is
encountered during assembly, MASM does not generate the object module.

For example, the .ERRNDEF directive produces an error if some label has not
been defined. In this example, .ERRNDEF at the beginning of the conditional
block makes sure that a  publevel  actually exists.

    .ERRNDEF    publevel
            IF          publevel LE 2
            PUBLIC      var1, var2
            ELSE
            PUBLIC      var1, var2, var3
            ENDIF

These directives use the syntax given in the previous section. The following
list summarizes the conditional-error directives.

Directive                 Use
────────────────────────────────────────────────────────────────────────────
.ERR                      Forces an error where the directives occur in
                            the source file. The error is generated
                            unconditionally when the directive is
                            encountered, but the directives can be placed
                            within conditional-assembly blocks to limit the
                            errors to certain situations.

.ERRE and .ERRNZ          Tests the value of an expression and
                            conditionally generates an error based on the
                            result.

.ERRDEF and               Tests whether a symbol is defined and
.ERRNDEF                  conditionally generates an error based on the
                            result.

.ERRB and .ERRNB          Tests whether a specified argument was passed to
                            a macro and conditionally generates an error
                            based on the result.

.ERRIDN and               Compares two macro arguments and conditionally
.ERRDIF                   generates an error based on the result. (
                            .ERRIDNI and .ERRDIFI perform the same action
                            but are case sensitive.)



1.4  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

╓┌─────────────────────────────────────┌─────────────────────────────────────╖
Topic                                 Access
────────────────────────────────────────────────────────────────────────────
Predefined symbols                    From the "MASM 6.0 Contents" screen,
                                        choose "Predefined Symbols"

Operator precedence                   From the list of tables on the "MASM
                                        6.0 Contents" screen, choose
                                        "Operator Precedence"

Data types                            Choose "Directives" from the "MASM
Topic                                 Access
────────────────────────────────────────────────────────────────────────────
Data types                            Choose "Directives" from the "MASM
                                        6.0 Contents" screen; then choose
                                        "Data Allocation" or "Complex Data
                                        Types" from the resulting screen

Registers                             From the "MASM 6.0 Contents" screen,
                                        choose "Language Overview"; then
                                        choose "Processor Register Summary"

Processor directives                  To see a table of directives, choose
                                        "Processor Selection" from the "MASM
                                        6.0 Contents" screen

Conditional assembly and conditional  Choose "Directives" from the "MASM
errors                                6.0 Contents" screen

EVEN, ALIGN,                          From the "MASM 6.0 Contents" screen,
OPTION                                choose "Directives," then
                                        "Miscellaneous"
Topic                                 Access
────────────────────────────────────────────────────────────────────────────
                                        "Miscellaneous"

Radix specifiers                      From the "MASM 6.0 Contents" screen,
                                        choose "Language Overview"

ML command-line options               From the "Microsoft Advisor Contents"
                                        screen, choose "Macro Assembler"
                                        from the " Command Line" list








Chapter 2  Organizing MASM Segments
────────────────────────────────────────────────────────────────────────────

A segment is a collection of instructions or data whose addresses are all
relative to the same segment register. The code in your assembly-language
program defines and organizes them.

Segments can be defined by using simplified segment directives or full
segment definitions. Section 2.2, "Using Simplified Segment Directives,"
covers the directives you can use to begin, end, and organize segment
program modules. It also discusses how to access far data and code with
simplified segment directives.

Section 2.3, "Using Full Segment Definitions," describes how to order,
combine, and divide segments, as well as how to use the SEGMENT directive to
define full segments. It also tells you how to create a segment group so
that you can use just one segment address to access all the data.

Most of the information in this chapter also applies to writing modules to
be called from other programs. Exceptions are noted when they apply. See
Chapter 8, "Sharing Data and Procedures among Modules and Libraries," for
more information about multiple-module programming.


2.1  Overview of Memory Segments

A physical segment is an area of memory in which all locations are
contiguous and share the same segment address. A segment always begins on a
16-byte (paragraph) boundary (unless an alignment attribute is specified
with ALIGN). While 16-bit segments can occupy up to 64K (kilobytes), 32-bit
segments can be as large as 4 gigabytes.

Segments reflect the architecture of the original 8086 processor. Prior to
the 80386 processors and OS/2 2.x, assembly-language programming meant using
segmented memory. A flat address space is now available on 80386/486
processors in 32-bit mode. This space is still segmented at the hardware
level, but it allows you to ignore most segmentation concerns.

Segments provide a means for associating similar kinds of data. Most
programs have segments for code, data, constant data, and the stack. These
logical segments are allocated by the assembler at assembly time.

You can define segments in two ways: with simplified segment directives and
with full segment definitions. You can also use both kinds of segment
definitions in the same program.

Simplified segment directives are easier to use than full segment
definitions.

Simplified segment directives hide many of the details of segment definition
and assume the same conventions used by Microsoft high-level languages. (See
Section 2.2.) The simplified segment directives generate necessary code,
specify segment attributes, and arrange segment order.

Full segment definitions require more complex syntax but provide more
complete control over how the assembler generates segments. (See Section
2.3.) If you use full segment definitions, you must write code to handle all
the tasks performed automatically by the simplified segment directives.


2.2  Using Simplified Segment Directives

Structuring a MASM program using simplified segments requires use of several
directives to assign standard names, alignment, and attributes to the
segments in your program. These directives define the segments in such a way
that linking with Microsoft high-level languages is easy.

The simplified segment directives are .MODEL, .CODE, .CONST, .DATA, .DATA?,
.FARDATA, .FARDATA?, .STACK, .STARTUP, and .EXIT. These directives and the
arguments they take are discussed in the following sections.

The main module is where execution begins.

MASM programs consist of modules made up of segments. Every program written
only in MASM has one main module, where program execution begins. This main
module can contain code, data, or stack segments defined with all of the
simplified segment directives. Any additional modules should contain only
code and data segments. Every module that uses simplified segments must,
however, begin with the .MODEL directive.


The following example shows the structure of a main module using simplified
segment directives. It uses the default processor (8086), the default
operating system (OS_DOS), and the default stack distance (NEARSTACK).
Additional modules linked to this main program would use only the .MODEL,
.CODE, and .DATA directives and the END statement.

    ; This is the structure of a main module
    ;  using simplified segment directives

            .MODEL small, c ; This statement is required before you
                            ;  can use other simplified segment
                            ;  directives

            .STACK          ; Use default 1-kilobyte stack

            .DATA           ; Begin data segment

                            ; Place data declarations here

            .CODE           ; Begin code segment
            .STARTUP        ; Generate start-up code

                            ; Place instructions here

            .EXIT           ; Generate exit code
            END

A module must always finish with the END directive.

The .DATA and .CODE statements do not require any separate statements to
define the end of a segment. They close the preceding segment and then open
a new segment. The .STACK directive opens and closes the stack segment but
does not close the current segment. The END statement closes the last
segment and marks the end of the source code. It must be at the end of every
module, whether or not it is the main module.


2.2.1  Defining Basic Attributes with .MODEL

The .MODEL directive defines the attributes that affect the entire module:
memory model, default calling and naming conventions, operating system, and
stack type. This directive enables use of simplified segments and controls
the name of the code segment and the default distance for procedures.

You must place .MODEL in your source file before any other simplified
segment directive. The syntax is

    .MODEL memorymodel «, modeloptions »

The memorymodel field is required and must appear immediately after the
.MODEL directive. The use of modeloptions, which define the other
attributes, is optional. The modeloptions must be separated by commas. You
can also use equates passed from the ML command line to define the
modeloptions.

The list below summarizes the memorymodel field and the modeloptions fields
(language, operating system, and stack distance):

Field                             Description
────────────────────────────────────────────────────────────────────────────
Memory model                      TINY, SMALL, COMPACT, MEDIUM, LARGE,
                                    HUGE, or FLAT. Determines size of code
                                    and data pointers. This field is
                                    required.

Language                          C, BASIC, FORTRAN, PASCAL, SYSCALL, or
                                    STDCALL. Sets calling and naming
                                    conventions for procedures and public
                                    symbols.

Operating system                  OS_OS2 or OS_DOS. Determines behavior of
                                    .STARTUP and .EXIT.

Stack distance                    NEARSTACK or FARSTACK. Specifying
                                    NEARSTACK groups the stack segment into
                                    a single physical segment (DGROUP) along
                                    with data. SS is assumed to equal DS.
                                    FARSTACK does not group the stack with
                                    DGROUP; thus SS does not equal DS.


You can use no more than one reserved word from each field. The following
examples show how you can combine various fields:

    .MODEL   small                  ; Small memory model
            .MODEL   large, c, farstack     ; Large memory model,
                                            ;  C conventions,
                                            ;  separate stack
            .MODEL   medium, pascal, os_os2 ; Medium memory model,
                                            ;  Pascal conventions,
                                            ;  OS/2 start-up/exit

The next four sections give more detail on each field.


Defining the Memory Model

MASM supports the standard memory models used by Microsoft high-level
languages─tiny, small, medium, compact, large, huge, and flat. You specify
the memory model with attributes of the same name placed after the .MODEL
directive. Your choice of a memory model does not limit the kind of
instructions you can write. It does, however, control segment defaults and
determine whether data and code are near or far by default (see Table 2.1).


Table 2.1  Attributes of Memory Models

╓┌─────────────┌─────────────┌─────────────┌────────────────┌────────────────╖
Memory Model  Default Code  Default Data  Operating        Data and Code
                                            System           Combined
────────────────────────────────────────────────────────────────────────────
Memory Model  Default Code  Default Data  Operating        Data and Code
                                            System           Combined
────────────────────────────────────────────────────────────────────────────
Tiny          Near          Near          DOS              Yes

Small         Near          Near          DOS, OS/2 1.x    No

Medium        Far           Near          DOS, OS/2 1.x    No

Compact       Near          Far           DOS, OS/2 1.x    No

Large         Far           Far           DOS, OS/2 1.x    No

Huge          Far           Far           DOS, OS/2 1.x    No

Flat          Near          Near          OS/2 2.x         Yes

────────────────────────────────────────────────────────────────────────────



When writing assembler modules for a high-level language, you should use the
same memory model as the calling language. Generally, choose the smallest
memory model available that can contain your data and code, since near
references are more efficient than far references.

The predefined symbol @Model returns the memory model. It encodes memory
models as integers 1 through 7. See Section 1.2.3 for more information on
predefined symbols, and see online help for an example of how to use them.

The seven memory models supported by MASM 6.0 divide into three groups.

Small, Medium, Compact, Large, and Huge Models - The traditional memory
models recognized by many DOS and OS/2 1.x languages are small, medium,
compact, large, and huge. Small model supports one data segment and one code
segment. All data and code are near by default. Large model supports
multiple code and multiple data segments. All data and code are far by
default. Medium and compact models are in between. Medium model supports
multiple code and single data segments; compact model supports multiple data
segments and a single code segment.

Huge model implies individual data items larger than a single segment, but
the implementation of huge data items must be coded by the programmer. Since
the assembler provides no direct support for this feature, huge model is
essentially the same as large model.

In each of these models, you can override the default. For example, you can
make large data items far in small model, or internal procedures near in
large model.

Tiny Model - OS/2 does not support tiny model, but DOS does under MASM 6.0.
This model places all data and code in a single segment. Therefore, the
total program size can be no more than 64K. The default is near for code and
static data items; you cannot override this default. However, you can
allocate far data dynamically at run time using DOS memory allocation
services.

Tiny model produces DOS .COM files. Specifying  .MODEL tiny  automatically
sends a /TINY to the linker. Therefore, /AT is not necessary with  .MODEL
tiny. However, /AT does not insert a .MODEL directive. It only verifies that
there are no base or pointer fixups, and sends /TINY to the linker.

Flat Model - The flat memory model is a nonsegmented configuration available
for 32-bit operating systems. It is similar to tiny model in that all code
and data go in a single 32-bit segment.

OS/2 2.x uses flat model when you specify the .386 or .486 directive before
.MODEL FLAT. All data and code (including system resources) are in a single
32-bit segment. Segment registers are initialized automatically at load
time; the programmer needs to modify them only when mixing 16-bit and 32-bit
segments in a single application. CS, DS, ES, and SS are all assumed to the
supergroup FLAT. FS and GS are assumed to ERROR, since 32-bit versions of
OS/2 reserve the use of these registers. Addresses and pointers passed to
system services are always 32-bit near addresses and pointers. Although the
theoretical size of the single flat segment is four gigabytes, OS/2 2.0
actually limits it to 512 megabytes in flat model.


Choosing the Language Convention

The language type is most important when you write a mixed-language program.


The language option facilitates compatibility with high-level languages by
determining the internal encoding for external and public symbol names, the
code generated for procedure initialization and cleanup, and the order that
arguments are passed to a procedure with INVOKE. It also facilitates
compatibility with high-level-language modules. The PASCAL, BASIC, and
FORTRAN conventions are identical. C and SYSCALL have the same calling
convention but different naming conventions. OS/2 system calls require the
PASCAL calling convention for OS/2 1.x, but require the SYSCALL convention
for OS/2 2.x. Specifying STDCALL for the calling convention enables a
different calling convention and the same naming convention (see Section
20.1).

Procedure definitions (PROC) and high-level procedure calls (INVOKE)
automatically generate code consistent with the calling convention of the
specified language. The PROC, INVOKE, PUBLIC, and EXTERN directives all use
the naming convention of the language. These directives follow the default
language conventions from the .MODEL directive unless you specifically
override the default. Chapter 7, "Controlling Program Flow," tells how to
use these directives. You can also use the OPTION directive to set the
language type. (See Section 1.3.2.) Not specifying a language type in either
the .MODEL, OPTION, EXTERN, PROC, INVOKE, or PROTO statement causes the
assembler to generate an error.

The predefined symbol @Interface provides information about the language
parameters. See online help for a description of the bit flags.

See Chapter 20, "Mixed-Language Programming," for more information on
calling and naming conventions. See Chapter 7, "Controlling Program Flow,"
for information about writing procedures and prototypes. See Chapter 8,
"Sharing Data and Procedures among Modules and Libraries," for information
on multiple-module programming.


Specifying the Operating System

The operating-system options (OS_DOS or OS_OS2) are arguments of .MODEL.
They specify the start-up and exit code generated by the .STARTUP and .EXIT
directives. (See Section 2.2.6.) If you do not use .STARTUP and .EXIT, you
can omit this option. The default is OS_DOS.


Setting the Stack Distance

The NEARSTACK setting places the stack segment in a group, DGROUP, shared
with data. The .STARTUP directive then generates code to adjust SS:SP so
that SS (Stack Segment register) holds the same address as DS (Data Segment
register). If you do not use .STARTUP, you must make this adjustment
yourself or your program may fail to run. (See Section 2.2.6 for information
about start-up code.) In this case, you can use DS to access stack items
(including parameters and local variables) and SS to access near data.
Furthermore, since stack items share the same segment address as near data,
you can reliably pass near pointers to stack items.

Having SS equal to DS gives some programming advantages.

The FARSTACK setting gives the stack a segment of its own. That is, SS does
not equal DS. The default stack type, NEARSTACK, is a convenient setting for
most programs. Use FARSTACK for special cases such as memory-resident
programs and dynamic-link libraries (DLLs) when you cannot assume that the
caller's stack is near.

The stack specification also affects the ASSUME statement generated by
.MODEL and .STACK. You can use the predefined symbol @Stack to determine if
the stack location is DGROUP (for near stacks) or STACK (for far stacks).


2.2.2  Specifying a Processor and Coprocessor

MASM supports a set of directives for selecting processors and coprocessors.
Once you select a processor, you must use only the instruction set available
for that processor. The default is the 8086 processor. If you always want
your code to run on this processor, you do not need to add any processor
directives.

To enable a different processor mode and the additional instructions
available on that processor, use the directives .186, .286, .386, and .486.


The .286P, .386P, and .486P directives enable the instructions available
only at higher privilege levels in addition to the normal instruction set
for the given processor. Privileged instructions are not necessary for
writing applications, even for OS/2. Generally, you don't need privileged
instructions unless you are writing operating-systems code or device
drivers.

Processor directives affect availability of various MASM language features.


In addition to enabling different instruction sets, the processor directives
also affect the behavior of extended language features. For example, the
INVOKE directive pushes arguments onto the stack. If the .286 directive is
in effect, INVOKE takes advantage of operations possible only on 80286 and
later processors.

Use the directives .8087 (the default), .287, .387, and .NO87 to select a
math coprocessor instruction set. The .NO87 directive turns off assembly of
all coprocessor instructions. Note that .486 also enables assembly of all
coprocessor instructions because the 80486 processor has a complete set of
coprocessor registers and instructions built into the chip. The processor
instructions imply the corresponding coprocessor directive. The coprocessor
directives are provided to override the defaults.


2.2.3  Creating a Stack

The stack is the section of memory used for pushing or popping registers and
storing the return address when a subroutine is called. The stack often
holds temporary and local variables.

If your main module is written in a high-level language, that language
handles the details of creating a stack. Use the .STACK directive only when
you write a main module in assembly language.

The .STACK directive creates a stack segment. By default, the assembler
allocates 1K of memory for the stack. This size is sufficient for most small
programs.

To create a stack of a size other than the default size, give .STACK a
single numeric argument indicating stack size in bytes:

    .STACK  2048            ; Use 2K stack

For a description of how stack memory is used with procedure calls and local
variables, see Chapter 7, "Controlling Program Flow."


2.2.4  Creating Data Segments

Programs can contain both near and far data. In general, you should place
important and frequently used data in the near data area, where data access
is faster. This area can get crowded, however, because (in 16-bit operating
systems) the total amount of all near data in all modules cannot exceed 64K.
Therefore, you may want to place infrequently used or particularly large
data items in a far data segment.

The .DATA, .DATA?, .CONST, .FARDATA, and .FARDATA? directives create data
segments. You can access the various segments within DGROUP without
reloading segment registers (see Section 2.3.4, "Defining Segment Groups").
These four directives also prevent instructions from appearing in data
segments by assuming CS to ERROR. (See Section 2.3.3 for information about
ASSUME.)


Near Data Segments

The .DATA directive creates a near data segment. This segment contains the
frequently used data for your program. It can occupy up to 64K in DOS or 512
megabytes under flat model in OS/2 2.0. It is placed in a special group
identified as DGROUP, which is also limited to 64K.

Near data pointers always point to DGROUP.

When you use .MODEL, the assembler automatically defines DGROUP for your
near data segment. The segments in DGROUP form near data, which can normally
be accessed directly through DS or SS.

You can also define the .DATA? and .CONST segments that go into DGROUP
unless you are using flat model. Although all of these segments (along with
the stack) are eventually grouped together and handled as data segments,
.DATA? and .CONST enhance compatibility with Microsoft high-level languages.
In Microsoft languages, .CONST is used for defining constant data such as
strings and floating-point numbers that must be stored in memory. The .DATA?
segment is used for storing uninitialized variables. You can follow this
convention if you wish. If you use C start-up code, .DATA? is initialized to
0.

You can use @data to determine the group of the data segment and @DataSize
to determine the size of the memory model set by the .MODEL directive. The
predefined symbols @WordSize and @CurSeg return the size attribute and name
of the current segment, respectively. See Section 1.2.3, "Predefined
Symbols."


Far Data Segments

The compact, large, and huge memory models use far data addresses by
default. With these memory models, however, you can still use .DATA, .DATA?,
and .CONST to create data segments. The effect of these directives does not
change from one memory model to the next. They always contribute segments to
the default data area, DGROUP, which has a total limit of 64K.


When you use .FARDATA or .FARDATA? in the small and medium memory models,
the assembler creates far data segments FAR_DATA and FAR_BSS, respectively.
You can access variables with:

    mov     ax, SEG farvar2
            mov     ds, ax

See Section 3.1.2 for more information on far data.


2.2.5  Creating Code Segments

Whether you are writing a main module or a module to be called from another
module, you can have both near and far code segments. This section explains
how to use near and far code segments and how to use the directives and
predefined equates that relate to code segments.


Near Code Segments

The small memory model is often the best choice for assembly programs that
are not linked to modules in other languages, especially if you do not need
more than 64K of code. This memory model defaults to near (two-byte)
addresses for code and data, which makes the program run faster and use less
memory.

When you use .MODEL and simplified segment directives, the .CODE directive
in your program instructs the assembler to start a code segment. The next
segment directive closes the previous segment; the END directive at the end
of your program closes remaining segments. The example at the beginning of
Section 2.2, "Using Simplified Segment Directives," shows how to do this.

You can use the predefined symbol @CodeSize to determine whether code
pointers default to NEAR or FAR.


Far Code Segments

When you need more than 64K of code, use the medium, large, or huge memory
model to create far segments.

The medium, large, and huge memory models use far code addresses by default.
In the larger memory models, the assembler creates a different code segment
for each module. If you use multiple code segments in the small, compact, or
tiny model, the linker combines the .CODE segments for all modules into one
segment.

The assembler assigns names to code segments.

For far code segments, the assembler names each code segment MODNAME_TEXT,
in which MODNAME is the name of the module. With near code, the assembler
names every code segment _TEXT, causing the linker to concatenate these
segments into one. You can override the default name by providing an
argument after .CODE. (See Appendix E, "Default Segment Names," for a
complete list of segment names generated by MASM.)

With far code, a single module can contain multiple code segments. The .CODE
directive takes an optional text argument that names the segment. For
instance, the example below creates two distinct code segments, FIRST_TEXT
and SECOND_TEXT.

    .CODE   FIRST
            .
            .       ; First set of instructions here
            .
            .CODE   SECOND
            .
            .       ; Second set of instructions here
            .

Whenever the processor executes a far call or jump, it loads CS with the new
segment address. No special action is necessary other than making sure that
you use far calls and jumps. See Section 3.1.2, "Near and Far Addresses."

────────────────────────────────────────────────────────────────────────────
NOTE
The ASSUME directive is never necessary when you change code segments. In
MASM 6.0, the assembler always assumes that the CS register contains the
address of the current code segment or group. See Section 2.3.3 for more
information about ASSUME used with segment registers.
────────────────────────────────────────────────────────────────────────────


2.2.6  Starting and Ending Code with .STARTUP and .EXIT

The easiest way to begin and end a program is to use the .STARTUP and .EXIT
directives in the main module. The main module contains the starting point
and usually the termination point. You do not need these directives in a
module called by another module.

.STARTUP generates the start-up code required by either DOS or OS/2.

These directives make programs easy to maintain. They automatically generate
code appropriate to the operating system and stack types specified with
.MODEL. Thus, you can specify the program is for a different operating
system or stack type by altering keywords in the .MODEL directive.

To start a program, place the .STARTUP directive where you want execution to
begin. Usually, this location immediately follows the .CODE directive:

    .CODE
            .STARTUP
            .
            .       ; Place executable code here
            .
            .EXIT
            END

Note that .EXIT generates executable code, while END does not. The END
directive informs the assembler that it has reached the end of the module.
All modules must end with the END directive whether you use simplified or
full segments.

If you do not use .STARTUP, you must give the starting address as an
argument to the END directive. When .STARTUP is present, the assembler
ignores any argument to END.

The code generated by .STARTUP depends on the operating system specified
after .MODEL.

If your program uses DOS for its operating system (the default), the
initialization code sets DS to DGROUP, and adjusts SS:SP so that it is
relative to the group for near data, DGROUP. To initialize a DOS program
with the default NEARSTACK attribute, .STARTUP generates the following code:


    @Startup:
            mov     dx, DGROUP
            mov     ds, dx
            mov     bx, ss
            sub     bx, dx
            shl     bx, 1   ; If .286 or higher, this is
            shl     bx, 1   ;  shortened to shl bx, 4
            shl     bx, 1
            shl     bx, 1
            cli             ; Not necessary in .286 or higher
            mov     ss, dx
            add     sp, bx
            sti             ; Not necessary in .286 or higher
            .
            .
            .
            END     @Startup

A DOS program with the FARSTACK attribute does not need to adjust SS:SP, so
it just initializes DS:

    @Startup:
            mov     dx, DGROUP
            mov     ds, dx
            .
            .
            .
            END     @Startup

OS/2 initializes DS so that it points to DGROUP and sets SS:SP as desired.
Thus, when the OS_OS2 attribute is given, .STARTUP generates only a starting
address. This does not show up in the listing file, however, since the /Sg
option for listing files shows only the generated instructions.

When the program terminates, you can return an exit code to the operating
system. Applications that check exit codes usually assume that an exit code
of 0 means no problem occurred and that 1 means an error terminated the
program. The .EXIT directive accepts the exit code as its one optional
argument:

    .EXIT   1       ; Return exit code 1

This directive generates a DOS interrupt or OS/2 system call, depending on
the operating system specified in .MODEL. The code generated under DOS
depends on the argument provided to .EXIT. One example is

    mov     al, value
            mov     ah, 04Ch
            int     21h

if a return value is specified. The return value can be a constant, a memory
reference, or a register that can be moved into the AL register. If no
return value is specified, the first line in the example code above is not
generated.

For OS/2, .EXIT invokes DosExit if you provide a prototype for DosExit and
if you include OS2.LIB. The listing file shows the statements generated by
INVOKE if the /Sg command-line option is specified. If you specify a return
value as an expression, the code generated passes the expression instead of
the register contents to the DosExit function. See Chapter 17 for
information on writing programs for OS/2.


2.3  Using Full Segment Definitions

If you need complete control over segments, you can fully define the
segments in your program. This section explains segment definitions,
including how to order segments and how to define the segment types.

If you write a program under DOS without .MODEL and .STARTUP, you must
initialize registers yourself and use the END directive to indicate the
starting address. Under OS/2 you do not have to initialize registers.
Section 2.3.2, "Controlling the Segment Order," describes typical start-up
code.


2.3.1  Defining Segments with the SEGMENT Directive

The SEGMENT directive begins a segment, and the ENDS directive ends a
segment:

    name SEGMENT «align» «READONLY»
    «combine» «use» «'class'»
    statements
    name ENDS

The name defines the name of the segment. Within a module, all segment
definitions with the same name are treated as though they reference the same
segment. The linker also combines identically named segments from different
modules unless the combine type is PRIVATE. In addition, segments can be
nested.

Options used with the SEGMENT directive can be in any order.

The optional types that follow the SEGMENT directive give the linker and the
assembler instructions on how to set up and combine segments. The list below
summarizes these types; the following sections explain them in more detail.


Type                              Description
────────────────────────────────────────────────────────────────────────────
align                             Defines the memory boundary on which a
                                    new segment begins.

READONLY                          Tells the assembler to report an error
                                    if it detects an instruction modifying
                                    any item in a
                                    READONLY segment.

combine                           Determines how the linker combines
                                    segments from different modules when
                                    building executable files.

use (80386/486 only)              Determines the size of a segment. USE16
                                    indicates that offsets in the segment
                                    are 16 bits wide. USE32 indicates 32-bit
                                    offsets.

class                             Provides a class name for the segment.
                                    The linker automatically groups segments
                                    of the same class in memory.


Types can be specified in any order. You can specify only one attribute from
each of these fields; for example, you cannot have two different align
types.

Once you define a segment, you can reopen it later with another SEGMENT
directive. When you reopen a segment, you need only give the segment name.

────────────────────────────────────────────────────────────────────────────
NOTE

The PAGE align type and the PUBLIC combine type are distinct from the PAGE
and PUBLIC directives. The assembler distinguishes them by means of context.
────────────────────────────────────────────────────────────────────────────


Aligning Segments

The optional align type in the SEGMENT directive defines the range of memory
addresses from which a starting address for the segment can be selected. The
align type can be any one of these:

Align Type                        Starting Address
────────────────────────────────────────────────────────────────────────────
BYTE                              Next available byte address.

WORD                              Next available word address.

DWORD                             Next available doubleword address.

PARA                              Next available paragraph address (16
                                    bytes per paragraph). Default.

PAGE                              Next available page address (256 bytes
                                    per page).


The linker uses the alignment information to determine the relative starting
address for each segment. The operating system calculates the actual
starting address when the program is loaded.


Making Segments Read-Only

The optional READONLY attribute is helpful when creating read-only code
segments for protected mode or when writing code to be placed in read-only
memory (ROM). It protects against illegal self-modifying code.

The READONLY attribute causes the assembler to check for instructions that
modify the segment and to generate an error if it finds any. The assembler
generates an error if you attempt to write directly to a read-only segment.



Combining Segments

The optional combine type in the SEGMENT directive defines how the linker
combines segments having the same name but appearing in different modules.
The combine type controls linker behavior, not assembler behavior. The
combine types are described in full detail in online help and are summarized
below.

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Combine Type                      Linker Action
────────────────────────────────────────────────────────────────────────────
PRIVATE                           Does not combine the segment with
                                    segments from other modules, even if
                                    they have the same name.
                                    Default.

PUBLIC                            Concatenates all segments having the
                                    same name to form a single, contiguous
                                    segment.

STACK                             Concatenates all segments having the
Combine Type                      Linker Action
────────────────────────────────────────────────────────────────────────────
STACK                             Concatenates all segments having the
                                    same name and causes the operating
                                    system to set SS:00 to the bottom and
                                    SS:SP to the top of the resulting
                                    segment. Data initialization is
                                    unreliable, as discussed below.

COMMON                            Overlaps segments. The length of the
                                    resulting area is the length of the
                                    largest of the combined segments. Data
                                    initialization is unreliable, as
                                    discussed below.

MEMORY                            Used as a synonym for the PUBLIC combine
                                    type.

AT address                        Assumes address as the segment location.
                                    An AT segment cannot contain any code or
                                    initialized data, but it is useful for
Combine Type                      Linker Action
────────────────────────────────────────────────────────────────────────────
                                    initialized data, but it is useful for
                                    defining structures or variables that
                                    correspond to specific far memory
                                    locations, such as a screen buffer or
                                    low memory.
                                    The AT combine type cannot be used in
                                    protected-mode programs.



Do not place initialized data in STACK or COMMON segments. With these
combine types, the linker overlays initialized data for each module at the
beginning of the segment. The last module containing initialized data writes
over any data from other modules.

────────────────────────────────────────────────────────────────────────────
NOTE

Normally, you should provide at least one stack segment (having STACK
combine type) in a program. If no stack segment is declared, LINK displays a
warning message. You can ignore this message if you have a specific reason
for not declaring a stack segment. For example, you would not have a
separate stack segment in a DOS tiny model (.COM) program, nor would you
need a separate stack in a DLL library that used the caller's stack.
────────────────────────────────────────────────────────────────────────────


Setting Segment Word Sizes (80386/486 Only)

The use type in the SEGMENT directive specifies the segment word size on the
80386/486 processors. Segment word size determines the default operand and
address size of all items in a segment.

The 80386/486 can operate in 16-bit or 32-bit mode.

The size attribute can be USE16, USE32, or FLAT. If the 80386 or 80486
processor has been selected with the .386 or .486 directive, and this
directive precedes .MODEL, then USE32 is the default. This attribute
specifies that items in the segment are addressed with a 32-bit offset
rather than a 16-bit offset. If .MODEL precedes the .386 or .486 directive,
USE16 is the default. To make USE32 the default, put .386 or .486 before
.MODEL. You can override the USE32 default with the USE16 attribute.


────────────────────────────────────────────────────────────────────────────
NOTE
Mixing 16-bit and 32-bit segments in the same program is possible but
usually is necessary only in systems programming.
────────────────────────────────────────────────────────────────────────────


Setting Segment Order with Class Type

Segments of the same class are grouped together in the executable file.

The optional class type in the SEGMENT directive helps control segment
ordering. Two segments with the same name are not combined if their class is
different. The linker arranges segments so that all segments identified with
a given class type are next to each other in the executable file. However,
within a particular class, the linker orders segments in the order
encountered. The .ALPHA, .SEQ, or .DOSSEG directive determines this order in
each .OBJ file. The most common application for specifying a class type is
to place all code segments first in the executable file.


2.3.2  Controlling the Segment Order

The assembler normally positions segments in the object file in the order in
which they appear in source code. The linker, in turn, processes object
files in the order in which they appear on the command line. Within each
object file, the linker outputs segments in the order they appear, subject
to any group, class, and .DOSSEG requirements.

You can usually ignore segment ordering. However, it is important whenever
you want certain segments to appear at the beginning or end of a program or
when you make assumptions about which segments are next to each other in
memory. For tiny model (.COM) programs, code segments must appear first in
the executable file, because execution must start at the address 100h.


Segment Order Directives

You can control the order in which segments appear in the executable program
with three directives. The default, .SEQ, arranges segments in the order in
which they are declared.

The .ALPHA directive specifies alphabetical segment ordering within a
module. .ALPHA is provided for compatibility with early versions of the IBM
assembler. If you have trouble running code from older books on assembly
language, try using .ALPHA.

The .DOSSEG directive specifies the DOS segment-ordering convention. It
places segments in the standard order required by Microsoft languages. Do
not use .DOSSEG in a module to be called from another module.

The .DOSSEG directive orders segments in this order:


    1.  Code segments

    2.  Data segments, in this order:

        a.  Segments not in class BSS or STACK

        b.  Class BSS segments

        c.  Class STACK segments



When you declare two or more segments to be in the same class, the linker
automatically makes them contiguous. This rule overrides the
segment-ordering directives. (See "Setting Segment Order with Class Type" in
the previous section for more about segment classes.)


Linker Control

Most of the segment-ordering techniques (class names, .ALPHA, .SEQ) control
the order in which the assembler outputs segments. Usually, you are more
interested in the order in which segments appear in the executable file. The
linker controls this order.

The linker processes object files in the order in which they appear on the
command line. Within each module, it then outputs segments in the order
given in the object file. If the first module defines segments DSEG and
STACK and the second module defines CSEG, then CSEG is output last. If you
want to place CSEG first, there are two ways to do so.

.DOSSEG handles segment ordering.

The simpler method is to use .DOSSEG. This directive is output as a special
record to the object file linker, and it tells the linker to use the
Microsoft segment-ordering convention. This convention overrides
command-line order of object files, and it places all segments of class
'CODE'  first. (See Section 2.3.1, "Defining Segments with the SEGMENT
Directive.")

The other method is to define all the segments as early as possible (in an
include file, for example, or in the first module). These definitions can be
"dummy segments"─that is, segments with no content. The linker observes the
segment ordering given, then later combines the empty segments with segments
in other modules that have the same name.

For example, you might include the following at the start of the first
module of your program or in an include file:

    _TEXT   SEGMENT WORD PUBLIC 'CODE'
    _TEXT   ENDS
    _DATA   SEGMENT WORD PUBLIC 'DATA'
    _DATA   ENDS
    CONST   SEGMENT WORD PUBLIC 'CONST'
    CONST   ENDS
    STACK   SEGMENT PARA STACK 'STACK'
    STACK   ENDS

Later in the program, the order in which you write  _TEXT,  _DATA, or other
segments does not matter because the ultimate order is controlled by the
segment order defined in the include file.


2.3.3  Setting the ASSUME Directive for Segment Registers

Many of the assembler instructions assume a default segment. For example,
JMP assumes the segment associated with the CS register, PUSH and POP assume
the segment associated with the SS register, and MOV instructions assume the
segment associated with the DS register.


The assembler must know the location of segment addresses.

When the assembler needs to reference an address, it must know what segment
contains the address. It finds this by using the default segment or group
addresses assigned with the ASSUME directive. The syntax is

    ASSUME  segregister:seglocation [[,segregister:seglocation]]
    ASSUME  dataregister:qualifiedtype [[,dataregister:qualifiedtype]]
    ASSUME  register:ERROR [[,register:ERROR]]
    ASSUME  [[register:»NOTHING
    [[, register: NOTHING]]

The seglocation must be the name of the segment or group that is to be
associated with segregister. Subsequent instructions that assume a default
register for referencing labels or variables automatically assume that if
the default segment is segregister, the label or variable is in the
seglocation. Beginning with MASM 6.0, the assembler automatically sets CS to
have the address of the current code segment. Therefore, you do not need to
include

    ASSUME CS : MY_CODE

at the beginning of your program if you want the current segment associated
with CS.

────────────────────────────────────────────────────────────────────────────
NOTE
Using the ASSUME directive to tell the assembler which segment to associate
with a segment register is not the same as telling the processor. The ASSUME
directive  affects only assembly-time assumptions. You may need to use
instructions to change run-time assumptions. Initializing segment registers
at run time is discussed in Section 3.1.1.1, "Informing the Assembler about
Segment Values."
────────────────────────────────────────────────────────────────────────────

The ASSUME directive can define a segment for each of the segment registers.
The segregister can be CS, DS, ES, or SS (and FS and GS on the 80386/486).
The seglocation must be one of the following:


    ■   The name of a segment defined in the source file with the SEGMENT
        directive

    ■   The name of a group defined in the source file with the GROUP
        directive

    ■   The keyword NOTHING, ERROR, or FLAT

    ■   A SEG expression (see Section 3.2.2, "Immediate Operands")

    ■   A string equate (text macro) that evaluates to a segment or group name
        (but not a string equate that evaluates to a SEG expression)


It is legal to combine assumes to FLAT with assumes to specific segments.
Combinations might be necessary in operating-system code that handles both
16- and 32-bit segments.

The keyword NOTHING cancels the current segment assumptions. For example,
the statement ASSUME NOTHING cancels all register assumptions made by
previous ASSUME statements.

The ASSUME directive can be used anywhere in your program.

Usually, a single ASSUME statement defines all four segment registers at the
start of the source file. However, you can use the ASSUME directive at any
point to change segment assumptions.

Using the ASSUME directive to change segment assumptions is often equivalent
to changing assumptions with the segment-override operator (:) (see Section
3.2.3, "Direct Memory Operands"). The segment-override operator is more
convenient for one-time overrides, whereas the ASSUME directive may be more
convenient if previous assumptions must be overridden for a sequence of
instructions.

You can also prevent the use of a register with

    ASSUME  SegRegister : ERROR

The assembler does an  ASSUME CS:ERROR  when you use simplified directives
to create data segments, effectively preventing instructions or code labels
from appearing in a data segment.

See Section 3.3.2 for information on other applications of ASSUME.


2.3.4  Defining Segment Groups

A group is a collection of segments totalling not more than 64K in 16-bit
mode. Each code or data item in the group can be addressed relative to the
beginning of the group through DS or SS.

Segments within a group can be treated as if they shared the same segment
address.

A group lets you develop separate segments for different kinds of data and
then combine these into one segment (a group) for all the data. Using a
group can save you from having to continually reload segment registers to
access different segments. As a result, the program uses fewer instructions
and runs faster.

The most common example of a group is the specially named group for near
data, DGROUP. In the Microsoft segment model, several segments (_DATA, _BSS,
CONST, and STACK) are combined into a single group called DGROUP. Microsoft
high-level languages place all near data segments in this group. (By
default, the stack is placed here, too.) The .MODEL directive automatically
defines DGROUP. The DS register normally points to the beginning of the
group, giving you relatively fast access to all data in DGROUP.

The syntax of the group directive is

    name GROUP segment [[,segment]]...

The name labels the group. It can refer to a group that was previously
defined. This feature lets you add segments to a group one at a time. For
example, if MYGROUP  was previously defined to include  ASEG  and  BSEG,
then the statement

    MYGROUP GROUP   CSEG

is perfectly legal. It simply adds  CSEG  to the group  MYGROUP;  ASEG  and
BSEG  are not removed.

Each segment can be any valid segment name (including a segment defined
later in source code), with one restriction: a segment cannot belong to more
than one group.

The GROUP directive does not affect the order in which segments of a group
are loaded. You can place any number of 16-bit segments in a group as long
as the total size does not exceed 65,536 bytes. If the processor is in
32-bit mode, the maximum size is four gigabytes. You need to make sure that
non-grouped segments do not get placed between grouped segments in such a
way that the size of the group exceeds 64K or 4 gigabytes. Neither can you
place a 16-bit and a 32-bit segment in the same group.


2.4  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topic                                 Access
────────────────────────────────────────────────────────────────────────────
Memory models                         Choose "Memory Models" from the list
                                        of tables on the "MASM 6.0 Contents"
                                        screen

@Model, @CodeSize, @DataSize          Choose "Predefined Symbols" from the
                                        "MASM 6.0 Contents" screen

Calling conventions                   From the MASM Index, choose "Calling
                                        Convention"

Coprocessor Directives                From the "MASM 6.0 Contents" screen,
                                        choose "Directives"; then choose
                                        "Processor Selection"

Simplified and full (complete)        From the "MASM 6.0 Contents" screen,
segment control                       choose "Directives"; then choose
                                        "Simplified Segment Control" or
                                        "Complete Segment Control"







Chapter 3  Using Addresses and Pointers
────────────────────────────────────────────────────────────────────────────

Most processor and operating-system modes require the use of segmented
addresses to access the code and data for MASM applications. The address of
the code or data in a segment is relative to an address in a segment
register. You can also use pointers to access data in MASM programs.

The first section of this chapter describes how to initialize default
segment registers to access near and far addresses. The next section
describes how to use the available addressing modes to access the code and
data. It also describes the related operators, syntax, and displacements.

The third section of this chapter explains how to use the TYPEDEF directive
to declare pointers (variables containing addresses) and the ASSUME
directive to give the assembler information about registers containing
pointers. This section also shows you how to do typical pointer operations
and how to write code that works for pointer variables in any memory model.



3.1  Programming Segmented Addresses

Before you use segmented addresses in your programs, you need to initialize
the segment registers. The initialization process depends on the registers
used and on your choice of simplified segment directives or full segment
definitions. The simplified segment directives (introduced in Section 2.2)
handle most of the initialization process for you. This section explains how
to inform the assembler and the processor of segment addresses, and how to
access the near and far code and data in those segments.


3.1.1  Initializing Default Segment Registers

The segmented architecture of the 8086-family of processors does not require
you to specify two addresses every time you access memory. As Chapter 2,
"Organizing MASM Segments," explains, the 8086 family of processors uses a
system of default segment registers to simplify access to the most commonly
used data and code.

The segment registers DS, SS, and CS are normally initialized to default
segments at the beginning of a program. If you write the main module in a
high-level language, the compiler initializes the segment registers. If you
write the

main module in assembly language, you must initialize them yourself. Follow
these two steps to initialize segments:


    1.  Tell the assembler which segment is associated with a register. The
        assembler must know the default segments at assembly time.

    2.  Tell the processor which segment is associated with a register by
        writing the necessary code to load the correct segment value into the
        segment register on the processor.


These steps are discussed separately in the following sections.


3.1.1.1  Informing the Assembler about Segment Values

Use ASSUME to inform the assembler about default segments.

The first step in initializing segments is to tell the assembler which
segment to associate with a register. You do this with the ASSUME directive.
If you use simplified segment directives, the assembler generates the
appropriate ASSUME statements automatically. If you use full segment
definitions, you must code the ASSUME statements for registers other than CS
yourself. (ASSUME can also be used on general-purpose registers, as
explained in Section 3.3.2, "Defining Register Types with ASSUME.")

With simplified segment directives, the .STARTUP directive and the start-up
code initialize DS to be equal to SS (unless you specify FARSTACK), which
allows default data to be accessed through either SS or DS. This can improve
efficiency in the code generated by compilers. The "DS equals SS" convention
may not work with certain applications, such as memory-resident programs in
DOS and multithread programs in OS/2. The code generated for .STARTUP is
shown in Section 2.2.6, "Starting and Ending Code with .STARTUP and .EXIT."
You can use similar code to set DS equal to SS in programs using full
segment definitions.

Here is an example using full segment definitions; it is equivalent to the
ASSUME statement generated with simplified segment directives in small model
with NEARSTACK:

    ASSUME cs:_TEXT, ds:DGROUP, ss:DGROUP

In the example above, DS and SS are part of the same segment group. It is
also possible to have different segments for data and code, and to use
ASSUME to set ES, as shown below:

    ASSUME cs:MYCODE, ds:MYDATA, ss:MYSTACK, es:OTHER

Correct use of the ASSUME statement can help find addressing errors. With
.CODE, the assembler assumes CS to the current segment. When you use the
simplified segment directives .DATA, .DATA?, .CONST, .FARDATA, or .FARDATA?,
the assembler automatically assumes CS to ERROR. This prevents

instructions from appearing in these segments. If you use full segment
definitions, you can accomplish the same by placing  ASSUME CS:ERROR  in a
data segment.

With either simple or full segments, you can cancel the control of an ASSUME
statement by assuming NOTHING. No assumptions is the default condition. For
example, you cancel the assumption for ES above with the following
statement:

    ASSUME es:NOTHING

Prior to the .MODEL statement (or in its absence), the assembler sets the
ASSUME statement for DS, ES, and SS to the current segment.


3.1.1.2  Informing the Processor about Segment Values

The second step in initializing segments is to inform the processor of
segment values at run time. How segment values are initialized at run time
differs for each segment register and depends on your use of simplified
segment directives or full segment definitions and on the operating system.


Specifying a Starting Address - The CS segment register and the IP
(instruction pointer) register are initialized automatically if you use the
.STARTUP directive with simplified segment directives. If you use full
segment definitions, you must specifically set a label in the code segment
at the instruction you want executed first. Then provide that label as an
argument to the END directive. Both CS and IP are set at load time to the
start address the linker gets from the END directive:

    _TEXT   SEGMENT WORD PUBLIC 'CODE
            ORG     100h    ; Use this declaration for .COM files only
    start:                  ; First instruction here
            .
            .
            .
    _TEXT   ENDS
            END     start   ; Name of starting label

The operating system automatically resolves the value of CS:IP at load time.
The label specified as the start address becomes the initial value of IP. In
an executable (.EXE) file, the start address is encoded into the header and
is initialized by the operating system at load time. In a .COM file, the
initial IP is always assumed to be 100h. Therefore, you must use the ORG
directive to set the start address to 100h. CS and IP cannot be directly
modified except through jump, call, and interrupt instructions.

DS is initialized automatically under OS/2, but you must initialize it for
DOS.

Initializing DS - The DS register is automatically initialized to the
correct value (DGROUP) if you use .STARTUP or if you are writing a program
for OS/2. If you do not use .STARTUP with DOS, you must initialize DS using
the following instructions:

    mov     ax, DGROUP
            mov     ds, ax

The initialization requires two instructions because the segment name is a
constant and the assembler does not allow a constant to be loaded directly
to a segment register. The example above loads DGROUP, but you can load any
valid segment or group.

SS and SP are initialized automatically.

Initializing SS and SP - The SS and SP registers are initialized
automatically if you use the .STACK directive with simplified segments or if
you define a segment that has the STACK combine type with full segment
definitions. Using the STACK directive initializes SS to the stack segment.
If you want SS to be equal to DS, use .STARTUP or its equivalent. (See
"Combining Segments" in Section 2.3.1.) For an executable file, the values
are encoded into the executable header and resolved at link time. For a .COM
file, SS is initialized to the first address of the 64K program segment and
SP is initialized to 0FFFEh.

If you do not need to access far data in your program, you do not need to
initialize the ES register, although you can do so. Use the same technique
as for the DS register. You can initialize SS to a far stack in the same
way.


3.1.2  Near and Far Addresses

Addresses which have an implied segment name or segment registers associated
with them are called "near addresses." Addresses which have an explicit
segment associated with them are called "far addresses." The assembler
handles near and far code automatically, as described below. You must
specify how to handle far data.

The Microsoft segment model puts all near data and the stack in a group
called DGROUP. Near code is put in a segment called _TEXT. Each module's far
code or far data is placed in a separate segment. This convention is
described in Section 2.3.2, "Controlling the Segment Order."

The assembler cannot determine the address for some program components,
which are said to be relocatable. The assembler generates a fixup record and
the linker provides the address once the location of all segments has been
determined. Usually a relocatable operand references a label, but there are
exceptions. Examples in the next two sections include information about the
relocatability of near and far data.

Near Code - Control transfers within near code do not require changes to
segment registers. The processor automatically handles changes to the offset
in the IP register when control-flow instructions such as JMP, CALL, and RET
are used. The statement

    call    nearproc        ; Change code offset

changes the IP register to the new address but leaves the segment unchanged.
When the procedure returns, the processor resets IP to the offset of the
next instruction after the call.

Far Code - The processor automatically handles segment register changes when
dealing with far code. The statement

    call    farproc         ; Change code segment and offset

automatically moves the segment and offset of the  farproc  procedure to the
CS and IP registers. When the procedure returns, the processor sets CS to
the original code segment and sets IP to the offset of the next instruction
after the call.

Near Data - Near data can usually be accessed directly. That is, a segment
register already holds the correct segment for the data item. The term "near
data" is often used to refer to the data in the DGROUP group.

After the first initialization of the DS and SS registers, these registers
normally point into DGROUP. If you modify the contents of either of these
registers during the execution of the program, the register may need to be
reloaded prior to being used for addressing DGROUP data.

If a stack variable is accessed directly through BP or SP, the SS register
is the default. Otherwise, the default is DS:

    nearvar WORD    0
            .
            .
            .
            mov     ax, nearvar ; Access near data through DS or SS
            mov     ax, [bp+6]  ; Access near data through SS

In this example,  nearvar  is a relocatable label. The assembler does not
know where the memory for  nearvar  will be allocated. The linker provides
the address at link time. The expression  [bp+6]  is not relocatable. The
linker does not need to provide an address for this expression.

Far Data - To read or modify a far address, a segment register must point to
the segment of the data. This requires two steps. First load the segment
(normally either ES or DS) with the correct value, and then (optionally) set
an assume of the segment register to the segment of the address (or to
NOTHING).

────────────────────────────────────────────────────────────────────────────
NOTE
In flat model (OS/2 2.x), far addresses are rarely used. By default, all
addressing is relative to the initial values of the segment registers. Thus,
this section on far addressing does not apply to most flat model programs.
────────────────────────────────────────────────────────────────────────────

You can initialize ES.

One method commonly used to access far data is to initialize the ES segment
register. This example shows two ways to do this:

    ; First method
            mov     ax, SEG farvar  ; Load segment of the far address
            mov     es, ax
            mov     ax, es:farvar   ; Provide an explicit segment
                                    ;  override on the addressing
    ; Second method
            mov     ax, SEG farvar2 ; Load the segment of the
                                    ;  far address
            mov     ex, ax
            ASSUME  ES:SEG farvar2  ; Tell the assembler that ES points
                                    ;  to the segment containing farvar2
            mov     ax, farvar2     ; The assembler provides the ES
                                    ;  override since it knows that
                                    ;  the label is addressable

After loading the segment of the address into the ES segment register, you
can either explicitly override the segment register so that the addressing
is correct (method 1) or allow the assembler to insert the override for you
(method 2). The assembler uses ASSUME statements to determine which segment
register can be used to address a segment of memory. To use the segment
override operator, the left operand must be a segment register, not a
segment name. (See Section 3.2.3 for more information on segment overrides.)


If an instruction needs a segment override, the resulting code is slightly
larger and slower, since the override must be encoded into the instruction.
However, the resulting code may still be smaller than the code for multiple
loads of the default segment register for the instruction.

The DS, SS, FS, and GS segment registers (FS and GS are available only on
the 80386/486 processors) may also be used to provide for addressing through
other segments.

If a program uses ES to access far data, it need not restore ES when
finished (unless the program uses flat model). Some compilers require that
you restore ES before returning to a module written in a high-level
language.

You can reinitialize DS.

For a series of memory accesses to far data, you can reinitialize DS to the
far data and then restore DS when you are finished. Use the ASSUME directive
to let the assembler know that DS is no longer associated with the default
data segment, as shown below:

    push    ds               ; Save original segment
            mov     ax, SEG fararray ; Move segment into data register
            mov     ds, ax           ; Initialize segment register
            ASSUME  ds:SEG fararray  ; Tell assembler where data is
            mov     ax, fararray[0]  ; Direct access faster
            mov     dx, fararray[2]  ; (A relocatable expression)
            .
            .
            .
            pop     ds               ; Restore segment
            ASSUME  ds:@DATA         ;  and default assumption

The additional overhead of saving and restoring the DS register in this data
access method may be worthwhile to avoid repeated segment overrides.

If a program changes DS to access far data, it should restore DS when
finished. This allows procedures to assume that DS is the segment for near
data. This is a convention used in many compilers, including Microsoft
compilers.

Relocatable Data - The memory expression  es:farvar  is a relocatable memory
expression, since the assembler cannot determine the address at assembly
time.

Since no label is referenced, you may expect

    mov ax, _myseg:0

to be nonrelocatable (in small model). However, in this case,  _myseg:0  is
a location in a local module whose memory location is dependent on the link
order, so  mov ax, _myseg:0  is relocatable.

A group name is also an immediate constant representing the beginning of the
group. The first three expressions below are relocatable expressions; the
fourth is not.

    mov ax, DGROUP             ; Relocatable
            mov ax, @data              ; Relocatable
            mov ax, mygroup            ; Relocatable
            mov ax, ds:0               ; Not relocatable


3.2  Specifying Addressing Modes

The 8086 family of processors recognizes four kinds of instruction operands:
register, immediate, direct memory, and indirect memory. Each type of
operand corresponds to a different addressing mode.

The four types of operands are summarized in the following list and
described at length in the rest of this section.

Operand Type                      Addressing Mode
────────────────────────────────────────────────────────────────────────────
Register                          An 8-bit or 16-bit register on the
                                    8086-80486; can also be 32-bit on the
                                    80386/486

Immediate                         A constant value contained in the
                                    instruction itself

Direct memory                     A fixed location in memory

Indirect memory                   A memory location determined at run time
                                    by using the address stored in one or
                                    two registers and a constant



3.2.1  Register Operands

A register operand specifies that the value in a particular register is an
operand. Code for the register or registers used in operands is encoded into
the instruction at assembly time.

Register operands can be used anywhere you need an operand. The following
examples show typical register operands:

    mov     bx, 10          ; Load constant to BX
            add     ax, bx          ; Add AX and BX
            jmp     di              ; Jump to the address in DI

Register operands have a specific use related to addresses.

An offset stored in a base or index register is often used as a pointer into
memory. An offset can be stored in one of the base or index registers; the
register can then be used as an indirect memory operand (see Section 3.2.4).
For example:

    mov     [bx], dl ; Store DL in indirect memory operand
            inc     bx       ; Increment register operand
            mov     [bx], dl ; Store DL in new indirect memory operand

This example moves the value in DL to two consecutive bytes of a memory
location pointed to by BX. Any instruction that changes the register value
also changes the data item pointed to by the register.


3.2.2  Immediate Operands

An immediate operand is a constant value that is specified at assembly time.
It can be a constant or the result of a constant expression. Immediate
values are usually encoded into the internal representation of the
instruction at assembly time. These are typical examples:

    mov     cx, 20          ; Load constant to register
            add     var, 1Fh        ; Add hex constant to variable
            sub     bx, 25 * 80     ; Subtract constant expression

The OFFSET Operator - Address constants are a special case of immediate
operand and consist of an offset or segment value. The OFFSET operator
specifies the offset of a memory location, as shown below:

    mov     bx, OFFSET var  ; Load offset address

For information on differences between MASM 5.1 behavior and MASM 6.0
behavior related to OFFSET, see Appendix A.

An OFFSET expression is resolved at link time.

Since segments in different modules may be combined into a single segment,
the true base of the segment is not known. Thus, the offset cannot be
resolved until link time and  var  is a relocatable immediate.

The SEG Operator - The SEG operator specifies the segment of a memory
location:

    mov     ax, SEG farvar  ; Load segment address
            mov     es, ax

A SEG expression is resolved at load time.

The actual value of a particular segment is never known until the program is
loaded into memory. Constant segments are encoded into the header of the
executable file at link time. Executable files in the DOS .COM format (tiny
model) cannot contain relocatable segment expressions.

When you use the SEG operator with a variable that is not external, MASM 6.0
returns the address of the frame (the segment, group, or segment register)
if one has been explicitly set. Otherwise, it returns the group if one has
been specified. In the absence of a defined group, SEG returns the segment
where the variable is defined.

For external variables that are not defined in a segment, the linker fills
in the segment portion of the address, which may be a segment or group.

This behavior can be changed with the /Zm command-line option or with the
OPTION OFFSET:SEGMENT statement (see Appendix A, "Differences between MASM
6.0 and 5.1"). Section 1.3.2 introduces the OPTION directive.


3.2.3  Direct Memory Operands

A direct memory operand specifies the data at a given address. The address
and size of the data are encoded into the internal representation of the
instruction. However, the instruction acts on the contents of the address,
not the address itself. You must usually specify the size of these operands
so that the instruction knows how much memory to operate on.

The offset value of a direct memory operand is not resolved until link time,
and the segment must always be in a segment register at run time. The
assembler automatically handles address resolution.

You usually represent a direct memory operand in source code as a symbolic
name previously declared with a data directive such as BYTE, as illustrated
below:

    .DATA?          ; Segment for uninitialized data
    var     BYTE   ?        ; Reserve one byte at current address
                            ;  and assign this address to var
            .CODE
            .
            .
            .
            mov     var, al ; Load contents of byte register into
                                address specified by var

Any location in memory can be a direct memory operand as long as a size is
specified and the location is fixed. The data at the address can change, but
the address cannot. By default, instructions that use direct memory
addressing use the DS register. You can create an expression that points to
a memory location using any of the following operators:

Operator Name                     Symbol
Plus
────────────────────────────────────────────────────────────────────────────
Minus                             -
Index                             [ ]
Structure member                  .
Segment override                  :

These operators are discussed in more detail below.

Several operators can be used in expressions that evaluate to direct memory
operands.

Plus and Minus - The result of combining a memory operand and a constant
number with the plus or minus operator is a direct memory operand. However,
the result of combining two memory operands with the minus operator is an
immediate operand. For example:

    memvar  EQU     array + 5       ; Address five bytes beyond
    array
    immexp  EQU     mem1 - mem2     ; Distance between addresses

The second expression is legal only if both addresses are in the same
segment.

The expression  mem1 - mem2  is not relocatable, since the reference to the
two labels represents a difference in addresses (offsets). The linker does
not need to know about the labels in this statement.

Index - The index operator (brackets enclosing an index value) specifies the
register or registers for indirect operands. It should contain a constant
index when used with direct memory operands. It is equivalent to the plus
operator. For example, the following statements are the same:

    mov     ax, array[5]
            mov     ax, array+5

Any direct memory operand can be enclosed in the index operator. The
following are equivalent:

    mov     ax, var
            mov     ax, [var]

Some programmers prefer to enclose the operand in brackets to show that the
contents, not the address, are used.

Structure Field - The structure operator (a period) accesses elements of a
structure. A field within a structure variable can be accessed as a direct
memory operand:

    mov     bx, structvar.field1

The address of the structure operand is the sum of the offsets of  structvar
    and  field1. See Section 5.2, "Structures and Unions," for more information
about structures.

Segment Override - The segment override operator (a colon) specifies a
segment portion of the address that is different from the default segment.
When used with instructions, this operator can apply to segment registers or
segment names:

    mov     ax, es:farvar           ; Use segment override

The assembler will not generate a segment override if the default segment is
explicitly provided. Thus, the following two statements are equivalent:

    mov     [bx], ax
            mov     ds:[bx], ax

A segment name override or the segment override operator forces the operand
to be an address expression.

    mov     WORD PTR FARSEG:0, ax   ; Segment name override
            mov     WORD PTR es:100h, ax    ; Legal and equivalent
            mov     WORD PTR es:[100h], ax  ;  expressions
    ;       mov     WORD PTR [100h], ax     ; Illegal, not an address

As the example shows, a constant expression cannot be an address expression
unless it has a segment override.


3.2.4  Indirect Memory Operands

Like direct memory operands, indirect memory operands specify the contents
of a given address. However, the processor calculates the address at run
time by referring to the contents of registers. Since values in the
registers can change at run time, indirect memory operands provide dynamic
access to memory.

Indirect memory operands make possible run-time operations such as pointer
indirection and dynamic indexing of array elements, including indexing of
multidimensional arrays.

Strict rules govern which registers can be used for indirect memory operands
under 16-bit versions of the 8086-based processors. The rules change
significantly for 32-bit processors starting with the 80386. However, the
new rules apply only to code that does not need to be backward compatible.

This section first discusses features of indirect operands in either mode.
Then it explains the specific 16-bit rules and 32-bit rules separately.


3.2.4.1  Indirect Operands with 16- and 32-Bit Registers

Some rules and options for indirect memory operands always apply, regardless
of the size of the register. For example, you must always specify the
register and operand size for indirect memory operands. But you can use
various syntaxes to indicate an indirect memory operand. This section
describes the rules that apply to both 16-bit and 32-bit register modes.

Certain rules govern the use of base and index registers.

Specifying Indirect Memory Operands - The index operator specifies the
register or registers for indirect operands. The processor uses the data
pointed to by the register. For example, the following instruction moves the
word-sized data at the address contained in DS:BX into AX:

    mov     ax, WORD PTR [bx]

When you specify more than one register, the processor adds the two
addresses together to determine the effective address (the address of the
data to operate on):

    mov     ax, [bx+si]

An indirect memory operand can have a displacement.

Specifying Displacements - You can specify an address displacement─ a
constant value to add to the effective address. A direct memory specifier is
the most common displacement:

    mov     ax, table[si]

In the relocatable expression above, the displacement  table  is the base
address of an array; SI holds an index to an array element. The SI value is
calculated at run time, often in a loop. The element loaded into AX depends
on the value of SI at the time the instruction is executed.

Each displacement can be an address or numeric constant. If there is more
than one displacement, the assembler adds them together at assembly time and
encodes the total displacement. For example, in the statement

    table   WORD    100 DUP (0)
            .
            .
            .
            mov     ax, table[bx][di]+6

both  table  and  6  are displacements. The assembler adds the value of
table  to  6  to get the total displacement. However, this statement is not
legal:

    mov ax, mem1[si] + mem2

Indirect memory operands must always have a size.

Specifying Operand Size - Indirect memory operands must always have a
specified size. Often the size is specified by the size of the identifier.
In the example above, the size of the  table  array determines the operand
size. If an indirect memory operand is used with a register operand, the
register size determines the size of the memory object:

    mov     ax, [bx]        ; Size is 2 bytes - same as
    AX
            mov     table[bx], 0    ; Size is 2 bytes - from size
                                    ;  of table

If there is no address or register operand, the size must be given
specifically with the PTR operator, as shown below:

    inc     WORD PTR [bx]           ; Word size
            mov     BYTE PTR [bp+6], 0      ; Byte size

Syntax Options - The assembler allows a variety of syntaxes for indirect
memory operands. However, all registers must be inside brackets. You can
enclose each register in its own pair of brackets, or you can place the
registers in the same pair of brackets separated by a plus operator (+). All
the following variations are legal and equivalent:

    mov     ax, table[bx][di]
            mov     ax, table[di][bx]
            mov     ax, table[bx+di]
            mov     ax, [table+bx+di]
            mov     ax, [bx][di]+table

All of these statements move the value in  table  indexed by  BX+DI  into
AX.

Registers pointing into arrays must be zero-based and scaled for the size of
the array.

Scaling Indexes - The value of index registers pointing into arrays must
often be adjusted for zero-based arrays and scaled according to the size of
the array items. For a word array, the item number must be multiplied by two
(shifted left two places). When you are using 16-bit registers, scaling must
be done with separate instructions, as shown below:

    mov     bx, 5           ; Get sixth element (adjust
    for 0)
            shl     bx, 1           ; Scale by two (word size)
            inc     wtable[bx]      ; Increment sixth element in table

When using 32-bit registers on the 80386/486 processor, you can include
scaling in the operand, as described in Section 3.2.4.3, "Indirect Memory
Operands with 32-Bit Registers."

Accessing Structure Elements  - The structure member operator can be used in
indirect memory operands to access structure elements. In this example, the
structure member operator loads the  year  field of the fourth element of
the  students  array into AL:

    STUDENT STRUCT
    grade WORD    ?
    name  BYTE    20 DUP (?)
    year  BYTE    ?
    STUDENT ENDS

    students        STUDENT  < >
            .
            .                               ; Assume array initialized
            .                               ;  earlier
            mov     bx, OFFSET students     ; Point to array of students
            mov     ax, 4                   ; Get fourth element
            mov     di, SIZE STUDENT        ; Get size of STUDENT
            mul     di                      ; Multiply size times
                                            ;  elements to point to
                                            ;  current element
                                            ; Load field from element:
            mov     al, (STUDENT PTR[bx+di]).year

See Section 5.2 for more information on MASM structures.


3.2.4.2  Indirect Memory Operands with 16-Bit Registers

For 8086-based computers and DOS, you must follow the strict indexing rules
established for the 8086 processor. Only four registers are allowed─BP, BX,
SI, and DI─and those only in certain combinations.

BP and BX are base registers. SI and DI are index registers. You can use
either a base or an index register by itself. But if you combine two
registers, one must be a base and one an index. Here are legal and illegal
forms:

    mov     ax, [bx+di]     ; Legal
            mov     ax, [bx+si]     ; Legal
            mov     ax, [bp+di]     ; Legal
            mov     ax, [bp+si]     ; Legal
    ;       mov     ax, [bx+bp]     ; Illegal - two base registers
    ;       mov     ax, [di+si]     ; Illegal - two index registers

Table 3.1 shows the modes in which registers can be used to specify indirect
memory operands.

Table 3.1  Indirect Addressing Modes with 16-Bit Registers

╓┌─────────────────────┌────────────────────────┌────────────────────────────╖
Mode                  Syntax                   Effective Address
────────────────────────────────────────────────────────────────────────────
Register indirect     [BX]                     Contents of register
                        [BP]
                        [DI]
Mode                  Syntax                   Effective Address
────────────────────────────────────────────────────────────────────────────
                        [DI]
                        [SI]

────────────────────────────────────────────────────────────────────────────

Base or index         displacement[BX]         Contents of register plus
                        displacement[BP]         displacement
                        displacement[DI]
                        displacement[SI]

────────────────────────────────────────────────────────────────────────────

Base plus index       [BX][DI]                 Contents of base register
                        [BP][DI]                 plus contents of index
                        [BX][SI]                 register
                        [BP][SI]

────────────────────────────────────────────────────────────────────────────

Mode                  Syntax                   Effective Address
────────────────────────────────────────────────────────────────────────────

Base plus index with  displacement[BX][DI]     Sum of base register, index
displacement          displacement[BP][DI]     register, and displacement
                        displacement[BX][SI]
                        displacement[BP][SI]

────────────────────────────────────────────────────────────────────────────



Different combinations of registers and displacements have different
timings, as shown in the Macro Assembler Reference.


3.2.4.3  Indirect Memory Operands with 32-Bit Registers

Instructions for the 80386/486 processor can be given in two segment
modes─16-bit and 32-bit. Indirect memory operands are different in each
mode. The segment mode is independent of the register size; you can use
32-bit registers in either mode.

In 16-bit mode, the 80386/486 operates in the mode used by all other
8086-based processors, with one difference: you can use 32-bit registers. If
the 80386/486 processor is enabled (with the .386 or .486 directive), 32-bit
general-purpose registers are available in either segment mode. Using them
eliminates many of the limitations of 16-bit indirect memory operands. Using
80386/486 features can make your DOS programs run faster and more
efficiently if you are willing to sacrifice backward compatibility with
other processors.

In 32-bit mode, an offset address can be up to four gigabytes. (Segments are
still represented in 16 bits.) This effectively eliminates size restrictions
on each segment, since few programs need four gigabytes of memory. OS/2 2.x
uses 32-bit mode and flat model, which spans all segments. XENIX 386 uses
32-bit mode with multiple segments.

Any general-purpose 32-bit register can be used as either the base or the
index.

80386/486 Enhancements - On the 80386/486, the processor allows any
general-purpose 32-bit register to be used as either the base or the index
register (except ESP, which can be a base but not an index). The same
register can also be used as both the base and index, but you cannot combine
16-bit and 32-bit registers. Several examples are shown below:

    add     edx, [eax]              ; Add double
            mov     dl, [esp+10]            ; Add byte from stack
            dec     WORD PTR [edx][eax]     ; Decrement word
            cmp     ax, array[ebx][ecx]     ; Compare word from array
            jmp     FWORD PTR table[ecx]    ; Jump into pointer table

The index register can have a scaling factor of 1, 2, 4, or 8.

Scaling Factors - With 80386/486 registers, the index register can have a
scaling factor of 1, 2, 4, or 8. Any register except ESP can be the index
register and can have a scaling factor. Specify the scaling factor by using
the multiplication operator (*) adjacent to the register.

You can use scaling to index into arrays with different sizes of elements.
For example, the scaling factor is 1 for byte arrays (no scaling needed), 2
for word arrays, 4 for doubleword arrays, and 8 for quadword arrays. There
is no performance penalty for using a scaling factor. Scaling is illustrated
in the following examples:

    mov     eax, darray[edx*4]     ; Load double of double
    array
            mov     eax, [esi*8][edi]      ; Load double of quad array
            mov     ax, wtbl[ecx+2][edx*2] ; Load word of word array

Scaling is also necessary on earlier processors, but it must be done with
separate instructions before the indirect memory operand is used, as
described in Section 3.2.4.2, "Indirect Memory Operands with 16-Bit
Registers."

The number of registers and the scaling factor affect base and index
registers.

The default segment register is SS if the base register is EBP or ESP; it is
DS for all other base registers. If two registers are used, only one can
have a scaling factor. The register with the scaling factor is defined as
the index register. The other register is defined as the base. If scaling is
not used, the first register is the base. If only one register is used, it
is considered the base for deciding the default segment unless it is scaled.
The following examples illustrate how to determine the base register:

    mov   eax, [edx][ebp*4] ; EDX base (not scaled - seg
    DS)
            mov   eax, [edx*1][ebp] ; EBP base (not scaled - seg SS)
            mov   eax, [edx][ebp]   ; EDX base (first - seg DS)
            mov   eax, [ebp][edx]   ; EBP base (first - seg SS)
            mov   eax, [ebp*2]      ; EBP base (only - seg SS)

Mixing 16-Bit and 32-Bit Registers - Statements can mix 16-bit and 32-bit
registers if the register use is correct. For example, the following
statement is legal for either 16-bit or 32-bit segments:

    mov     eax, [bx]

This statement moves the 32-bit value pointed to by BX into the EAX
register. Although BX is a 16-bit pointer, it can still point into a 32-bit
segment.

However, the following statement is never legal, since the CX register
cannot be used as a 16-bit pointer (although ECX can be used as a 32-bit
pointer):

    ;       mov     eax, [cx]       ; illegal

Operands that mix 16-bit and 32-bit registers are also illegal:

    ;       mov     eax, [ebx+si]   ; illegal

The following statement is legal in either mode:

    mov     bx, [eax]

This statement moves the 16-bit value pointed to by EAX into the BX
register. This works fine in 32-bit mode. However, in 16-bit mode, moving a
32-bit pointer into a 16-bit segment is illegal. If EAX contains a 16-bit
value (the top half of the 32-bit register is 0), the statement works.
However, if the top half of the EAX register is not 0, the operand points
into a part of the segment that doesn't exist, and this generates an error.
If you use 32-bit registers as indexes in 16-bit mode, you must make sure
that the index registers contain valid 16-bit addresses.


3.3  Accessing Data with Pointers and Addresses

In high-level languages, a "pointer" (or pointer variable) is an address
that is stored in a variable. Assembly language also uses pointer variables,
but the term "pointer" has a wider use. The indirect memory operands
discussed in the previous section can be thought of as pointers stored in
registers.

An address can be stored in a pointer variable for later use. Program
procedures (including OS/2 systems calls) frequently pass pointer variables
onto the stack to transfer data between the calling program and the called
procedure.

A pointer variable must be transferred to registers before it can be used.

Regardless of the reason for maintaining it, a pointer variable to data
cannot in itself be directly used in MASM statements. (Pointers to code can
be used directly.) It must first be loaded into registers as an indirect
memory operand.

There is a difference between a far address and a far pointer. A "far
address" is the address of a variable located in a far data segment. A "far
pointer" is a variable that can specify both a segment and an offset. Like
any other variable, a pointer variable can be located in either the default
(near) data segment or in a far segment.

Previous versions of MASM allow pointer variables but provide little support
for them. In previous versions, any address loaded into a variable can be
considered a pointer, as in the following statements:

    Var     BYTE    0               ; Variable
    npVar   WORD    Var             ; Near pointer to variable
    fpVar   DWORD   Var             ; Far pointer to variable

If a variable is initialized to the name of another variable, the
initialized variable is a pointer, as shown in the example above. However,
in previous versions of MASM, the CodeView debugger recognizes  npVar  and
fpVar  as word and doubleword variables. CodeView does not treat them as
pointers, nor does it recognize the type of data they point to (bytes, in
the example).

The new directive TYPEDEF and the new capabilities of ASSUME make it easier
to manage pointers in registers and variables. These directives are
discussed in the next two sections. Basic pointer and address operations are
covered in Section 3.3.3.


3.3.1  Defining Pointer Types with TYPEDEF

Once defined, a TYPEDEF is considered the same as an intrinsic type.

You can define types for pointer variables using the TYPEDEF directive. A
type so defined is considered the same as the intrinsic types provided by
the assembler and can be used in the same contexts. The syntax for TYPEDEF
when used to define pointers is

    typename TYPEDEF «distance» PTR  qualifiedtype

The typename is the name assigned to the new type. The distance can be NEAR,
FAR, or any distance modifier. The qualifiedtype can be any previously
intrinsic or defined MASM type, or a type previously defined with TYPEDEF.
(See Section 1.2.6, "Data Types," for a full definition of qualifiedtype.)

Here are some examples of user-defined types:

    PBYTE   TYPEDEF      PTR BYTE   ; Pointer to bytes
    NPBYTE  TYPEDEF NEAR PTR BYTE   ; Near pointer to bytes
    FPBYTE  TYPEDEF FAR  PTR BYTE   ; Far pointer to bytes
    PWORD   TYPEDEF      PTR WORD   ; Pointer to words
    NPWORD  TYPEDEF NEAR PTR WORD   ; Near pointer to words
    FPWORD  TYPEDEF FAR  PTR WORD   ; Far pointer to words

    PPBYTE  TYPEDEF      PTR PBYTE  ; Pointer to pointer to bytes
                                    ;  (in C, an array of strings)
    PVOID   TYPEDEF      PTR        ; Pointer to any type of data

    STRUCT  PERSON                  ; Structure type
    name  BYTE    20 DUP (?)
    num   WORD    ?
    PERSON  ENDS
    PPERSON TYPEDEF      PTR PERSON ; Pointer to structure type

The distance of a pointer can either be set specifically or determined
automatically by the memory model (set by .MODEL) and the segment size (16
or 32 bits). If you don't use .MODEL, near pointers are the default.

In 16-bit mode, a near pointer is two bytes that contain the offset of the
object pointed to. A far pointer requires four bytes, and it contains both
the offset and the segment. In 32-bit mode, a near pointer is four bytes and
a far pointer is six bytes. If you specify the distance with NEAR or FAR,
the default distance of the current segment size is used. You can use
NEAR16, NEAR32, FAR16, and FAR32 to override the defaults set by the current
segment size. In flat model, NEAR is the default.

A pointer type created with TYPEDEF can be used to declare pointer
variables. Here are some examples using the pointer types defined above:

    ; Type declarations
    Array   WORD    25 DUP (0)
    Msg     BYTE    "This is a string", 0
    pMsg    PBYTE   Msg             ; Pointer to string
    pArray  PWORD   Array           ; Pointer to word array
    npMsg   NPBYTE  Msg             ; Near pointer to string
    npArray NPWORD  Array           ; Near pointer to word array
    fpArray FPWORD  Array           ; Far pointer to word array
    fpMsg   FPBYTE  Msg             ; Far pointer to string

    S1      BYTE    "first", 0      ; Some strings
    S2      BYTE    "second", 0
    S3      BYTE    "third", 0
    pS123   PBYTE   S1, S2, S3, 0   ; Array of pointers to strings
    ppS123  PPBYTE  pS123           ; A pointer to pointers to strings

    Andy    PERSON  <>              ; Structure variable
    pAndy   PPERSON Andy            ; Pointer to structure variable

                                    ; Procedure prototype

    EXTERN  ptrArray:PBYTE          ; External variable
    Sort    PROTO   pArray:PBYTE    ; Parameter for prototype

    ; Parameter for procedure
    Sort    PROC    pArray:PBYTE
            LOCAL   pTmp:PBYTE      ; Local variable
            .
            .
            .
            ret
    Sort    ENDP

Once defined, pointer types can be used in any context where intrinsic types
are allowed.


3.3.2  Defining Register Types with ASSUME

Beginning with MASM 6.0, you can use the ASSUME directive with
generalpurpose registers to specify that a register is a pointer to a
certain size of object. For example:

    ASSUME  bx:PTR WORD     ; BX is word pointer until further
                                    ;  notice
            inc     [bx]            ; Increment word pointed to by BX
            add     bx, 2           ; Point to next word
            mov     [bx], 0         ; Word pointed to by BX = 0
            .
            .                       ; Other pointer operations with BX
            .
            ASSUME  bx:NOTHING      ; Cancel assumptions

In this example, BX is specified to be a pointer to a word. After a sequence
of using BX as a pointer, the assumption is cancelled by assuming NOTHING.

Without the assumption to PTR WORD, many instructions need a size specifier.
The INC and MOV statements from the examples above would have to be written
like this to specify the sizes of the memory operands:

    inc     WORD PTR [bx]
            mov     WORD PTR [bx], 0

When you have used ASSUME, attempts to use the register for other purposes
generate assembly errors. In the example above, while the PTR WORD
assumption is in effect, any use of BX inconsistent with its ASSUME
declaration generates an error. For example,

    ;       mov     al, [bx]       ; Can't move word to byte register

You can also use the PTR operator to override defaults:

    mov     ax, BYTE PTR [bx] ; Legal

Similarly, you can use ASSUME to prevent the use of a register as a pointer
or even to disable a register:

    ASSUME  bx:WORD, dx:ERROR
    ;       mov     al, [bx] ; Error - BX is an integer, not a pointer
    ;       mov     ax, dx   ; Error - DX disabled

See Section 2.3.3 for information on using ASSUME with segment registers.


3.3.3  Basic Pointer and Address Operations

You can do these basic operations with pointers and addresses:


    ■   Initialize a pointer variable by storing an address in it

    ■   Load an address into registers, directly or from a pointer


The sections in the rest of this chapter describe variations of these tasks
with both pointers and addresses. The examples in these sections assume that
you have previously defined the following pointer types with the TYPEDEF
directive:

    PBYTE   TYPEDEF      PTR BYTE   ; Pointer to bytes
    NPBYTE  TYPEDEF NEAR PTR BYTE   ; Near pointer to bytes
    FPBYTE  TYPEDEF FAR  PTR BYTE   ; Far pointer to bytes


3.3.3.1  Initializing Pointer Variables

Let the assembler initialize pointer variables when possible.

If the value of a pointer is known at assembly time, the assembler can
initialize it automatically so that no processing time is wasted on the task
at run time. The following example illustrates how to do this:

    Msg     BYTE    "String", 0
    pMsg    PBYTE   Msg

If a pointer variable can be conditionally defined to one of several
constant addresses, initialization must be delayed until run time. The
technique is different for near pointers than for far pointers, as shown
below:

    Msg1    BYTE    "String1"
    Msg2    BYTE    "String2"
    npMsg   NPBYTE  ?
    fpMsg   FPBYTE  ?
            .
            .
            .
            mov     npMsg, OFFSET Msg1              ; Load near pointer

            mov     WORD PTR fpMsg[0], OFFSET Msg2  ; Load far offset
            mov     WORD PTR fpMsg[2], SEG Msg2     ; Load far segment

If you know that the segment for a far pointer is currently in a register,
you can load it directly:

    mov     WORD PTR fpMsg[2], ds           ; Load segment
    of
                                                    ;  far pointer

Dynamic Addresses - Often the address to be initialized is dynamic. You know
the register or registers containing the address, and you want to save them
in a variable for later use. Typical situations include memory allocated by
DOS (see interrupt 21h function 48h in online help) and addresses found by
the SCAS or CMPS instructions (see Section 5.1.3.1). The technique for
saving dynamic addresses is illustrated below:

    ; Dynamically allocated buffer
    fpBuf   FPBYTE  0               ; Initialize so offset will be zero
            .
            .
            .
            mov     ah, 48h         ; Allocate memory
            mov     bx, 10h         ; Request 16 paragraphs
            int     21h             ; Call DOS
            jc      error           ; Return segment in AX
            mov     WORD PTR fpBuf[2], ax   ; Load segment
            .                               ;  (offset is already 0)
            .
            .
    error:                          ; Handle error

There are several options for copying pointers.

Copying Pointers - Sometimes one pointer variable must be initialized by
copying from another. Here are two ways to copy a far pointer:

    fpBuf1  FPBYTE  ?
    fpBuf2  FPBYTE  ?
            .
            .
            .
    ; Copy through registers is faster, but requires a spare register
            mov     bx, WORD PTR fpBuf1[0]
            mov     WORD PTR fpBuf2[0], bx
            mov     bx, WORD PTR fpBuf1[2]
            mov     WORD PTR fpBuf2[2], bx

    ; Copy through stack is slower, but does not use a register
            push    WORD PTR fpBuf1[0]
            push    WORD PTR fpBuf1[2]
            pop     WORD PTR fpBuf2[2]
            pop     WORD PTR fpBuf2[0]

Pointers passed as procedure arguments are pushed onto the stack.

Pointers as Arguments - When a pointer is passed as an argument to a
procedure, it must be pushed onto the stack. The procedure then sets up a
stack frame so that it can access the arguments from the stack. This
technique is discussed in detail in Section 7.3.2, "Passing Arguments on the
Stack." Pushing a pointer is illustrated below:

    ; Push a far pointer (segment always pushed first)
            push    WORD PTR fpMsg[2]       ; Push segment
            push    WORD PTR fpMsg[0]       ; Push offset

Pushing an address is somewhat different:

    ; Push a far address as a far pointer
            mov     ax, SEG fVar    ; Load and push segment
            push    ax
            mov     ax, OFFSET fVar ; Load and push offset
            push    ax

On the 80186 and later processors, you can shorten pushing a constant to one
step:

    push    SEG fVar        ; Push segment
            push    OFFSET fVar     ; Push offset


3.3.3.2  Loading Addresses into Registers

Loading an address into a pair of registers is one of the most common tasks
in assembly-language programming. You cannot do processing work with a
constant address or a pointer variable until the address is loaded into
registers.

Certain register pairs have standard uses.

You often load addresses into particular segment:offset pairs. The following
pairs have specific uses:

Segment:Offset Pair        Standard Use
────────────────────────────────────────────────────────────────────────────
DS:SI                      Source for string operations
ES:DI                      Destination for string operations
DS:DX                      Input for DOS functions
ES:BX                      Output from DOS functions

In addition, you can use ES:SI, DS:DI, DS:BX, or any segment:offset pair for
your own indirect memory operands. You can use SS:BP with a displacement to
access procedure arguments or local variables in procedures.

Addresses from Data Segments - For near addresses, you need only load the
offset; the segment is assumed as SS for stack-based data and as DS for
other data. You must load both segment and offset for far pointers.

Here is an example of loading an address to DS:BX from a near data segment:


    .DATA
    Msg     BYTE    "String"
            .
            .
            .
            mov     bx, OFFSET Msg  ; Load address to BX
                                    ;  (DS already loaded)

If the data is in a far data segment, it is loaded like this:

    .FARDATA
    Msg     BYTE    "String"
            .
            .
            .
            mov     ax, SEG Msg     ; Load address to ES:BX
            mov     es, ax
            mov     bx, OFFSET Msg

Stack Variables - The technique for loading the address of a stack variable
is significantly different from the technique for loading near addresses.
You may need to put the correct segment value into ES for string operations.
The following example illustrates how to load the address of a local (stack)
variable to ES:DI:

    Task    PROC
            LOCAL   Arg[4]:BYTE

            push    ss      ; Since it's stack-based, segment is SS
            pop     es      ; Copy SS to ES
            lea     di, Arg ; Load offset to DI

Use LEA to load the offset of an indirect memory operand.

The local variable in this case actually evaluates to SS:[BP-4]. This is an
offset from the stack frame (described in Section 7.3.2, "Passing Arguments
on the Stack"). Since you cannot use the OFFSET operator to get the offset
of an indirect memory operand, you must use the LEA (Load Effective Address)
instruction.

Use MOV and OFFSET to load the offset of a direct memory operand.

Direct Memory Operands - To get the address of a direct memory operand, you
can use the MOV instruction with OFFSET or the LEA instruction. MASM 6.0
automatically optimizes the LEA statement by generating the smaller and
faster code, as shown in this example:


    lea     si, Msg        ; If you code this statement,
            mov     si, OFFSET Msg ;  MASM 6.0 generates this code

The LEA instruction can be used to determine the address of indirect memory
operands, as shown below.

    lea     si, [bx]        ; Legal - LEA required for indirect
    ;      mov     si, OFFSET [bx] ; Illegal - no OFFSET on indirect

Far Pointers  - Use the LES and LDS instructions to load far pointers. Use
the MOV instruction to load a near pointer. The following example shows how
to load a far pointer to ES:DI and a near pointer to SI (assuming DS as the
segment):

    InBuf   BYTE    20 DUP (1)
    OutBuf  BYTE    20 DUP (0)

    npIn    NPBYTE  InBuf
    fpOut   FPBYTE  OutBuf
            .
            .
            .
            les     di, fpOut      ; Load far pointer to ES:DI

            mov     si, npIn       ; Load near pointer to SI (assume DS)

Copying between Segment Pairs - Copying from one register pair to another is
complicated by the fact that you cannot copy one segment register directly
to another. Two methods are shown below. Timings are for the 8088 processor:


    ; Copy DS:SI to ES:DI, generating smaller code
            push    ds              ; 1 byte, 14 clocks
            pop     es              ; 1 byte, 12 clocks
            mov     di, si          ; 2 bytes, 2 clocks

    ; Copy DS:SI to ES:DI, generating faster code
            mov     di, ds          ; 2 bytes, 2 clocks
            mov     es, di          ; 2 bytes, 2 clocks
            mov     di, si          ; 2 bytes, 2 clocks


3.3.3.3  Model-Independent Techniques

Use conditional assembly to write memory-model independent code.

Often you may want to write code that is memory-model independent. If you
are writing libraries that must be available for different memory models,
you can use conditional assembly to handle different sizes of pointers. You
can use the predefined symbols @DataSize and @Model to test the current
assumptions.

Use conditional assembly to handle pointers that have no specified distance.


You can use conditional assembly to write code that works with pointer
variables that have no specified distance. The predefined symbol @DataSize
tests the pointer size for the current memory model:

    Msg1    BYTE    "String1"
    pMsg    PBYTE   ?
            .
            .
            .
            IF      @DataSize
            mov     WORD PTR pMsg[0], OFFSET Msg1   ; Load far offset
            mov     WORD PTR pMsg[2], SEG Msg1      ; Load far segment
            ELSE
            mov     pMsg, OFFSET Msg1               ; Load near pointer
            ENDIF

In the following example, a procedure receives as an argument a pointer to a
word variable. The code inside the procedure uses @DataSize to determine
whether the current memory model supports far or near data. It loads and
processes the data accordingly:

    ; Procedure that receives an argument by reference
    mul8    PROC    arg:PTR WORD

            IF      @DataSize
            les     bx, arg     ; Load far pointer to ES:BX
            mov     ax, es:[bx] ; Load the data pointed to
            ELSE
            mov     bx, arg     ; Load near pointer to BX (assume DS)
            mov     ax, [bx]    ; Load the data pointed to
            ENDIF
            shl     ax, 1       ; Multiply by 8
            shl     ax, 1
            shl     ax, 1
            ret
    mul8    ENDP

If you have many routines, writing the conditionals for each case can be
tedious. The following conditional statements generate the proper
instructions and segment overrides automatically.

    ; Equates for conditional handling of pointers
            IF @DataSize
    lesIF   TEXTEQU    <les>
    ldsIF   TEXTEQU    <lds>
    esIF    TEXTEQU    <es:>
            ELSE
    lesIF   TEXTEQU    <mov>
    ldsIF   TEXTEQU    <mov>
    esIF    TEXTEQU    <>
            ENDIF

Once you define these conditionals, you can use them to simplify code that
must handle several types of pointers. This next example rewrites the above
mul8  procedure to use conditional code.

    mul8    PROC    arg:PTR WORD

            lesIF   bx, arg         ; Load pointer to BX or ES:BX
            mov     ax, esIF [bx]   ; Load the data from [BX] or ES:[BX]
            shl     ax, 1           ; Multiply by 8
            shl     ax, 1
            shl     ax, 1
            ret
    mul8    ENDP

The conditional statements from the examples above can be defined once in an
include file and used whenever you need to handle pointers.


3.4  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

╓┌─────────────────────────────────────┌─────────────────────────────────────╖
Topics                                Access
────────────────────────────────────────────────────────────────────────────
LROFFSET, THIS                        From the "MASM 6.0 Contents" screen,
                                        choose "Operators"; then choose
                                        "Address"

LFS, LGS, and LSS                     From the "MASM 6.0 Contents" screen,
Topics                                Access
────────────────────────────────────────────────────────────────────────────
LFS, LGS, and LSS                     From the "MASM 6.0 Contents" screen,
                                        choose "Processor Instructions";
                                        then choose "Data
                                        Transfer"

ALIGN, EVEN, ORG                      From the "MASM 6.0 Contents" screen,
                                        choose "Directives"; then choose
                                        "Miscellaneous"

NEAR, NEAR16, NEAR32, FAR16, FAR32,   From the "MASM 6.0 Contents" screen,
and TYPE                              choose "Operators"; then choose
                                        "Type and Size"

PTR                                   From the "MASM 6.0 Contents" screen,
                                        choose "Operators"; then choose
                                        "Miscellaneous"

PUSHCONTEXT and POPCONTEXT            Access from the Macro Assembler
                                        Index
Topics                                Access
────────────────────────────────────────────────────────────────────────────
                                        Index

ASSUME, .MODEL                        From the "MASM 6.0 Contents" screen,
                                        choose "Directives"; then choose
                                        "Simplified Segment Control"

@DataSize, @Model                     From the "MASM 6.0 Contents" screen,
                                        choose "Predefined Symbols"








Chapter 4  Defining and Using Integers
────────────────────────────────────────────────────────────────────────────

The 8086 family of processors is designed to operate on integer data;
therefore, most assembler statements are integer operations. Even string
elements (discussed in Chapter 5, "Defining and Using Complex Data Types")
are byte-sized integers to the assembler.

This chapter covers the concepts essential for using integer variables in
assembly-language programs. The first section shows how to declare integer
variables. The second section describes basic integer operations including
moving, loading, and sign-extending integers, as well as calculating with
integers. Finally, the last section describes how to do various operations
with integers at the bit level, such as using bitwise logical instructions
and shifting and rotating bits.

The complex data types introduced in the next chapter─arrays, strings,
structures, unions, and records─use many of the integer operations
illustrated in this chapter, since the components of complex data types are
often integers. Floating-point operations require a different set of
instructions and techniques. These are covered in Chapter 6, "Using
Floating-Point and Binary Coded Decimal Numbers."


4.1  Declaring Integer Variables

You declare integer variables in the data segment of your program to
allocate memory for data. The EQU and = directives define integer constants.
Integer variables allocated with the data allocation directives can be
initialized in several ways. MASM 6.0 provides new forms of the data
allocation directives. This section discusses these features and explains
how to use the SIZEOF and TYPE operators to provide information to the
assembler about the types in your program. For information on symbolic
integer constants, see Section 1.2.4, "Integer Constants and Constant
Expressions."


4.1.1  Allocating Memory for Integer Variables

When you declare an integer variable by assigning a label to a data
allocation directive, the assembler allocates memory space for the integer.
The variable's name becomes a label for the memory space. The syntax is

    «name» directive initializer

These directives, listed below, indicate the integer's size and value range.


╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Directive                         Description of Initializers
BYTE, DB (bytes)                  Allocates unsigned numbers  from
                                    0 to 255.
────────────────────────────────────────────────────────────────────────────
SBYTE (signed bytes)              Allocates signed numbers from
                                    -128 to +127.

WORD, DW (words = 2 bytes)        Allocates unsigned numbers from
                                    0 to 65,535 (64K).

SWORD (signed words)              Allocates signed numbers from
                                    -32,768 to +32,767.

DWORD, DD (doublewords = 4 bytes) Allocates unsigned numbers from
                                    0 to 4,294,967,295 (4 megabytes).

SDWORD (signed doublewords)       Allocates signed numbers from
Directive                         Description of Initializers
BYTE, DB (bytes)                  Allocates unsigned numbers  from
                                    0 to 255.
────────────────────────────────────────────────────────────────────────────
SDWORD (signed doublewords)       Allocates signed numbers from
                                    -2,147,483,648 to +2,147,483,647.

FWORD, DF (farwords = 6 bytes)    Allocates 6-byte (48-bit) integers.
                                    These values are normally used only as
                                    pointer variables on the 80386/486
                                    processors.

QWORD, DQ (quadwords = 8 bytes)   Allocates 8-byte integers used with
                                    8087-family coprocessor instructions.

TBYTE, DT (10 bytes)              Allocates 10-byte (80-bit) integers if
                                    the initializer has a radix specifying
                                    the base of the number.



See Chapter 6 for information on the REAL4, REAL8, and REAL10 directives
that allocate real numbers.




The assembler enforces only the size of initializers.

MASM does not enforce the range of values assigned to an integer. If the
value does not fit in the space allocated, however, the assembler generates
an error.

The SIZEOF and TYPE operators, when applied to a type, return the size of an
integer of that type. The following list gives the size attribute associated
with each data type.

Data Type                       Bytes
BYTE
────────────────────────────────────────────────────────────────────────────
WORD, SWORD                     2
DWORD, SDWORD                   3
FWORD                           6
QWORD                           8
TBYTE                           10

The SBYTE, SWORD, and SDWORD data types are new to MASM 6.0. Use of these
signed data types tells the assembler to treat the initializers as signed
data. It is important to use these signed types with high-level constructs
such as .IF, .WHILE, and .REPEAT (see Section 7.2.1, "Loop-Generating
Directives"), and with PROTO and INVOKE directives (see Sections 7.3.6,
"Declaring Procedure Prototypes," and 7.3.7, "Calling Procedures with
INVOKE").

The assembler stores integers with the least significant bytes lowest in
memory. Note that assembler listings and most debuggers show the bytes of a
word in the opposite order─high byte first.

Figure 4.1 illustrates the integer formats.

(This figure may be found in the printed book.)

TYPEDEF can define integer aliases.

Although the TYPEDEF directive's primary purpose is to define pointer
variables (see Section 3.3.1), you can also use TYPEDEF to create an alias
for any integer type. For example, these declarations

    char    TYPEDEF SBYTE
    longint TYPEDEF DWORD
    float   TYPEDEF REAL4
    double  TYPEDEF REAL8

allow you to use  char,  longint,  float, or  double  in your programs if
you prefer the C data labels.


4.1.2  Data Initialization

You can initialize variables when you declare them by giving initial
values─that is, constants or expressions that evaluate to integer constants.
The assembler generates an error if you specify an initial value too large
for the specified variable type. Variables can also be initialized with ? if
there are no initial values.

You can declare and initialize variables in one step with the data
directives, as these examples show.

    integer         BYTE    16          ; Initialize byte to 16
    negint          SBYTE   -16         ; Initialize signed byte to -16
    expression      WORD    4*3         ; Initialize word to 12
    signedexp       SWORD   4*3         ; Initialize signed word to 12
    empty           QWORD   ?           ; Allocate uninitialized long
                                        ;  integer
                    BYTE    1,2,3,4,5,6 ; Initialize six unnamed bytes
    long            DWORD   4294967295  ; Initialize doubleword to
                                        ;  4,294,967,295
    longnum         SDWORD  -2147433648 ; Initialize signed doubleword

                                        ;  to -2,147,433,648
    tb              TBYTE   2345t       ; Initialize 10-byte binary
                                        ;  number

See Section 5.1, "Arrays and Strings," for information on arrays and on
using the DUP operator to allocate initializer lists.

Once you have declared integer variables in your program, you can use them
in integer operations such as adding, moving, loading, and exchanging. The
next section describes these operations.


4.2  Integer Operations

You often need to copy, move, exchange, load, and sign-extend integer
variables in your MASM code. This section shows how to do these operations
as well as how to add, subtract, multiply, and divide integers; push and pop
integers onto the stack; and do bit-level manipulations with logical, shift,
and rotate instructions.

The PTR operator tells the assembler the size of the operand.

Since MASM instructions require operands to be the same size, you may need
to operate on data in a size other than the size originally declared. The
PTR operator lets you do this. For example, you can use the PTR operator to
access the high-order word of a DWORD-size variable. The syntax for the PTR
operator is

    type PTR expression

where the PTR operator forces expression to be treated as having the type
specified. An example of this use is

    .DATA
    num     DWORD   0
            .CODE

    mov     ax, WORD PTR num[0] ; Loads a word-size value
    from
            mov     dx, WORD PTR num[2] ;  a doubleword variable

You might choose not to use PTR, in contrast to this example. In that case,
trying to move  num[0]  into AX generates an error.


4.2.1  Moving and Loading Integers

The primary instructions for moving integers from operand to operand and
loading them into registers are MOV (Move), XCHG (Exchange), XLAT
(Translate), CWD (Convert Word to Double), and CBW (Convert Byte to Word).


4.2.1.1  Moving Integers

The most common method of moving data, the MOV instruction, can be thought
of as a copy instruction, since it always copies the source operand to the
destination operand. Immediately after a MOV instruction, both the source
and destination operands contain the same value.

The statements in the following example illustrate each type of memory move
that can be performed with a single instruction. Note that you cannot move
memory operands to memory operands in one operation.

    ; Immediate value moves
            mov     ax, 7       ; Immediate to register
            mov     mem, 7      ; Immediate to memory direct
            mov     mem[bx], 7  ; Immediate to memory indirect
    ; Register moves
            mov     mem, ax     ; Register to memory direct
            mov     mem[bx], ax ; Register to memory indirect
            mov     ax, bx      ; Register to register
            mov     ds, ax      ; General register to segment
                                ;  register

    ; Direct memory moves
            mov     ax, mem     ; Memory direct to register
            mov     ds, mem     ; Memory to segment register

    ; Indirect memory moves
            mov     ax, mem[bx] ; Memory indirect to register
            mov     ds, mem[bx] ; Memory indirect to segment register

    ; Segment register moves
            mov     mem, ds     ; Segment register to memory
            mov     mem[bx], ds ; Segment register to memory indirect
            mov     ax, ds      ; Segment register to general
                                ;  register

This next example shows several common types of moves that require two
instructions.

    ; Move immediate to segment register
            mov     ax, DGROUP  ; Load immediate to general register
            mov     ds, ax      ; Store general register to segment
                                ;  register

    ; Move memory to memory
            mov     ax, mem1    ; Load memory to general register
            mov     mem2, ax    ; Store general register to memory

    ; Move segment register to segment register
            mov     ax, ds      ; Load segment register to general
                                ;  register
            mov     es, ax      ; Store general register to segment
                                ;  register

The MOVSX and MOVZX instructions for the 80386/486 processors extend and
copy values in one step. See Section 4.2.1.4, "Extending Signed and Unsigned
Integers."


4.2.1.2  Exchanging Integers

The XCHG (Exchange) instruction exchanges the data in the source and
destination operands. Data can be exchanged between registers or between
registers and memory, but not from memory to memory:

    xchg    ax, bx       ; Put AX in BX and BX in AX
            xchg    memory, ax   ; Put "memory" in AX and AX in "memory"
    ;       xchg    mem1, mem2   ; Illegal- can't exchange between
                                ;  memory location

In some circumstances, register-to-register moves are faster with XCHG than
with MOV. If speed is important in your programs, check the Reference to
find the fastest clock speeds for various operand combinations allowed with
MOV  and XCHG.


4.2.1.3  Translating Integers from Tables

The XLAT (Translate) instruction loads data from a table into memory. The
instruction is useful for translating bytes from one coding system to
another. The syntax is

    XLAT[[B]] [[[[segment:]]memory]]

XLAT and XLATB are synonyms.

The BX register must contain the address of the start of the table. By
default, the DS register contains the segment of the table, but you can use
a segment override to specify a different segment. Also, you need not give
the operand except when specifying a segment override. (See Section 3.2.3,
"Direct Memory Operands," for information about the segment override
operator.)

Before the XLAT instruction executes, the AL register should contain a value
that points into the table (the start of the table is position 0). After the
instruction executes, AL contains the table value pointed to. For example,
if AL contains 7, the assembler puts the eighth byte of the table in the AL
register.

This example, illustrating XLAT, looks up hexadecimal characters in a table
to convert an eight-bit binary number to a string representing a hexadecimal
number.

    ; Table of hexadecimal digits
    hex     BYTE    "0123456789ABCDEF"
    convert BYTE    "You pressed the key with ASCII code "
    key     BYTE    ?,?,"h",13,10,"$"
            .CODE
            .
            .
            .
            mov     ah, 8               ; Get a key in AL
            int     21h                 ; Call DOS
            mov     bx, OFFSET hex      ; Load table address
            mov     ah, al              ; Save a copy in high byte
            and     al, 00001111y       ; Mask out top character
            xlat                        ; Translate
            mov     key[1], al          ; Store the character
            mov     cl, 12              ; Load shift count
            shr     ax, cl              ; Shift high character into
                                        ;  position
            xlat                        ; Translate
            mov     key, al             ; Store the character
            mov     dx, OFFSET convert  ; Load message
            mov     ah, 9               ; Display character
            int     21h                 ; Call DOS


4.2.1.4  Extending Signed and Unsigned Integers

Since moving data to a different-sized register is illegal, you must
"sign-extend" integers to convert signed data to a larger register or
register pair.

Sign-extending means copying the sign bit of the unextended operand to all
bits of the extended operand. The instructions in the following list
sign-extend values as shown. They work only on signed values in the
accumulator register.

Instruction    Function
────────────────────────────────────────────────────────────────────────────
CBW            Convert byte to word
CWD            Convert word to doubleword
CWDE           Convert word to doubleword extended (80386/486 only)
CDQ            Convert doubleword to quadword (80386/486 only)

On the 80386/486, the CWDE instruction converts a signed 16-bit value in AX
to a signed 32-bit value in EAX. The CDQ instruction converts a signed
32-bit value in EAX to a signed 64-bit value in the EDX:EAX register pair.

This example converts signed integers using CBW, CWD, CWDE, and CDQ.

    .DATA
    mem8    SBYTE   -5
    mem16   SWORD   -5
    mem32   SDWORD  -5
            .CODE
            .
            .
            .
            mov     al, mem8    ; Load 8-bit -5 (FBh)
            cbw                 ; Convert to 16-bit -5 (FFFBh) in AX

            mov     ax, mem16   ; Load 16-bit -5 (FFFBh)
            cwd                 ; Convert to 32-bit -5 (FFFF:FFFBh)
                                ;  in DX:AX
            mov     ax, mem16   ; Load 16-bit -5 (FFFBh)
            cwde                ; Convert to 32-bit -5 (FFFFFFFBh)
                                ;  in EAX
            mov     eax, mem32  ; Load 32-bit -5 (FFFFFFFBh)
            cdq                 ; Convert to 64-bit -5
                                ;  (FFFFFFFF:FFFFFFFBh) in EDX:EAX

Conversion instructions do not operate on unsigned numbers.

The procedure is different for unsigned values. Unsigned values are extended
by filling the upper bits with zeros rather than by sign extension. Because
the sign-extend instructions do not work on unsigned integers, you must set
the value of the higher register to zero.

This example shows sign extension for unsigned numbers.

    .DATA
    mem8    BYTE    251
    mem16   WORD    251
            .CODE
            .
            .
            .
            mov     al, mem8  ; Load 251 (FBh) from 8-bit memory
            sub     ah, ah    ; Zero upper half (AH)

            mov     ax, mem16 ; Load 251 (FBh) from 16-bit memory
            sub     dx, dx    ; Zero upper half (DX)

The 80386/486 processors provide instructions that move and extend a value
to a larger data size in a single step. MOVSX moves a signed value into a
register and sign-extends it. MOVZX moves an unsigned value into a register
and zeroextends it.

    ; 80386/486 instructions
            movzx   dx, bl      ; Load unsigned 8-bit value into
                                ;  16-bit register and zero-extend

These special 80386 and 80486 instructions usually execute much faster than
the equivalent 8086-80286 instructions.


4.2.2  Pushing and Popping Stack Integers

A stack is an area of memory for storing data temporarily. Unlike other
segments that store data starting from low memory, the stack stores data in
reverse order─starting from high memory. Data is always pushed or popped
from the top of the stack. The data on the stack can be the calling
addresses of procedures or interrupts, procedure arguments, or any operands,
flags, or registers your program needs to store temporarily.

At first, the stack is an uninitialized segment of a finite size. As data is
added to the stack at run time, the stack grows downward from high memory to
low memory. When items are removed from the stack, it shrinks upward from
low to high memory.


4.2.2.1  Saving Operands on the Stack

PUSH and POP always operate on word-sized data.

The PUSH instruction stores a two-byte operand on the stack. The POP
instruction retrieves a previously pushed value. When a value is pushed onto
the stack, the assembler decreases the SP (Stack Pointer) register by 2. On
8086-based processors, the SP register always points to the top of the
stack. The PUSH and POP instructions use the SP register to keep track of
the current position.

When a value is popped off the stack, the assembler increases the SP
register by 2. Although the stack always contains word values, the SP
register points to byte addresses. Thus, SP changes in multiples of two.
When a PUSH or POP instruction executes in a 32-bit code segment (one with
USE32 use type), the assembler transfers a four-byte value, and ESP changes
in multiples of four.

────────────────────────────────────────────────────────────────────────────
NOTE
The 8086 and 8088 processors differ from later Intel processors in how they
push and pop the SP register. If you give the statement  push sp  with the
8086 or 8088, the word pushed is the word in SP after the push operation.
────────────────────────────────────────────────────────────────────────────

Figure 4.2 illustrates how pushes and pops change the SP register.

(Please refer to the printed book.)

(This figure may be found in the printed book.)

On the 8086, PUSH and POP take only registers or memory expressions as their
operands. The other processors allow an immediate value to be an operand for
PUSH. For example, the following statement is legal on the 80186-80486
processors:

    push     7              ; 3 clocks on 80286

That statement is faster than these equivalent statements, which are
required on the 8088 or 8086:

    mov     ax, 7           ; 2 clocks plus
            push    ax              ; 3 clocks on 80286

There are two ways to clean up the stack.

Words are popped off the stack in reverse order: the last item pushed is the
first popped. To return the stack to its original status, you can do the
same number of pops as pushes. You can subtract the correct number of words
from the SP register if you want to restore the stack without using the
values on it.

To reference operands on the stack, keep in mind that the values pointed to
by the BP (Base Pointer) and SP registers are relative to the SS (Stack
Segment) register. The BP register is often used to point to the base of a
frame of reference (a stack frame) within the stack.

This example shows how you can access values on the stack using indirect
memory operands with BP as the base register.

    push    bp              ; Save current value of BP
            mov     bp, sp          ; Set stack frame
            push    ax              ; Push first;  SP = BP - 2
            push    bx              ; Push second; SP = BP - 4
            push    cx              ; Push third;  SP = BP - 6
            .
            .
            .
            mov     ax, [bp-6]      ; Put third in AX
            mov     bx, [bp-4]      ; Put second in BX
            mov     cx, [bp-2]      ; Put first in CX
            .
            .
            .
            add     sp, 6           ; Restore stack pointer
                                    ;  two bytes per push
            pop     bp              ; Restore BP

Creating labels for stack variables makes code easier to read.

If you use these stack values often in your program, you may want to give
them labels. For example, you can use TEXTEQU to create a label such as
count TEXTEQU <bp-6>. Now you can replace the  mov ax, [bp - 6]  statement
in the example above with  mov ax, count. Section 9.1, "Text Macros," gives
more information about the TEXTEQU directive.


4.2.2.2  Saving Flags on the Stack

Flags can be pushed and popped onto the stack with the PUSHF and POPF
instructions. You can use these instructions to save the status of flags
before a procedure call and then to restore the original status after the
procedure. You can also use them within a procedure to save and restore the
flag status of the caller. The 32-bit versions of these instructions are
PUSHFD and POPFD.


This example saves the flags register before calling the  systask
procedure:

    pushf
            call    systask
            popf

If you do not need to store the entire flag register, you can use the LAHF
instruction to manually load and store the status of the lower byte of the
flag register in the AH register. (You need to save AH before making a
procedure call.) SAHF restores the value.


4.2.2.3  Saving Registers on the Stack (80186-80486 Only)

Starting with the 80186 processor, the PUSHA and POPA instructions push or
pop all the general-purpose registers with only one instruction. These
instructions save the status of all registers before a procedure call and
then restore them after the return. Using PUSHA and POPA is significantly
faster and takes fewer bytes of code than pushing and popping each register
individually.

The processor pushes the registers in the following order: AX, CX, DX, BX,
SP, BP, SI, and DI. The SP word pushed is the value before the first
register is pushed.

The processor pops the registers in the opposite order. The 32-bit versions
of these instructions are PUSHAD and POPAD.


4.2.3  Adding and Subtracting Integers

You can use the ADD, ADC, INC, SUB, SBB, and DEC instructions for adding,
incrementing, subtracting, and decrementing values in single registers. You
can also combine them to handle larger values that require two registers for
storage.


4.2.3.1  Adding and Subtracting Integers Directly

The ADD, INC (Increment), SUB, and DEC (Decrement) instructions operate on
8- and 16-bit values on the 8086-80286 processors, and on 8-, 16-, and
32-bit values on the 80386/486 processors. They can be combined with the ADC
and SBB instructions to work on 32-bit values on the 8086 and 64-bit values
on the 80386/486 processors (see Section 4.2.3.2).


These instructions have two requirements:


    1.  If there are two operands, only one operand can be a memory operand.

    2.  If there are two operands, both must be the same size.


PTR allows you to operate on data in sizes different from its declared type.


To meet the second requirement, you can use the PTR operator to force an
operand to the size required (see Section 4.2, "Integer Operations"). For
example, if  Buffer  is an array of bytes and BX points to an element of the
array, you can add a word from  Buffer  with

    add     ax, WORD PTR Buffer[bx] ; Adds a word from the
                                            ;  byte variable

The next example shows 8-bit signed and unsigned addition and subtraction.

    DATA
    mem8    BYTE    39
            .CODE

    ; Addition

                            ;                    signed    unsigned
            mov     al, 26   ; Start with register   26       26
            inc     al       ; Increment              1        1
            add     al, 76   ; Add immediate         76     + 76
                            ;                     ----     ----
                            ;                      103      103
            add     al, mem8 ; Add memory            39     + 39
                            ;                     ----     ----
            mov     ah, al   ; Copy to AH          -114      142
                                                    +overflow
            add     al, ah   ; Add register                  142
                            ;                              ----
                            ;                                28+carry

    ; Subtraction

                            ;                   signed    unsigned
            mov     al, 95   ; Load register         95       95
            dec     al       ; Decrement             -1       -1
            sub     al, 23   ; Subtract immediate   -23      -23
                            ;                     ----     ----
                            ;                       71       71
            sub     al, mem8 ; Subtract memory     -122     -122
                            ;                     ----     ----
                            ;                      -51      205+sign

            mov     ah, 119  ; Load register        119
            sub     al, ah   ;  and subtract        -51
                            ;                     ----
                            ;                       86+overflow

The INC and DEC instructions treat integers as unsigned values and do not
update the carry flag for signed carries and borrows.


Your programs must include error-recovery for overflows and carries.

When the sum of eight-bit signed operands exceeds 127, the processor sets
the overflow flag. (The overflow flag is also set if both operands are
negative and the sum is less than or equal to -128.) Placing a JO (Jump on
Overflow) or INTO (Interrupt on Overflow) instruction in your program at
this point can transfer control to error-recovery statements. When the sum
exceeds 255, the processor sets the carry flag. A JC (Jump on Carry)
instruction at this point can transfer control to error-recovery statements.


In the subtraction example above, the processor sets the sign flag if the
result goes below 0. At this point, you can use a JS (Jump on Sign)
instruction to transfer control to error-recovery statements.


4.2.3.2  Adding and Subtracting in Multiple Registers

You can add and subtract numbers larger than the register size on your
processor with the ADC (Add with Carry) and SBB (Subtract with Borrow)
instructions. If the operations prior to an ADC or SBB instruction do not
set the carry flag, these instructions are identical to ADD and SUB. When
you operate on large values in more than one register, use ADD and SUB for
the least significant part of the number and ADC or SBB for the most
significant part.

The following example illustrates multiple-register addition and
subtraction. You can also use this technique with 64-bit operands on the
80386/486 processors.


    .DATA
    mem32   DWORD   316423
    mem32a  DWORD   316423
    mem32b  DWORD   156739
            .CODE
            .
            .
            .
    ; Addition
            mov     ax, 43981               ; Load immediate     43981
            sub     dx, dx                  ;  into DX:AX
            add     ax, WORD PTR mem32[0]   ; Add to both     + 316423
            adc     dx, WORD PTR mem32[2]   ;  memory words     ------
                                            ; Result in DX:AX   360404

    ; Subtraction
            mov     ax, WORD PTR mem32a[0]  ; Load mem32        316423
            mov     dx, WORD PTR mem32a[2]  ;  into DX:AX
            sub     ax, WORD PTR mem32b[0]  ; Subtract low    - 156739
            sbb     dx, WORD PTR mem32b[2]  ;  then high        ------
                                            ; Result in DX:AX   159684

For 32-bit registers on the 80386/486, only two steps are necessary. If your
program needs to be assembled for more than one processor, you can assemble
the statements conditionally, as shown in this example:

    .DATA
    mem32   DWORD   316423
    mem32a  DWORD   316423
    mem32b  DWORD   156739
    p386    TEXTEQU (@Cpu AND 08h)
            .CODE
            .
            .
            .
    ; Addition
            IF      p386
            mov     eax, 43981  ; Load immediate
            add     eax, mem32  ; Result in EAX
            ELSE
            .
            .       ; do steps in previous example
            .
            ENDIF

    ; Subtraction
            IF      p386
            mov     eax, mem32a ; Load memory
            sub     eax, mem32b ; Result in EAX
            ELSE
            .
            .       ; do steps in previous example
            .
            ENDIF

Since the status of the carry flag affects the results of calculations with
ADC and SUB, be sure to turn off the carry flag with the CLC (Clear Carry
Flag) instruction or use ADD for the first calculation when appropriate.


4.2.4  Multiplying and Dividing Integers

The 8086 family of processors uses different multiplication and division
instructions for signed and unsigned integers. Multiplication and division
instructions also have special requirements depending on the size of the
operands and the processor the code runs on.


4.2.4.1  Using Multiplication Instructions

The MUL instruction multiplies unsigned numbers. IMUL multiplies signed
numbers. For both instructions, one factor must be in the accumulator
register (AL for 8-bit numbers, AX for 16-bit numbers, EAX for 32-bit
numbers). The other factor can be in any single register or memory operand.
The result overwrites the contents of the accumulator register.

Multiplying two 8-bit numbers produces a 16-bit result returned in AX.
Multiplying two 16-bit operands yields a 32-bit result in DX:AX. The
80386/486 processor handles 64-bit products in the same way in the EDX:EAX
pair.

This example illustrates multiplication of signed 16- and 32-bit integers.

    .DATA
    mem16   SWORD   -30000
            .CODE
            .
            .
            .
    ; 8-bit signed multiply
            mov     al, 23     ; Load AL                     23
            mov     bl, 24     ; Load BL                   * 24
            mul     bl         ; Multiply BL              -----
                                ; Product in AX              552
                                ;  overflow and carry set

    ; 16-bit unsigned multiply
            mov     ax, 50     ; Load AX                     50
                                ;                         -30000
            imul    mem16      ; Multiply memory          -----
                                ; Product in DX:AX      -1500000
                                ;  overflow and carry set

A nonzero number in the upper half of the result (AH for byte, DX or EDX for
word) sets the overflow and carry flags.

On the 80186-80486 processors, the IMUL instruction supports three different
operand combinations. The first syntax option allows for 16-bit multipliers
producing a 16-bit product or 32-bit multipliers for 32-bit products on the
80386/486. The result overwrites the destination. The syntax for this
operation is

    IMUL register16, immediate

Multiplication by an immediate operand is possible on the 80386/486.

The second syntax option specifies three operands for IMUL. The first
operand must be a 16-bit register operand, the second a 16-bit memory or
register operand, and the third a 16-bit immediate operand. IMUL multiplies
the memory (or register) and immediate operands and stores the product in
the register operand with this syntax:

IMUL register16, memory16 | register16, immediate

For the 80386/486 only, a third option for IMUL allows an additional operand
for multiplication of a register value by a register or memory value. This
is the syntax:

    IMUL register,{register | memory}

The destination can be any 16-bit or 32-bit register. The source must be the
same size as the destination.

In all of these options, products too large to fit in 16 or 32 bits set the
overflow and carry flags. The following examples show these three options
for IMUL.

    imul    dx, 456     ; Multiply DX times 456 on 80186-80486
            imul    ax, [bx],6  ; Multiply the value pointed to by BX
                                ;  by 6 and put the result in AX

            imul    dx, ax      ; Multiply DX times AX on 80386
            imul    ax, [bx]    ; Multiply AX by the value pointed to
                                ;  by BX on 80386

The IMUL instruction with multiple operands can be used for either signed or
unsigned multiplication, since the 16-bit product is the same in either
case. To get a 32-bit result, you must use the single-operand version of MUL
or IMUL.


4.2.4.2  Using Division Instructions

The DIV instruction divides unsigned numbers, and IDIV divides signed
numbers. Both return a quotient and a remainder.

Table 4.1 summarizes the division operations. The dividend is the number to
be divided, and the divisor is the number to divide by. The quotient is the
result. The divisor can be in any register or memory location except the
registers where the quotient and remainder are returned.

Table   4.1 Division Operations

Size of        Dividend       Size of
Operand        Register       Divisor        Quotient  Remainder
────────────────────────────────────────────────────────────────────────────
16 bits        AX             8 bits         AL        AH

32 bits        DX:AX          16 bits        AX        DX

64 bits        EDX:EAX        32 bits        EAX       EDX
(80386
and 80486)

────────────────────────────────────────────────────────────────────────────


Unsigned division does not require careful attention to flags. The following
examples illustrate signed division, which can be more complex.

    .DATA
    mem16   SWORD   -2000
    mem32   SDWORD  500000
            .CODE
            .
            .
            .
    ; Divide 16-bit unsigned by 8-bit
            mov     ax, 700               ; Load dividend      700
            mov     bl, 36                ; Load divisor DIV    36
            div     bl                    ; Divide BL       ------
                                        ; Quotient in AL      19
                                        ; Remainder in AH          16

    ; Divide 32-bit signed by 16-bit
            mov     ax, WORD PTR mem32[0] ; Load into DX:AX
            mov     dx, WORD PTR mem32[2] ;                 500000
            idiv    mem16                 ;              DIV -2000
                                        ; Divide memory   ------
                                        ; Quotient in AX    -250
                                        ; Remainder in DX           0

    ; Divide 16-bit signed by 16-bit
            mov     ax, WORD PTR mem16    ; Load into AX     -2000
            cwd                           ; Extend to DX:AX
            mov     bx,-421               ;               DIV -421
            idiv    bx                    ; Divide by BX     -----
                                        ; Quotient in AX       4
                                        ; Remainder in DX        -316

If the dividend and divisor are the same size, sign-extend or zero-extend
the dividend so that it is the length expected by the division instruction.
See Section 4.2.1.4, "Extending Signed and Unsigned Integers."


4.3  Manipulating Integers at the Bit Level

The instructions introduced so far in this chapter accessed integers at the
byte or word level. The logical, shift, and rotate instructions described in
this section, however, access the individual bits of the integers. You can
use logical instructions to evaluate characters and do other text and screen
operations. The shift and rotate instructions do similar tasks by shifting
and rotating bits through registers. This section discusses some
applications of these bit-level operations.


4.3.1  Logical Operations

The logical instructions─AND, OR, XOR, and NOT─operate on each bit in one
operand and on the corresponding bit in the other. The following list shows
how each instruction works. Except for NOT, these instructions require two
integers of the same size.


Instruction                       Sets a Bit to 1 under These Conditions
────────────────────────────────────────────────────────────────────────────
AND                               Both corresponding bits in the operands
                                    have the value 1.

OR                                Either of the corresponding bits in the
                                    operands has the value 1.

XOR                               Either, but not both, of the
                                    corresponding bits in the operands has
                                    the value 1.

NOT                               The corresponding bit in the operand is
                                    0. (This instruction takes only one
                                    operand.)


────────────────────────────────────────────────────────────────────────────
NOTE
Do not confuse logical instructions with the logical operators, which
perform these operations at assembly time, not run time. Although the names
are the same, the assembler recognizes the difference from context.
────────────────────────────────────────────────────────────────────────────

The following example shows the result of the AND, OR, XOR, and NOT
instructions operating on a value in the AX register and in a mask. A mask
is a binary or hexadecimal number with appropriate bits set for the intended
operation.

    mov     ax, 035h   ; Load value                  00110101
            and     ax, 0FBh   ; Clear bit 2             AND 11111011
                                ;                             --------
                                ; Value is now 31h            00110001
            or      ax, 016h   ; Set bits 4,2,1          OR  00010110
                                ;                             --------
                                ; Value is now 37h            00110111
            xor     ax, 0ADh   ; Toggle bits 7,5,3,2,0   XOR 10101101
                                ;                             --------
                                ; Value is now 9Ah            10011010
            not     ax         ; Value is now 65h            01100101

Use AND, OR, and XOR to set or clear specific bits.

You can use the AND instruction to clear the value of specific bits
regardless of their current settings. To do this, put the target value in
one operand and a mask of the bits you want to clear in the other. The bits
of the mask should be 0 for any bit positions you want to clear and 1 for
any bit positions you want to remain unchanged.

You can use the OR instruction to force specific bits to 1 regardless of
their current settings. The bits of the mask should be 1 for any bit
positions you want to set and 0 for any bit positions you want to remain
unchanged.

You can use the XOR instruction to toggle the value of specific bits
(reverse them from their current settings). This instruction sets a bit to 1
if the corresponding bits are different or to 0 if they are the same. The
bits of the mask should be 1 for any bit positions you want to toggle and 0
for any bit positions you want to remain unchanged.

The following examples show an application for each of these instructions.
The code illustrating the AND instruction converts a "y" or "n" read from
the keyboard to uppercase, since bit 5 is always clear in uppercase letters.
In the example for OR, the first statement is faster and uses fewer bytes
than  cmp bx, 0. When the operands for XOR are identical, each bit cancels
itself, producing 0.

    ; Converts characters to uppercase
            mov     ah, 7           ; Get character without echo
            int     21h
            and     al, 11011111y   ; Convert to uppercase by clearing

                                    ;  bit 5
            cmp     al, 'Y'         ; Is it Y?
            je      yes             ; If so, do Yes actions
            .                       ;  else do No actions
            .
    yes:    .

    ; Compares operand to 0
            or      bx, bx          ; Compare to 0
                                    ;  2 bytes, 2 clocks on 8088
            jg      positive        ; BX is positive
            jl      negative        ; BX is negative
                                    ; else BX is zero

    ; Sets a register to 0
            xor     cx, cx          ; 2 bytes, 3 clocks on 8088
            sub     cx, cx          ; 2 bytes, 3 clocks on 8088
            mov     cx, 0           ; 3 bytes, 4 clocks on 8088

On the 80386 and 80486, the BSF (Bit Scan Forward) and the BSR (Bit Scan
Reverse) instructions perform operations similar to those of the logical
instructions. They scan the contents of a register to find the first-set or
last-set bit. You can use BSF or BSR to find the position of a set bit in a
mask or to check if a register value is 0.


4.3.2  Shifting and Rotating Bits

The 8086-based processors provide a complete set of instructions for
shifting and rotating bits. Shift instructions move bits a specified number
of places to the right or left. The last bit in the direction of the shift
goes into the carry flag, and the first bit is filled with 0 or with the
previous value of the first bit.

Rotate instructions also move bits a specified number of places to the right
or left. For each bit rotated, the last bit in the direction of the rotate
operation moves into the first bit position at the other end of the operand.
With some variations, the carry bit is used as an additional bit of the
operand. Figure 4.3 illustrates the eight variations of shift and rotate
instructions for eight-bit operands. Notice that SHL and SAL are identical.


(This figure may be found in the printed book.)

All shift instructions use the same format. Before the instruction executes,
the destination operand contains the value to be shifted; after the
instruction executes, it contains the shifted operand. The source operand
contains the number of bits to shift or rotate. It can be the immediate
value 1 or the CL register. The 8088 and 8086 processors do not accept any
other values or registers with these instructions.


The shift instruction allows you to change masks during program execution.

Masks for logical instructions can be shifted to new bit positions. For
example, an operand that masks off a bit or group of bits can be shifted to
move the mask to a different position, allowing you to mask off a different
bit each time the mask is used. This technique, illustrated in the following
example, is useful only if the mask value is unknown until run time.


    .DATA
    masker  BYTE    00000010y   ; Mask that may change at run time
            .CODE
            .
            .
            .
            mov     cl, 2       ; Rotate two at a time
            mov     bl, 57h     ; Load value to be changed 01010111y
            rol     masker, cl  ; Rotate two to left       00001000y
            or      bl, masker  ; Turn on masked values    ---------
                                ; New value is 05Fh        01011111y
            rol     masker, cl  ; Rotate two more          00100000y
            or      bl, masker  ; Turn on masked values    ---------
                                ; New value is 07Fh        01111111y

Starting with the 80186 processor, you can use eight-bit immediate values
larger than 1 as the source operand for shift or rotate instructions, as
shown below:

    shr     bx, 4   ;  9 clocks, 3 bytes on 80286

The following statements are equivalent if the program must run on the 8088
or 8086 processor:

    mov     cl, 4   ;  2 clocks, 3 bytes on 80286
            shr     bx, cl  ;  9 clocks, 2 bytes on 80286
                            ; 11 clocks, 5 bytes


4.3.3  Multiplying and Dividing with Shift Instructions

You can use the shift and rotate instructions (SHR, SHL, SAR, and SAL) for
multiplication and division. Shifting an integer right by one bit has the
effect of dividing by two; shifting left by one bit has the effect of
multiplying by two. You can take advantage of shifts to do fast
multiplication and division by powers of two. For example, shifting left
twice multiplies by four, shifting left three times multiplies by eight, and
so on.

Use SHR (Shift Right) to divide unsigned numbers. You can use SAR (Shift
Arithmetic Right) to divide signed numbers, but SAR rounds numbers down─IDIV
always rounds up. Division using SAR must adjust for this difference.
Multiplication by shifting is the same for signed and unsigned numbers, so
you can use either SAL or SHL.

Use shifts instead of MUL or DIV to optimize your code.

Since the multiply and divide instructions are very slow on the 8088 and
8086 processors, using shifts instead can often speed operations by a factor
of 10 or more. For example, on the 8088 or 8086 processor, these statements
take only four clocks:

    sub     ah, ah    ; Clear AH
            shl     ax, 1     ; Multiply byte in AL by 2

The following statements produce the same results, but take between 74 and
81 clocks on the 8088 or 8086. The same statements take 15 clocks on the
80286 and between 11 and 16 clocks on the 80386.

    mov     bl, 2     ; Multiply byte in AL by 2
            mul     bl

You can put multiplication and division operations in macros so they can be
changed if the constants in a program change, as shown in the two macros
below.

    mul_10  MACRO   factor       ; Factor must be unsigned
            mov     ax, factor   ; Load into AX
            shl     ax, 1        ; AX = factor * 2
            mov     bx, ax       ; Save copy in BX
            shl     ax, 1        ; AX = factor * 4
            shl     ax, 1        ; AX = factor * 8
            add     ax, bx       ; AX = (factor * 8) + (factor * 2)
            ENDM                 ; AX = factor * 10

    div_512 MACRO   dividend     ; Dividend must be unsigned
            mov     ax, dividend ; Load into AX
            shr     ax, 1        ;  AX = dividend / 2 (unsigned)
            xchg    al, ah       ; xchg is like rotate right 8
                                ;  AL = (dividend / 2) / 256
            cbw                  ; Clear upper byte
            ENDM                 ;  AX = (dividend / 512)

Since RCR and RCL use the carry flag, clear it before multiple-register
shifts.

If you need to shift a value that is too large to fit in one register, you
can shift each part separately. The RCR (Register Carry Right) and RCL
(Register Carry Left) instructions carry values from the first register to
the second by passing the leftmost or rightmost bit through the carry flag.


This example shifts a multiword value.


    .DATA
    mem32    DWORD  500000
            .CODE

    ; Divide 32-bit unsigned by 16
            mov     cx, 4                ; Shift right 4        500000
    again:  shr     WORD PTR mem32[2], 1 ; Shift into carry  DIV    16
            rcr     WORD PTR mem32[0], 1 ; Rotate carry in      ------
            loop    again                ;                       31250

Since the carry flag is treated as part of the operand (it's like using a
nine-bit or 17-bit operand), the flag value before the operation is crucial.
The carry flag can be set by a previous instruction, but you can also set it
directly by using the CLC (Clear Carry Flag), CMC (Complement Carry Flag),
and STC (Set Carry Flag) instructions.


On the 80386 and 80486, an alternate method for multiplying quickly by
constants takes advantage of the LEA (Load Effective Address) instruction
and the scaling of indirect memory operands. By using a 32-bit value as both
the index and the base register in an indirect memory operand, you can
multiply by the constants 2, 3, 4, 5, 8, and 9 more quickly than you can by
using the MUL instruction. LEA calculates the offset of the source operand
and stores it into the destination register, EBX, as this example shows:

    lea     ebx, [eax*2]        ; EBX = 2 * EAX
            lea     ebx, [eax*2+eax]    ; EBX = 3 * EAX
            lea     ebx, [eax*4]        ; EBX = 4 * EAX
            lea     ebx, [eax*4+eax]    ; EBX = 5 * EAX
            lea     ebx, [eax*8]        ; EBX = 8 * EAX
            lea     ebx, [eax*8+eax]    ; EBX = 9 * EAX

Section 3.2.4.3, "Indirect Memory Operands with 32-Bit Registers," discusses
scaling of 80386 indirect memory operands, and Section 3.3.3.2, "Loading
Addresses into Registers," introduces LEA.

This chapter has covered the integer operations you use in your MASM
programs. The next chapter looks at more complex data types─arrays, strings,
structures, unions, and records. Many of the operations presented in this
chapter can also be applied to the data structures discussed in Chapter 5,
"Defining and Using Complex Data Types."


4.4  Related Topics in Online Help

Online help features additional information about the topics discussed in
this chapter. From the "MASM 6.0 Contents" screen for MASM online help,
select the following topics:

╓┌─────────────────────────────────────┌─────────────────────────────────────╖
Topic                                 Access
────────────────────────────────────────────────────────────────────────────
BYTE, WORD, ...                       Choose "Directives" and then "Data
                                        Allocation"

Bitwise logical operations            Choose "Operators" and then from the
                                        list of operators, choose "Logical
                                        and Shift"

Location counter                      Choose "Predefined Symbols" for
                                        information on the $ symbol
Topic                                 Access
────────────────────────────────────────────────────────────────────────────
                                        information on the $ symbol

BSF, BSR, SHLD, SHRD, and SET         From the "Processor Instructions"
condition                             categories, choose "Logical and
                                        Shift"

LES,  LFS,  LGS                       From the "Processor Instructions"
                                        categories, choose "Data Transfer"

.RADIX directive                      Choose "Directives" and then choose
                                        "Miscellaneous"

MOD                                   Choose "Operators," and then
                                        "Arithmetic"

OPATTR, .TYPE, HIGH, LOW, HIGHWORD,   Choose "Operators," then
and  LOWWORD                          "Miscellaneous"

OPTION EXPR32,                        Choose "Directives," and then
Topic                                 Access
────────────────────────────────────────────────────────────────────────────
OPTION EXPR32,                        Choose "Directives," and then
OPTION EXPR16,                        "OPTION"








Chapter 5  Defining and Using Complex Data Types
────────────────────────────────────────────────────────────────────────────

With the complex data types available in MASM 6.0─arrays, strings, records,
structures, and (new to version 6.0) unions─you can access data either as a
unit or as individual elements that make up the unit. The individual
elements of complex data types are often the integer types discussed in
Chapter 4, "Defining and Using Integers."

Section 5.1 first discusses how to declare, reference, and initialize arrays
and strings. This section summarizes the general steps needed to process
arrays and strings and describes the MASM instructions for moving,
comparing, searching, loading, and storing operations.

Section 5.2 covers similar information for structures and unions: how to
declare structure and union types, how to define structure and union
variables, and how to reference structures and unions and their fields.

Section 5.3 explains how to declare record types, define record variables,
and use record operators.

All three sections also describe how to use the LENGTHOF, SIZEOF, and TYPE
operators with each complex data type.


5.1  Arrays and Strings

An assembly-language array is a sequence of fixed-size variables. A string
is an array of characters. You can access the elements in an array or string
relative to the first element.

This section explains and illustrates the essential ways to handle arrays
and strings in your programs. It covers arrays first, beginning with the two
ways to declare an array and continuing with how to reference it. The
section then explains the special requirements for declaring and
initializing a string. Finally, it describes the processing of arrays and
strings.


5.1.1  Declaring and Referencing Arrays

You can declare an array in two ways: you can specify a list of array
elements, or you can use the DUP operator to specify a group of identical
elements.

To declare an array, you must supply a label name, a type, and a series of
elements separated by commas. You can access each element of an array
relative to the first. In the examples below,  warray  and  xarray  are
arrays.

    warray  WORD    1, 2, 3, 4
    xarray  DWORD   OFFFh, OAAAh

The assembler stores the elements consecutively in memory, with the first
address referenced by the label name.

Initializer lists can be longer than one line.

Beginning with MASM 6.0, initializer lists of array declarations can span
multiple lines. The first initializer must appear on the same line as the
data type, all entries must be initialized, and, if you want the array to
continue to the new line, the line must end with a comma. These examples
show legal multiple-line array declarations:

    big             BYTE    21, 22, 23, 24, 25,
                            26, 27, 28

    somelist        WORD    10,
                            20,
                            30

If you do not want to use the new LENGTHOF and SIZEOF operators discussed
later in this section, then an array may span more than one logical line,
although a separate type declaration is needed on each logical line:

    var1    BTYE    10, 20, 30
            BYTE    40, 50, 60
            BYTE    70, 80, 90


The DUP Operator

You can also declare an array with the DUP operator. This operator can be
used with any of the data allocation directives described in Section 4.1.1.
In the syntax

    count DUP (initialvalue [[,initialvalue]]...)

the count value sets the number of times to repeat the last initialvalue.
Each initial value is evaluated only once and can be any expression that
evaluates to an integer value, a character constant, or another DUP
operator. The initial value (or values) must always be placed within
parentheses. For example, the statement

    barray  BYTE    5 DUP (1)

allocates the integer  1  five times for a total of five bytes.

The following examples show various ways to use the DUP operator to allocate
data elements.

    array   DWORD   10 DUP (1)                    ; 10 doublewords
                                                ;  initialized to 1
    buffer  BYTE    256 DUP (?)                   ; 256-byte buffer

    masks   BYTE    20 DUP (040h, 020h, 04h, 02h) ; 80-byte buffer
                                                ;  with bit masks
    three_d DWORD   5 DUP (5 DUP (5 DUP (0)))     ; 125 doublewords
                                                ;  initialized to 0


Referencing Arrays

Once an array is defined, you can refer to its first element by typing the
array name (no brackets required). The array name refers to the first object
of the given type in the list of initial values.

If  warray  has been defined as

    warray WORD 2, 4, 6, 8, 10

then referencing  warray  in your program refers to the first word─the word
containing  2.

To refer to the next element (in an array of words), use either of these two
forms, each of which refers to the array element two bytes past the
beginning of warray:

    warray+2
    warray[2]

This element can be used as you would any data item:

    mov     ax, warray[2]
            push    warray+2

When used with a variable name, brackets only add a number to the address.
If  warray  refers to the address  2400h, then  warray[2]  refers to the
address  2402h. The BOUND instruction (80186-80486 only) can be used to
verify that an index value is within the bounds of an array.

Array indexes are not scaled. The index is a distance in bytes.

In assembly language, array indexes are zero-based and unscaled. The number
within brackets always represents an absolute distance in bytes. In
practical terms, the fact that indexes are unscaled means that if an element
is larger than one byte, you must multiply the index of the element by its
size (in the example above,  2), and then add the result to the address of
the array. Thus, the expression  warray[4]  represents the third element,
which is four bytes past the beginning of the array. Similarly, the
expression  warray[6]  represents the fourth element.

You can also determine an index at run time:

    mov     si, cx          ; CX holds index value
            shl     si, 7           ; Scale for word referencing
            mov     ax, warray[si]  ; Move element into AX

The offset required to access an array element can be calculated with the
following formula:

nth element of array = array[(n-1) * size of element]


LENGTHOF, SIZEOF, and TYPE for Arrays

When applied to arrays, the LENGTHOF, SIZEOF, and TYPE operators return
information about the length and size of the array and about the type of the
initializers.

The LENGTHOF operator returns the number of items in the definition. It can
be applied only to an integer label. This is useful for determining the
number of elements you need to process in an array of integers. For an array
or string label, SIZEOF returns the number of bytes used by the initializers
in the definition. TYPE returns the size of the elements of the array. These
examples illustrate these operators:

    array   WORD    40 DUP (5)

    larray  EQU     LENGTHOF array    ; 40 elements
    sarray  EQU     SIZEOF   array    ; 80 bytes
    tarray  EQU     TYPE     array    ;  2 bytes per element

    num     DWORD   4, 5, 6, 7,
                    8, 9, 10, 11

    lnum    EQU     LENGTHOF num      ;  8 elements
    snum    EQU     SIZEOF   num      ; 32 bytes
    tnum    EQU     TYPE     num      ;  4 bytes per element

    warray  WORD    40 DUP (40 DUP (5))

    len     EQU     LENGTHOF warray   ; 1600 elements
    siz     EQU     SIZEOF   warray   ; 3200 bytes
    typ     EQU     TYPE     warray   ;    2 bytes per element


5.1.2  Declaring and Initializing Strings

A string is an array of bytes. Initializing a string like  "Hello, there"
allocates and initializes one byte for each character in the string. An
initialized string can be no longer than 255 characters.

Strings declared with types other than BYTE must fit the memory space
allocated.

For data directives other than BYTE, a string may initialize only a single
element. This element must be short enough to fit into the specified size
and conform to the expression word size in effect (see Section
1.2.4,"Integer Constants and Constant Expressions"), as shown in these
examples:

    wstr    WORD    "OK"
    dstr    DWORD   "ADCD"  ; Legal under EXPR32 only

As with arrays, string initializers can span multiple lines. The line must
end with a comma if you want the string to continue to the next line.

    str1    BYTE    "This is a long string that does not ",
                    "fit on one line."

You can also have an array of pointers to strings. For example:

    PBYTE   TYPEDEF PTR BYTE
            .DATA
    msg1    BYTE    "Operation completed successfully."
    msg2    BYTE    "Unknown command"
    msg3    BYTE    "File not found"
    pmsg1   PBYTE   msg1
    pmsg2   BPBYTE  msg2
    pmsg3   PBYTE   msg3

    errors  WORD    pmsg1, pmsg2, pmsg3    ; An array of pointers
                                            ;  to strings

Strings must be enclosed in single (') or double (") quotation marks. To put
a single quotation mark inside a string enclosed by single quotation marks,
use two single quotation marks. Likewise, if you need quotation marks inside
a string enclosed by double quotation marks, use two sets. These examples
show the various uses of quotation marks:

    char    BYTE    'a'
    message BYTE    "That's the message."       ; That's the message.
    warn    BYTE    'Can''t find file.'         ; Can't find file.
    string  BYTE    "This ""value"" not found." ; This "value"

                                                not found.

You can always use single quotation marks inside a string enclosed by double
quotation marks, as the initialization for  message  shows, and vice versa.



The ? Initializer

The actual values stored when you use ? depend on the other data in your
program.

You do not have to initialize all elements in an array to a value. If there
is no initial value, you can initialize the array elements with the ?
operator. The ? operator either is treated as a zero or causes a byte to be
left unspecified in the object file. Object files contain records for
initialized data. An unspecified byte left in the object file means that no
records contain initialized data for that address.

The actual values stored in arrays allocated with ? depend on certain
conditions. The ? initializer is treated as a zero in a DUP statement that
contains initializers in addition to the ? initializer. An unspecified byte
is left in the object file if the ? initializer does not appear in a DUP
statement, or if the DUP statement contains only ? initializers for nested
DUP statements.


Length-Specified Strings

Often there are reasons to know the length of a string. To use the DOS
functions for writing to a file, for example, CX must contain the length of
the string before the interrupt is called, as shown in this example.

    msg     BYTE    "This is a length-specified string"
            .
            .
            .
            mov     ah, 40h
            mov     bx, 1
            mov     cx, LENGTHOF msg
            mov     dx, OFFSET msg
            int     21h

Some high-level languages also expect strings passed to procedures to have a
certain format. For example, Pascal procedures require the first byte of a
string passed as a parameter to contain the length of the string. You can
write this length into the first byte with

    msg     BYTE    LENGTHOF msg - 1, "This is a Pascal string"

Interfacing with high-level languages requires special techniques with
strings.

Other languages such as Basic have string descriptions─a kind of structure
containing both the length and the address of the string. For example, this
structure  DESC  could be used in a procedure accessed from Basic:

    DESC    STRUCT
    len   WORD    ?       ; Length of string1
    off   WORD    ?       ; Offset of string1
    DESC    ENDS

    string1 BYTE    "This string goes in a string descriptor"
    msg     DESC    {LENGTHOF string1, string1}

See Section 5.2, "Structures and Unions."


Null-Terminated and $-Terminated Strings

Null-terminated and $-terminated strings have a special use with DOS
functions. Strings in modules shared with C need to end with a null
character (0).

    str1    BYTE    "This string ends with a null character", 0

DOS file names also require a null character at the end. This example opens
a file named  "MYFILE.ASM".

    name1   BYTE    "MYFILE.ASM", 0
            .
            .
            .
            mov     ah, 3Dh
            mov     dx, OFFSET name1
            int     21h

DOS function 9 requires a string to end with a dollar sign ($) so that it
can recognize the end of the string to write to the screen, as shown in this
example.

    msg     BYTE    "This is a dollar-terminated string$"
            .
            .
            .
            mov     ah, 09h
            mov     dx, OFFSET msg
            int     21h


LENGTHOF, SIZEOF, and TYPE for Strings

Because the assembler considers strings as simply arrays of byte elements,
the LENGTHOF and SIZEOF operators return the same values for strings as they
do for arrays, as illustrated in this example. The TYPE operator considers
msg  to be one data unit and returns 1.

    msg     BYTE    "This string extends ",
                    "over three ",
                    "lines."

    lmsg    EQU     LENGTHOF msg      ; 37 elements
    smsg    EQU     SIZEOF   msg      ; 37 bytes
    tmsg    EQU     TYPE     msg      ;  1 byte per element


5.1.3  Processing Arrays and Strings

The 8086-family instruction set has seven string instructions for fast and
efficient processing of entire strings and arrays. The term "string" in
"string instructions" refers to a sequence of elements, not just character
strings. These instructions work directly only on arrays of bytes and words
on the 8086-80486 and on arrays of bytes, words, and doublewords on the
80386 and 80486. Processing larger elements must be done indirectly with
loops.


The following list gives capsule descriptions of the five instructions
discussed in this section. Two additional instructions not described here
are the INS and OUTS instructions that transfer values to and from a memory
port.

Instruction   Description
────────────────────────────────────────────────────────────────────────────
MOVS          Copies a string from one location to another
STOS          Stores values from the accumulator register to a string
CMPS          Compares values in one string with values in another
LODS          Loads values from a string to the accumulator register
SCAS          Scans a string for a specified value

All of these instructions use registers in a similar way and have a similar
syntax. Most are used with the repeat instruction prefixes REP, REPE (or
REPZ), and REPNE (or REPNZ). REPZ is a synonym for REPE (Repeat While Equal)
and REPNZ is a synonym for REPNE (Repeat While Not Equal).


This section first explains the general procedures for using all string
instructions. It then illustrates each instruction with an example.


5.1.3.1  Overview of String Operations

The string instructions have specific requirements for the location of
strings and the use of registers. To operate on any string, follow these
three steps:

All string operations follow three basic steps.


    1.  Set the direction flag to indicate the direction in which you want to
        process the string. The STD instruction sets the flag, while CLD
        clears it.

        If the direction flag is clear, the string is processed upward (from
        low addresses to high addresses, which is from left to right through
        the string). If the direction flag is set, the string is processed
        downward (from high addresses to low addresses, or from right to
        left). Under DOS, the direction flag is normally clear if your program
        has not changed it.

    2.  Load the number of iterations for the string instruction into the CX
        register.

        If you want to process a 100-byte string, move 100 into CX. If you
        wish the string instruction to terminate conditionally (for example,
        during a search when a match is found), load the maximum number of
        iterations that can be performed without an error.

    3.  Load the starting offset address of the source string into DS:SI and
        the start-ing address of the destination string into ES:DI. Some
        string instructions take only a destination or source, not both (see
        Table 5.1).

        Normally, the segment address of the source string should be DS, but
        you can use a segment override to specify a different segment for the
        source operand. You cannot override the segment address for the
        destination string. Therefore, you may need to change the value of ES.
        See Section 3.1 for information on changing segment registers.

────────────────────────────────────────────────────────────────────────────
NOTE
Although you can use a segment override on the source operand, a segment
override combined with a repeat prefix can cause problems in certain
situations on all processors except the 80386/486. If an interrupt occurs
during the string operation, the segment override is lost and the rest of
the string operation processes incorrectly. Segment overrides can be used
safely when interrupts are turned off or with an 80386/486
processor.───────────────────────────────────────────────────────────────────



You can adapt these steps to the requirements of any particular string
operation. The syntax for the string instructions is:

    «prefix» CMPS «segmentregister:»
    source, «ES:» destination
                    LODS «segmentregister:» source
    «prefix» MOVS «ES:» destination,
    «segmentregister:» source
    «prefix» SCAS «ES:» destination
    «prefix» STOS «ES:« destination

Some instructions have special forms for byte, word, or doubleword operands.
If you use the form of the instruction that ends in B (BYTE), W (WORD), or D
(DWORD) with LODS, SCAS, and STOS, the assembler knows whether the element
is in the AL, AX, or EAX register. Therefore, these instruction forms do not
require operands.

Table 5.1 lists each string instruction with the type of repeat prefix it
uses and indicates whether the instruction works on a source, a destination,
or both.

Table 5.1  Requirements for String Instructions

╓┌─────────────┌───────────────┌───────────────────┌─────────────────────────╖
Instruction   Repeat Prefix   Source/Destination  Register Pair
────────────────────────────────────────────────────────────────────────────
MOVS          REP             Both                DS:SI, ES:DI
SCAS          REPE/REPNE      Destination         ES:DI
CMPS          REPE/REPNE      Both                DS:SI, ES:DI
LODS          None            Source              DS:SI
STOS          REP             Destination         ES:DI
INS           REP             Destination         ES:DI
OUTS          REP             Source              DS:SI
────────────────────────────────────────────────────────────────────────────


The instruction automatically increments DI or SI.

The repeat prefix causes the instruction that follows it to repeat for the
number of times specified in the count register or until a condition becomes
true. After each iteration, the instruction increments or decrements SI and
DI so that it points to new array elements. The string instructions work on
these elements. The direction flag determines whether SI and DI are
incremented (flag clear) or decremented (flag set). The size of the
instruction determines whether SI and DI are altered by one, two, or four
bytes each time.

These are the conditions that determine the number of repetitions specified
by a prefix.

Prefix                            Description
────────────────────────────────────────────────────────────────────────────
REP                               Repeats instruction CX times

REPE, REPZ                        Repeats instruction CX times, or as long
                                    as elements are equal, whichever is
                                    fewer

REPNE, REPNZ                      Repeats instruction CX times, or as long
                                    as elements are not equal, whichever is
                                    fewer


The prefixes apply to only one string instruction at a time. To repeat a
block of instructions, use a loop construction (see Section 7.2, "Loops").

At run time, if a string instruction is preceded by a repeat sequence, the
processor takes the following steps:


    1.  Checks the CX register and exits if CX is 0. If the REPE prefix is
        used, the loop exits if the zero flag is set; if REPNE is used, the
        loop exits if the zero flag is clear.

    2.  Performs the string operation once.

    3.  Increases SI and/or DI if the direction flag is clear. Decreases SI
        and/or DI if the direction flag is set. The amount of increase or
        decrease is 1 for byte operations, 2 for word operations, and 4 for
        doubleword operations (80386/486 only).

    4.  Decrements CX (no flags are modified).

    5.  Checks the zero flag at this point if the REPE or REPNE prefix is used
        (for SCAS or CMPS). If the repeat condition does not hold, execution
        proceeds to the next instruction.

    6.  Proceeds to the next iteration and repeats from step 1.


At loop end, SI and DI point to the element immediately after the match.

When the repeat loop ends, SI (or DI) points to the position following a
match (when using SCAS or CMPS), so you need to decrement or increment DI or
SI to point to the element where the match occurred.

Although string instructions (except LODS) are most often used with repeat
prefixes, they can also be used by themselves. In this case, the SI and/or
DI registers are adjusted as specified by the direction flag and the size of
operands. However, you must decrement the CX register and set up a loop for
the repeated action.


5.1.3.2  String Instructions

To use the 8086-family string instructions, apply the steps outlined in the
previous section. Examples in this section illustrate each instruction.

You can also use the techniques in this section with structures and unions,
since arrays and strings can be fields in structures and unions (see Section
5.2).

Moving Array Data - The MOVS instruction copies data from one area of memory
to another. To move data, first load the count and the source and
destination addresses into the appropriate registers. Then use REP with the
MOVS instruction.

    .MODEL  small
            .DATA
    source  BYTE    10 DUP ('0123456789')
    destin  BYTE    100 DUP (?)
            .CODE
            mov     ax, @data           ; Load same segment
            mov     ds, ax              ;  to both DS
            mov     es, ax              ;  and ES
            .
            .
            .
            cld                         ; Work upward
            mov     cx, LENGTHOF source ; Set iteration count to 100
            mov     si, OFFSET source   ; Load address of source
            mov     di, OFFSET destin   ; Load address of destination
            rep     movsb               ; Move 100 bytes

Storing Data in Arrays - The STOS instruction stores a specified value in
each position of a string. The string is the destination, so it must be
pointed to by ES:DI. The value to store must be in the accumulator.

This example stores the character  'a'  in each byte of a 100-byte string.
Notice that it does this by storing 50 words rather than 100 bytes. This
makes the code faster by reducing the number of iterations. To fill an odd
number of bytes, you would have to adjust for the last byte.

    .MODEL  small, C
            .DATA
    destin  BYTE    100 DUP (?)
    ldestin EQU     (LENGTHOF destin) / 2
            .CODE
            .                           ; Assume ES = DS
            .
            .
            cld                         ; Work upward
            mov     ax, 'aa'            ; Load character to fill
            mov     cx, ldestin         ; Load length of string
            mov     di, OFFSET destin   ; Load address of destination
            rep     stosw               ; Store 'aa' into array

Comparing Arrays - The CMPS instruction compares two strings and points to
the address after which a match or nonmatch occurs. If the values are the
same, the zero flag is set. Either string can be considered as the
destination or the source unless a segment override is used.

This example using CMPSB assumes that the strings are in different segments.
Both segments must be initialized to the appropriate segment register.

    .MODEL  large, C
            .DATA
    string1 BYTE    "The quick brown fox jumps over the lazy dog"
            .FARDATA
    string2 BYTE    "The quick brown dog jumps over the lazy fox"
    lstring EQU     LENGTHOF string2
            .CODE
            mov     ax, @data           ; Load data segment
            mov     ds, ax              ;  into DS
            mov     ax, @fardata        ; Load far data segment
            mov     es, ax              ;  into ES
            .
            .
            .
            cld                         ; Work upward
            mov     cx, lstring         ; Load length of string
            mov     si, OFFSET string1  ; Load offset of string1
            mov     di, OFFSET string2  ; Load offset of string2
            repe    cmpsb               ; Compare
            jcxz    allmatch            ; CX is 0 if no nonmatch
            .
            .
            .
    allmatch:                           ; Special case for all match

Loading Data from Arrays - The LODS instruction loads a value from a string
into a register. The string is the source; the value is in the accumulator.
This instruction normally is not used with a repeat instruction prefix,
since something must be done with each element before going on to the next.

The code in this example loads, processes, and displays each byte in a
string of bytes.

    .DATA
    info    BYTE    0, 1, 2, 3, 4, 5, 6, 7, 8, 9
    linfo   WORD    LENGTHOF info
            .CODE
            .
            .
            .
            cld                       ; Work upward
            mov     cx, linfo         ; Load length
            mov     si, OFFSET info   ; Load offset of source
            mov     ah, 2             ; Display character function

    get:
            lodsb                     ; Get a character
            add     al, '0'           ; Convert to ASCII
            mov     dl, al            ; Move to DL
            int     21h               ; Call DOS to display character
            loop    get               ; Repeat

Searching Arrays - The SCAS instruction scans a string for a specified
value. As the loop executes, this instruction compares the value pointed to
by DI with the value in the accumulator. If values are the same, the zero
flag is set.

After a REPNE SCAS, the zero flag is cleared if no match was found. After a
REPE SCAS, the zero flag is set if all values matched.

This example assumes that ES is not the same as DS and that the address of
the string is stored in a pointer variable. The LES instruction loads the
far address of the string into ES:DI.

    .DATA
    string  BYTE    "The quick brown fox jumps over the lazy dog"
    pstring PBYTE   string             ; Far pointer to string
    lstring EQU     LENGTHOF string    ; Length of string
            .CODE
            .
            .
            .
            cld                        ; Work upward
            mov     cx, lstring        ; Load length of string
            les     di, pstring        ; Load address of string
            mov     al, 'z'            ; Load character to find
            repne   scasb              ; Search
            jcxz    notfound           ; CX is 0 if not found
            .                          ; ES:DI points to character
            .                          ;  after first 'z'
            .
    notfound:                          ; Special case for not found


5.2  Structures and Unions

A structure is a group of possibly dissimilar data types and variable
declarations that can be accessed as a unit or by any of its components. The
fields within the structure can have different sizes and data types.

Unions are identical to structures, except that the fields of a union
overlap in memory, which allows you to define different data formats for the
same memory space. Unions can store different types of data depending on the
situation. They can also store data as one data type and retrieve it as
another data type.

Whereas each field in a structure has an offset relative to the first byte
of the structure, all the fields in a union start at the same offset. The
size of a structure is the sum of its components, while the size of a union
is the length of the longest field.

A MASM structure is similar to a struct in the C language, a STRUCTURE in
FORTRAN, and a RECORD in Pascal. Unions in MASM are similar to unions in C
and FORTRAN, and to variant records in Pascal.

Follow these steps when using structures and unions:


    1.  Declare a structure (or union) type.

    2.  Define one or more variables having that type.

    3.  Reference the fields directly or indirectly with the field (dot)
        operator.


You can use the entire structure or union variable or just the individual
fields as operands in assembler statements. This section explains the
allocating, initializing, and nesting of structures and unions.

MASM 6.0 extends the functionality of structures and also makes some changes
to MASM 5.1 behavior. You can still retain MASM 5.1 behavior if you prefer
by specifying OPTION OLDSTRUCTS in your program. See Section 1.3.2 for
information about the OPTION directive, and Section 5.2.3 for information
about referencing structures and unions.


5.2.1  Declaring Structure and Union Types

When you declare a structure or union type, you create a template for data
that contains the sizes and, optionally, the initial values for fields in
the structure or union but that allocates no memory.

The STRUCT keyword marks the beginning of a type declaration for a
structure. (STRUCT and STRUC are synonyms.) STRUCT and UNION type
declarations have the following format:

    name {STRUCT | UNION}  «alignment»
    «,NONUNIQUE »
    fielddeclarations
    name ENDS

The fielddeclarations are a series of one or more variable declarations. You
can declare default initial values individually or with the DUP operator
(see Section 5.2.2, "Defining Structure and Union Variables"). Section
5.2.3, "Referencing Structures, Unions, and Fields," explains the NONUNIQUE
keyword. Structures and unions can also be nested in MASM 6.0 (see Section
5.2.4).


Initializing Fields

If you provide initializers for the fields of a structure or union when you
declare the type, these initializers become the default value for the fields
when you define a variable of that type. Section 5.2.2 explains default
initializers.

When you initialize the fields of a union type, the type and value of the
first field become the default value and type for the union. In this example
of an initialized union declaration, the default type for the union is
DWORD:

    DWB     UNION
    d     DWORD   00FFh
    w     WORD    ?
    b     BYTE    ?
    DWB     ENDS

If the size of the first member is less than the size of the union, the
assembler initializes the rest of the union to zeros. When initializing
strings in a type, make sure the initial values are long enough to
accommodate the largest possible string.


Field Names

Structure and union field names in MASM 6.0 must be unique within a given
nesting level because they represent the offset from the beginning of the
structure to the corresponding field.

A nested structure has its own level.

In MASM 6.0, a label and a structure field may have the same name, but not a
text macro and a field name. Also, field names between structures need not
be unique. Field names do need to be unique if you place OPTION M510 or
OPTION OLDSTRUCTS in your code or use the /Zm option from the command line,
since versions of MASM prior to 6.0 require unique field names (see Appendix
A).


Alignment Value and Offsets for Structures

Data access to structures is faster on aligned fields than on unaligned
fields. Therefore, alignment gains speed at the cost of space. Alignment
improves access on 16-bit processors but makes no difference on code
executing on an 8-bit 8088 processor.

The way the assembler aligns structure fields determines the amount of space
required to store a variable of that type. Each field in a structure has an
offset relative to 0. If you specify an alignment in the structure
declaration (or with the /Zpn command-line option), the offset for each
field may be modified by the alignment (or n).

The only values accepted for alignment are 1, 2, and 4. The default is 1. If
the type declaration includes an alignment, the fields are aligned to the
minimum of the field's size and the alignment. Any padding required to reach
the correct offset for the field is added prior to allocating the field. The
padding consists of zeros and always precedes the field.

If the number of bytes in the field is greater than the alignment value, the
element will be padded such that the offset of the element is divisible by
the alignment value. If the number of bytes is greater than or equal to the
alignment value, the offset of the element is padded such that it is
divisible by the element size.

The size of the structure must also be evenly divisible by the structure
alignment value, so zeros may be added at the end of the structure.

If neither the alignment nor the /Zp command-line option is used, the offset
is incremented by the size of each data directive. This is the same as a
default alignment equal to 1. The alignment specified in the type
declaration overrides the /Zp command-line option.

These examples show how offsets are determined:

    STUDENT2    STRUCT  2   ; Alignment value is 2
    score     WORD    1   ; Offset is  0
    id        BYTE    2   ; Offset is  2
    year      DWORD   3   ; Offset is  4; one byte padding added
    sname     BYTE    4   ; Offset is  8
    STUDENT2    ENDS

One byte of padding is added at the end of the first byte-sized field.
Otherwise the offset of the  year  field would be 3, which is not divisible
by the alignment value of 2. The size of this structure is now 9 bytes.
Since 9 is not evenly divisible by 2, one byte of padding is added at the
end of  student2.

    STUDENT4    STRUCT  4            ; Alignment value is 4
    sname     BYTE    1            ; Offset is  0
    score     WORD    10 DUP (100) ; Offset is  2
    year      BYTE    2            ; Offset is 22; 1 byte padding
                                    ;  added so offset of next field
                                    ;  is divisible by 4
    id        DWORD   3            ; Offset is 24
    STUDENT4    ENDS

The alignment value affects memory allocation of structure variables.

The alignment value affects the alignment of structure variables, so adding
an alignment value affects memory usage. This feature provides compatibility
with structures in Microsoft C.

With MASM 6.0, C programmers can use the H2INC utility to translate C
structures to MASM (see Chapter 16).


5.2.2  Defining Structure and Union Variables

Once you have declared a structure or union type, variables of that type can
be defined. For each variable defined, memory is allocated in the current
segment in the format declared by the type. The syntax for defining a
structure or union variable is:

    [[name]] typename < [[initializer
    [[,initializer]]...]] >

    [[name]] typename { [[initializer
    [[,initializer]]...]] }

    [[name]] typename constant
    DUP ({ [[initializer [[,initializer]]...]]
    })

The name is the label assigned to the variable. If no name is given, the
assembler allocates space for the variable but does not give it a symbolic
name. The typename is the name of a previously declared structure or union
type.

An initializer can be given for each field. The type of each initializer
must be the type of the corresponding field defined in the type declaration.
For unions, the type of the initializer must be the same as the type for the
first field. An initialization list can also be repeated using the DUP
operator.

The list of initializers can be broken only after a comma unless you use a
line continuation character () at the end of the line. The last curly brace
or angle bracket must appear on the same line as the last initializer. You
can also use the line continuation character to extend a line as shown in
the  Item4 declaration below. Angle brackets and curly braces can be
intermixed in an initialization as long as they match. This example using
the  ITEMS  structure illustrates the options for initializing lists:

    ITEMS       STRUCT
    Iname     BYTE      'Item Name'
    Inum      WORD      ?
    ITYPE     UNION
        oldtype BYTE      0
        newtype WORD      ?
    ENDS
    ITEMS       ENDS
            .
            .
            .
            .DATA
    Item1   ITEMS   < >              ; Accepts default initializers
    Item2   ITEMS   { }              ; Accepts default initializers
    Item3   ITEMS   <'Bolts', 126>   ; Overrides default value of first
                                    ;  2 fields; use default of
                                    ;  the third field
    Item4   ITEMS   { 
                    'Bolts',        ; Item name
                    126            ; Part number
                    }

The angle brackets or curly braces are required even if no initial value is
given, as in  Item1  and  Item2  in the example. If initial values are given
for more than one field, the values must be separated by commas, as shown in
    Item3.

You need not initialize all fields in a structure. If an initial value is
blank, the assembler automatically uses the default initial value of the
field, which was originally provided in the structure type declaration. If
there is no default value, the field is undefined.

For nested structures or unions (see Section 5.2.4), however, these are
equivalent:

    Item5   ITEMS   {'Bolts', ,     }
    Item6   ITEMS   {'Bolts', , { } }

A variable and an array of union type  WB  look like this:

    WB      UNION
    w     WORD    ?
    b     BYTE    ?
    WB      ENDS

    num     WB      {0Fh}                       ; Store 0Fh
    array   WB      (40 / SIZEOF WB) DUP ({2})  ; Allocates and
                                                ;  initializes 10 unions

(This figure may be found in the printed book.)

In MASM 6.0, control structures (such as IF, macros, and directives) are
also allowed within structure and union declarations.


Arrays as Field Initializers

Default initializers for string or array fields set the size for the field.


The length of the array that can override the contents of a field in a
variable definition is fixed by the size of the initializer. The override
cannot contain more elements than the default. Specifying fewer override
array elements changes the first n values of the default where n is the
number of values in the override. The rest of the array elements take their
default values from the initializer.


Strings as Field Initializers

If the override is shorter, the assembler pads the override with spaces to
equal the length of the initializer. If the initializer is a string and the
override value is not a string, the override value must be enclosed in angle
brackets or curly braces.

A string may be used to override any member of type BYTE (or SBYTE). The
string does not need to be enclosed in angle brackets or curly braces unless
mixed with other override methods.

The string fields for structure variables are the length defined by the type
declaration.

If a structure has an initialized string field or an array of bytes, any new
string assigned to a variable of the field that is smaller than the default
is padded with spaces. The assembler adds four spaces at the end of  'Bolts'
    in the variables of type  ITEMS  above. The  Iname  field in the  ITEMS
structure cannot contain a field initializer longer than  'Item Name'.


Structures as Field Initializers

Initializers for structure variables must be enclosed in curly braces or
angle brackets, but you can specify overrides with fewer elements than the
defaults.

This example illustrates the use of default values with structures as field
initializers:

    DISKDRIVES      STRUCT
    a1            BYTE ?
    b1            BYTE ?
    c1            BYTE ?
    DISKDRIVES      ENDS

    INFO            STRUCT
    buffer        BYTE    100 DUP (?)
    crlf          BYTE    13, 10
    query         BYTE    'Filename: ' ; String <= can override
    endmark       BYTE    36
    drives        DISKDRIVES <0, 1, 1>
    INFO            ENDS

    info1   INFO    { , , 'Dir' }

    ; Illegal since name in query field is too long
    ; and a string cannot initialize a field defined with DUP:
    ; info2  INFO    {"TESTFILE", , "DirectoryName",}

    lotsof  INFO    { , , 'file1', , {0,0,0} },
                    { , , 'file2', , {0,0,1} },
                    { , , 'file3', , {0,0,2} }

The diagram below shows how the assembler stores  info1.

(This figure may be found in the printed book.)

The initialization for  drives  gives default values for all three fields of
the structure. The fields left blank in  info1  use the default values for
those fields. The  info2  declaration is illegal since  "DirectoryName"  is
longer than the initial string for that field, and the  "TESTFILE"  string
cannot initialize a field defined with DUP.


Arrays of Structures and Unions

You can define an array of structures using the DUP operator (see Section
5.1.1, "Declaring and Referencing Arrays") or by creating a list of
structures. For example, you can define an array of structure variables like
this:

    Item7   ITEMS    30 DUP ({,,{10}})

The  Item7  array defined here has 30 elements of type  ITEMS, with the
third field of each element (the union) initialized to  10.

You can also list array elements as shown in this example:

    Item8   ITEMS    {'Bolts', 126, 10},
                    {'Pliers',139, 10},
                    {'Saws',  414, 10}


Structure Redefinition

The assembler generates an error for a structure redefinition unless all of
the following are the same:


    ■   Field names

    ■   Offsets of named fields

    ■   Initialization lists

    ■   Field alignment value


Additionally, all fields must be present and at the same offset.


LENGTHOF, SIZEOF, and TYPE for Structures

The size of a structure determined by SIZEOF is the offset of the last
field, plus the size of the last field, plus any padding required for proper
alignment (see Section 5.2.1 for information about alignment). This example,
using the data declarations above, shows how to use the LENGTHOF, SIZEOF,
and TYPE operators with structures:

    INFO            STRUCT
    buffer        BYTE    100 DUP (?)
    crlf          BYTE    13, 10
    query         BYTE    'Filename: '
    endmark       BYTE    36
    drives        DISKDRIVES <0, 1, 1>
    INFO            ENDS

    info1   INFO    { , , 'Dir' }
    lotsof  INFO    { , , 'file1', , {0,0,0} },
                    { , , 'file2', , {0,0,1} },
                    { , , 'file3', , {0,0,2} }

    sinfo1  EQU     SIZEOF    info1  ; 116 = number of bytes in

                                    ;  initializers
    linfo1  EQU     LENGTHOF  info1  ; 1 = number of items
    tinfo1  EQU     TYPE      info1  ; 116 = same as size

    slotsof EQU     SIZEOF    lotsof ; 116 * 3 = number of bytes in
                                    ;  initializers
    llotsof EQU     LENGTHOF  lotsof ; 3 = number of items
    tlotsof EQU     TYPE      lotsof ; 116 = same as size for structure

                                    ;  of type INFO


LENGTHOF, SIZEOF, and TYPE for Unions

The size of a union determined by SIZEOF is the size of the longest field
plus any padding required. The length of a union variable determined by
LENGTHOF equals the number of initializers defined inside angle brackets or
curly braces. TYPE returns a value indicating the type of the longest field.


    DWB     UNION
    d     DWORD   ?
    w     WORD    ?
    b     BYTE    ?
    DWB     ENDS

    num     DWB     {0FFFFh}
    array   DWB     (100 / SIZEOF DWB) DUP ({0})

    snum    EQU     SIZEOF   num      ; = 4
    lnum    EQU     LENGTHOF num      ; = 1
    tnum    EQU     TYPE     num      ; = 4
    sarray  EQU     SIZEOF   array    ; = 100 (4*25)
    larray  EQU     LENGTHOF array    ; = 25
    tarray  EQU     TYPE     array    ; = 4


5.2.3  Referencing Structures, Unions, and Fields

Like other variables, structure variables can be accessed by name. You can
access fields within structure variables with this syntax:

    variable.field

In MASM 6.0, references to fields must always be fully qualified, with both
the structure or union name and the dot operator preceding the field name.
Also, in MASM 6.0, the dot operator can be used only with structure fields,
not as an alternative to the plus operator; nor can the plus operator be
used as an alternative to the dot operator.

This example shows several ways to reference the fields of a structure
called  date.

    DATE    STRUCT                            ; Defines structure
    type
    month BYTE    ?
    day   BYTE    ?
    year  WORD    ?
    DATE    ENDS

    yesterday       DATE    {9, 30, 1987}     ; Declare structure
                                            ;  variable
            .
            .
            .
            mov     al, yesterday.day         ; Use structure variables
            mov     bx, OFFSET yesterday      ; Load structure address
            mov     al, (DATE PTR [bx]).month ; Use as indirect operand
            mov     al, [bx].date.month       ; This is necessary if
                                            ;  month were already a

                                            ;  field in a different
                                            ;  structure

Under OPTION M510 or OPTION OLDSTRUCTS, unique structure names do not need
to be qualified. See Section 1.3.2 for information on the OPTION directive.


If the NONUNIQUE keyword appears in a structure definition, all fields of
the structure must be fully qualified when referenced, even if the OPTION
OLDSTRUCTS directive appears in the code. Also, in MASM 6.0, all references
to a field must be qualified.

Even if the initialized union is the size of a WORD or DWORD, members of
structures or unions are accessible only through the field's names.

In the following example, the two MOV statements show how you can access the
elements of an array of structures.

    WB      UNION
    w     WORD    ?
    b     BYTE    ?
    WB      ENDS

    array   WB      (100 / SIZEOF WB) DUP ({0})

            mov     array[12].w, 40
            mov     array[32].b,  2

(This figure may be found in the printed book.)

The  WB  union cannot be used directly as a WORD variable. However, you can
define a union containing both the structure and a WORD variable and access
either field. (The next section discusses nested structures and unions.)

You can use unions to access the same data in more than one form. For
example, one application of structures and unions is to simplify the task of
reinitializing a far pointer. If you have a far pointer declared as

    FPWORD  TYPEDEF FAR PTR WORD

            .DATA
    BoxB    FPWORD ?
    BoxA    FPWORD ?
    BoxB2   uptr   < >

you must follow these steps to point  BoxB  to  BoxA:

    mov     bx,  OFFSET BoxA
            mov     WORD PTR BoxB[2], ds
            mov     WORD PTR BoxB, bx

When you do this, you must remember whether the segment or the offset is
stored first. However, if your program contains this union:

    uptr      UNION
    dwptr   FPWORD   0
    STRUCT
        offs  WORD     0
        segm  WORD     0
    ENDS
    uptr      ENDS

you can initialize a far pointer with these steps:

    mov     BoxB2.segm, ds
            mov     BoxB2.offs, bx
            lds     si, BoxB2.dwptr

This code moves the segment and the offset into the pointer and then moves
the pointer into a register with the other field of the union. Although this
technique does not reduce the code size, it avoids confusion about the order
for loading the segment and offset.


5.2.4  Nested Structures and Unions

Structures and unions in MASM 6.0 can be nested in several ways. This
section explains how to refer to the fields in a nested structure or union.
The example below illustrates the four techniques for nesting and how to
reference the fields. Note the syntax for nested structures. The discussion
of these techniques follows the example.

    ITEMS           STRUCT
    Inum          WORD    ?
    Iname         BYTE    'Item Name'
    ITEMS           ENDS

    INVENTORY       STRUCT
    UpDate        WORD    ?
    oldItem       ITEMS   { 
                            ?,
                            'AF8'        ; Named variable of
                            }             ;  existing structure
                    ITEMS   { ?, '94C' }  ; Unnamed variable of
                                        ;  existing type
    STRUCT ups                          ; Named nested structure
        source      WORD    ?
        shipmode    BYTE    ?
    ENDS
    STRUCT                              ; Unnamed nested structure
        f1          WORD    ?
        f2          WORD    ?
    ENDS
    INVENTORY       ENDS

            .DATA

    yearly  INVENTORY       { }

    ; Referencing each type of data in the yearly structure:

            mov     ax, yearly.oldItem.Inum
            mov     yearly.ups.shipmode, 'A'
            mov     yearly.Inum, 'C'
            mov     ax, yearly.f1

To nest structures and unions, you can use any of these techniques:


    ■   The field of a structure or union can be a named variable of an
        existing structure or union type, as in the  oldItem  field. The field
        names in  oldItem  are not unique, so the full field names must be
        used when referencing those fields in the statement

        mov     ax, yearly.oldItem.Inum


    ■   To declare a named structure or union inside another structure or
        union, give the STRUCT or UNION keyword first and then define a label
        for it. Fields of the nested structure or union must always be
        qualified, as shown in this example:

        mov     yearly.ups.shipmode, 'A'


    ■   As shown in the  Items  field of  Inventory, you can also use unnamed
        variables of existing structures or unions inside another structure or
        union. In this case you can reference its fields directly, as shown in
        this example:

        mov     yearly.Inum, 'C'
                        mov     ax, yearly.f1



Offsets of nested structures are relative to the nested structure, not the
root structure. In the example above, the offset of  yearly.ups.shipmode  is
    (current address of yearly) + 8 + 2. It is relative to the  ups  structure,
not the  yearly  structure.


5.3  Records

Records are similar to structures, except that fields in records are bit
strings. Each bit field in a record variable can be used separately in
constant operands or expressions. The processor cannot access bits
individually at run time, but it can access bit fields with instructions
that manipulate bits.

Record fields are bits, not bytes or words.

Records are bytes, words, or doublewords in which the individual bits or
groups of bits are considered fields. In general, the three steps for using
record variables are the same as those for other complex data types:


    1.  Declare a record type.

    2.  Define one or more variables having the record type.

    3.  Reference record variables using shifts and masks.


Once defined, the record variable can be used as an operand in assembler
statements.

This section explains the record declaration syntax and the use of the MASK
and WIDTH operators. It also shows a few applications of record variables
and constants.


5.3.1  Declaring Record Types

A record type creates a template for data with the sizes and, optionally,
the initial values for bit fields in the record, but it does not allocate
memory space for the record.

The RECORD directive declares a record type for an 8-bit, 16-bit, or 32-bit
record that contains one or more bit fields. The maximum size is based on
the expression word size. See OPTION EXPR16 and OPTION EXPR32 in Section
1.3.2. The syntax is

    recordname RECORD field [[,field]]...

The field declares the name, width, and initial value for the field. The
syntax for each field is:

    fieldname:width[[=expression]]

Global labels, macro names, and record field names must all be unique, but
record field names can have the same names as structure field names or
global labels. Width is the number of bits in the field, and expression is a
constant giving the initial (or default) value for the field. Record
definitions can span more than one line if the continued lines end with
commas.

If expression is given, it declares the initial value for the field. The
assembler generates an error message if an initial value is too large for
the width of its field.

The assembler shifts bits in a record to the right if all bits are not used.


The first field in the declaration always goes into the most significant
bits of the record. Subsequent fields are placed to the right in the
succeeding bits. If the fields do not total exactly 8, 16, or 32 bits as
appropriate, the entire record is shifted right, so the last bit of the last
field is the lowest bit of the record. Unused bits in the high end of the
record are initialized to 0.

The following example creates a byte record type  color  having four fields:
    blink,  back,  intense, and  fore. The contents of the record type are
shown after the example. Since no initial values are given, all bits are set
to 0. Note that this is only a template maintained by the assembler. No data
is created.

    COLOR   RECORD  blink:1, back:3, intense:1, fore:3

(This figure may be found in the printed book.)

The next example creates a record type  cw  having six fields. Each record
declared with this type occupies 16 bits of memory. Initial (default) values
are given for each field. They can be used when data is declared for the
record. The bit diagram after the example shows the contents of the record
type.

    CW      RECORD  r1:3=0, ic:1=0, rc:2=0, pc:2=3, r2:2=1, masks:6=63

(This figure may be found in the printed book.)


5.3.2  Defining Record Variables

Once you have declared a record type, you can define record variables of
that type. For each variable, memory is allocated to the object file in the
format declared by the type. The syntax is

    [[name]] recordname <[[initializer
    [[,initializer]]...]] > <$IAngle
    brackets (<< ra);records>

    [[name]] recordname {
    [[initializer [[,initializer]]...]]
    }

    [[name]] recordname constant
    DUP ( [[initializer [[,initializer]]...]]
    )

The recordname is the name of a record type that was previously declared by
using the RECORD directive.

A fieldlist for each field in the record can be a list of integers,
character constants, or expressions that correspond to a value compatible
with the size of the field. Curly braces or angle brackets are required even
if no initial value is given.

If you use the DUP operator (see Section 5.1.1, "Declaring and Referencing
Arrays") to initialize multiple record variables, only the angle brackets
and initial values, if given, need to be enclosed in parentheses. For
example, you can define an array of record variables with

    xmas    COLOR   50 DUP ( <1, 2, 0, 4> )

You do not have to initialize all fields in a record. If an initial value is
blank, the assembler automatically stores the default initial value of the
field. If there is no default value, the assembler clears each bit in the
field.

The definition in the example below creates a variable named  warning  whose
type is given by the record type  color. The initial values of the fields in
the

variable are set to the values given in the record definition. The initial
values override any default record values, had any been given in the
declaration.

    COLOR   RECORD  blink:1,back:3,intense:1,fore:3 ; Record
                                                    ;  declaration
    warning COLOR   <1, 0, 1, 4>                    ; Record
                                                    ;  definition

(This figure may be found in the printed book.)


LENGTHOF, SIZEOF, and TYPE with Records

The SIZEOF and TYPE operators applied to a record name return the number of
bytes used by the record. SIZEOF for a record variable returns the number of
bytes used by the variable. You cannot use LENGTHOF with record types, but
you can with the variables of that type. LENGTHOF returns the number of
items in an initializer. The record can be used as an operand. The value of
the operand is a bit mask of the defined record. This example illustrates
these points.

    ; Record definition
    ; 9 bits stored in 2 bytes
    RGBCOLOR        RECORD  red:3,  green:3,  blue:3

            mov     ax, RGBCOLOR          ; Equivalent to "mov ax,
                                        ;  01FFh"
    ;       mov     ax, LENGTHOF RGBCOLOR ; Illegal since LENGTHOF can
                                        ;  apply only to data label
            mov     ax, SIZEOF   RGBCOLOR ; Equivalent to "mov ax, 2"

            mov     ax, TYPE     RGBCOLOR ; Equivalent to "mov ax, 2"


    ; Record instance
    ; 8 bits stored in 1 byte
    RGBCOLOR2       RECORD red:3, green:3, blue:2
    rgb             RGBCOLOR2 <1, 1, 1>     ; Initialize to 025h

            mov     ax, RGBCOLOR2           ; Equivalent to "mov ax,
                                            ;  00FFhh"
            mov     ax, LENGTHOF rgb        ; Equivalent to "mov ax,
    1"
            mov     ax, SIZEOF   rgb        ; Equivalent to "mov ax,
    1"
            mov     ax, TYPE     rgb        ; Equivalent to "mov ax,
    1"


5.3.3  Record Operators

The WIDTH operator (which is used only with records) returns the width in
bits of a record or record field. The MASK operator returns a bit mask for
the bit positions occupied by the given record field. A bit in the mask
contains a 1 if that bit corresponds to a bit field. The example below shows
how to use MASK and WIDTH.

    .DATA
    COLOR           RECORD  blink:1, back:3, intense:1, fore:3
    message         COLOR   <1, 5, 1, 1>
    wblink  EQU     WIDTH blink         ; "wblink"     = 1
    wback   EQU     WIDTH back          ; "wback"      = 3
    wintense EQU    WIDTH intense       ; "wintense"   = 1
    wfore   EQU     WIDTH fore          ; "wfore"      = 3
    wcolor  EQU     WIDTH color         ; "wcolor"     = 8
            .CODE
            .
            .
            .
            mov     ah, message         ; Load initial   0101 1001
            and     ah, NOT MASK back   ; Turn off   AND 1000 1111
                                        ; "back"         ---------
                                        ;                0000 1001
            or      ah, MASK blink      ; Turn on     OR 1000 0000
                                        ; "blink"        ---------
                                        ;                1000 1001
            xor     ah, MASK intense    ; Toggle     XOR 0000 1000
                                        ; "intense"      ---------
                                        ;                1000 0001
            .
            IF      (WIDTH color) GE 8  ; If color is 16 bit, load
            mov     ax, message         ;  into 16-bit register
            ELSE                        ; else
            mov     al, message         ;  load into low 8-bit register
            xor     ah, ah              ;  and clear high 8-bits
            ENDIF

This example illustrates several ways in which record fields can be used as
operands and in expressions.

    ; Rotate "back" of "cursor" without changing other
    values

                mov     al, cursor       ; Load value from memory
                mov     ah, al           ; Save a copy for work      1101
    1001=ah/al
                and     al, NOT MASK back; Mask out old bits     AND
    1000 1111=mask
                                        ;  to save old cursor       ---------
                                        ;                           1000
    1001=al
                mov     cl, back         ; Load bit position
                shr     ah, cl           ; Shift to right            0000
    1101=ah
                inc     ah               ; Increment                 0000
    1110=ah

                shl     ah, cl           ; Shift left again          1110
    0000=ah
                and     ah, MASK back    ; Mask off extra bits   AND
    0111 0000=mask
                                        ;  to get new cursor        ---------
                                        ;                           0110
    0000 ah
                or      ah, al           ; Combine old and new    OR
    1000 1001 al
                                        ;                           ---------
                mov     cursor, ah       ; Write back to memory      1110
    1001 ah

Record variables are often used with the logical operators to perform
logical operations on the bit fields of the record, as in the previous
example using the MASK operator.


5.4  Related Topics in Online Help

In addition to information on all the instructions and directives mentioned
in this chapter, information on the following topics can be found in online
help, starting at the "MASM 6.0 Contents" screen:

Topic                             Access
────────────────────────────────────────────────────────────────────────────
INS, OUTS                         Choose "Processor Instructions" and then
                                    "System and I/O Access"

LABEL                             Choose "Directives" and then "Code
                                    Labels"

RECORD, UNION, STRUCT, MASK, ORG   Choose "Directives" and then choose
, WIDTH, and ALIGN                "Complex Data Types"

SHRD, SHLD, BSF, and BSR          From "Processor Instructions," choose
                                    "Logical and Shifts"

BOUND                             From "Processor Instructions," choose
                                    "Data
                                    Transfer"








Chapter 6  Using Floating-Point and Binary Coded Decimal Numbers
────────────────────────────────────────────────────────────────────────────

MASM requires different techniques for handling floating-point (real)
numbers and binary coded decimal (BCD) numbers than for handling integers.
You have two choices for working with real numbers─a math coprocessor or
emulation routines.

Math coprocessors─the 8087, 80287, and 80387 chips─work with the main
processor to handle real-number calculations. The 80486 processor performs
floating-point operations directly. All information in this chapter
pertaining to the 80387 coprocessor applies to the 80486 processor as well.


This chapter begins with a summary of the directives and formats of
floating-point data; you need to use these to allocate memory storage and
initialize variables before you can work with floating-point numbers.

The chapter then explains how to use a math coprocessor for floating-point
operations. It covers these areas:


    ■   The architecture of the registers

    ■   The operands for the coprocessor instruction formats

    ■   The coordination of coprocessor and main processor memory access

    ■   The basic groups of coprocessor instructions─for loading and storing
        data, doing arithmetic calculations, and controlling program flow


The next main section describes emulation libraries. With the emulation
routines provided with all Microsoft high-level languages, you can use
coprocessor instructions as though your computer had a math coprocessor.
However, some coprocessor instructions are not handled by emulation, as this
section explains.

Finally, because math coprocessor and emulation routines can also operate on
BCD numbers, this chapter discusses the instruction set for these numbers.


6.1  Using Floating-Point Numbers

Before using floating-point data in your program, you need to allocate the
memory storage for the data. You can then initialize variables either as
real numbers in decimal form or as encoded hexadecimals. The assembler
stores allocated data in 10-byte IEEE format. This section looks at
floating-point declarations and floating-point data formats.


6.1.1  Declaring Floating-Point Variables and Constants

You can allocate real constants using the REAL4, REAL8, and REAL10
directives. The list below shows the size of the floating-point number each
of these directives allocates.

Directive       Size
────────────────────────────────────────────────────────────────────────────
REAL4           Short (32-bit) real numbers
REAL8           Long (64-bit) real numbers
REAL10          10-byte (80-bit) real numbers and BCD numbers

The possible ranges for floating-point variables are given in Table 6.1.

Table   6.1 Ranges of Floating-Point Variables

                        Significant
Data Type     Bits   Digits             Approximate Range
────────────────────────────────────────────────────────────────────────────
Short real    32     6-7                ±1.18 x 10-38 to ±3.40 x 10(38)

Long real     64     15-16              ±2.23 x 10-308 to ±1.79 x 10(308)

10-byte real  80     19                 ±3.37 x 10-4932 to ±1.18 x 10
                                        (4932)

────────────────────────────────────────────────────────────────────────────


With previous versions of MASM, the DD, DQ, and DT directives could be used
to allocate real constants. These directives are still supported by MASM
6.0, but this means that the variables are integers rather than
floating-point values. Although this makes no difference in the assembly
code, CodeView displays the values incorrectly.

There are two forms for specifying floatingpoint numbers.

You can specify floating-point constants either as decimal constants or as
encoded hexadecimal constants. You can express decimal real-number constants
in the form

    [[+ | -]] integer.[[fraction]][[E]][[[[+
    | -]]exponent]]

For example, the numbers  2.523E1  and  -3.6E-2  are written in the correct
decimal format. These numbers can be used as initializers for real-number
variables.

Digits of real numbers are always evaluated as base 10. During assembly, the
assembler converts real-number constants given in decimal format to a binary
format. The sign, exponent, and mantissa of the real number are encoded as
bit fields within the number.

You can also specify the encoded format directly with hexadecimal digits
(0-9 plus A-F). The number must begin with a decimal digit (0-9) and a
leading zero if necessary, and end with the real-number designator (R). It
cannot be signed.

For example, the hexadecimal number  3F800000r  can be used as an
initializer for a doubleword-sized variable.

The maximum range of exponent values and the number of digits required in
the hexadecimal number depend on the directive. The number of digits for
encoded numbers used with REAL4, REAL8, and REAL10 must be 8, 16, and 20
digits, respectively. If the number has a leading zero, the number must be
9, 17, or 21 digits.

Examples of decimal constant and hexadecimal specifications are shown here:


    ; Real numbers
    short   REAL4    25.23              ; IEEE format
    double  REAL8    2.523E1            ; IEEE format
    tenbyte REAL10   2523.0E-2          ; 10-byte real format

    ; Encoded as hexadecimals
    ieeeshort       REAL4    3F800000r             ; 1.0 as IEEE short
    ieeedouble      REAL8    3FF0000000000000r     ; 1.0 as IEEE long
    temporary       REAL10   3FFF8000000000000000r ; 1.0 as 10-byte
                                                    ;  real

Section 6.1.2, "Storing Numbers in Floating-Point Format," explains the IEEE
formats--the way the assembler actually stores the data.

Pascal or C programmers may prefer to create language-specific TYPEDEF
declarations, as illustrated in this example:

    ; C-language specific
    float           TYPEDEF REAL4
    double          TYPEDEF REAL8
    long_double     TYPEDEF REAL10
    ; Pascal-language specific
    SINGLE          TYPEDEF REAL4
    DOUBLE          TYPEDEF REAL8
    EXTENDED        TYPEDEF REAL10

For applications of TYPEDEF other than aliasing, see Section 3.3.1,
"Defining Pointer Types with TYPEDEF."


6.1.2  Storing Numbers in Floating-Point Format

The assembler stores real numbers in the IEEE format.

The assembler stores the floating-point variables in the IEEE format. MASM
6.0 does not support .MSFLOAT and Microsoft binary format, which are
available in previous versions.

Figure 6.1 illustrates the IEEE format for encoding short (four-byte), long
(eight-byte), and 10-byte real numbers. Although this figure places the
most-significant bit first for illustration, low bytes actually appear first
in memory.

(This figure may be found in the printed book.)

This is how the parts of a real number are stored in the IEEE format:


    1.  Sign bit (0 for positive or 1 for negative) in the upper bit of the
        first byte.

    2.  Exponent in the next bits in sequence (8 bits for a short real number,
        11 bits for a long real number, and 15 bits for a 10-byte real
        number).

    3.  Mantissa in the remaining bits. The first bit is always assumed to be
        1. The length is 23 bits for short real numbers, 52 bits for long real
        numbers, and 63 bits for 10-byte reals.


The exponent field represents a multiplier 2n. To accommodate negative
exponents (such as 2-6), the value in the exponent field is biased; that is,
the actual exponent is determined by subtracting the appropriate bias value
from the value in the exponent field. For example, the bias for short reals
is 127. If the value in the exponent field is 130, the exponent represents a
value of 2130-127, or 23. The bias for long reals is 1,023. The bias for
10-byte reals is 16,383.

Notice that the 10-byte real format stores the integer part of the mantissa.
This differs from the 4-byte and 8-byte formats, in which the integer part
is implicit.

Once you have declared floating-point data for your program, you can use
coprocessor or emulator instructions to access the data. The next section
focuses on the coprocessor architecture, instructions, and operands required
for floating-point operations.


6.2  Using a Math Coprocessor

When used with real numbers, packed BCD numbers, or long integers,
coprocessors (the 8087, 80287, 80387, and 80486) calculate many times faster
than the 8086-based processors. The coprocessor handles data with its own
registers. The organization of these registers reflects four possible
formats for using operands (as explained in Section 6.2.2, "Instruction and
Operand Formats").

This section also describes how the coprocessor performs various tasks:
transferring data to and from the coprocessor, coordinating processor and
coprocessor operations, and controlling program flow.


6.2.1  Coprocessor Architecture

The coprocessor accesses memory as the CPU does, but it has its own data and
control registers--eight data registers organized as a stack and seven
control registers similar to the 8086 flag registers. The coprocessor's
instruction set provides direct access to these registers.

The eight coprocessor data registers form a stack.

The eight 80-bit data registers of the 8087-based coprocessors are organized
as a stack although they need not be used as a stack. As data items are
pushed into the top register, previous data items move into higher-numbered
registers, which are lower on the stack. Register 0 is the top of the stack;
register 7 is the bottom. The syntax for specifying registers is shown
below:

    ST «(number)»

The number must be a digit between 0 and 7 or a constant expression that
evaluates to a number from 0 to 7. ST is another way to refer to ST(0).

All coprocessor data is stored in registers in the 10-byte real format. The
registers and the register format are shown in Figure 6.2.

(This figure may be found in the printed book.)

Internally, all calculations are done on numbers of the same type. Since
10-byte real numbers have the greatest precision, lower-precision numbers
are guaranteed not to lose precision as a result of calculations. The
instructions that transfer values between the main memory and the
coprocessor automatically convert numbers to and from the 10-byte real
format.


6.2.2  Instruction and Operand Formats

Because of the stack organization of registers, you can consider registers
either as elements on a stack or as registers much like 8086-family
registers. Table 6.2 lists the four main groups of coprocessor instructions
and the general syntax for each. The names given to the instruction format
reflect the way the instruction uses the coprocessor registers. The
instruction operands are placed in the coprocessor data registers before the
instruction executes.

Table 6.2  Coprocessor Operand Formats

Instruction                           Implied Operands
Format             Syntax                               Example
────────────────────────────────────────────────────────────────────────────
Classical stack    Faction            ST, ST(1)         fadd

Memory             Faction memory     ST                fadd memloc

Register           Faction  ST(num),  ─                 fadd st(5), st
                    ST                                   fadd st, st(3)
                    Faction  ST, ST(
                    num)

Register pop       FactionP  ST(num    ─                 faddp st(4), st
                    ), ST

────────────────────────────────────────────────────────────────────────────


All coprocessor instructions begin with F.

You can easily recognize coprocessor instructions because, unlike all
8086-family instruction mnemonics, they start with the letter F. Coprocessor
instructions can never have immediate operands and, with the exception of
the FSTSW instruction, they cannot have processor registers as operands.


6.2.2.1  Classical-Stack Format

Instructions in the classical-stack format treat the coprocessor registers
like items on a stack─thus its name. Items are pushed onto or popped off the
top elements of the stack. Since only the top item can be accessed on a
traditional stack, there is no need to specify operands. The first (top)
register (and the second if the instruction needs two operands) is always
assumed.

In coprocessor arithmetic operations, the top of the stack (ST) is the
source operand and the second register [ST(1)] is the destination. The
result of the operation goes into the destination operand, and the source is
popped off the stack. The result is left at the top of the stack.

Instructions that load constants are one example of instructions that
require the classical-stack format. In this case, the constant created by
the instruction is the implied source, and the top of the stack is the
destination.

This example illustrates the classical-stack format, and Figure 6.3 shows
the status of the register stack after each instruction:

    fld1               ; Push 1 into first position
                fldpi              ; Push pi into first position
                fadd               ; Add pi and 1 and pop

(This figure may be found in the printed book.)


6.2.2.2  Memory Format

Instructions using the memory format, such as data transfer instructions,
also treat coprocessor registers like items on a stack. However, with this
format, items are pushed from memory onto the top element of the stack or
popped from the top element to memory. You must specify the memory operand.


Some coprocessor instructions operate on integers or BCDs.

Some instructions that use the memory format specify how a memory operand is
to be interpreted─as an integer (I) or as a binary coded decimal (B). The
letter I or B follows the initial F in the syntax. For example, FILD
interprets its operand as an integer and FBLD interprets its operand as a
BCD number. If the instruction name does not include a type letter, the
instruction works on real numbers.

You can also use memory operands in calculation instructions that operate on
two values (see Section 6.2.4, "Using Coprocessor Instructions"). The memory
operand is always the source. The stack top (ST) is always the implied
destination. The result of the operation replaces the destination without
changing its stack position, as shown in this example and Figure 6.4:

    .DATA
    m1       REAL4  1.0
    m2       REAL4  2.0
            .CODE
            .
            .
            .
            fld    m1      ; Push m1 into first position
            fld    m2      ; Push m2 into first position
            fadd   m1      ; Add m2 to first position
            fstp   m1      ; Pop first position into m1
            fst    m2      ; Copy first position to m2

(This figure may be found in the printed book.)


6.2.2.3  Register Format

Instructions using the register format treat coprocessor registers as
registers rather than as stack elements. Instructions that use this format
require two register operands; one of them must be the stack top (ST).

In the register format, specify all operands by name. The first operand is
the destination; its value is replaced with the result of the operation. The
second operand is the source; it is not affected by the operation. The stack
position of the operands does not change.

The only instructions using the register operand format are the FXCH
instruction and the arithmetic instructions that do calculations on two
values. With the FXCH instruction, the stack top is implied and need not be
specified, as shown in this example and Figure 6.5:

    fadd    st(1), st   ; Add second position to first -
                                ;  result goes in second position
            fadd    st, st(2)   ; Add first position to third -
                                ;  result goes in first position
            fxch    st(1)       ; Exchange first and second positions

(This figure may be found in the printed book.)


6.2.2.4  Register-Pop Format

The register-pop format treats coprocessor registers as a modified stack.
The source register must always be the stack top. Specify the destination
with the register's name.

Instructions with this format place the result of the operation into the
destination operand, and the stack top pops off the stack. The effect is
that both values being operated on are lost and the result of the operation
is saved in the specified destination register. The register-pop format is
used only for instructions that do calculations on two values, as in this
example and Figure 6.6:

    faddp   st(2), st ; Add first and third positions and
    pop -
                            ;  first position destroyed;
                            ;  third moves to second and holds result

(This figure may be found in the printed book.)


6.2.3  Coordinating Memory Access

The math coprocessor works simultaneously with the main processor. However,
since the coprocessor cannot handle device input or output, data originates
in the main processor.

The processor and coprocessor exchange data through memory.

The main processor and the coprocessor have their own registers, which are
completely separate and inaccessible to each other. They usually exchange
data through memory, since memory is available to both.

When using the coprocessor, follow these three steps:


    1.  Load data from memory to coprocessor registers.

    2.  Process the data.

    3.  Store the data from coprocessor registers back to memory.


Step 2, processing the data, can occur while the main processor is handling
other tasks. Steps 1 and 3 must be coordinated with the main processor so
that the processor and coprocessor do not try to access the same memory at
the same time; otherwise, problems of coordinating memory access can occur.
Since the processor and coprocessor work independently, they may not finish
working on memory in the order in which you give instructions. Two potential
timing conflicts can occur; they are handled in different ways.

One timing conflict results if a coprocessor instruction follows a processor
instruction. The processor may have to wait until the coprocessor finishes
if the next processor instruction requires the result of the coprocessor's
calculation. You do not have to write your code to avoid this conflict,
however. The assembler coordinates this timing automatically for the 8088
and 8086 processors, and the processor coordinates it automatically on the
80186-80486 processors. This is the first case shown in the example later in
this section.

Another conflict results if a processor instruction that accesses memory
follows a coprocessor instruction that accesses the same memory. The
processor can try to load a variable that is still being used by the
coprocessor. You need careful synchronization to control the timing, and
this synchronization is not automatic on the 8087 coprocessor. For code to
run correctly on the 8087, you must include the WAIT or FWAIT instruction
(they are mnemonics for the same instruction) to ensure that the coprocessor
finishes before the processor begins, as shown in the second example. In
this situation, the processor does not generate the FWAIT instruction
automatically.

    ; Processor instruction first - No wait needed
            mov     WORD PTR mem32[0], ax   ; Load memory
            mov     WORD PTR mem32[2], dx
            fild    mem32                   ; Load to register

    ; Coprocessor instruction first - Wait needed (for 8087)
            fist    mem32                   ; Store to memory
            fwait                           ; Wait until coprocessor
                                            ;  is done
            mov     ax, WORD PTR mem32[0]   ; Move to register
            mov     dx, WORD PTR mem32[2]

When generating code for the 8087 coprocessor, the assembler automatically
inserts a WAIT instruction before the coprocessor instruction. However, if
you use the .286 or .386 directive, the compiler assumes that the
coprocessor instructions are for the 80287 or 80387 and does not insert the
WAIT instruction.

If your code does not need to run on an 8086 or 8088 processor, you can make
your programs shorter and more efficient by using the .286 or .386
directive.


6.2.4  Using Coprocessor Instructions

The 8087 family of coprocessors has separate instructions for each of the
following operations:


    ■   Loading and storing data

    ■   Doing arithmetic calculations

    ■   Controlling program flow


The following sections explain the available instructions and show how to
use them for each of the operations listed above. See Section 6.2.2,
"Instruction and Operand Formats," for general syntax information.


6.2.4.1  Loading and Storing Data

Data-transfer instructions transfer data between main memory and the
coprocessor registers or between different coprocessor registers. Two
principles govern data transfers:


    ■   The choice of instruction determines whether a value in memory is
        considered an integer, a BCD number, or a real number. The value is
        always considered a 10-byte real number once it is transferred to the
        coprocessor.

    ■   The size of the operand determines the size of a value in memory.
        Values in the coprocessor always take up 10 bytes.


Load commands transfer data, and store commands remove data.

You can transfer data to stack registers using load commands. These commands
push data onto the stack from memory or from coprocessor registers. Store
commands remove data. Some store commands pop data off the register stack
into memory or coprocessor registers; others simply copy the data without
changing it on the stack.

If you use constants as operands, you cannot load them directly into
coprocessor registers. You must allocate memory and initialize a variable to
a constant value. That variable can then be loaded by using one of the load
instructions listed below.

A few special instructions are provided for loading certain constants. You
can load 0, 1, pi, and several common logarithmic values directly. Using
these instructions is faster and often more precise than loading the values
from initialized variables.

All instructions that load constants have the stack top as the implied
destination operand. The constant to be loaded is the implied source
operand.

The coprocessor data area, or parts of it, can also be moved to memory and
later loaded back. You may want to do this to save the current state of the
coprocessor before executing a procedure. After the procedure ends, restore
the previous status. Saving coprocessor data is also useful when you want to
modify coprocessor behavior by writing certain data to main memory,
operating on the data with 8086-family instructions, and then loading it
back to the coprocessor data area.

You can use the following instructions for transferring numbers to and from
registers:

╓┌──────────────────────┌────────────────────────────────────────────────────╖
Instruction(s)         Description
────────────────────────────────────────────────────────────────────────────
Instruction(s)         Description
────────────────────────────────────────────────────────────────────────────
FLD, FST, FSTP         Loads and stores real numbers
FILD, FIST, FISTP      Loads and stores binary integers
FBLD                   Loads BCD
FBSTP                  Stores BCD
FXCH                   Exchanges register values
FLDZ                   Pushes 0 into ST
FLD1                   Pushes 1 into ST
FLDPI                  Pushes the value of pi into ST
FLDCW mem2byte         Loads the control word into the coprocessor
F«N»STCW mem2byte      Stores the control word in memory
FLDENV mem14byte       Loads environment from memory
F«N»STENV mem14byte    Stores environment in memory
FRSTOR mem94byte       Restores state from memory
F«N»SAVE mem94byte     Saves state in memory
FLDL2E                 Pushes the value of log2e into ST
FLDL2T                 Pushes log210 into ST
FLDLG2                 Pushes log102 into ST
FLDLN2                 Pushes loge2 into ST


The following example and Figure 6.7 illustrate some of these instructions:


    .DATA
    m1      REAL4   1.0
    m2      REAL4   2.0
            .CODE
            fld     m1      ; Push m1 into first item
            fld     st(2)   ; Push third item into first
            fst     m2      ; Copy first item to m2
            fxch    st(2)   ; Exchange first and third items
            fstp    m1      ; Pop first item into m1

(This figure may be found in the printed book.)


6.2.4.2  Doing Arithmetic Calculations

Most of the coprocessor instructions for doing arithmetic operations have
several forms, depending on the operand used. You do not need to specify the
operand type in the instruction if both operands are stack registers, since
register values are always 10-byte real numbers. The arithmetic instructions
are listed below. In most cases, the result replaces the destination
register.

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Instruction                       Description
────────────────────────────────────────────────────────────────────────────
FADD                              Adds the source and destination

FSUB                              Subtracts the source from the
                                    destination

FSUBR                             Subtracts the destination from the
                                    source

FMUL                              Multiplies the source and the
                                    destination

FDIV                              Divides the destination by the source

Instruction                       Description
────────────────────────────────────────────────────────────────────────────

FDIVR                             Divides the source by the destination

FABS                              Sets the sign of ST to positive

FCHS                              Reverses the sign of ST

FRNDINT                           Rounds ST to an integer

FSQRT                             Replaces the contents of ST with its
                                    square root

FSCALE                            Multiplies the stack-top value by 2 to
                                    the power contained in ST(1)

FPREM                             Calculates the remainder of ST divided
                                    by ST(1)




80387 Only

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Instruction                       Description
────────────────────────────────────────────────────────────────────────────
FSIN                              Calculates the sine of the value in ST

FCOS                              Calculates the cosine of the value in ST

FSINCOS                           Calculates the sine and cosine of the
                                    value in ST

FPREM1                            Calculates the partial remainder by
                                    performing modulo division on the top
                                    two stack registers

FXTRACT                           Breaks a number down into its exponent
                                    and mantissa and pushes the mantissa
                                    onto the register stack
Instruction                       Description
────────────────────────────────────────────────────────────────────────────
                                    onto the register stack

F2XM1                             Calculates 2(x)-1

FYL2X                             Calculates Y * log2 X

FYL2XP1                           Calculates Y * log2 (X+1)

FPTAN                             Calculates the tangent of the value in
                                    ST

FPATAN                            Calculates the arctangent of the ratio Y
                                    /X

F«N»INIT                          Resets the coprocessor and restores all
                                    the default conditions in the control
                                    and status words

F«N»CLEX                          Clears all exception flags and the busy
Instruction                       Description
────────────────────────────────────────────────────────────────────────────
F«N»CLEX                          Clears all exception flags and the busy
                                    flag of the status word

FINCSTP                           Adds 1 to the stack pointer in the
                                    status word

FDECSTP                           Subtracts 1 from the stack pointer in
                                    the status word

FFREE                             Marks the specified register as empty



The following example illustrating several arithmetic instructions solves
quadratic equations. It does no error checking and fails for some values
because it attempts to find the square root of a negative number. You could
revise the code using the FTST (Test for Zero) instruction to check for a
negative number or 0 before the square root is calculated. If  b2 - 4ac  is
negative or 0, the code can jump to routines that handle these two special
cases.

    .DATA
    a       REAL4   3.0
    b       REAL4   7.0
    cc      REAL4   2.0
    posx    REAL4   0.0
    negx    REAL4   0.0

            .CODE
            .
            .
            .
    ; Solve quadratic equation - no error checking
    ; The formula is: -b +/- squareroot(b2 - 4ac) / (2a)
            fld1               ; Get constants 2 and 4
            fadd    st,st      ; 2 at bottom
            fld     st         ; Copy it
            fmul    a          ; = 2a

            fmul    st(1),st   ; = 4a
            fxch               ; Exchange
            fmul    cc         ; = 4ac

            fld     b          ; Load b
            fmul    st,st      ; = b2
            fsubr              ; = b2 - 4ac
                                ; Negative value here produces error
            fsqrt              ; = square root(b2 - 4ac)
            fld     b          ; Load b
            fchs               ; Make it negative
            fxch               ; Exchange

            fld     st         ; Copy square root
            fadd    st,st(2)   ; Plus version = -b + root(b2 -
    4ac)
            fxch               ; Exchange
            fsubp   st(2),st   ; Minus version = -b - root(b2 -
    4ac)

            fdiv    st,st(2)   ; Divide plus version
            fstp    posx       ; Store it
            fdivr              ; Divide minus version
            fstp    negx       ; Store it

The examples in online help contain an enhanced version of this procedure.


6.2.4.3  Controlling Program Flow

The math coprocessors have several instructions that set control flags in
the status word. The 8087-family control flags can be used with conditional
jumps to direct program flow in the same way that 8086-family flags are
used. Since the coprocessor does not have jump instructions, you must
transfer the status word to memory so that the flags can be used by
8086-family instructions.

An easy way to use the status word with conditional jumps is to move its
upper byte into the lower byte of the processor flags, as shown in this
example:

    fstsw   mem16      ; Store status word in memory
            fwait              ; Make sure coprocessor is done
            mov     ax, mem16  ; Move to AX
            sahf               ; Store upper word in flags

The SAHF (Store AH into Flags) instruction in the example above transfers AH
into the low bits of the flags register.

You can save several steps by loading the status word directly to AX on the
80287 with the FSTSW and FNSTSW instructions. This is the only case in which
data can be transferred directly between processor and coprocessor
registers, as shown in this example:

    fstsw   ax

The coprocessor control flags and their relationship to the status word are
described in Section 6.2.4.4, "Control Registers."

The 8087-family coprocessors provide several instructions for comparing
operands and testing control flags. All these instructions compare the stack
top (ST) to a source operand, which may either be specified or implied as
ST(1).

The compare instructions affect the C3, C2, and C0 control flags, but not
the C1 flag. Table 6.3 shows the flags set for each possible result of a
comparison or test.

Table 6.3  Control-Flag Settings after Comparison or Test

After FCOM        After FTEST                         C3  C2  C0
────────────────────────────────────────────────────────────────────────────
ST > source       ST is positive                      0   0   0
ST < source       ST is negative                      0   0   1
ST = source       ST is 0                             1   0   0
Not comparable    ST is NAN or  projective infinity   1   1   1
────────────────────────────────────────────────────────────────────────────

Variations on the compare instructions allow you to pop the stack once or
twice and to compare integers and zero. For each instruction, the stack top
is always the implied destination operand. If you do not give an operand,
ST(1) is the implied source. With some compare instructions, you can specify
the source as a memory or register operand.

All instructions summarized in the following list have implied operands:
either ST as a single-destination operand or ST as the destination and ST(1)
as the source. These are the instructions for comparing and testing flags.

Some instructions have a wait version and a no-wait version. The no-wait
versions have N as the second letter.

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Instruction                       Description
────────────────────────────────────────────────────────────────────────────
FCOM                              Compares the stack top to the source.
                                    The
                                    source and destination are unaffected by
                                    the comparison.

FTST                              Compares ST to 0.

FCOMP                             Compares the stack top to the source and
                                    then pops the stack.

FUCOM, FUCOMP, FUCOMPP            Compare the source to ST and set the
                                    condition codes of the status word
Instruction                       Description
────────────────────────────────────────────────────────────────────────────
                                    condition codes of the status word
                                    according to the result (80386/486 only).

F«N»STSW mem2byte                 Stores the status word in memory.

FXAM                              Sets the value of the control flags
                                    based on the type of the number in ST.

FPREM                             Finds a correct remainder for large
                                    operands. It uses the C2 flag to
                                    indicate whether the remainder returned
                                    is partial (C2 is set) or complete (C2
                                    is clear). (If the bit is set, the
                                    operation should be repeated. It also
                                    returns the least-significant three bits
                                    of the quotient in C0, C3, and C1.)

FNOP                              Copies the stack top onto itself, thus
                                    padding the executable file and taking
Instruction                       Description
────────────────────────────────────────────────────────────────────────────
                                    padding the executable file and taking
                                    up processing time without having any
                                    effect on registers or memory.

FDISI, FNDISI, FENI, FNENI        Enables or disables interrupts (8087
                                    only).

FSETPM                            Sets protected mode. Requires a .286P or
                                    .386P directive (80287, 80387, and 80486
                                    only).



The following example illustrates some of these instructions. Notice how
conditional blocks are used to enhance 80287 code.

    .DATA
    down    REAL4   10.35      ; Sides of a rectangle
    across  REAL4   13.07
    diamtr  REAL4   12.93      ; Diameter of a circle
    status  WORD    ?
    P287    EQU     (@Cpu AND 00111y)
            .CODE
            .
            .
            .
    ; Get area of rectangle
            fld     across     ; Load one side
            fmul    down       ; Multiply by the other

    ; Get area of circle:  Area = PI * (D/2)2
            fld1               ; Load one and
            fadd    st, st     ;  double it to get constant 2
            fdivr   diamtr     ; Divide diameter to get radius
            fmul    st, st     ; Square radius
            fldpi              ; Load pi
            fmul               ; Multiply it

    ; Compare area of circle and rectangle
            fcompp             ; Compare and throw both away
            IF      p287
            fstsw   ax         ; (For 287+, skip memory)
            ELSE
            fnstsw  status     ; Load from coprocessor to memory
            mov     ax, status ; Transfer memory to register
            ENDIF
            sahf               ; Transfer AH to flags register
            jp      nocomp     ; If parity set, can't compare
            jz      same       ; If zero set, they're the same
            jc      rectangle  ; If carry set, rectangle is bigger
            jmp     circle     ;  else circle is bigger

    nocomp:                    ; Error handler
            .
            .
            .
    same:                      ; Both equal
            .
            .
            .
    rectangle:                 ; Rectangle bigger
            .
            .
            .
    circle:                    ; Circle bigger

Additional instructions for the 80387/486 are FLDENVD and FLDENVW for
loading the environment; FNSTENVD, FNSTENVW, FSTENVD, and FSTENVW for
storing the environment state; FNSAVED, FNSAVEW, FSAVED, and FSAVEW for
saving the coprocessor state; and FRSTORD and FRSTORW for restoring the
coprocessor state.

The size of the code segment, not the operand size, determines the number of
bytes loaded or stored with these instructions. The instructions ending with
W store the 16-bit form of the control register data, and the instructions
ending with D store the 32-bit form. For example, in 16-bit mode FSAVEW
saves the 16-bit control register data. If you need to store the 32-bit form
of the control register data, use FSAVED.


6.2.4.4  Control Registers

Some of the flags of the seven 16-bit control registers control coprocessor
operations, while others maintain the current status of the coprocessor. In
this sense, they are much like the 8086-family flags registers (see Figure
6.8).

(This figure may be found in the printed book.)

Of the control registers, only the status word register is commonly used
(the others are used mostly by systems programmers). The format of the
status word register is shown in Figure 6.9, which shows how the coprocessor
control flags align with the processor flags. C3 overwrites the zero flag,
C2 overwrites the parity flag, and C0 overwrites the carry flag. C1
overwrites an undefined bit, so it cannot be used directly with conditional
jumps, although you can use the TEST instruction to check C1 in memory or in
a register. The status word register also overwrites the sign and
auxiliary-carry flags, so you cannot count on their being unchanged after
the operation.

(This figure may be found in the printed book.)


6.3  Using Emulator Libraries

If you do not have a math coprocessor or an 80486 processor, you can do most
floating-point operations by writing assembly-language procedures and
accessing the emulator from a high-level language. All Microsoft high-level
languages come with the emulator library.

However, you cannot use a Microsoft emulator library with stand-alone
assembler programs, since the library depends on the high-level-language
start-up code.

With emulator libraries, you can use most floating-point instructions.

To use the emulator, first write the procedure using coprocessor
instructions. Then assemble it using the /FPi option of your compiler.
Finally, link it with your high-level-language modules. In MASM 6.0 you can
enter options in the Programmer's WorkBench (PWB) environment, or you can
use the OPTION EMULATOR in your source code.

In emulation mode, the assembler generates instructions for the linker that
the Microsoft emulator can use. The form of the OPTION directive in the
example below tells the assembler to use emulation mode. This option
(introduced in Section 1.3.2) can be defined only once in a module.

    OPTION EMULATOR

Emulator libraries do not allow for all of the coprocessor instructions. The
following floating-point instructions are not emulated:

(This figure may be found in the printed book.)

The set of emulated instructions is different under OS/2 2.x. If you use a
coprocessor instruction that is not emulated, your program generates a
run-time error when it tries to execute the unemulated instruction.

See Chapter 20, "Mixed-Language Programming," for information about writing
assembly-language procedures for high-level languages.


6.4  Using Binary Coded Decimal Numbers

Binary coded decimal (BCD) numbers allow calculations on large numbers
without rounding errors. The 8087-family coprocessors can do fast
calculations with packed BCD numbers. See Section 6.4.2.2 for details. The
8086-family processors can also do some calculations with packed BCD
numbers, but the process is slower and more complicated. See Section 6.4.2
for details.

This section explains how to define BCD numbers and then how to use them in
calculations.


6.4.1  Defining BCD Constants and Variables

Unpacked BCD numbers are made up of bytes containing a single decimal digit
in the lower four bits of each byte. Packed BCD numbers are made up of bytes
containing two decimal digits: one in the upper four bits and one in the
lower four bits. The leftmost digit holds the sign (0 for positive, 1 for
negative).

Packed BCD numbers are encoded in the 8087 coprocessor's packed BCD format.
They can be up to 18 digits long, packed two digits per byte. The assembler
zero-pads BCDs initialized with fewer than 18 digits. Digit 20 is the sign
bit, and digit 19 is reserved.

The TBYTE directive allocates packed BCD constants.

When you define an integer constant with the TBYTE directive and the current
radix is decimal (t), the assembler interprets the number as a packed BCD
number.

The syntax for specifying packed BCDs is exactly the same as for other
integers.

    pos1    TBYTE   1234567890  ; Encoded as 00000000001234567890h
    neg1    TBYTE   -1234567890 ; Encoded as 80000000001234567890h

Unpacked BCD numbers are stored one digit to a byte, with the value in the
lower four bits. They can be defined using the BYTE directive. For example,
an unpacked BCD number could be defined and initialized as shown below:

    unpackedr      BYTE    1,5,8,2,5,2,9   ; Initialized to 9,252,851
    unpackedf      BYTE    9,2,5,2,8,5,1   ; Initialized to 9,252,851

Least-significant digits can come either first or last, depending on how you
write the calculation routines that handle the numbers.


6.4.2  Calculating with BCDs

When you use the processor to calculate with BCDs, the result is not correct
unless you use the ASCII-adjust instructions to convert the result into the
valid BCD integer.


6.4.2.1  Unpacked BCD Numbers

Instructions for unpacked BCDs allow accurate BCD calculations.

To do processor arithmetic on unpacked BCD numbers, you must do the
eight-bit arithmetic calculations on each digit separately and assign the
result to the AL register. After each operation, use the corresponding BCD
instruction to adjust the result. The ASCII-adjust instructions do not take
an operand. They always work on the value in the AL register.

When a calculation using two one-digit values produces a two-digit result,
the AAA, AAS, AAM, and AAD instructions put the first digit in AL and the
second in AH. If the digit in AL needs to carry to or borrow from the digit
in AH, the instructions set the carry and auxiliary carry flags.

These instructions get their names from Intel mnemonics that use the term
"ASCII" to refer to unpacked BCD numbers and "decimal" to refer to packed
BCD numbers. The four ASCII-adjust instructions for unpacked BCDs are
described below:

Instruction                       Description
────────────────────────────────────────────────────────────────────────────
AAA                               Adjusts after an addition operation.

AAS                               Adjusts after a subtraction operation.

AAM                               Adjusts after a multiplication operation.
                                    Always use with MUL, not with IMUL.

AAD                               Adjusts before a division operation.
                                    Unlike other BCD instructions, AAD
                                    converts a BCD value to a binary value
                                    before the operation. After the
                                    operation, use AAM to adjust the
                                    quotient. The remainder is lost. If you
                                    need the remainder, save it in another
                                    register before adjusting the quotient.
                                    Then move it back to AL and adjust if
                                    necessary.


The following examples show how to use each of these instructions in BCD
addition, subtraction, multiplication, and division.

    ; To add 9 and 3 as BCDs:
            mov     ax, 9       ; Load 9
            mov     bx, 3       ;  and 3 as unpacked BCDs
            add     al, bl      ; Add 09h and 03h to get 0Ch
            aaa                 ; Adjust 0Ch in AL to 02h,
                                ;  increment AH to 01h, set carry
                                ; Result 12 (unpacked BCD in AX)

    ; To subtract 4 from 13:
            mov     ax, 103h    ; Load 13
            mov     bx, 4       ;  and 4 as unpacked BCDs
            sub     al, bl      ; Subtract 4 from 3 to get FFh (-1)
            aas                 ; Adjust 0FFh in AL to 9,
                                ;  decrement AH to 0, set carry
                                ; Result 9 (unpacked BCD in AX)

    ; To multiply 9 times 3:
            mov     ax, 903h    ; Load 9 and 3 as unpacked BCDs
            mul     ah          ; Multiply 9 and 3 to get 1Bh
            aam                 ; Adjust 1Bh in AL
                                ;  to get 27 (unpacked BCD in AX)

    ; To divide 25 by 2:
            mov     ax, 205h    ; Load 25
            mov     bl, 2       ;  and 2 as unpacked BCDs
            aad                 ; Adjust 0205h in AX
                                ;  to get 19h in AX
            div     bl          ; Divide by 2 to get
                                ;  quotient 0Ch in AL
                                ;  remainder 1 in AH
            aam                 ; Adjust 0Ch in AL
                                ;  to 12 (unpacked BCD in AX)
                                ;  (remainder destroyed)

If you process multidigit BCD numbers in loops, each digit is processed and
adjusted in turn.


6.4.2.2  Packed BCD Numbers

Packed BCD numbers are made up of bytes containing two decimal digits: one
in the upper four bits and one in the lower four bits. The 8086-family
processors provide instructions for adjusting packed BCD numbers after
addition and subtraction. You must write your own routines to adjust for
multiplication and division.

To do processor calculations on packed BCD numbers, you must do the
eight-bit arithmetic calculations on each byte separately. The result should
always be in the AL register. After each operation, use the corresponding
BCD instruction to adjust the result. The decimal-adjust instructions do not
take an operand. They always work on the value in the AL register.

The 8086-family processors provide DAA (Decimal Adjust after Addition) and
DAS (Decimal Adjust after Subtraction) for adjusting packed BCD numbers
after addition and subtraction.

These examples show DAA and DAS used for adding and subtracting BCDs.

    ;To add 88 and 33:
            mov     ax, 8833h   ; Load 88 and 33 as packed BCDs
            add     al, ah      ; Add 88 and 33 to get 0BBh
            daa                 ; Adjust 0BBh to 121 (packed BCD:)
                                ;  1 in carry and 21 in AL

    ;To subtract 38 from 83:
            mov     ax, 3883h   ; Load 83 and 38 as packed BCDs
            sub     al, ah      ; Subtract 38 from 83 to get 04Bh
            das                 ; Adjust 04Bh to 45 (packed BCD:)
                                ;  0 in carry and 45 in AL

Unlike the ASCII-adjust instructions, the decimal-adjust instructions never
affect AH. The assembler sets the auxiliary carry flag if the digit in the
lower four bits carries to or borrows from the digit in the upper four bits,
and it sets the carry flag if the digit in the upper four bits needs to
carry to or borrow from another byte.

Multidigit BCD numbers are usually processed in loops. Each byte is
processed and adjusted in turn.


6.5  Related Topics in Online Help

In addition to information on the instructions and directives mentioned in
this chapter, information on the following topics can be found in online
help, starting from the "MASM 6.0 Contents" screen.

Topic                             Access
────────────────────────────────────────────────────────────────────────────
Control registers                 Choose "Language Overview," and then
                                    choose "Coprocessor Status Word,"
                                    "Coprocessor
                                    Control Word," or "Coprocessor
                                    Environment"

ML options                        Choose "ML Command Line"

Coprocessor instructions          Choose "Coprocessor Instructions"

MATHDEMO.ASM                      Choose "Example Code" and then "Map of
                                    Demos"









Chapter 7  Controlling Program Flow
────────────────────────────────────────────────────────────────────────────

Very few programs actually execute all lines sequentially from .STARTUP to
.EXIT. Rather, complex program logic and efficiency dictate that you control
the flow of your program─jumping from one point to another, repeating an
action until a condition is reached, and passing control to procedures. This
chapter describes various means for controlling program flow and several
features that simplify coding program-control constructs.

The first section covers jumps from one point in the program to another. It
explains how MASM 6.0 optimizes both unconditional and conditional jumps
under certain circumstances, so that you do not have to specify every
attribute. The section also describes instructions you can use to test
conditional jumps.

The next section describes loop and decision structures that repeat actions
or evaluate conditions. They discuss some new MASM directives, such as
.WHILE and .REPEAT, that generate appropriate compare, loop, and jump
instructions for you, and the new .IF, .ELSE, and .ELSEIF directives that
generate jump instructions.

A number of improvements to procedure automation are covered in Section 7.3.
These include extended functionality for PROC, a PROTO directive that lets
you write procedure prototypes similar to those used in C, an INVOKE
directive that automates parameter passing, and new options for the
stack-frame setup inside procedures.

Finally, the last section explains how to pass control to an interrupt
routine.


7.1  Jumps

Jumps are the most direct method for changing program control from one
location to another. At the processor level, jumps work by changing the
value of the IP (Instruction Pointer) register from the address of the
current instruction to a target address, by changing the CS register for far
jumps, and by changing the CS register for far jumps. The many forms of the
jump instructions handle jumps based on conditions, flags, and bit settings.


This section first describes unconditional jumps, including the new jump
optimization features of MASM 6.0 and the use of indirect operands to
specify the jump's destination and to construct jump tables. The section
then discusses conditional jumps─extending jumps, jumps based on bit or flag
status, anonymous jumps, labels for jump targets, and decision directives
that generate conditional jumps.


7.1.1  Unconditional Jumps

Jumps in assembler programs are either conditional or unconditional. The
assembler executes conditional jumps only when the jump condition is true.
You use the JMP instruction to jump unconditionally to a specified address.
Its single operand contains the target address, which can be short, near, or
far.

Unconditional jumps are often used to skip over code that should not be
executed, as shown in this example.

    ; Handle one case
    label1: .
            .
            .
            jmp continue
    ; Handle second case
    label2: .
            .
            .
            jmp continue
            .
            .
            .
    continue:

The distance of the target from the jump instruction and the size of the
operand determine the assembler's encoding of the instruction. The larger
the distance, the more bytes the assembler uses to code the instruction. In
previous versions of MASM, unconditional NEAR jumps sometimes generate
inefficient code. Unspecified FAR jumps result in phase errors.


7.1.1.1  Jump Optimizing

Beginning with MASM 6.0, the assembler determines the smallest encoding
possible for the direct unconditional jump. You do not specify a distance
operator, so you do not have to determine the correct distance of the jump.
If you do specify a distance, however, and it is too short, the assembler
generates an error. A specified distance that is too long causes a less
efficient jump to be generated than the assembler would generate if the
distance had not been specified.

MASM 6.0 optimizes jumps if the following conditions are met:


    ■   You do not specify SHORT, NEAR, FAR, NEAR16, NEAR32, FAR16, FAR32, or
        PROC as the distance of the target.

    ■   The target of the jump is not external and is in the same segment as
        the jump instruction. If the target is in a different segment (but in
        the same group), it is treated as if external.


If these two conditions are met, MASM uses the instruction, distance, and
size of the operand to determine how best to optimize the encoding for the
jump. No syntax changes are necessary.

────────────────────────────────────────────────────────────────────────────
NOTE
This information about jump optimizing also applies to conditional jumps on
the 80386/486.
────────────────────────────────────────────────────────────────────────────


7.1.1.2  Indirect Operands

Indirect operands specify a register or data memory location that holds the
address of the jump's destination. Indirect operands differ from the
operands of direct jumps by being a memory expression instead of an
immediate expression. For indirect jumps, you can specify the encoding for
the instruction by giving the size (WORD, DWORD, or FWORD) attributes for
the operand.

The default rules are based on the .MODEL and the default segment size.

    jmp     [bx]          ; Uses .MODEL and segment size
                                ;  defaults
            jmp     WORD PTR [bx] ; A NEAR16 indirect call

If the indirect operand is a register, the jump is always a NEAR16 jump for
a 16-bit register, and FAR32 for a 32-bit register:

    jmp     bx            ; NEAR16 jump
            jmp     ebx           ; FAR32  jump

A DWORD indirect operand, however, is an ambiguous case:

    jmp     DWORD PTR [var] ; A NEAR32 jump in a 32-bit
    segment;
                                    ;  a FAR16 jump in a 16-bit segment

In this case, you must define a type with TYPEDEF to specify the indirect
operand.

    NFP     TYPEDEF PTR NEAR32
    FFP     TYPEDEF PTR FAR16
            jmp     NFP PTR [var] ; NEAR32 indirect jump
            jmp     FFP PTR [var] ; FAR16  indirect jump

You can use an unconditional jump as a form of conditional jump by
specifying the address in a register or indirect memory operand. Also, you
can use indirect memory operands to construct jump tables that work like C
switch statements,

Pascal CASE statements, or Basic ON GOTO, ON GOSUB, or SELECT CASE
statements, as shown in this example:

    NPVOID  TYPEDEF NEAR PTR VOID
            .DATA
    ctl_tbl NPVOID  extended,    ; Null key (extended code)
                    ctrla,       ; Address of CONTROL-A key routine
                    ctrlb        ; Address of CONTROL-B key routine
            .CODE
            .
            .
            .
            mov     ah, 8h       ; Get a key
            int     21h
            cbw                  ; Stretch AL into AX
            mov     bx, ax       ; Copy
            shl     bx, 1        ; Convert to address
            jmp     ctl_tbl[bx]  ; Jump to key routine

    extended:
            mov     ah, 8h       ; Get second key of extended key
            int     21h
            .                    ; Use another jump table
            .                    ;  for extended keys
            .
            jmp     next
    ctrla:  .                    ; CONTROL-A code here
            .
            .
            jmp     next
    ctrlb:  .                    ; CONTROL-B code here
            .
            .
            jmp     next
            .
            .
    next:   .                    ; Continue

In this example, the indirect memory operands point to addresses of routines
for handling different keystrokes.


7.1.2  Conditional Jumps

The most common way to transfer control in assembly language is with a
conditional jump. This is a two-step process: first test the condition, and
then jump if the condition is true or continue if it is false.

The conditional jump instructions check flag status.

Conditional-jump instructions (except JCXZ) use the status of one or more
flags as their condition. Thus, any statement that sets a flag under
specified conditions can be the test statement. The most common test
statements use the CMP or TEST instructions. The jump statement can be any
one of 31 conditional-jump instructions. Conditional-jump instructions take
a single operand containing the target address.


7.1.2.1  Jump Extending

In earlier versions of MASM, the NEAR and FAR operators cannot be used with
conditional jumps on the 8086-80286 processors. MASM 6.0 automatically
expands the jump instruction to include an unconditional jump to the
destination, as long as a distance or size other than SHORT is specified or
implicitly required from the operands. That is, MASM now generates the code
that previously you had to write.

Conditional jumps cannot refer to labels more than 128 bytes away.
Therefore, in versions of MASM prior to 6.0, they are often combined with
unconditional jumps, which have no such limitation. For example, the
following statement is valid as long as  target  is not far away:

    ; Jump to target less than 128 bytes away
            jz      target  ; If previous operation resulted in
                            ;  zero, jump to target

However, once  target  becomes too distant, the following sequence is
necessary to enable a longer jump. Note that this sequence is logically
equivalent to the example above:

    ; Jumps to distant targets previously required two steps
            jnz     skip    ; If previous operation result is
                            ;  NOT zero, jump to "skip"
            jmp     target  ;  Otherwise, jump to target
    skip:

If the instruction is any of the conditional-jump instructions (except JCXZ
and JECXZ ) and the target is greater than 128 bytes or is in a far segment,
then jump-extending for an instruction such as  je target  generates two
instructions to replace it:


    1.  The logical negation of the jump instruction, with a destination that
        skips over the second line it generates

    2.  An unconditional jump to the target destination


For example, if  target  is more than 128 bytes away, MASM generates these
lines of code for  je target:

    jne $ + 2 + (length in bytes of the next instruction)
            jmp NEAR PTR target

Now the conditional jump executes correctly.

The assembler generates this same code sequence if you specify the distance
with NEAR PTR, FAR PTR, or SHORT. Therefore,

    jz      NEAR PTR target

becomes

    jne     $ + 5
            jmp     NEAR PTR target

even if  target  is nearby.

When  skip  is more than 128 bytes away, this example

    mov     ax, cx
            jz      skip     ; Skip is more than 128 bytes away
            .
            .                ; (additional code here)
            .
    skip:

generates code that looks like this:

    7327:0000 8BC1           MOV       AX,CX
    7327:0002 7503           JNZ       0007
    7327:0004 E9C000         JMP       00C7
    7327:0007                (more code here)

MASM 6.0 enables this jump expansion feature by default, but you can turn it
off with the NOLJMP form of the OPTION directive. See Section 1.3.2 for
information about the OPTION directive.

If the assembler generates code to extend a conditional jump, it issues a
level 3 warning saying that the conditional jump has been lengthened. You
can set the warning level to 1 for development and to level 3 for a final
optimizing pass to see if you can shorten jumps by reorganizing.

If you specify the distance for the jump and the target is out of range for
that distance, a "Jump out of Range" error results.

Since the JCXZ and JECXZ instructions do not have logical negations,
expansion of the jump instruction to handle targets with unspecified
distances cannot be performed for those instructions. Therefore the distance
must always be short.

The size and distance of the target operand determines the encoding for
conditional or unconditional jumps to externals or targets in different
segments. The new jump-extending and optimization features do not apply in
this case.

────────────────────────────────────────────────────────────────────────────
NOTE

Conditional jumps on the 80386 and 80486 processors can be to targets up to
32K bytes away, so jump extension occurs only for targets greater than that
distance.
────────────────────────────────────────────────────────────────────────────


7.1.2.2  Jumps Based on Comparisons

The CMP instruction is specifically designed to test for conditional jumps.
It does not change the destination operand─it compares two values without
changing either of them. Instructions that change operands (such as SUB or
AND) can also be used to test conditions.

SUB and CMP set the same flags.

Internally, the CMP instruction is the same as the SUB instruction, except
that CMP does not change the destination operand. Both set flags according
to the result that the subtraction generates.

Table 7.1 lists conditional-jump instructions for each comparison
relationship and shows the flags that are tested to see if the relationship
is true. Note the difference in instructions depending on the sign of the
operands. Some of these are equivalent to instructions listed in the
previous section.

Table   7.1 Conditional-Jump Instructions Used after Compare Instruction

╓┌──────────────┌──────────────┌──────────────┌──────────────┌───────────────╖
Jump           Signed         Flags Tested   Unsigned       Flags Tested
Condition      Compare        (Jump if True)  Compare        (Jump if True)
────────────────────────────────────────────────────────────────────────────
=    (Equal)   JE             ZF = 1         JE             ZF = 1

(Not equal)    JNE            ZF = 0         JNE            ZF = 0

>    (Greater  JG or JNLE     ZF = 0 and     JA or JNBE     CF = 0 and
than)                         SF = 0F                       ZF = 0

<=   (Less     JLE or JNG     ZF = 1 or      JBE or JNA     CF = 1 or
than                          SF  0F                        ZF = 1
        or
equal to)

<    (Less     JL or JNGE     SF  0F         JB or JNAE     CF = 1
than)

>=  (Greater   JGE or JNL     SF = 0F        JAE or JNB     CF = 0
Jump           Signed         Flags Tested   Unsigned       Flags Tested
Condition      Compare        (Jump if True)  Compare        (Jump if True)
────────────────────────────────────────────────────────────────────────────
>=  (Greater   JGE or JNL     SF = 0F        JAE or JNB     CF = 0
than
        or
equal to)

────────────────────────────────────────────────────────────────────────────



In the CMP instruction, the mnemonic names always refer to the relationship
of the first operand to the second operand. For instance, in this example JG
tests whether the first operand is greater than the second.

    cmp     ax, bx  ; Compares ax and bx
            jg      contin  ; Equivalent to:  If ( ax > bx ) goto
                            ;  contin
            jl      next    ; Equivalent to:  If ( ax < bx ) goto next

Several conditional instructions have two names. For example, JG and JNLE
(Jump if Not Less or Equal) are equivalent. You can use whichever name seems
more mnemonic in context.


7.1.2.3  Testing Bits and Jumping

Using CMP is not the only way to check a condition prior to a jump. You can
also check the status of bits in the operands using the TEST instruction.
This instruction tests for conditions prior to jumps by comparing specific
bits rather than entire operands. Jump execution depends on whether certain
bits are on or off.

Pairs of operands cannot be both registers or both memory locations.

The TEST instruction is the same as the AND instruction, except that TEST
changes neither operand. If the result of the operation is 0, the zero flag
is set, but the 0 is not actually written to the destination operand. The
following example shows an application of TEST.

    .DATA
    bits    BYTE    ?
            .CODE
            .
            .
            .
    ; If bit 2 or bit 4 is set, then call task_a
                                ; Assume "bits" is 0D3h    11010011
            test    bits, 10100y ; If 2 or 4 is set     AND 00010100
            jz      skip1        ;                          --------
            call    task_a       ; Then call task_a         00010000
    skip1:                       ; Jump taken
            .
            .
            .
    ; If bits 2 and 4 are clear, then call task_b
                                ; Assume "bits" is 0E9h    11101001
            test    bits, 10100y ; If 2 and 4 are clear AND 00010100
            jnz     skip2        ;                          --------
            call    task_b       ; Then call task_b         00000000
    skip2:                       ; Jump taken

Generally, when you use TEST, one of the operands is a mask in which the
bits to be tested are the only bits set. The other operand contains the
value to be tested. If all the bits set in the mask are clear in the operand
being tested, the zero flag is set. If any of the flags set in the mask are
also set in the operand, the zero flag is cleared.


7.1.2.4  Jumping Based on Flag Status

Your code can jump based on the condition of flags rather than on the
relationships of operands. Use the following conditional-jump instructions:


╓┌───────────────────┌───────────────────────────────────────────────────────╖
Instruction         Jumps if
────────────────────────────────────────────────────────────────────────────
JO                  The overflow flag is set

JNO                 The overflow flag is clear

JC                  The carry flag is set (same as JB)
Instruction         Jumps if
────────────────────────────────────────────────────────────────────────────
JC                  The carry flag is set (same as JB)

JNC                 The carry flag is clear (same as JAE)

JZ                  The zero flag is set (same as JE)

JNZ                 The zero flag is clear (same as JNE)

JS                  The sign flag is set

JNS                 The sign flag is clear

JP                  The parity flag is set

JNP                 The parity flag is clear

JPE                 Parity is even (parity flag set)

JPO                 Parity is odd (parity flag clear)
Instruction         Jumps if
────────────────────────────────────────────────────────────────────────────
JPO                 Parity is odd (parity flag clear)

JCXZ                CX is 0

JECXZ               ECX is 0
(80386/486 only)



The following example shows two ways to use the instructions from the list
above:

    ; Uses JO to handle overflow condition
            add     ax, bx      ; Add two values
            jo      overflow    ; If value too large, adjust

    ; Uses JNZ to check for zero as the result of subtraction
            sub     ax, bx      ; Subtract
            jnz     skip        ; If the result is not zero, continue
            call    zhandler    ; Else do special case


7.1.2.5  Anonymous Labels

Anonymous labels are alternatives to named labels.

Coding jumps in assembly language requires that you invent many label names.
One alternative to continually thinking up new label names is using
anonymous labels, which you can use anywhere in your program. But because
anonymous labels do not provide meaningful names, they are best used for
conditionally testing a few lines of code. You should mark major divisions
of a program with actual named labels.

Use two at signs (@) followed by a colon (:) as an anonymous label. To jump
to the nearest preceding anonymous label, use @B (back) in the jump
instruction's operand field; to jump to the nearest following anonymous
label, use @F (forward) in the operand field.

The jump in the example below uses an anonymous label:

    ; DX is 20, unless CX is less than -20, then make DX 30
            mov     dx, 20
            cmp     cx, -20
            jge     @F
            mov     dx, 30
    @:

The items  @B  and  @F  always refer to the nearest occurrences of @:, so
there is never any conflict between different anonymous labels.


7.1.2.6  Decision Directives

The high-level structures you can use for decision-making are the .IF,
.ELSEIF, and .ELSE statements. These directives generate conditional jumps.
The expression following the .IF directive is evaluated, and if true, the
following instructions are executed until the next .ENDIF, .ELSE, or .ELSEIF
directive is reached. The .ELSE statements execute if the expression is
false. Using the .ELSEIF directive puts a new expression to be evaluated
inside the alternative part of the original .IF statement. The syntax is

    .IF condition1
    statements
    «.ELSEIF condition2
    statements»
    «.ELSE
    statements»
    .ENDIF

The decision structure

    .IF     cx = 20
            mov     dx, 20
            .ELSE
            mov     dx, 30
            .ENDIF

generates this code:

    .IF  cx == 20
    0017  83 F9 14        *         cmp    cx, 014h
    001A  75 05           *         jne    @C0001
    001C  BA 0014                   mov    dx, 20
                                .ELSE
    001F  EB 03           *         jmp    @C0003
    0021                  *@C0001:
    0021  BA 001E                   mov   dx, 30
                                .ENDIF
    0024                  *@C0003:


7.2  Loops

Loops repeat an action until a termination condition is reached. This
condition can be a counter or the result of an expression's evaluation. MASM
6.0 offers many ways to set up loops in your programs. The following list
compares MASM loop structures.

Instructions                      Action
────────────────────────────────────────────────────────────────────────────
LOOP                              Automatically decrements CX. When CX = 0,
                                    the loop ends. The top of the loop
                                    cannot be greater than 128 bytes from
                                    the LOOP instruction. (This is true for
                                    all LOOP instructions.)

LOOPE, LOOPZ, LOOPNE, LOOPNZ      Loops while equal (or not equal). Checks
                                    CX and a condition. The loop ends when
                                    the condition is true. Set CX to a
                                    number out of range if you don't want a
                                    count to control the loop.

JCXZ, JECXZ                       Branches to a label only if CX = 0 (ECX
                                    on the 80386). Useful for testing
                                    condition of CX before beginning loop.
                                    If CX = 0 before entering the loop, CX
                                    decrements to -1 on the first iteration
                                    and then must be decremented 65,535
                                    times before it reaches 0 again. Unlike
                                    conditional-jump instructions, which can
                                    jump to either a near or a short label
                                    under the 80386 or 80486, the loop
                                    instructions JCXZ and JECXZ always jump
                                    to a short label.

Conditional jumps                 Acts only if certain conditions met.
                                    Necessary if several conditions must be
                                    tested. See Section 7.1.2, "Conditional
                                    Jumps."

The following examples illustrate these loop constructions.

    ; The LOOP instruction: For 200 to 0 do task
            mov     cx, 200         ; Set counter
    next:   .                       ; Do the task here
            .
            .
            loop    next            ; Do again
                                    ; Continue after loop

    ; The LOOPNE instruction: While AX is not 'Y', do task
            mov     cx, 256         ; Set count too high to interfere
    wend:   .                       ; But don't do more than 256 times
            .                       ; Some statements that change AX
            .
            cmp     al, 'Y'         ; Is it Y or too many times?
            loopne  wend            ; No? Repeat
                                    ; Yes? Continue

    ; Using JCXZ:  For 0 to CX do task
                                    ; CX counter set previously
            jcxz    done            ; Check for 0
    next:   .                       ; Do the task here
            .
            .
            loop    next            ; Do again
    done:                           ; Continue after loop


7.2.1  Loop-Generating Directives

These directives are new to MASM 6.0.

The high-level control structures new to MASM 6.0 generate loop structures
for you. These new directives are similar to the while and repeat loops of C
or Pascal. They can make your assembly programs less repetitive and easier
to code, as well as easier to read. The assembler generates the appropriate
assembly code. The .BREAK and .CONTINUE directives are also implemented to
interrupt loop execution. These directives are summarized in the following
list:

Directives                        Action
────────────────────────────────────────────────────────────────────────────
.WHILE, .ENDW                     The statements between .WHILE condition
                                    and .ENDW execute while the condition is
                                    true.

.REPEAT, .UNTIL                   The loop executes at least once and
                                    continues until the condition given
                                    after .UNTIL is true. Generates
                                    conditional jumps.

.REPEAT, .UNTILCXZ                Compares label to an expression and
                                    generates appropriate loop instructions.


These constructs work much as they do in a high-level language such as C or
Pascal. Keep in mind the following points:


    ■   These directives generate appropriate processor instructions. They are
        not new instructions.

    ■   They require proper use of signed and unsigned data declarations.


These directives cause a set of instructions to execute based on the
evaluation of some condition. This condition can be an expression that
evaluates to a negative or nonnegative value, an expression using the binary
operators in C (&&, ||, or !), or the state of a flag. See Section 7.2.2.1
for more information about expression operators.

The evaluation of the condition requires the assembler to know if the
operands in the condition are signed or unsigned. To state explicitly that a
named memory location contains a signed integer, use the signed data
allocation directives: SBYTE, SWORD, and SDWORD.


7.2.1.1  .WHILE Loops

As with while loops in C or Pascal, the test condition for .WHILE is checked
before the statements inside the loop execute. If the test condition is
false, the loop does not execute. While the condition is true, the
statements inside the loop repeat.

Use the .ENDW directive to mark the end of the .WHILE loop. When the
condition becomes false, program execution begins at the first statement
following the .ENDW directive. The .WHILE directive generates appropriate
compare and jump statements. The syntax is

.WHILE condition statements .ENDW

For example, this loop copies one buffer to another until a `$' character
(marking the end of the string) is found:

    .DATA
            buf1    BYTE "This is a string",'$'
            buf2    BYTE 100 DUP (?)
            .CODE
            sub     bx, bx            ; Zero out bx
            .WHILE  (buf1[bx] != '$')
            mov     al, buf1[bx]      ; Get a character
            mov     buf2[bx], al      ; Move it to buffer 2
            inc     bx                ; Count forward
            .ENDW


7.2.1.2  .REPEAT Loops

MASM's .REPEAT directive allows for loop constructions like the do loop of C
and the REPEAT loop of Pascal. The loop executes until the condition
following the .UNTIL (or .UNTILCXZ) directive becomes true. Since the
condition is checked at the end of the loop, the loop always executes at
least once. The .REPEAT directive generates conditional jumps. The syntax
is:

    .REPEAT
    statements
    .UNTIL condition

    .REPEAT
    statements
    .UNTILCXZ «condition»

A condition is optional with .UNTILCXZ.

where condition can also be expr1 == expr2 or expr1 != expr2. When two
conditions are used, expr2 can be an immediate expression, a register, or
(if expr1 is a register) a memory location.

For example, the following code fills up a buffer with characters typed at
the keyboard. The loop ends when the ENTER key (character 13) is pressed:

    .DATA
    buffer  BYTE    100 DUP (0)
            .CODE
            sub     bx, bx             ; Zero out bx
            .REPEAT
            mov     ah, 01h
            int     21h                ; Get a key
            mov     buffer[bx], al     ; Put it in the buffer
            inc     bx                 ; Increment the count
            .UNTIL (al == 13)          ; Continue until al is 13

The .UNTIL directive generates conditional jumps, but the .UNTILCXZ
directive generates a LOOP instruction, as shown by the listing file code
for these examples. In a listing file, assembler-generated code is preceded
by an asterisk.

    ASSUME  bx:PTR SomeStruct

                .REPEAT
            *@C0001:
                    inc    ax
                .UNTIL  ax==6
            *         cmp    ax, 006h
            *         jne    @C0001

    .REPEAT
            *@C0003:
                    mov    ax, 1
                .UNTILCXZ
            *         loop   @C0003

                .REPEAT
            *@C0004:
                .UNTILCXZ   [bx].field != 6
            *         cmp    [bx].field, 006h
            *         loope  @C0004


7.2.1.3  .BREAK and .CONTINUE Directives

.BREAK and .CONTINUE interrupt loop execution.

The .BREAK and .CONTINUE directives can be used to terminate a .REPEAT or
.WHILE loop prematurely. These directives allow an optional .IF clause for
conditional breaks. The syntax is

    .BREAK «.IF condition»
    .CONTINUE «.IF condition»

Note that .ENDIF is not used with the .IF forms of .BREAK and .CONTINUE in
this context. The .BREAK and .CONTINUE directives work the same way as the
break and continue instructions in C. Execution continues at the instruction
following the .UNTIL, .UNTILCXZ, or .ENDW of the nearest enclosing loop.

Instead of causing the loop execution to end as .BREAK does, .CONTINUE
causes loop execution to jump directly to the code that evaluates the loop
condition of the nearest enclosing loop.

The following loop accepts only the keys in the range `0' to `9' and
terminates when ENTER is pressed.

    .WHILE 1                ; Loop forever
            mov     ah, 08h         ; Get key without echo
            int     21h
            .BREAK .IF al == 13     ; If ENTER, break out of the loop
            .CONTINUE .IF (al < '0') || (al > '9')
                                    ; If not a digit, continue looping
            mov     dl, al          ; Save the character for processing
            mov     ah, 02h         ; Output the character
            int     21h
            .ENDW

If you assemble the source code above with the /Fl and /Sg command-line
options and then view the results in the listing file, you would see this
code:

    .WHILE 1
    0017                    *@C0001:
    0017  B4 08                       mov    ah, 08h
    0019  CD 21                       int    21h
                                .BREAK .IF al == 13
    001B  3C 0D             *         cmp    al, 00Dh
    001D  74 10             *         je     @C0002
                                .CONTINUE .IF (al  '0') || (al  '9')
    001F  3C 30             *         cmp    al, '0'
    0021  72 F4             *         jb     @C0001
    0023  3C 39             *         cmp    al, '9'
    0025  77 F0             *         ja     @C0001
    0027  8A D0                       mov    dl, al
    0029  B4 02                       mov    ah, 02h
    002B  CD 21                       int    21h
                                .ENDW
    002D  EB E8             *         jmp    @C0001
    002F                    *@C0002:

The high-level control structures can be nested. That is, .REPEAT or .WHILE
loops can contain .REPEAT or .WHILE loops as well as .IF statements.

If the code generated by a .WHILE loop, .REPEAT loop, or .IF statement
generates a conditional or unconditional jump, MASM uses the jump extension
and jump optimization techniques described in Sections 7.1.1, "Unconditional
Jumps," and 7.1.2, "Conditional Jumps," to encode the jump appropriately.


7.2.2  Writing Loop Conditions

You can express the conditions of the .IF, .REPEAT, and .WHILE directives
using relational operators, and you can express the attributes of the
operand with the PTR operator. To write loop conditions, you also need to
know how the assembler evaluates the operators and operands in the
condition. This section explains the operators, attributes, precedence
level, and expression evaluation order for the conditions used with
loop-generating directives.


7.2.2.1  Expression Operators

The binary relational operators in MASM 6.0 high-level control structures
are listed below. The same binary operators are used in C. These operators
generate MASM compare, test, and conditional jump instructions.

╓┌──────────────────────┌────────────────────────────────────────────────────╖
Operator               Meaning
────────────────────────────────────────────────────────────────────────────
==                     Equal
!=                     Not equal
>                      Greater than
>=                     Greater than or equal to
<                      Less than
<=                     Less than or equal to
&                      Bit test
!                      Logical NOT
&&                     Logical AND
||                     Logical OR
Operator               Meaning
────────────────────────────────────────────────────────────────────────────
||                     Logical OR


A condition without operators (other than !) tests for nonzero as it does in
C. For example,  .WHILE (x)  is the same as  .WHILE (x != 0), and  .WHILE
(!x)  is the same as  .WHILE (x == 0).

Flag names can be operands in a condition.

You can also use the flag names (ZERO?, CARRY?, OVERFLOW?, SIGN?, and
PARITY?) as operands in conditions with the high-level control structures as
in .WHILE (CARRY?). The particular flag set determines the outcome of the
condition. Use flag names when you want to generate the compare or other
instructions that set the flags.


7.2.2.2  Signed and Unsigned Operands

Registers, constants, and memory locations are unsigned by default.

Expression operators generate unsigned jumps by default. However, if either
side of the operation is signed, then the entire operation is considered
signed. The default for the operands in registers, constants, and named
memory locations is also to be unsigned.

You can use the PTR operator to tell the assembler that a particular operand
in a register or constant is a signed number, as in these examples:

    .WHILE  SWORD PTR [bx] <= 0
            .IF     SWORD PTR mem1 >  0

Without the PTR operator, the assembler would treat the contents of BX as an
unsigned value.

You can also specify the size attributes of operands in memory locations
with SBYTE, SWORD, and SDWORD, for use with .IF, .WHILE, and .REPEAT.

    .DATA
    mem1    SBYTE   ?
    mem2    WORD    ?
            .IF     mem1 > 0
            .WHILE  mem2 < bx
            .WHILE  SWORD PTR ax < count


7.2.2.3  Precedence Level

As with C, you can concatenate conditions with the && operator for AND, the
|| operator for OR, and the ! operator for negate. The precedence level is
!, &&, and ||, with ! having the highest precedence. Like expressions in
high-level languages, associativity is evaluated left to right.


7.2.2.4  Expression Evaluation

The assembler evaluates conditions created with high-level control
structures according to short-circuit evaluation. If the evaluation of a
particular condition automatically determines the final result (such as a
condition that evaluates to false in a compound statement concatenated with
AND), the evaluation does not continue.

For example, in this .WHILE statement,

    .WHILE (ax > 0) && (WORD PTR [bx] == 0)

the assembler evaluates the first condition. If this condition is false
(that is, if AX is less than or equal to 0), the evaluation is finished. The
second condition is not checked and the loop does not execute, because a
compound condition containing a && requires both expressions to be true for
the entire condition to be true.





7.3  Procedures

Organizing your code into procedures that execute specific tasks divides
large programs into manageable units, allows for separate testing, and makes
code more efficient for repetitive tasks.

Assembly-language procedures are comparable to functions in C; subprograms,
functions, and subroutines in Basic; procedures and functions in Pascal; or
subroutines and functions in FORTRAN.

Two instructions control the use of assembly-language procedures; CALL
pushes the return address onto the stack and transfers control to a
procedure, and RET pops the return address off the stack and returns control
to that location.

The PROC and ENDP directives mark the beginning and end of a procedure.
Additionally, PROC can automatically


    ■   Preserve register values that should not change but that the procedure
        might otherwise alter

    ■   Set up a local stack pointer, so that you can access parameters and
        local variables placed on the stack

    ■   Adjust the stack when the procedure ends


Sections 7.3.1 through 7.3.3 give information on techniques for calling
procedures and accessing parameters. Sections 7.3.4 through 7.3.5 show how
to allocate and access local variables and parameters.

Sections 7.3.6 and 7.3.7 introduce new directives in MASM 6.0 to further
automate calling procedures and passing arguments. The PROTO directive
allows you to declare prototypes for your procedures. INVOKE handles
procedure calls and stack cleanup. Section 7.3.8 describes the automatic
stack setup and cleanup generated with PROC.


7.3.1  Defining Procedures

Procedures require a label at the start of the procedure and a return at the
end. Procedures are normally defined by using the PROC directive at the
start of the procedure and the ENDP directive at the end. The RET
instruction is normally placed immediately before the ENDP directive. The
assembler makes sure that the distance of the RET instruction matches the
distance defined by the PROC directive. The basic syntax for PROC is

    label PROC [[NEAR|FAR]]
        .
        .
        .
    RET [[constant]]
    label ENDP

The CALL instruction pushes the address of the next instruction in your code
onto the stack and passes control to a specified address. The syntax is

    CALL {label | register | memory}

The operand contains a value calculated at run time. Since that operand can
be a register, direct memory operand, or indirect memory operand, you can
write call tables similar to the jump table illustrated in Section 7.1.1.2.


Calls can be near or far. Near calls push only the offset portion of the
calling address and therefore must be within the same segment or group. You
can specify the type for the target operand, but if you do not, MASM uses
the declared distance (NEAR or FAR) for operands that are labels and for the
size of register or memory operands. Then the assembler encodes the call
appropriately, as it does with unconditional jumps (see Sections 7.1.1,
"Unconditional Jumps," and 7.1.2, "Conditional Jumps").

MASM 6.0 optimizes a call to a far label when the label is in the current
segment by generating the code for a near call, saving one byte.

You can define procedures without PROC and ENDP, but if you do, you must
make sure that the size of the CALL matches the size of the RET. You can
specify the RET instruction as RETN (Return Near) or RETF (Return Far) to
override the default size:

    call    NEAR PTR task ; Call is declared near
            .                     ; Return comes to here
            .
            .
    task:                         ; Procedure begins with near label
            .
            .                     ; Instructions go here
            .
            retn                  ; Return declared near

The syntax for RETN and RETF is

    label: | label NEAR
    statements
    RETN [[constant]]

    label LABEL FAR
    statements
    RETF [[constant]]

The RET instruction (and its RETF and RETN variations) allows an optional
constant operand that specifies a number of bytes to be added to the value
of the SP register after the return. This operand adjusts for arguments
passed to the procedure before the call, as shown in the example in Section
7.3.4, "Using Local Variables."

Incorrect size for RET can cause your program to fail.

When you define procedures without PROC and ENDP, you must make sure that
calls have the same size as corresponding returns. For example, RETF pops
two words off the stack. If a NEAR call is made to a procedure with a far
return, not only is the popped value meaningless, but the stack status may
cause the execution to return to a random memory location, resulting in
program failure.

There is an also an extended PROC syntax that automates many of the details
of accessing arguments and saving registers. See Section 7.3.3, "Declaring
Parameters with the PROC Directive."


7.3.2  Passing Arguments on the Stack

Each time you call a procedure, you may want it to operate on different
data. This data, called "arguments," can be passed in various ways. For
example, arguments can be passed to a procedure in registers or in
variables. However, the

most common method of passing arguments is to use the stack. Microsoft
languages have specific conventions for passing arguments. Chapter 20,
"Mixed-Language Programming," explains these conventions for
assembly-language modules shared with modules from high-level languages.

This section describes how a procedure accesses the arguments passed to it
on the stack. Each argument is accessed as an offset from BP. However, if
you use the PROC directive to declare parameters, the assembler calculates
these offsets for you and lets you refer to parameters by name. The next
section, "Declaring Parameters with the PROC Directive," explains how to use
PROC this way.

This example shows how to pass arguments to a procedure. The procedure
expects to find those arguments on the stack. As this example shows,
arguments must be accessed as offsets of BP.

    ; C-style procedure call and definition

            mov     ax, 10     ; Load and
            push    ax         ;  push constant as third argument
            push    arg2       ; Push memory as second argument
            push    cx         ; Push register as first argument
            call    addup      ; Call the procedure
            add     sp, 6      ; Destroy the pushed arguments
            .                  ;  (equivalent to three pops)
            .
            .
    addup   PROC    NEAR       ; Return address for near call
                                ;  takes two bytes
            push    bp         ; Save base pointer - takes two bytes
                                ;  so arguments start at fourth byte
            mov     bp, sp     ; Load stack into base pointer
            mov     ax, [bp+4] ; Get first argument from
                                ;  fourth byte above pointer
            add     ax, [bp+6] ; Add second argument from
                                ;  sixth byte above pointer
            add     ax, [bp+8] ; Add third argument from
                                ;  eighth byte above pointer
            mov     sp, bp
            pop     bp         ; Restore BP
            ret                ; Return result in AX
    addup   ENDP

Figure 7.1 shows the stack condition at key points in the process.

(This figure may be found in the printed book.)

Starting with the 80186 processor, the ENTER and LEAVE instructions simplify
the stack setup and restore instructions at the beginning and end of
procedures.

However, ENTER uses a lot of time. It is necessary only with nested,
statically scoped procedures. Thus, a Pascal compiler may sometimes generate
ENTER. The LEAVE instruction, on the other hand, is an efficient way to do
the stack cleanup. LEAVE reverses the effect of the last ENTER instruction
by restoring BP and SP to their values before the procedure call.


7.3.3  Declaring Parameters with the PROC Directive

With the PROC directive, you can specify registers to be saved, define
parameters to the procedure, and assign symbol names to parameters (rather
than as offsets from BP). This section describes how to use the PROC
directive to automate the parameter-accessing techniques described in the
last section.

For example, the diagram below shows a valid PROC statement for a procedure
called from C. It takes two parameters,  var1  and  arg1, and uses (and must
save) the DI and SI registers:

(This figure may be found in the printed book.)

The syntax for PROC is

    label PROC [[attributes]]
    [[USES reglist]] [[, parameter[[:tag]]...
    ]]

The following list describes the parts of the PROC directive.

Argument                          Description
────────────────────────────────────────────────────────────────────────────
label                             The name of the procedure.

attributes                        Any of several attributes of the
                                    procedure, including the distance,
                                    langtype, and visibility of the
                                    procedure. The syntax for attributes is
                                    given in Section 7.3.3.1.

reglist                           A list of registers following the USES
                                    keyword that the procedure uses and that
                                    should be saved on entry. Registers in
                                    the list must be separated by blanks or
                                    tabs, not by commas. The assembler
                                    generates prologue code to push these
                                    registers onto the stack. When you exit,
                                    the assembler generates epilogue code to
                                    pop the saved register values off the
                                    stack.

parameter                         The list of parameters passed to the
                                    procedure on the stack. The list can
                                    have a variable number of parameters.
                                    See the discussion below for the syntax
                                    of parameter. This list can be longer
                                    than one line if the continued line ends
                                    with a comma.


This diagram shows a valid PROC definition that uses several attributes:

(This figure may be found in the printed book.)


7.3.3.1  Attributes

The syntax for the attributes field is

    «distance» «langtype» «visibility»
    «<prologuearg>»

The list below explains each of these options.

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Argument                          Description
────────────────────────────────────────────────────────────────────────────
distance                          Controls the form of the RET instruction
                                    generated. Can be NEAR or FAR. If
                                    distance is not specified, it is
                                    determined from the model declared with
Argument                          Description
────────────────────────────────────────────────────────────────────────────
                                    determined from the model declared with
                                    the .MODEL directive. For TINY, SMALL,
                                    COMPACT, and FLAT, NEAR is assumed. For
                                    MEDIUM, LARGE, and HUGE, FAR is assumed.
                                    For 80386/486 programming with 16- and
                                    32-bit segments, NEAR16, NEAR32, FAR16,
                                    or FAR32 can be specified.

langtype                          Determines the calling convention used
                                    to access param-
                                    eters and restore the stack. The BASIC,
                                    FORTRAN, and PASCAL langtypes convert
                                    procedure names to uppercase, place the
                                    last parameter in the parameter list
                                    lowest on the stack, and generate a RET,
                                    which adjusts the stack upward by the
                                    number of bytes in the argument list.

                                    The C and STDCALL langtype prefixes an
Argument                          Description
────────────────────────────────────────────────────────────────────────────
                                    The C and STDCALL langtype prefixes an
                                    underscore to the procedure name when
                                    the procedure's scope is PUBLIC or
                                    EXPORT and places the first parameter
                                    lowest on the stack. SYSCALL is
                                    equivalent to the C calling convention
                                    with no underscore prefixed to the
                                    procedure's name. STDCALL uses caller
                                    stack cleanup when :VARARG is specified;
                                    otherwise the called routine must clean
                                    up the stack (see Chapter 20).

visibility                        Indicates whether the procedure is
                                    available to other modules. The
                                    visibility can be PRIVATE, PUBLIC, or
                                    EXPORT. A procedure name is PUBLIC
                                    unless it is explicitly declared as
                                    PRIVATE. If the visibility is EXPORT,
                                    the linker places the procedure's name
Argument                          Description
────────────────────────────────────────────────────────────────────────────
                                    the linker places the procedure's name
                                    in the export table for segmented
                                    executables. EXPORT also enables PUBLIC
                                    visibility.

                                    You can explicitly set the default
                                    visibility with the
                                    OPTION directive. OPTION PROC:PUBLIC
                                    sets the default to public. See Section
                                    1.3.2 for more information.

prologuearg                       Specifies the arguments that affect the
                                    generation of prologue and epilogue code
                                    (the code MASM generates when it
                                    encounters a PROC directive or the end
                                    of a procedure). See Section 7.3.8 for
                                    an explanation of prologue and epilogue
                                    code.

Argument                          Description
────────────────────────────────────────────────────────────────────────────




7.3.3.2  Parameters

The parameters are separated from the reglist by a comma if there is a list
of registers. In the syntax:

    parmname [[:tag»

parmname is the name of the parameter. The tag can be either the
qualifiedtype or the keyword VARARG. However, only the last parameter in a
list of parameters can use the VARARG keyword. The qualifiedtype is
discussed in Section 1.2.6, "Data Types." An example showing how to
reference VARARG parameters appears later in this section. Procedures can be
nested if they do not have parameters or USES register lists. This diagram
shows a procedure definition with one parameter definition.

(This figure may be found in the printed book.)

The following example shows the procedure in Section 7.3.2, "Passing
Arguments on the Stack," rewritten to use the extended PROC functionality.
Prior to the procedure call, you must push the arguments onto the stack
unless you use INVOKE (see Section 7.3.7, "Calling Procedures with INVOKE").


    addup   PROC NEAR C,
            arg1:WORD, arg2:WORD, count:WORD
            mov     ax, arg1
            add     ax, count
            add     ax, arg2
            ret
    addup   ENDP

If the arguments for a procedure are pointers, the assembler does not
generate any code to get the value or values that the pointers reference;
your program must still explicitly treat the argument as a pointer. (See
Chapter 3, "Using Addresses and Pointers," for more information about using
pointers.)

In the example below, even though the procedure declares the parameters as
near pointers, you still must code two MOV instructions to get the values of
the parameters─the first MOV gets the address of the parameters, and the
second MOV gets the parameter.

    ; Call from C as a FUNCTION returning an integer

            .MODEL medium, c
            .CODE
    myadd   PROC   arg1:NEAR PTR WORD, arg2:NEAR PTR WORD

            mov     bx, arg1     ; Load first argument
            mov     ax, [bx]
            mov     bx, arg2     ; Add second argument
            add     ax, [bx]

            ret

    myadd   ENDP
            END

You can use conditional-assembly directives to make sure that your pointer
parameters are loaded correctly for the memory model. For example, the
following version of  myadd  treats the parameters as FAR parameters if
necessary:

    .MODEL  medium, c       ; Could be any model
            .CODE
    myadd   PROC    arg1:PTR WORD,   arg2:PTR WORD

            IF      @DataSize
            les     bx, arg1        ; Far parameters
            mov     ax, es:[bx]
            les     bx, arg2
            add     ax, es:[bx]
            ELSE
            mov     bx, arg1        ; Near parameters
            mov     ax, [bx]
            mov     bx, arg2
            add     ax, [bx]
            ENDIF

            ret
    myadd   ENDP

            END


7.3.3.3  Using VARARG

In the PROC statement, you can append the :VARARG keyword to the last
parameter to indicate that a variable number of arguments can be passed if
you use the C, SYSCALL, or STDCALL calling conventions (see Section 20.1). A
label must precede :VARARG so that the arguments can be accessed as offsets
from the variable name given. This example illustrates VARARG:

    addup3  PROTO NEAR C, argcount:WORD, arg1:VARARG

            invoke  addup3, 3, 5, 2, 4

    addup3  PROC    NEAR C, argcount:WORD, arg1:VARARG
            sub     ax, ax        ; Clear work register
            sub     si, si

            .WHILE  argcount > 0  ; Argcount has number of arguments
            add     ax, arg1[si]  ; Arg1 has the first argument
            dec     arg1          ; Point to next argument
            inc     si
            inc     si
            .ENDW

            ret                   ; Total is in AX
    addup3  ENDP

Passing non-default-sized pointers in the VARARG portion of the parameter
list can be done by explicitly passing the segment portion and the offset
portion of the address separately.

────────────────────────────────────────────────────────────────────────────
NOTE

When you use the extended PROC features and the assembler encounters a RET
instruction, it automatically generates instructions to pop saved registers,
remove local variables from the stack, and, if necessary, remove parameters.
It generates this code for each RET instruction it encounters. You can
reduce code size by having only one return and jumping to it from various
locations.
────────────────────────────────────────────────────────────────────────────


7.3.4  Using Local Variables

In high-level languages, local variables are visible only within a
procedure. In Microsoft languages, these variables are usually stored on the
stack. In assembly-language programs, you can also have local variables.
These variables should not be confused with labels or variable names that
are local to a module, as described in Chapter 8, "Sharing Data and
Procedures among Modules and Libraries."

This section outlines the standard methods for creating local variables. The
next section shows how to use the LOCAL directive to make the assembler
automatically generate local variables. When you use this directive, the
assembler generates the same instructions as those used in this section but
handles some of the details for you.

If your procedure has relatively few variables, you can usually write the
most efficient code by placing these values in registers. Local (stack) data
is more efficient when you have a large amount of local data for the
procedure.

Local variables are stored on the stack.

To use local variables you must save stack space for the variable at the
start of the procedure. The variable can then be accessed by its position in
the stack. At the end of the procedure, you need to restore the stack
pointer, which restores the memory used by local variables.

This example subtracts two bytes from the SP register to make room for a
local word variable. This variable can then be accessed as  [bp-2].

    push    ax                 ; Push one argument
            call    task               ; Call
            .
            .
            .

    task    PROC    NEAR
            push    bp                 ; Save base pointer
            mov     bp, sp             ; Load stack into base pointer
            sub     sp, 2              ; Save two bytes for local
                                        ;  variable
            .
            .
            .
            mov     WORD PTR [bp-2], 3 ; Initialize local variable
            add     ax, [bp-2]         ; Add local variable to AX
            sub     [bp+4], ax         ; Subtract local from argument
            .                          ; Use [bp-2] and [bp+4] in
            .                          ;  other operations
            .
            mov     sp, bp             ; Clear local variables
            pop     bp                 ; Restore base
            ret     2                  ; Return result in AX and pop
    task    ENDP                       ;  two bytes to clear parameter

Notice that the instruction  mov sp,bp  at the end of the procedure restores
the original value of SP. The statement is required only if the value of SP
is changed inside the procedure (usually by allocating local variables). The
argument passed to the procedure is removed with the RET instruction.
Contrast this to the example in Section 7.3.2, "Passing Arguments on the
Stack," in which the calling code adjusts the stack for the argument.

Figure 7.2 shows the state of the stack at key points in the process.

(This figure may be found in the printed book.)


7.3.5  Creating Local Variables Automatically

Section 7.3.4 described how to create local variables on the stack. This
section shows you how to automate the process with the LOCAL directive.

The LOCAL directive generates code to set up the stack for local variables.


You can use the LOCAL directive to save time and effort when working with
local variables. When you use this directive, simply list the variables you
want to create, giving a type for each one. The assembler calculates how
much space is required on the stack. It also generates instructions to
properly decrement SP (as described in the previous section) and to reset SP
when you return from the procedure.

When you create local variables this way, your source code can then refer to
each local variable by name rather than as an offset of the stack pointer.
Moreover, the assembler generates debugging information for each local
variable.

The procedure in the previous section can be generated more simply with the
following code:

    task    PROC    NEAR    arg:WORD
            LOCAL   loc:WORD
            .
            .
            .
            mov     loc, 3    ; Initialize local variable
            add     ax, loc   ; Add local variable to AX
            sub     arg, ax   ; Subtract local from argument
            .                 ; Use "loc" and "arg" in other operations
            .
            .
            ret
    task    ENDP

The LOCAL directive must be on the line immediately following the PROC
statement. It cannot be used after the first instruction in a procedure. The
LOCAL directive has the following syntax:

    LOCAL vardef [[, vardef]]...

Each vardef defines a local variable. A local variable definition has this
form:

    label[[ [count] ]][[:qualifiedtype]]

These are the parameters in local variable definitions:

Argument                          Description
────────────────────────────────────────────────────────────────────────────
label                             The name given to the local variable.
                                    You can use this name to access the
                                    variable.

count                             The number of elements of this name and
                                    type to allocate on the stack. You can
                                    allocate a simple array on the stack
                                    with count. The brackets around count
                                    are required. If this field is omitted,
                                    one data object is assumed.

qualifiedtype                     A simple MASM type or a type defined
                                    with other types and attributes. See
                                    Section 1.2.6, "Data Types," for more
                                    information.


If the number of local variables exceeds one line, you can place a comma at
the end of the first line and continue the list on the next line. Another
method is to use several consecutive LOCAL directives.

You must initialize local variables.

The assembler does not initialize local variables. Your program must include
code to perform any necessary initializations. For example, the following
code fragment sets up a local array and initializes it to zero:

    arraysz EQU     20

    aproc   PROC    USES di
            LOCAL   var1[arraysz]:WORD, var2:WORD
            .
            .
            .
    ; Initialize local array to zero
            push    ss
            pop     es              ; Set ES=SS
            lea     di, var1        ; ES:DI now points to array
            mov     cx, arraysz     ; Load count
            sub     ax, ax
            rep     stosw           ; Store zeros
    ; Use the array...
            .
            .
            .
            ret
    aproc   ENDP

Even though you can reference stack variables by name, the assembler treats
them as offsets from BP, and they are not visible outside the procedure. In
this procedure,  array  is a local variable.

    index   EQU   10
    test    PROC  NEAR
    LOCAL   array[index]:WORD
            .
            .
            .
            mov     bx, index
    ;       mov     array[bx], 5           ; Not legal!

The second MOV statement may appear to be legal, but since  array  is an
offset of BP, this statement is the same as

    ;       mov [bp + bx + arrayoffset], 5   ; Not legal!

BP and BX can be added only to SI and DI. This example would be legal,
however, if the index value were moved to SI or DI. This type of error in
your program can be difficult to find unless you keep in mind that local
variables in procedures are offsets of BP.


7.3.6  Declaring Procedure Prototypes

MASM 6.0 provides a new directive, INVOKE, to handle many of the details
important to procedure calls, such as pushing parameters according to the
correct calling conventions. In order to use INVOKE, the procedure called
must have previously been declared with a PROC statement, an EXTERNDEF (or
EXTERN) statement, or a TYPEDEF. You can also place a prototype defined with
PROTO before the INVOKE if the procedure type does not appear before the
INVOKE. Procedure prototypes defined with PROTO inform the assembler of
types and numbers of arguments so the assembler can check for errors and
provide automatic conversions when INVOKE calls the procedure.


Place prototypes after data declarations or in a separate include file.

Prototypes in MASM perform the same function as prototypes in the C language
and other high-level languages. A procedure prototype includes the procedure
name, the types, and (optionally) the names of all parameters the procedure
expects. Prototypes are usually placed at the beginning of an assembly
program or in a separate include file. They are especially useful for
procedures called from other modules and other languages, enabling the
assembler to check for unmatched parameters. If you write routines for a
library, you may want to put prototypes into an include file for all the
procedures used in that library. See Chapter 8, "Sharing Data and Procedures
among Modules and Libraries," for more information about using include
files.

Declaring procedure prototypes is optional. You can use the PROC directive
and the CALL instruction, as shown in the previous section.

In MASM 6.0, using the PROTO directive is one way to define procedure
prototypes. The syntax for a prototype definition is the same as for a
procedure declaration (see Section 7.3.3, "Declaring Parameters with the
PROC Directive"), except that you do not include the list of registers,
prologuearg list, or the scope of the procedure.

Also, the PROTO keyword precedes the langtype and distance attributes. The
attributes (like C and FAR) are optional, but if not specified, the defaults
are based on any .MODEL or OPTION LANGUAGE statement. The names of the
parameters are also optional, but you must list parameter types. A label
preceding :VARARG is also optional in the prototype but not in the PROC
statement.

If a PROTO and a PROC for the same function appear in the same module, they
must match in attribute, number of parameters, and parameter types. The
easiest way to create prototypes with PROTO for your procedures is to write
the procedure and then copy the first line (the line that contains the PROC
keyword) to a location in your program that follows the data declarations.
Change PROC to PROTO and remove the USES reglist, the prologuearg field, and
the visibility field. It is important that the prototype follow the
declarations for any types used in it to avoid any forward references used
by the parameters in the prototype.

The prototype defined with PROTO statement and the PROC statement for two
procedures are given below.

    ;  Procedure prototypes

    addup     PROTO NEAR C argcount:WORD, arg2:WORD, arg3:WORD

    myproc    PROTO FAR C, argcount:WORD, arg2:VARARG

    ; Procedure declarations

    addup     PROC NEAR C, argcount:WORD, arg2:WORD, arg3:WORD

    myproc    PROC FAR C PUBLIC <callcount> USES di si,
            argcount:WORD,
            arg2:VARARG

When you call a procedure with INVOKE, the assembler checks the arguments
given by INVOKE against the parameters expected by the procedure. If the
data types of the arguments do not match, MASM either reports an error or
converts the type to the expected type. These conversions are explained in
the next section.


7.3.7  Calling Procedures with INVOKE

INVOKE generates a sequence of instructions that push arguments and call a
procedure. This helps maintain code if arguments or langtype for a procedure
is changed. INVOKE generates procedure calls and automatically handles the
following tasks:


    ■   Converts arguments to the expected types

    ■   Pushes arguments on the stack in the correct order

    ■   Cleans up the stack when the procedure returns


If arguments do not match in number or if the type is not one the assembler
can convert, an error results.

If VARARG is an option in a procedure, INVOKE can pass arguments in addition
to those in the parameter list without generating an error or warning. The
extra arguments must be at the end of the INVOKE argument list. All other
arguments must match in number and type.

The syntax for INVOKE is

    INVOKE   expression  «, arguments»

where expression can be the procedure's label or an indirect reference to a
procedure, and arguments can be an expression, a register pair, or an
expression preceded with ADDR. (The ADDR operator is discussed below.)

Procedures that have these procedure prototypes

    addup   PROTO NEAR C argcount:WORD, arg2:WORD, arg3:WORD

    myproc  PROTO FAR C, argcount:WORD, arg2:VARARG

and these procedure declarations

    addup   PROC NEAR C, argcount:WORD, arg2:WORD, arg3:WORD

    myproc  PROC FAR C PUBLIC <callcount> USES di si,
            argcount:WORD,
            arg2:VARARG

may have INVOKE statements that look like this:

    INVOKE  addup,   ax, x,  y
            INVOKE  myproc,  bx, cx, 100, 10

The assembler can convert some arguments and parameter type combinations so
that the correct type can be passed. The signed or unsigned qualities of the
arguments in the INVOKE statements determine how the assembler converts them
to the types expected by the procedure.

The  addup  procedure, for example, expects parameters of type WORD, but the
arguments passed by INVOKE to the  addup  procedure can be any of these
types:


    ■   BYTE, SBYTE, WORD, or SWORD

    ■   An expression whose type is specified with the PTR operator to be one
        of those types

    ■   An 8-bit or 16-bit register

    ■   An immediate expression in the range -32K to +64K

    ■   A NEAR PTR


If the type is smaller than that expected by the procedure, MASM widens the
argument to match.


7.3.7.1  Widening Arguments

For INVOKE to correctly handle type conversions, you must use the signed
data types for any signed assignments. This list shows the cases in which
MASM widens an argument to match the type expected by a procedure's
parameters.

Type Passed                       Type Expected
────────────────────────────────────────────────────────────────────────────
BYTE, SBYTE                       WORD, SWORD, DWORD, SDWORD

WORD, SWORD                       DWORD, SDWORD

When possible, MASM widens arguments to match parameter types.

The assembler generates instructions such as XOR and CBW to perform the
conversion. You can see these generated instructions in the listing file by
using the /Sg command-line option. The assembler can extend a segment if far
data is expected, and it can convert the type given in the list to the types
expected. If the assembler cannot convert the type, however, it generates an
error.


7.3.7.2  Detecting Errors

When the assembler widens arguments, it may require the use of a register
that could overwrite another argument.

For example, if a procedure with the C calling convention is called with
this INVOKE statement,

    INVOKE  myprocA, ax, cx, 100, arg

where  arg  is a BYTE variable and  myproc  expects four arguments of type
WORD, the assembler widens and then pushes the variable with this code:

    mov     al, DGROUP:arg
            xor     ah, ah
            push    ax

As a result, the assembler generates code that also uses the AX register and
therefore overwrites the first argument passed to the procedure in AX. The
assembler generates an error in this case, requiring you to rewrite the
INVOKE statement for this procedure.

The INVOKE directive uses as few registers as possible. However, widening
arguments or pushing constants on the 8088 and 8086 requires the use of the
AX register, and sometimes the DX register or the EAX and EDX on the
80386/486. This means that the content of AL, AH, AX, and EAX must
frequently be overwritten, so you should avoid using these registers to pass
arguments. As an alternative you can use DL, DH, DX, and EDX, since these
registers are rarely used.


7.3.7.3  Invoking Far Addresses

You can pass a FAR pointer in a segment::offset pair, as shown below. Note
the use of double colons to separate the register pair. The registers could
be any other register pair, including a pair that a DOS call uses to return
values.

    FPWORD   TYPEDEF FAR PTR WORD
    SomeProc PROTO var1:DWORD, var2:WORD, var3:WORD

            pfaritem    FPWORD     faritem
            .
            .
            .
            les         bx, pfaritem
            INVOKE      SomeProc, ES::BX, arg1, arg2

However, you cannot give INVOKE two arguments, one for the segment and one
for the offset, and have INVOKE combine the two for an address.


7.3.7.4  Passing an Address

You can use the ADDR operator to pass the address of an expression to a
procedure that is expecting a NEAR or FAR pointer. This example generates
code to pass a far pointer (to  arg1) to the procedure  proc1.

    PBYTE   TYPEDEF FAR PTR BYTE
    arg1    BYTE    "This is a string"
    proc1   PROTO   NEAR C fparg:PBYTE
            .
            .
            .
    INVOKE  proc1, ADDR arg1

See Section 3.3.1 for information on defining pointers with TYPEDEF.


7.3.7.5  Invoking Procedures Indirectly

You can make an indirect procedure call such as  call [bx + si]  by using a
pointer to a function prototype with TYPEDEF, as shown in this example:

    FUNCPROTO       TYPEDEF PROTO NEAR ARG1:WORD, ARG2:WORD
    FUNCPTR         TYPEDEF PTR FUNCPROTO

            .DATA
    pfunc   FUNCPTR OFFSET proc1, OFFSET proc2

            .CODE
            mov     si, Num            ; Num contains 0 or 2
            INVOKE  FUNCPTR PTR [si]   ; Selects proc1 or proc2

You can also use ASSUME to accomplish the same task. The ASSUME statement
associates the type  PFUNC  with the BX register.

    ASSUME  BX:FUNCPTR
            mov     si, Num
            INVOKE  FUNCPTR PTR [bx+si]


7.3.7.6  Checking the Code Generated

The INVOKE directive generates code that may vary depending on the processor
mode and calling conventions in effect. You can check your listing files to
see the code generated by the INVOKE directive if you use the /Sg
command-line option.


7.3.8  Generating Prologue and Epilogue Code

When you use the PROC directive with its extended syntax and argument list,
the assembler automatically generates the prologue and epilogue code in your
procedure. "Prologue code" is generated at the start of the procedure; it
sets up a stack pointer so you can access parameters from within the
procedure. It also saves space on the stack for local variables, initializes
registers such as DS, and pushes registers that the procedure uses.
Similarly, "epilogue code" is the code at the end of the procedure that pops
registers and returns from the procedure.

The assembler automatically generates the prologue code when it encounters
the first instruction after the PROC directive. It generates the epilogue
code when it encounters a RET or IRET instruction. Using the
assembler-generated prologue and epilogue code saves you time and decreases
the number of repetitive lines of code in your procedures.

The generated prologue or epilogue code depends on the


    ■   Local variables defined

    ■   Arguments passed to the procedure

    ■   Current processor selected (affects epilogue code only)

    ■   Current calling convention

    ■   Options passed in the prologuearg of the PROC directive

    ■   Registers being saved


The prologuearg list contains options specifying how the prologue or
epilogue code should be generated. The next section explains how to use
these options, gives the standard prologue and epilogue code, and explains
the techniques for defining your own prologue and epilogue code.


7.3.8.1  Using Automatic Prologue and Epilogue Code

The standard prologue and epilogue code handles parameters and local
variables. If a procedure does not have any parameters or local variables,
the prologue and epilogue code that sets up and restores a stack pointer is
omitted, unless FORCEFRAME is included in the prologuearg list. (FORCEFRAME
is discussed later in this section.) Prologue and epilogue code also
generates a push and pop for each register in the register list unless the
register list is empty.

RETN and RETF suppress epilogue code generation.

When a RET is used without an operand, the assembler generates the standard
epilogue code. If you do not want the standard epilogue generated, you can
use RETN or RETF with or without operands. RET with an integer operand does
not generate epilogue code, but it does generate the right size of return.

In the examples below showing standard prologue and epilogue code,
localbytes  is a variable name used in this example to represent the number
of bytes needed on the stack for the locals declared,  parmbytes  represents
the number of bytes that the parameters take on the stack, and  registers
represents the list of registers to be pushed or popped.

The standard prologue code is the same in any processor mode:

    push bp
            mov bp, sp
            sub sp, localbytes  ; if localbytes is not 0
            push registers

The standard epilogue code is:

    pop registers
            mov sp, bp    ; if localbytes is not 0
            pop bp
            ret parmbytes ; use parmbytes only if lang is not C

The standard prologue and epilogue code recognizes two operands passed in
the prologuearg list, LOADDS and FORCEFRAME. These operands modify the
prologue code. Specifying LOADDS saves and initializes DS. Specifying
FORCEFRAME as an argument generates a stack frame even if no arguments are
sent to the procedure and no local variables are declared. If your procedure
has any parameters or locals, you do not need to specify FORCEFRAME.

Specifying LOADDS generates this prologue code:

    push bp
            mov bp, sp
            sub sp, localbytes  ; if localbytes is not 0
            push ds
            mov ax, DGROUP
            mov ds, ax
            push registers

Specifying LOADDS generates the following epilogue code:

    pop registers
            pop ds
            mov sp, bp
            pop bp
            ret parmbytes ; use parmbytes only if lang is not C


7.3.8.2  User-Defined Prologue and Epilogue Code

If you want a different set of instructions for prologue and epilogue code
in your procedures, you can write macros that are executed instead of the
standard prologue and epilogue code. For example, while you are debugging
your procedures, you may want to include a stack check or track the number
of times a procedure is called. You can write your own prologue code to do
these things whenever a procedure executes. Different prologue code may also
be necessary if you are writing applications for Microsoft Windows or any
other environment application for DOS. User-defined prologue macros will
respond correctly if you specify FORCEFRAME in the prologuearg of a
procedure.

To write your own prologue or epilogue code, the OPTION directive must
appear in your program. It disables automatic prologue and epilogue code
generation. When you specify

    OPTION PROLOGUE : macroname

    OPTION EPILOGUE : macroname

the assembler calls the macro specified in the OPTION directive instead of
generating the standard prologue and epilogue code. The prologue macro must
be a macro function, and the epilogue macro must be a macro procedure.

The assembler expects your prologue or epilogue macro to have this form:

    macroname  MACRO procname, /
                                                    flag, /
                                        parmbytes, /
                                        localbytes, /
                                            <reglist>, /
                                            userparms

The following list explains the arguments passed to your macro. Your macro
must have formal parameters to match all the actual arguments passed.

╓┌───────────┌───────────────────────────────┌───────────────────────────────╖
Argument    Description
────────────────────────────────────────────────────────────────────────────
procname    The name of the procedure.

flag        A 16-bit flag containing the
            following information:

            Bit = Value                     Description

            Bit 0, 1, 2                     For calling conventions
                                            (000=unspecified language type,
                                            001=C, 010=SYSCALL, 011=
                                            STDCALL, 100=PASCAL, 101=
                                            FORTRAN, 110=BASIC)

            Bit 3                           Undefined (not necessarily
Argument    Description
────────────────────────────────────────────────────────────────────────────
            Bit 3                           Undefined (not necessarily
                                            zero)

            Bit 4                           Set if the caller restores the
                                            stack (Use RET, not RETn)

            Bit 5                           Set if procedure is FAR

            Bit 6                           Set if procedure is PRIVATE

            Bit 7                           Set if procedure is EXPORT

            Bit 8                           Set if the epilogue was
                                            generated as a result of an
                                            IRET instruction and cleared
                                            if the epilogue was generated
                                            as a result of a RET
                                            instruction

Argument    Description
────────────────────────────────────────────────────────────────────────────

            Bits 9-15                       Undefined (not necessarily
                                            zero)

parmbytes   The byte count of all the
            parameters given in the PROC
            statement.

localbytes  The count in bytes of all
            locals defined with the LOCAL
            directive.

reglist     A list of the registers
            following the USES operator in
            the procedure declaration.
            This list is enclosed by angle
            brackets (< >), and each item
            is separated by commas. This
            list is reversed for epilogues.
Argument    Description
────────────────────────────────────────────────────────────────────────────
            list is reversed for epilogues.

userparms   Any argument you want to pass
            to the macro. The
            prologuearg (if there is one)
            specified in the PROC
            directive is passed to this
            argument.



Your macro function must return the parmbytes parameter. However, if the
prologue places other values on the stack after pushing BP and these values
are not referenced by any of the local variables, the exit value must be the
number of bytes for procedure locals plus any space between BP and the
locals. Therefore parmbytes is not always equal to the bytes occupied by the
locals.

The following macro is an example of a user-defined prologue that counts the
number of times a procedure is called.

    ProfilePro      MACRO procname,       
                        flag,           
                        bytecount,      
                        numlocals,      
                        regs,           
                        macroargs

                    .DATA
    procname&count  WORD 0
                    .CODE
            inc     procname&count  ; Accumulates count of times the
                                    ;  procedure is called
            push    bp
            mov     bp, sp
                                    ; Other BP operations
            IFNB <regs>
                FOR r, regs
                push r
                ENDM
            ENDIF
            EXITM %bytecount
    ENDM

Your program must also include this statement before any procedures are
called that use the prologue:

    OPTION PROLOGUE:ProfilePro

If you define only a prologue or an epilogue macro, the standard prologue or
epilogue code is used for the one you do not define. The form of the code
generated depends on the .MODEL and PROC options used.

If you want to revert to the standard prologue or epilogue code, use
PROLOGUEDEF  or  EPILOGUEDEF  as the macroname in the OPTION statement.

    OPTION EPILOGUE:EPILOGUEDEF

You can completely suppress prologue or epilogue generation with

    OPTION PROLOGUE:None
    OPTION EPILOGUE:None

In this case, no user-defined macro is called, and the assembler does not
generate a default code sequence. This state remains in effect until the
next OPTION PROLOGUE or OPTION EPILOGUE is encountered.

See Chapter 9 for additional information about writing macros. The
PROLOGUE.INC file provided in the MASM 6.0 distribution disks can be used to
create the prologue and epilogue sequences for the Microsoft C Professional
Development System, version 6.0.


7.4  DOS Interrupts

In addition to jumps, loops, and procedures that alter program execution,
interrupt routines transfer execution to a different location. In this case,
control goes to an interrupt routine.

You can write your own interrupt routines, either to replace an existing
routine or to use an undefined interrupt number. You may want to replace the
processor's divide-overflow (0h) interrupts or DOS interrupts, such as the
critical-error (24h) and CONTROL+C (23h) handlers. The BOUND instruction
checks array bounds and calls interrupt 5 when an error occurs. If you use
this instruction, you need to write an interrupt handler for it.

This section summarizes the following:


    ■   How to call interrupts

    ■   How the processor handles interrupts

    ■   How to redefine an existing interrupt routine


The example routine in this section handles addition or multiplication
overflow and illustrates the steps necessary for writing an interrupt
routine. See Chapter 19, "Writing Memory-Resident Software" for additional
information about DOS and BIOS interrupts.

────────────────────────────────────────────────────────────────────────────
NOTE
Under OS/2, system access is made through calls to the Applications Program
Interface (API), not through interrupts. Microsoft Windows applications use
both interrupts and API calls.
────────────────────────────────────────────────────────────────────────────


7.4.1  Calling DOS and ROM-BIOS Interrupts

Interrupts are the only way to access DOS from assembly language. They are
called with the INT instruction, which takes one operand─an immediate value
between 0 and 255.

When calling DOS and ROM-BIOS interrupts, you usually need to place a
function number in the AH register. You can use other registers to pass
arguments to functions. Some interrupts and functions return values in
certain registers, although register use varies for each interrupt. This
code writes the text of  msg  to the screen.

    .DATA
    msg     BYTE    "This writes to the screen",$
            .CODE
            mov     dx, offset msg
            mov     ah, 09h
            int     21h

When the INT instruction executes, the processor takes the following six
steps:


    1.  Looks up the address of the interrupt routine in the interrupt
        descriptor table (also called the "interrupt vector"). This table
        starts at the lowest point in memory (segment 0, offset 0) and
        consists of four bytes (two segment and two offset) for each
        interrupt. Thus, the address of an interrupt routine equals the number
        of the interrupt multiplied by 4.

    2.  Clears the trap flag (TF) and interrupt enable flag (IF).

    3.  Pushes the flags register, the current code segment (CS), and the
        current instruction pointer (IP).

    4.  Jumps to the address of the interrupt routine, as specified in the
        interrupt descriptor table.

    5.  Executes the code of the interrupt routine until it encounters an IRET
        instruction.

    6.  Pops the instruction pointer, code segment, and flags.


Figure 7.3 illustrates how interrupts work.

(This figure may be found in the printed book.)

Some DOS interrupts should not normally be called. Some (such as 20h and
27h) have been replaced by other DOS interrupts. Others are used internally
by DOS.


7.4.2  Replacing or Redefining Interrupt Routines

One interrupt routine you may want to redefine is the routine called by
INTO. The INTO (Interrupt on Overflow) instruction is a variation of the INT
instruction. It calls interrupt 04h when the overflow flag is set. By
default, the routine for interrupt 4 simply consists of an IRET, so it
returns without doing anything. Using INTO is an alternative to using JO
(Jump on Overflow) to jump to an overflow routine.

To replace or redefine an existing interrupt, your routine must


    ■   Replace the address in the interrupt descriptor table with the address
        of your new routine and save the old address

    ■   Provide new instructions to handle the interrupt

    ■   Restore the old address when your routine ends


An interrupt routine can be written like a procedure by using the PROC and
ENDP directives. The routine should always be defined as FAR and should end
with an IRET instruction instead of a RET instruction.

────────────────────────────────────────────────────────────────────────────
NOTE

Since the assembler doesn't know whether you are going to terminate with
RET or  IRET, you can use the full extended PROC syntax (described in
Section 7.3.3, "Declaring Parameters with the PROC Directive") to write
interrupt procedures. However, you should not make interrupt procedures NEAR
or specify arguments for them. You can use the USES keyword, however, to
correctly generate code to save and to restore a register list in interrupt
procedures.
────────────────────────────────────────────────────────────────────────────

The STI (Set Interrupt Flag) and CLI (Clear Interrupt Flag) instructions
turn interrupts on or off. You can use CLI to turn off interrupt processing
so that an important routine cannot be stopped by a hardware interrupt.
After the routine has finished, use STI to turn interrupt processing back
on. Interrupts received while interrupt processing was turned off by CLI are
saved and executed when STI turns interrupts back on.

MASM 6.0 provides two new forms of the IRET instruction that suppress
epilogue sequences. This allows an interrupt to have local variables or use
a userdefined prologue. IRETF pops a FAR16 return address, and IRETFD pops a
FAR32 return address.

The following example uses DOS functions to save the address of the initial
interrupt routine in a variable and to put the address of the new interrupt
routine in the interrupt descriptor table. Once the new address has been
set, the new routine is called any time the interrupt is called. This new
routine prints a message and sets AX and DX to 0.

To replace the address in the interrupt descriptor table with the address of
your procedure, AL needs to be loaded with 04h and AH loaded with 35, the
Get Interrupt Vector function. The Set Interrupt Vector function requires 25
in AH.

Follow this example to replace an existing interrupt routine. To write an
interrupt handler for an unused interrupt, see online help for available
vectors.

    .MODEL LARGE, C, DOS
    FPFUNC  TYPEDEF FAR PTR
            .DATA
    msg     BYTE    "Overflow - result set to 0",13,10,"$"
    vector  FPFUNC  ?
            .CODE
            .STARTUP

            mov     ax, 3504h       ; Load interrupt 4 and call DOS
            int     21h             ;  Get Interrupt Vector function
            mov     WORD PTR vector[2],es ; Save segment
            mov     WORD PTR vector[0],bx ;  and offset

            push    ds              ; Save DS
            mov     ax, cs          ; Load segment of new routine
            mov     ds, ax
            mov     dx, OFFSET ovrflow   ; Load offset of new routine
            mov     ax, 2504h       ; Load interrupt 4 and call DOS
            int     21h             ;  Set Interrupt Vector function
            pop     ds              ; Restore
            .
            .
            .
            add     ax, bx          ; Do addition (or multiplication)
            into                    ; Call interrupt 4 if overflow
            .
            .
            .
            lds     dx, vector      ; Load original interrupt address
            mov     ax, 2504h       ; Restore interrupt number 4
            int     21h             ;  with DOS set vector function
            mov     ax, 4C00h       ; Terminate function
            int     21h

    ovrflow         PROC    FAR
                    sti             ; Enable interrupts
                                    ;  (turned off by INT)
                    mov     ah, 09h ; Display string function
                    mov     dx, OFFSET msg     ; Load address
                    int     21h     ; Call DOS
                    sub     ax, ax  ; Set AX to 0
                    sub     dx, dx  ; Set DX to 0
                    iret            ; Return
    ovrflow         ENDP
                    END

Before your program ends, you should restore the original address by loading
DX with the original interrupt address and using the DOS set vector function
to store the original address at the correct location.


7.5  Related Topics in Online Help

Other information available online which relates to topics in this chapter
is given in the list below:

Topic                             Access
────────────────────────────────────────────────────────────────────────────
OPTION directive                  From the "MASM 6.0 Contents" screen,
                                    choose "Directives," then choose
                                    "Miscellaneous"

DOS and ROM-BIOS interrupts       From the list of System Resources on the
                                    "MASM 6.0 Contents" screen, choose "DOS
                                    Calls" or "BIOS Calls"

BT, BTC, BTR, BTS                 From the "MASM 6.0 Contents" screen,
                                    choose "Processor Instructions" and then
                                    "Logical and Shifts"

Other forms of the LOOP           From the "MASM 6.0 Contents" screen,
instruction                       choose "Processor Instructions" and then
                                    "Control Flow"

Processor Flag Summary            From the "MASM 6.0 Contents" screen,
                                    choose "Processor Instructions"







Chapter 8  Sharing Data and Procedures among Modules and Libraries
────────────────────────────────────────────────────────────────────────────

To use symbols and procedures in more than one module, the assembler must be
able to recognize the shared data as global to all the modules where they
are used. MASM 6.0 provides new techniques to simplify data-sharing and give
a high-level interface to multiple-module programming. With these
techniques, you can place shared symbols in include files. This makes the
data declarations in the file available to all modules that use the include
file.

After an overview of the data-sharing methods, the next section of this
chapter focuses on organizing modules and using the include file to simplify
data-sharing. The first method allows you to create a single include file
that works in the modules where the symbol is used as well as where it is
defined.

Sharing procedures and data items using the PUBLIC and EXTERN directives in
the appropriate modules is the other method of data-sharing. The third
section of this chapter explains how to use PUBLIC and EXTERN.

You may also want to place commonly used routines in libraries. Section 8.4
explains how to create program libraries and access their routines.


8.1  Selecting Data-Sharing Methods

If data defined in one module is to be used in the other modules of a
multiple-module program, the data must be made public and external. MASM
provides several methods for doing this.

One method is to declare a symbol public (with the PUBLIC directive) in the
module where it is defined. This makes the symbol available to other
modules. Then place an EXTERN statement for that symbol in the rest of the
modules that use the public symbol. This statement informs the assembler
that the symbol is external─defined in another module.

As an alternative, you can use the COMM directive instead of PUBLIC and
EXTERN. However, communal variables have some limitations. You cannot depend
on their location in memory because they are allocated by the linker, and
they cannot be initialized.

These two data-sharing methods are still available, but MASM 6.0 introduces
a new directive, EXTERNDEF, that declares a symbol either public or
external, as appropriate. EXTERNDEF simplifies the declarations for global
(public and external) variables and encourages the use of include files.

The next section provides further details on using include files. Section
8.3, "Using Alternatives to Include Files," provides more information on
PUBLIC and EXTERN.


8.2  Sharing Symbols with Include Files

Place statements common to all modules in include files.

Include files can contain any valid MASM statement but typically consist of
type and symbol declarations. The assembler inserts the contents of the
include file into a module at the location of the INCLUDE directive. Include
files can simplify project organization by eliminating the need to
physically insert common declarations into more than one program or module.
Include files are always optional. See Section 8.3 for alternatives to using
include files.

The first part of this section explains how to organize symbol definitions
and the declarations that make the symbols global (available to all
modules). It then shows how to make both variables and procedures public
with EXTERNDEF, PROTO, and COMM. The last part of this section tells where
to place these directives in the modules and include files.


8.2.1  Organizing Modules

This section summarizes the organization of declarations and definitions in
modules and include files and the use of the INCLUDE directive.

Include Files - Type declarations that need to be identical in every module
should be placed in an include file. Doing so ensures consistency and can
save programming time when updating programs. Include files should contain
only symbol declarations and any other declarations that are resolved at
assembly time. (See Section 1.3.1, "Generating and Running Executable
Programs," for a list of assembly-time operations.) If the include file is
associated with more than one module, it cannot contain statements that
define and allocate memory for symbols unless you include the data
conditionally (see Section 1.3.3).

Modules - Label definitions that cause the assembler to allocate memory
space must be defined in a module, not in an include file. If any of these
definitions is located in the include file, it is copied into each file that
uses the include file, creating an error.

Include files are inserted at the location of the INCLUDE directive.

Once you have placed public symbols in an include file, you need to
associate that file with the main module. The INCLUDE statement is usually
placed before data and code segments in your modules. When the assembler
encounters an INCLUDE directive, it opens the specified file and assembles
all its statements. The assembler then returns to the original file and
continues the assembly process.

The INCLUDE directive takes the form

    INCLUDE filename

where filename is the full name or fully specified path of the include file.
For example, the following declaration inserts the contents of the include
file SCREEN.INC in your program:

    INCLUDE SCREEN.INC

You must make sure that the assembler can find include files.

The file name in the INCLUDE directive must be fully specified; no
extensions are assumed. If a full path name is not given, the assembler
searches first in the directory of the source file containing the INCLUDE
directive.

If the include file is not in the source file directory, the assembler
searches the paths specified in the assembler's command-line option /I, or
in PWB's Include Paths field in the MASM Option dialog box (accessed from
the Option menu). The /I option takes this form:

    /I path

Multiple /I options can be used to specify that multiple directives be
searched in the order they appear on the command line. If none of these
directories contains the desired include file, the assembler finally
searches in the paths specified in the INCLUDE environment variable. If the
include file still cannot be found, an assembly error occurs. The related /x
option tells the assembler to ignore the INCLUDE environment variable for
all subsequent assemblies.

An include file may specify another include file. The assembler processes
the second include file before returning to the first. Include files can be
nested this way as deeply as desired; the only limit is the amount of free
memory.

Put constants used in more than one module into the include file.

Include Files or Modules - You can use the EQU directive to create named
constants that cannot be redefined in your program (see Section 1.2.4,
"Integer Constants and Constant Expressions," for information about the EQU
directive). Placing a constant defined with EQU in an include file makes it
available to all modules that use that include file.

Placing TYPEDEF, STRUCT, UNION, and RECORD definitions in an include file
guarantees consistency in type definitions. If required, the variable
instances derived from these definitions can be made public among the
modules with EXTERNDEF declarations (see the next section). Macros
(including macros defined with TEXTEQU) must be placed in include files to
make them visible in other modules.

If you elect to use full segment definitions (along with, or instead of,
simplified definitions), you can force a consistent segment order in all
files by defining segments in an include file. This technique is explained
in Section 2.3.2, "Controlling the Segment Order."


8.2.2  Declaring Symbols Public and External

It is sometimes useful to make procedures and variables (such as large
arrays or status flags) global to all program modules. Global variables are
freely accessible within all routines; you do not have to explicitly pass
them to the routines that need them.

Variables can be made global to multiple modules in several ways. This
section describes three ways to make them global by using the EXTERNDEF,
PROTO, or COMM declarations within include files. Section 8.3.1 explains how
to use the PUBLIC and EXTERN directives within modules.

External identifiers must be unique.

These methods make symbols global to the modules in which they are used.
Therefore, symbols must be unique. The linker enforces this requirement.


8.2.2.1  Using EXTERNDEF

EXTERNDEF can appear in the defining or calling modules.

MASM treats EXTERNDEF as a public declaration in the defining module and as
an external declaration in accessing module(s). You can use the EXTERNDEF
statement in your include file to make a variable common among two or more
modules. EXTERNDEF works with all types of variables, including arrays,
structures, unions, and records. It also works with procedures.

As a result, a single include file can contain an EXTERNDEF declaration that
works in both the defining module and any accessing module. It is ignored in
modules that neither define nor access the variable. Therefore, an include
file for a library which is used in multiple .EXE files does not force the
definition of a symbol as EXTERN does.

The EXTERNDEF statement takes this form:

    EXTERNDEF [[langtype]] name:qualifiedtype

The name is the variable's identifier. The qualifiedtype is explained in
detail in Section 1.2.6, "Data Types."

The optional langtype specifier sets the naming conventions for the name it
precedes. It overrides any language specified in the .MODEL directive. The
specifier can be C, SYSCALL, STDCALL, PASCAL, FORTRAN, or BASIC. See Section
20.1, "Naming and Calling Conventions," for information on selecting the
appropriate langtype type.

The diagram below shows the statements that declare an array, make it
public, and use it in another module.

(This figure may be found in the printed book.)

The file position of EXTERNDEF directives is important. See Section 8.2.3,
"Positioning External Declarations," for more information.

The assembler does not check parameters when you call EXTERNDEF procedures.


You can also make procedures visible by using EXTERNDEF without PROTO inside
an include file. This method treats the procedure name as a simple
identifier, without the parameter list, so you forgo the assembler's ability
to check for the correct parameters during assembly.

The method for using EXTERNDEF for procedures is the same as using it with
variables. You can also use EXTERNDEF to make code labels global.


8.2.2.2  Using PROTO

When a procedure is defined in one module and called from another module, it
must be declared public in the defining module and external in the calling
modules; otherwise, assembly or linking errors occur.

You have three methods for declaring a procedure public. Using PUBLIC and
EXTERN is the only method prior to MASM 6.0. Section 8.3.1 explains the use
of PUBLIC and EXTERN. The previous section (8.2.2.1) explains the use of
EXTERNDEF. This section illustrates the use of PROTO.

A PROTO (prototype) declaration in the include file establishes a
procedure's interface in both the defining and calling modules. The PROTO
directive automatically generates an EXTERNDEF for the procedure unless the
procedure has been declared PRIVATE in the PROC statement. Defining a
prototype enables type-checking for the procedure arguments.

PROTO and INVOKE simplify procedure calls.

Follow these steps to create an interface for a procedure defined in one
module and called from other modules:


    1.  Place the PROTO declaration in the include file.

    2.  Define the procedure with PROC. The PROC directive declares the
        procedure PUBLIC by default.

    3.  Call the procedure with the INVOKE statement (or with CALL).


The following example is a PROTO declaration for the far procedure
CopyFile, which uses the C parameter-passing and naming conventions, and
takes the arguments  filename  and  numberlines. The diagram following the
example shows the file placement for these statements. This definition goes
into the include file:

    CopyFile PROTO FAR C filename:BYTE, numberlines:WORD

The procedure definition for  CopyFile  is

    CopyFile PROC FAR C USES cx, filename:BYTE, numberlines:WORD

To call the  CopyFile  procedure, you can use this INVOKE statement:

    INVOKE   CopyFile, NameVar, 200

(This figure may be found in the printed book.)

See Chapter 7, "Controlling Program Flow," for descriptions, syntax, and
examples of PROTO, PROC, and INVOKE.


8.2.2.3  Using COMM

Another way to share variables among modules is to add the COMM (communal)
declaration to your include file. Since communal variables are allocated by
the linker and cannot be initialized, you cannot depend on their location or
sequence.

Communal variables are supported by MASM primarily for compatibility with
communal variables in Microsoft C. Communal variables are not used in any
other Microsoft language, and they are not compatible with C++ and some
other languages.

Communal variables can reduce the size of executable files.

COMM declares a variable external but cannot be used with code. COMM also
instructs the linker to define the variable if it has not been explicitly
defined in a module. The memory space for communal variables may not be
assigned until load time, so using communal variables may reduce the size of
your executable file.

The COMM declaration has the syntax

    COMM [[langtype]] [[NEAR
    | FAR]] label:type«:count»

The label is the name of the variable. The langtype sets the naming
conventions for the name it precedes. It overrides any language specified in
the .MODEL directive.

If NEAR or FAR is not specified, the variable determines the default from
the current memory model (NEAR for TINY, SMALL, COMPACT, and FLAT; FAR for
MEDIUM, LARGE, and HUGE).

The type can be a constant expression, but it is usually a type such as
BYTE, WORD, or DWORD, or a structure, union, or record. If you first declare
the type with TYPEDEF, CodeView can provide type information. The count is
the number of elements. If no count is given, one element is assumed.

The following example creates the common far variable  DataBlock, which is a
1,024-element array of uninitialized signed doublewords:

    COMM FAR DataBlock:SDWORD:1024

────────────────────────────────────────────────────────────────────────────
NOTE

C variables declared outside functions (except static variables) are
communal unless explicitly initialized; they are the same as
assembly-language communal variables. If you are writing assembly-language
modules for C, you can declare the same communal variables in both C and
MASM include files. However, communal variables in C do not have to be
declared communal in assembler. The linker will match the EXTERN, PUBLIC,
and COMM statements for the variable.
────────────────────────────────────────────────────────────────────────────

EXTERNDEF is a flexible alternative to using COMM.

EXTERNDEF (explained in the previous section) is more flexible than COMM
because you can initialize variables defined with it, and you can use those
variables in code that depends on the position and sequence of the data.


8.2.3  Positioning External Declarations

Although LINK determines the actual address of an external symbol, the
assembler assumes a default segment for the symbol, based on the location of
the external directive in the source code. You should therefore position
EXTERN and EXTERNDEF directives according to these rules:


    ■   If you know which segment defines an external symbol, put the EXTERN
        statement in that segment.

    ■   If you know the group but not the segment, position the EXTERN
        statement outside any segment and reference the variable with the
        group name. For example, if  var1  is in DGROUP, you would reference
        the variable as  mov DGROUP:var1, 10.

    ■   If you know nothing about the location of an external variable, put
        the EXTERN statement outside any segment. You can use the SEG
        directive to access the external variable like this:

        mov ax, SEG var1
            mov es, ax
            mov ax, es:var1


    ■   If the symbol is an absolute symbol or a far code label, you can
        declare it external anywhere in the source code.


Always close opened segments.

Any segments opened in include files should always be closed so that
external declarations following an include statement are not incorrectly
placed inside a segment. Any include statements in your program should
immediately follow the .MODEL, OPTION, and processor directives.

For the same reason, if you want to be certain that an external definition
is outside a segment, you can use @CurSeg. The @CurSeg predefined symbol
returns a blank if the definition is not in a segment. For example,

    .DATA
            .
            .
            .
    @CurSeg ENDS                    ; Close segment
            EXTERNDEF var:WORD

See Section 1.2.3, "Predefined Symbols," for information about predefined
symbols such as @CurSeg.


8.3  Using Alternatives to Include Files

If your project uses only two modules (or if it is written with a version of
MASM prior to 6.0), you may want to continue using PUBLIC in the defining
module and EXTERN in the accessing module, and not create an include file
for the project. The EXTERN directive can be used in an include file, but
the include file containing EXTERN cannot be added to the module that
contains the corresponding PUBLIC directive for that symbol. This section
assumes that you are not using include files.


8.3.1  PUBLIC and EXTERN

The PUBLIC and EXTERN directives are less flexible than EXTERNDEF and PROTO
because they are module-specific: PUBLIC must appear in the defining module
and EXTERN must appear in the calling modules. This section shows how to use
PUBLIC and EXTERN. Information on where to place the external declarations
in your file is in Section 8.2.3, "Positioning External Declarations."

The PUBLIC directive makes a name visible outside the module in which it is
defined. This gives other program modules access to that identifier.

The EXTERN directive performs the complementary function. It tells the
assembler that a name referenced within a particular module is actually
defined and declared public in another module that will be specified at link
time.

A PUBLIC directive can appear anywhere in a file. Its syntax is

    PUBLIC [[langtype]] name[[,
    [[langtype]] name]] ...

The name must be the name of an identifier defined within the current source
file. Only code labels, data labels, procedures, and numeric equates can be
declared public.

If you specify the langtype field here, it overrides the language specified
by .MODEL. The langtype field can be C, SYSCALL, STDCALL, PASCAL, FORTRAN,
or BASIC. Section 7.3.3, "Declaring Parameters with the PROC Directive," and
Section 20.1, "Naming and Calling Conventions," provide more information on
specifying langtype types.

The EXTERN directive tells the assembler that an identifier is
external─defined in some other module that will be supplied at link time.
Its syntax is

    EXTERN «langtype» name:{ABS | qualifiedtype}

Section 1.2.6, "Data Types," describes qualifiedtype. The ABS (absolute)
keyword can be used only with external numeric constants. ABS causes the
identifier to be imported as a relocatable unsized constant. This identifier
can then be used anywhere a constant can be used. If the identifier is not
found in another module at link time, the linker generates an error.

In the following example, the procedure  BuildTable  and the variable  Var
are declared public. The procedure uses the Pascal naming and data-passing
conventions:

(This figure may be found in the printed book.)


8.3.2  Other Alternatives

You can also use the directives discussed earlier (EXTERNDEF, PROTO, and
COMM) without the include file. In this case, place the declarations to make
a symbol global in the same module where the symbol is defined. You might
want to use this technique if you are linking only a few modules that have
very little data in common.


8.4  Developing Libraries

As you create reusable procedures, you can place them in a library file for
convenient access. Although you can put any routine into a library, each
library usually contains related routines. For example, you might place
string-manipulation functions in one library, matrix calculations in
another, and port communications in another.

A library consists of combined object modules, each created from a single
source file. The object module is the smallest independent unit in a
library. If you link with one symbol in a module, you get the entire module,
but not the entire library.

A library can consist of two files─an include file containing necessary
declarations and constants and a .LIB file containing procedures already
assembled into object code.


8.4.1  Associating Libraries with Modules

You can choose either of two methods for associating your libraries with the
modules that use them: you can use the INCLUDELIB directive inside your
source files or link the modules from the command line.

Specify library names with INCLUDELIB.

To associate a specified library with your object code, use INCLUDELIB. You
can add this directive to the source file to specify the libraries you want
linked, rather than specifying them in the LINK command line. The INCLUDELIB
syntax is

    INCLUDELIB libraryname

The libraryname can be a file name or a complete path specification. If you
do not specify an extension, .LIB is assumed. The libraryname is placed in
the comment record of the object file. LINK reads this record and links with
the specified library file.

For example, the statement  INCLUDELIB GRAPHICS  passes a message from the
assembler to the linker telling LINK to use library routines from the file
GRAPHICS.LIB. If this statement is in the source file DRAW.ASM and
GRAPHICS.LIB is in the same directory, the program can be assembled and
linked with the following command line:

    ML DRAW.ASM

Link libraries with command-line options.

Without the INCLUDELIB directive, the program DRAW.ASM has to be linked with
either of the following command lines:

    ML DRAW.ASM GRAPHICS.LIB
    ML DRAW /link GRAPHICS

If you want to assemble and link separately, you can use

    ML /c DRAW.ASM
    LINK DRAW,,,GRAPHICS

LINK searches in a specific order.

If you do not specify a complete path in the INCLUDELIB statement or at the
command line, LINK searches for the library file in the following order:


    1.  In the current directory

    2.  In any directories in the library field of the LINK command line

    3.  In any directories in the LIB environment variable


The LIB utility provided with MASM 6.0 helps you create, organize, and
maintain run-time libraries.


8.4.2  Using EXTERN with Library Routines

In some cases, EXTERN helps you limit the size of your executable file by
specifying in the syntax an alternative name for a procedure. You would use
this form of the EXTERN directive when declaring a procedure or symbol that
may not need to be used.

The syntax looks like this:

    EXTERN «langtype» name « (altname)
    » :qualifiedtype

The addition of the altname to the syntax provides the name of an alternate
procedure that the linker uses to resolve the external reference if the
procedure given by name is not needed. Both name and altname must have the
same qualifiedtype.

When the linker encounters an external definition for a procedure that gives
an altname, the linker finishes processing that module before it links the
object module that contains the procedure given by name. If the program does
not reference any symbols in the name file's object from any of the linked
modules, the assembler uses altname to satisfy the external reference. This
saves space because the library object module is not brought in.

For example, assume that the contents of STARTUP.ASM include these
statements:

    EXTERN  init(dummy)
            .
            .
            .
    dummy   PROC
            .
            .
            .                     ; A procedure definition containing
    no
            ret                   ;  executable code

    dummy   ENDP
            .
            .
            .
            call   init   ; Defined in FLOAT.OBJ

In this example, the reference to the routine  init  (defined in FLOAT.OBJ)
does not force the module FLOAT.OBJ to be linked into the executable file.
If another reference causes FLOAT.OBJ to be linked into the executable file,
then  init  will refer to the  init  label in FLOAT.OBJ. If there are no
references which force FLOAT.OBJ to be loaded, then the alternate name for
init(dummy)  will be used by the linker.


8.5  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topic                             Access
────────────────────────────────────────────────────────────────────────────
LIB                               From the "Microsoft Advisor Contents"
                                    screen, choose "LIB" from the list of
                                    Microsoft Utilities

INCLUDE, INCLUDELIB,              From the "MASM 6.0 Contents" screen,
EXTERNDEF, COMM, and              choose "Directives," then "Scope and
PUBLIC                            Visibility"

TYPEDEF                           From the "MASM 6.0 Contents" screen,
                                    choose "Directives," then "Complex Data
                                    Types"

PROTO and INVOKE                  From the "MASM 6.0 Contents" screen,
                                    choose "Directives," then "Procedures
                                    and Code Labels"

OPTION directive                  From the "MASM 6.0 Contents" screen,
                                    choose "Directives," then "Miscellaneous"

@CurSeg                           From the "MASM 6.0 Contents" screen,
                                    choose "Predefined Symbols"

PWB Options menu                  From the "Microsoft Advisor Contents"
                                    screen, choose "Programmer's WorkBench"






Chapter 9  Using Macros
────────────────────────────────────────────────────────────────────────────

A "macro" is a symbolic name you give to a series of characters (a text
macro) or to one or more statements (a macro procedure or function). As the
assembler evaluates each line of your program, it scans the source code for
names of previously defined macros. When it finds one, it substitutes the
macro text for the macro name. In this way, you can avoid writing the same
code several places in your program.

This chapter describes the following types of macros:


    ■   Text macros, which expand to text within a source statement

    ■   Macro procedures, which expand to one or more complete statements and
        can optionally take parameters

    ■   Repeat blocks, which generate a group of statements a specified number
        of times or until a specified condition becomes true

    ■   Macro functions, which look like macro procedures and can be used like
        text macros but which also return a value

    ■   Predefined macro functions and string directives, which perform string
        operations


Macro processing is a text-processing mechanism that is done sequentially at
assembly time. By the end of assembly, all macros have been expanded and the
resulting text assembled into object code.

This chapter shows how to use macros for simple code substitutions as well
as how to write sophisticated macros with parameter lists and repeat loops.
It also describes how to use these features in conjunction with local
symbols, macro operators, and predefined macro functions.


9.1  Text Macros

You can give a sequence of characters a symbolic name and then use the name
in place of the text later in the source code. The named text is called a
text macro.

The syntax for defining a text macro is

    name TEXTEQU <text>
    name TEXTEQU macroId | textmacro
    name TEXTEQU %constExpr


where text is a sequence of characters enclosed in angle brackets, macroId
is a previously defined macro function (see Section 9.6), textmacro is a
previously defined text macro, and %constExpr is an expression that
evaluates to text. The use of angle brackets to delimit text is discussed in
more detail in Section 9.3.1, and the % operator is explained in Section
9.3.2.

Here are some examples:

    msg     TEXTEQU <Some text>         ; Text assigned to symbol
    string  TEXTEQU msg                 ; Text macro assigned to symbol
    msg     TEXTEQU <Some other text>   ; New text assigned to symbol
    value   TEXTEQU %(3 + num)          ; Text representation of
                                        ;  resolved expression assigned
                                        ;  to symbol

In the first line, text is assigned to the symbol  msg. In the second line,
the text of the  msg  text macro is assigned to a new text macro called
string. In the third line, new text is assigned to  msg. The result is that
msg  has the new text value, while  string  has the original text value. The
fourth line assigns  7  to  value  if  num  equals  4. If a text macro
expands to another text macro (or macro function, which is discussed in
Section 9.6), the resulting text macro will be recursively expanded.

Text macros are useful for naming strings of text that do not evaluate to
integers. For example, you might use a text macro to name a floating-point
constant or a bracketed expression. Here are some practical examples:

    pi      TEXTEQU <3.1416>            ; Floating point constant
    WPT     TEXTEQU <WORD PTR>          ; Sequence of key words
    arg1    TEXTEQU <[bp+4]>            ; Bracketed expression

────────────────────────────────────────────────────────────────────────────
NOTE

Use of the TEXTEQU directive to define text macros is new in MASM 6.0. In
previous versions, you can use the EQU directive for the same purpose. If
you have old code that worked under previous versions, it should still work
under 6.0. However, the more consistent and flexible TEXTEQU is recommended
for new code.
────────────────────────────────────────────────────────────────────────────


9.2  Macro Procedures

If your program needs to perform the same task many times, you can avoid
having to type the same statements each time by writing a macro procedure.
Macro procedures (commonly called macros) can be seen as text-processing
mechanisms that automatically generate repeated text.

The term "macro procedure" rather than macro is used when necessary to
distinguish between macro procedures and macro functions (a new feature of
MASM 6.0 described in Section 9.6, "Returning Values with Macro Functions").



9.2.1  Creating Macro Procedures

To define a macro procedure without parameters, place the desired statements
between the MACRO and ENDM directives:

name MACRO statements ENDM

For example, suppose you want a program to beep when it encounters certain
errors. A  beep  macro can be defined as follows:

    beep    MACRO
        mov  ah, 2          ;; Select DOS Print Char function
        mov  dl, 7          ;; Select ASCII 7 (bell)
        int  21h            ;; Call DOS
    ENDM

Macro comments must start with two semicolons instead of one.

The double semicolons mark the beginning of macro comments. Macro comments
appear in a listing file only at the macro's initial definition, not at the
point where it is called and expanded. Listings are usually easier to read
if the comments aren't always expanded. Regular comments (those with a
single semicolon) are listed in macro expansions. Appendix C discusses
listing files and shows examples of how macros are expanded in listings.

Once a macro is defined, you can call it anywhere in the program by using
the macro's name as a statement. The following example calls the  beep
macro two times if an error flag has been set.

    .IF     error   ; If error flag is true
            beep            ;  execute macro two times
            beep
            .ENDIF

The instructions in the macro take the place of the macro call when the
program is assembled. This would be the resulting code (from the listing
file):

    .IF     error
    0017  80 3E 0000 R 00   *         cmp    error, 000h
    001C  74 0C             *         je     @C0001
                                beep
    001E  B4 02               1         mov     ah, 2
    0020  B2 07               1         mov     dl, 7
    0022  CD 21               1         int     21h
                                beep
    0024  B4 02               1         mov     ah, 2
    0026  B2 07               1         mov     dl, 7
    0028  CD 21               1         int     21h
                                .ENDIF
    002A                  *@C0001:

Contrast this with the results of defining  beep  as a procedure using the
PROC directive and then calling it using the CALL instruction. The
instructions of the procedure occur only once in the executable file, but
you would also have the additional overhead of the CALL and RET
instructions.

Macros are usually faster than run-time procedures.

In some cases the same task can be done with either a macro or a procedure.
Macros are potentially faster because they have less overhead, but they
generate the same code multiple times rather than just once.


9.2.2  Passing Arguments to Macros

Parameters allow macros to execute variations of a general task.

By defining parameters for macros, you can define a general task and then
execute variations of it by passing different arguments each time you call
the macro. The complete syntax for a macro procedure includes a parameter
list:

name MACRO parameterlist statements ENDM

The parameterlist can contain any number of parameters. Use commas to
separate each parameter in the list. Parameter names cannot be reserved
words unless the keyword has been disabled with OPTION NOKEYWORD, the
compatibility modes have been set by specifying OPTION M510 (see Section
1.3.2), or the /Zm command-line option has been set.

To pass arguments to a macro, place the arguments after the macro name when
you call the macro:

macroname arglist

All text between matching quotation marks in an arglist is considered one
text item.

The  beep  macro introduced in the last section used the DOS interrupt to
write the bell character (ASCII 7). It can be rewritten with a parameter to
specify any character to write.

    writechar MACRO char
        mov  ah, 2                  ;; Select DOS Print Char function
        mov  dl, char               ;; Select ASCII char
        int  21h                    ;; Call DOS
    ENDM

Wherever  char  appears in the macro definition, the assembler replaces it
with the argument in the macro call. Each time you call  writechar, you can
print a different value:

    writechar 7             ; Causes computer to beep
            writechar 'A'           ; Writes A to screen

If you pass more arguments than there are parameters, the additional
arguments generate a warning (unless you use the VARARG keyword; see Section
9.4.3). If you pass fewer arguments than the macro procedure expects,
remaining parameters are assigned empty strings (unless default values have
been specified). This may cause errors. For example, if you call the
writechar  macro with no argument, it generates the following:

    mov     dl,

The assembler generates an error for the expanded statement but not for the
macro definition or the macro call.

Macros can be made more flexible by leaving off macro arguments or adding
additional ones. The next section tells some of the ways you can handle
missing or extra arguments.


9.2.3  Specifying Required and Default Parameters

You can specify required and default parameters for macros.

You can give macro parameters special attributes to make them more flexible
and improve error handling; you can make them required, give them default
values, or vary their number. Because variable parameters are used almost
exclusively with the FOR directive, discussion of them is postponed until
Section 9.4.3, "FOR Loops and Variable-Length Parameters."

The syntax for a required parameter is

    parameter:REQ

For example, you can rewrite the  writechar  macro to require the  char
parameter:

    writechar MACRO char:REQ
        mov  ah, 2                  ;; Select DOS Print Char function
        mov  dl, char               ;; Select ASCII char
        int  21h                    ;; Call DOS
    ENDM

If the call does not include a matching argument, the assembler reports the
error in the line that contains the macro call. The effect of REQ is to
improve error reporting.

A default value fills in missing parameters.

Another way to handle missing parameters is to specify a default value. The
syntax is

    parameter:=textvalue

Suppose that you often use  writechar  to beep by printing ASCII 7. The
following macro definition uses an equal sign to tell the assembler to
assume the parameter  char  is  7  unless you specify otherwise:

    writechar  MACRO char:=<7>
        mov  ah, 2                  ;; Select DOS Print Char function
        mov  dl, char               ;; Select ASCII char
        int  21h                    ;; Call DOS
    ENDM

In this case,  char  is not required. If you don't supply a value, the
assembler fills in the blank with the default value of  7  and the macro
beeps when called.

The default parameter value is enclosed in angle brackets so that the
supplied value will be recognized as a text value. Section 9.3.1, "Text
Delimiters (< >) and the Literal-Character Operator (!)," explains this in
more detail.

Missing arguments can also be handled with the IFB, IFNB, .ERRB, and .ERRNB
directives. They are described briefly in Section 1.3.3, "Conditional
Directives," and in online help. Here is a slightly more complex macro that
uses some of these techniques.

    Scroll MACRO distance:REQ, attrib:=<07h>, tcol, trow, bcol,
    brow
        IFNB <tcol>             ;; Ignore arguments if blank
            mov   cl, tcol
        ENDIF
        IFNB <trow>
            mov   ch, trow
        ENDIF
        IFNB <bcol>
            mov   dl, bcol
        ENDIF
        IFNB <brow>
            mov   dh, brow
        ENDIF
        IFDIFI <attrib>, <bh>   ;; Don't move BH onto itself
            mov   bh, attrib
        ENDIF
        IF distance LE 0        ;; Negative scrolls up, positive down
            mov   ax, 0600h + (-(distance) AND 0FFh)
        ELSE
            mov   ax, 0700h + (distance AND 0FFh)
        ENDIF
        int   10h
    ENDM

In this macro, the  distance  parameter is required. The  attrib  parameter
has a default value of  07h  (white on black), but the macro also tests to
make sure the corresponding argument isn't BH, since it would be inefficient
(though legal) to load a register onto itself. The IFNB directive is used to
test for blank arguments. These are ignored to allow the user to manipulate
rows and columns directly in registers CX and DX at run time.

The following are two valid ways to call the macro:

    ; Assume DL and CL already loaded
            dec     dh                   ; Decrement top row
            inc     ch                   ; Increment bottom row
            Scroll -3                    ; Scroll white on black dynamic
                                        ;  window up three lines
            Scroll 5, 17h, 2, 2, 14, 12  ; Scroll white on blue constant
                                        ;  window down five lines

This macro can generate completely different code, depending on its
arguments. In this sense, it is not comparable to a procedure, which always
has the same code regardless of arguments.


9.2.4  Defining Local Symbols in Macros

You can make a symbol local to a macro by declaring it at the start of the
macro with the LOCAL directive. Any identifier may be declared local.

You can choose whether you want numeric equates and text macros to be local
or global. If a symbol will be used only inside a particular macro, you can
declare it local so that the name will be available for other declarations
inside other macros or at the global level. On the other hand, it is
sometimes convenient to define text macros and equates that are not local,
so that their values can be shared between macros.

If you need to use a label inside a macro, you must declare it local, since
a label can occur only once in the source. The LOCAL directive makes a
special instance of the label each time the macro is called. This prevents
redefinition of the label.

All local symbols must be declared immediately following the MACRO statement
(although blank lines and comments may precede the local symbol). Separate
each symbol with a comma. Comments are allowed on the LOCAL statement.
Multiple LOCAL statements are also permitted. Here is an example macro that
declares local labels:

    power   MACRO   factor:REQ, exponent:REQ
        LOCAL   again, gotzero      ;; Local symbols
        sub     dx, dx              ;; Clear top
        mov     ax, 1               ;; Multiply by one on first loop
        mov     cx, exponent        ;; Load count
        jcxz    gotzero             ;; Done if zero exponent
        mov     bx, factor          ;; Load factor
    again:
        mul     bx                  ;; Multiply factor times exponent
        loop    again               ;; Result in AX
    gotzero:
    ENDM

If the labels  again  and  gotzero  were not declared local, the macro would
work the first time it is called, but it would generate redefinition errors
on subsequent calls. MASM implements local labels by generating different
names for them each time the macro is called. You can see this in listing
files. The labels in the  power  macro might be expanded to  ??0000  and
??0001  on the first call and to  ??0002  and  ??0003  on the second.


9.3  Assembly Time Variables and Macro Operators

In writing macros, you will often assign and modify values assigned to
symbols. These symbols can be thought of as assembly-time variables. Like
memory variables, they are symbols that represent values. But since macros
are processed at assembly time, any symbol modified in a macro must be
resolved as a constant by the end of assembly.

The three kinds of assembly-time variables are:


    ■   Macro parameters

    ■   Text macros

    ■   Macro functions


When a macro is expanded, the symbols are processed in the order shown
above. First macro parameters are replaced with the text of their actual
arguments. Then text macros are expanded.

Macro parameters are similar to procedure parameters in some ways, but they
also have important differences. In a procedure, a parameter has a type and
a memory location. Its value can be modified within the procedure. In a
macro, a parameter is a placeholder for the argument text. The value can
only be assigned to another symbol or used directly; it cannot be modified.
The macro may interpret the argument text it receives either as a numeric
value or as a text value.

It is important to understand the difference between text values and numeric
values. Numeric values can be processed with arithmetic operators and
assigned to numeric equates. Text values can be processed with macro
functions and assigned to text macros.

Macro operators are often helpful when processing assembly-time variables.
Table 9.1 shows the macro operators that MASM provides:

Table 9.1  MASM Macro Operators

Symbol  Name                              Description
────────────────────────────────────────────────────────────────────────────
< >     Text Delimiters                   Opens and closes a literal
                                            string.

!       Literal-Character Operator        Treats the next character as a
                                            literal character, even if it
                                            would normally have another
                                            meaning.

%       Expansion Operator                Causes the assembler to expand a
                                            constant expression or text
                                            macro.

&       Substitution Operator             Tells the assembler to replace a
                                            macro parameter or text macro
                                            name with its
                                            actual value.

────────────────────────────────────────────────────────────────────────────


The next sections explain these operators in detail.


9.3.1  Text Delimiters (< >) and the Literal-Character Operator (!)

The angle brackets (< >) are text delimiters. The most common reason to
delimit a text value is when assigning a text macro. You can do this with
TEXTEQU, as previously shown, or with the SUBSTR and CATSTR directives
discussed in Section 9.5, "String Directives and Predefined Functions."

By delimiting the text of macro arguments, you can pass text that includes
spaces, commas, semicolons, and other special characters. In the following
example, assume you have previously defined a macro called  work:

    work    <1, 2, 3, 4, 5> ; Passes one argument
                                    ;  with 15 characters
            work    1, 2, 3, 4, 5   ; Passes five arguments, each
                                    ;  with 1 character

Since angle brackets are delimiters, you can't include them as part of a
delimited text value. The literal-character operator (!) can be used to
override this limitation. It forces the assembler to treat the character
following it literally rather than as a special character.

    errstr  TEXTEQU <Expression !> 255>  ; errstr = "Expression
    > 255"

Text delimiters also have a special use with the FOR directive, as explained
in Section 9.4.3.


9.3.2  Expansion Operator (%)

The expansion operator (%) expands text macros or converts constant
expressions into their text representations. It performs these tasks
differently in different contexts, as discussed below.


9.3.2.1  The Expansion Operator with Constants

The expansion operator can be used in any context where a text value is
expected but a numeric value is supplied. In these contexts, it can be
thought of as a conversion operator to convert numeric values to text
values.

The expansion operator forces immediate evaluation of a constant expression
and replaces it with a text value consisting of the digits of the result.
The digits are generated in the current radix (default decimal).

This application of the expansion operator is useful when defining a text
macro:

    a       TEXTEQU <3 + 4>         ; a = "3 + 4"
    b       TEXTEQU %3 + 4          ; b = "7"

When assigning text macros, numeric equates can be used in the constant
expressions, but text macros cannot:

    num     EQU     4               ; num = 4
    numstr  TEXTEQU <4>             ; numstr = <4>
    a       TEXTEQU %3 + num        ; a = <7>
    b       TEXTEQU %3 + numstr     ; b = <7>

The expansion operator can be used when passing macro arguments. If you want
the value rather than the text of an expression to be passed, use the
expansion operator. Use of the expansion operator depends on whether you
want the expression to be evaluated inside the macro on each use, or outside
the macro once. The following macro

    work    MACRO   arg
        mov ax, arg * 4
    ENDM

can be called with these statements:

    work    2 + 3           ; Passes "2 + 3"
                                    ; Code: mov ax, 2 + 3 * 4 (14)
            work    %2 + 3          ; Passes 5
                                    ; Code: mov ax, 5 * 4 (20)

Notice that because of operator precedence, results can vary depending on
whether the expansion operator is used. Sometimes parentheses can be used
inside the macro to force evaluation in a particular order:

    work    MACRO   arg
        mov ax, (arg) * 4
    ENDM

            work    2 + 3           ; Code: mov ax, (2 + 3) * 4 (20)
            work    %2 + 3          ; Code: mov ax, (5) * 4 (20)

This example generates the same code regardless of whether you pass the
argument as a value or as text, but in some cases you need to specify how
the argument is passed.

The value for a default argument must be text, but frequently you need to
give a constant value. The expansion operator is one way to force the
conversion. The following statements are equivalent:

    work    MACRO   arg:=<07h>
    work    MACRO   arg:=%07h

The expansion operator also has several uses with macro functions. See
Section 9.6.


9.3.2.2  The Expansion Operator with Symbols

When you use the expansion operator on a macro argument, any text macros or
numeric equates in the argument are expanded:

    num     EQU     4
    numstr  TEXTEQU <4>

            work    2 + num         ; Passes "2 + num"
            work    %2 + num        ; Passes "6"
            work    2 + numstr      ; Passes "2 + numstr"
            work    %2 + numstr     ; Passes "6"

The arguments can optionally be enclosed in parentheses. For example, these
two statements are equivalent:

    work    %2 + num
            work    %(2 + num)


9.3.2.3  The Expansion Operator as the First Character on a Line

The expansion operator has a different meaning when used as the first
character on a line. In this case, it instructs the assembler to expand any
text macros and macro functions it finds on the rest of the line.

This feature makes it possible to use text macros with directives such as
ECHO, TITLE, and SUBTITLE that take an argument consisting of a single text
value. For instance, ECHO displays its argument to the standard output
device during assembly. Such expansion can be useful for debugging macros
and expressions, but the requirement that its argument be a single text
value may have unexpected results:

    ECHO    Bytes per element: %(SIZEOF array / LENGTHOF
    array)

Instead of evaluating the expression, this line just echoes it:

    Bytes per element: %(SIZEOF array / LENGTHOF array)

However, you can achieve the desired result by assigning the text of the
expression to a text macro and then using the expansion operator at the
beginning of the line to force expansion of the text macro.

    temp    TEXTEQU %(SIZEOF array / LENGTHOF array)
    %       ECHO    Bytes per element: temp

Note that you cannot get the same results by simply putting the % at the
beginning of the first echo line, because % expands only text macros, not
numeric equates or constant expressions.

Here are more examples of the use of the expansion operator at the start of
a line:

    ; Assume memmod, lang, and os are passed in with /D option
    %   SUBTITLE  Model: memmod  Language: lang  Operating System: os

    ; Assume num defined earlier
    tnum    TEXTEQU %num
    %       .ERRE   num LE 255, <Failed because tnum !> 255>


9.3.3  Substitution Operator (&)

In MASM 6.0, the substitution operator (&) enables substitution of macro
parameters, even when the parameter occurs within a larger word or within a
quoted string. It can also be used to concatenate two macro parameters after
they have been expanded.

The syntax for the substitution operator looks like this:

    &parametername&

The operators delimiting a name always tell the assembler to substitute the
actual argument for the name. However, the substitution operator is often
optional. The substitution operator is not necessary when there is a space
or separation character (comma, tab, or other operator) on that side. In the
case of a parameter name inside a string, at least one substitution operator
must appear.

The rules for using the substitution operator have changed significantly
since MASM 5.1, making macro behavior more consistent and flexible. If you
have macros written for a previous version of MASM, you can specify the old
behavior by using OLDMACROS or M510 with the OPTION directive (see Section
1.3.2).

In the macro

    work    MACRO   arg
        mov ax, &arg& * 4
    ENDM

the & symbols tell the assembler to replace the value of  arg  with the
corresponding argument. However, the characters on both the right and left
are spaces. Therefore, the operators are unnecessary. The macro would
normally be written like this:

    work    MACRO   arg
        mov ax, arg * 4
    ENDM

The substitution operator is used for one of the following reasons:


    ■   To paste together two parameter names or a parameter name and text

    ■   To indicate that a parameter name inside double or single quotation
        marks should be expanded rather than be treated as part of the quoted
        string


This macro illustrates both uses:

    errgen  MACRO   num, msg
        PUBLIC  err&num
        err&num BYTE    "Error &num: &msg"
    ENDM

When called with the following arguments,

    errgen  5, <Unreadable disk>

the macro generates this code:

    PUBLIC  err5
    err5    BYTE    "Error 5: Unreadable disk"

In the second line of the macro, the left & symbol must be provided because
it is adjacent to the  r  character, which is a valid identifier symbol. The
right & symbol is not needed because there is a space to the right of the
m. The statement pastes the text  err  to the argument value  5  to generate
the symbol  err5.

The substitution operator is used again inside quotation marks at the start
of the parameter names  num  and  msg  to indicate that these names should
be expanded. In this case, no pasting operation is necessary, so either
operator could be omitted, but not both. The macro line could have been
written as

    err&num BYTE    "Error num&: msg&"

or

    err&num BYTE    "Error &num&: &msg&"

The assembler processes substitution operators from left to right. This can
have unexpected results when you are pasting together two macro parameters.
For example, if  arg1  has the value  var  and  arg2  has the value  3, you
could paste them together with this statement:

    &arg1&&arg2&    BYTE    "Text"

Eliminating extra substitution operators, you might expect the following to
be equivalent:

    &arg1&arg2      BYTE    "Text"

However, this actually produces the symbol  vararg2  because in processing
from left to right the assembler associates both the first and the second &
symbols with the first parameter. The assembler replaces  &arg1&  by  var ,
producing  vararg2 . The  arg2  is never evaluated. The correct abbreviation
is

    arg1&&arg2      BYTE    "Text"

which produces the desired symbol  var3. The symbol  arg1&&arg2  is replaced
by  var&arg2, which is replaced by  var3.

The substitution operator is also necessary if you want a text macro
substituted inside quotes. For example,

    arg     TEXTEQU <hello>
    %echo   This is a string "&arg" ; Produces: This is a string "hello"
    %echo   This is a string "arg"  ; Produces: This is a string "arg"

The substitution operator can also be used in lines beginning with the
expansion operator (%) symbol, even outside macros (see Section 9.3.2.3).
Text macros are always expanded in such lines, but it may be necessary to
use the substitution operator to paste text macro names to adjacent
characters or symbol names, as shown below:

    text    TEXTEQU <var>
    value   TEXTEQU %5
    %       ECHO    textvalue is text&&value

This echoes the message

    textvalue is var5

Bit-test and macro expansion statements can be confused.

The single ampersand (&) is the bit-test operator in MASM, as it is for C.
This operator is also used in macro expansion as the substitute operator.
Macro substitution always occurs before evaluation of the high-level control
structures; therefore, in ambiguous cases, the & operator is treated as a
macro-expansion character. You can always guarantee the correct use of the
bit-test operator by enclosing the bit-test operands in parentheses. The
example below illustrates these two uses.

    test    MACRO   x
        .IF ax==&x      ; &x substituted with parameter value
        mov     ax, 10
        .ELSEIF ax&(x)  ; & is bitwise AND
        mov ax, 20
        .ENDIF
        ENDM


9.4  Defining Repeat Blocks with Loop Directives

A "repeat block" is an unnamed macro defined with a loop directive. It
generates the statements inside the repeat block a specified number of times
or until a given condition becomes true.

Several loop directives are available, providing different ways of
specifying the number of iterations. Some loop directives also provide a way
to specify arguments for each iteration. Although the number of iterations
is usually specified in the directive, you can use the EXITM directive to
exit from the loop early.

Repeat blocks can be used outside macros, but they frequently appear inside
macro definitions to perform some repeated operation in the macro.

This section explains the following four loop directives: REPEAT, WHILE,
FOR, and FORC. In previous versions of MASM, REPEAT was called REPT, FOR was
called IRP, and FORC was called IRPC. MASM 6.0 still recognizes the old
names.

────────────────────────────────────────────────────────────────────────────
NOTE

The REPEAT and WHILE directives should not be confused with the .REPEAT and
.WHILE directives (see Section 7.2.1, "Loop-Generating Directives"), which
generate loop and jump instructions for run-time program control.
────────────────────────────────────────────────────────────────────────────


9.4.1  REPEAT Loops

Repeat loops are expanded at assembly time.

The REPEAT directive is the simplest loop directive. It specifies the number
of times to generate the statements inside the macro. The syntax is

    REPEAT constexpr
    statements
    ENDM

The constexpr can be a constant or a constant expression, and must contain
no forward references. Since the repeat block will be expanded at assembly
time, the number of iterations must be known then.

Here is an example of a repeat block used to generate data. It initializes
an array containing sequential ASCII values for all uppercase letters.

    alpha   LABEL   BYTE            ;  Name the data generated
    letter  =       'A'             ;  Initialize counter
    REPEAT  26                      ;; Repeat for each letter
        BYTE    letter              ;; Allocate ASCII code for letter
        letter  = letter + 1        ;; Increment counter
    ENDM

Here is another use of REPEAT, this time inside a macro:

    beep    MACRO   iter:=<3>
        mov ah, 2                   ;; Character output function
        mov dl, 7                   ;; Bell character
        REPEAT iter                 ;; Repeat number specified by macro
            int 21h                 ;; Call DOS
        ENDM
    ENDM


9.4.2  WHILE Loops

The WHILE directive is similar to REPEAT, but the loop continues as long as
a given condition is true. The syntax is

    WHILE expression
    statements
    ENDM

The expression must be a value that can be calculated at assembly time.
Normally the expression uses relational operators, but it can be any
expression that evaluates to zero (false) or nonzero (true). Usually, the
condition changes during the evaluation of the macro so that the loop won't
attempt to generate an infinite amount of code. However, you can use the
EXITM directive to break out of the loop.

Loops are especially useful for generating lookup tables.

The following repeat block uses the WHILE directive to allocate variables
initialized to calculated values. This is a common technique for generating
lookup tables. Frequently it is faster to look up a value precalculated by
the assembler at assembly time than to have the processor calculate the
value at run time.

    cubes   LABEL   BYTE            ;; Name the data generated
    root    =   1                   ;; Initialize root
    cube    =   root * root * root  ;; Calculate first cube
    WHILE   cube LE 32767           ;; Repeat until result too large
        WORD   cube                 ;; Allocate cube
        root   =    root + 1        ;; Calculate next root and cube
        cube   =    root * root * root
    ENDM


9.4.3  FOR Loops and Variable-Length Parameters

With the FOR directive you can iterate through a list of arguments, doing
some operation on each of them in turn. It has the following syntax:

FOR parameter, <argumentlist> statements ENDM

The parameter is a placeholder that will be used as the name of each
argument inside the FOR block. The argument list must be a list of
comma-separated arguments and must always be enclosed in angle brackets, as
the following example illustrates:

    series  LABEL   BYTE
    FOR     arg, <1,2,3,4,5,6,7,8,9,10>
        BYTE  arg DUP (arg)
    ENDM

On the first iteration, the  arg  parameter is replaced with the first
argument, the value 1. On the second iteration  arg  is replaced with 2. The
result is an array with the first byte initialized to 1, the next two bytes
initialized to 2, the next three bytes initialized to 3, and so on.

In this example the argument list is given specifically, but in some cases
the list must be generated as a text macro. The value of the text macro must
include the angle brackets.

    arglist TEXTEQU <!<3,6,9!>>     ; Generate list as text macro
    FOR  arg, arglist
        .                           ; Do something to arg
        .
        .
    ENDM

Note the use of the literal character operator (!) to use angle brackets as
characters, not delimiters (see Section 9.3.1).

Variable parameter lists provide flexibility.

The FOR directive also provides a convenient way to process macros with a
variable number of arguments. To do this, add VARARG to the last parameter
to indicate that a single named parameter will have the actual value of all
additional arguments. For example, the following macro definition includes
the three possible parameter attributes─required, default, and variable.

    work    MACRO   rarg:REQ, darg:=<5>, varg:VARARG

The variable argument must always come last. If this macro is called with
the statement

    work 5, , 6, 7, a, b

the first argument is received as passed, the second is replaced by the
default value  5, and the last four are received as the single argument  <6,
7, a, b>. This is the same format expected by the FOR directive. The FOR
directive discards leading spaces but recognizes trailing spaces.

The following macro illustrates variable arguments:

    show    MACRO chr:VARARG
        mov     ah, 02h
        FOR arg, <chr>
            mov     dl, arg
            int     21h
        ENDM
    ENDM

When called with

    show  'O', 'K', 13, 10

the macro displays each of the specified characters one at a time.

The parameter in a FOR loop can have the required or default attribute. The
show  macro can be modified to make blank arguments generate errors:

    show    MACRO chr:VARARG
        mov     ah, 02h
        FOR arg:REQ, <chr>
            mov     dl, arg
            int     21h
        ENDM
    ENDM

The macro now generates an error if called with

    show  'O',, 'K', 13, 10

Another approach would be to use a default argument:

    show    MACRO chr:VARARG
        mov     ah, 02h
        FOR arg:=<' '>, <chr>
            mov     dl, arg
            int     21h
        ENDM
    ENDM

Now if the macro is called with

    show  'O',, 'K', 13, 10

it inserts the default character, a space, for the blank argument.


9.4.4  FORC Loops

The FORC directive is similar to FOR but takes a string of text rather than
a list of arguments. The statements are assembled once for each character
(including spaces) in the string, substituting a different character for the
parameter each time through.

The syntax looks like this:

    FORC parameter, < text>
    statements
    ENDM

The text must be enclosed in angle brackets. The following example
illustrates FORC:

    FORC arg, <ABCDEFGHIJKLMNOPQRSTUVWXYZ>
        BYTE  '&arg'             ;; Allocate uppercase letter
        BYTE  '&arg' + 20h       ;; Allocate lowercase letter
        BYTE  '&arg' - 40h       ;; Allocate ordinal of letter
    ENDM

Notice that the substitution operator must be used inside the quotation
marks to make sure that  arg  is expanded to a character rather than treated
as a literal string.

With earlier versions of MASM, FORC is often used for complex parsing tasks.
A long sentence can be examined character by character. Each character is
then either thrown away or pasted onto a token string, depending on whether
it is a separator character. In MASM 6.0, the predefined macro functions and
string processing directives discussed in Section 9.5 are usually more
efficient for these tasks.


9.5  String Directives and Predefined Functions

Predefined macro string functions are new to MASM 6.0.

The assembler provides the following directives for manipulating text:
SUBSTR, INSTR, SIZESTR, and CATSTR. Each of these has a corresponding
predefined macro function version: @SubStr, @InStr, @SizeStr, and @CatStr.

You use the directive versions to assign a processed value to a text macro
or numeric equate. For example, CATSTR, which concatenates a list of text
values, can be used like this:

    num     =       7
    newstr  CATSTR  <3 + >, %num, < = > , %3 + num ; "3 + 7 = 10"

Assignment with CATSTR and SUBSTR works like assignment with the TEXTEQU
directive. Assignment with SIZESTR and INSTR works like assignment with the
= operator.

The arguments to directives must be text values. Use the expansion operator
to make sure that constants and numeric equates are expanded to text.

The macro function versions are similar, but their arguments must be
enclosed in parentheses. Macro functions return text values and can be used
in any context where text is expected. Section 9.6 tells how to write your
own macro functions. An equivalent statement to the previous example using
CATSTR is

    num     =       7
    newstr  TEXTEQU @CatStr( <3 + >, %num, < = > , %3 + num )

Although the directive version is simpler in the example above, the function
versions are often convenient because they can be used as arguments to
string directives or to other macro functions.

Unlike the string directives, predefined macro function names are case
sensitive. Since MASM is not case sensitive by default, the case doesn't
matter unless you use the /Cp command-line option.

The following sections summarize the syntax for each of the string
directives and functions. The explanations focus on the directives, but the
functions work the same except where noted.


SUBSTR

    name SUBSTR string, start«, length»
    @SubStr( string, start«, length» )

The SUBSTR directive assigns a substring from a given string to a new
symbol, specified by name. Start specifies the position (1-based) in string
to start the substring. Length specifies the length of the substring. If
length is not given, it is assumed to be the remainder of the string
including the start character. The string

in the SUBSTR syntax, as well as in the syntax for the other string
directives and predefined functions, can be any textItem where textItem can
be text enclosed in angle brackets (< >), the name of a macro, or a constant
expression preceded by % (%constExpr).


INSTR

    name INSTR «start,» string, substring
    @InStr( «start», string, substring
    )

The INSTR directive searches a specified string for an occurrence of a given
substring and assigns its position (1-based) to name. The search is case
sensitive. Start is the position in string to start the search for
substring. If start is not given, it is assumed to be 1 (the start of the
string). If substring is not found, the position assigned to name is 0.

If the INSTR directive is used, the position value is assigned to a name as
if it were a numeric equate. If the @InStr function is used, the value is
returned as a string of digits in the current radix.

The @InStr function has a slightly different syntax than the INSTR
directive. You can omit the first argument and its associated comma from the
directive. You can leave the first argument blank with the function, but a
blank function argument must still have a comma. For example,

    pos     INSTR   <person>, <son>

is the same as

    pos     = @InStr( , <person>, <son> )

The return value could also be assigned to a text macro:

    strpos  TEXTEQU @InStr( , <person>, <son> )


SIZESTR

    name SIZESTR string
    @SizeStr( string )

The SIZESTR directive assigns the number of characters in string to name. An
empty string assigns a length of zero. Although the length is always a
positive number, it is assigned as a string of digits in the current radix
rather than as a numeric value.

If the SIZESTR directive is used, the size value is assigned to a name as if
it were a numeric equate. If the @SizeStr function is used, the value is
returned as a string of digits in the current radix.


CATSTR

    name CATSTR string«, string»...
    @CatStr( string«,  string»... )

The CATSTR directive concatenates a list of text values specified by string
into a single text value and assigns it to name. TEXTEQU is technically a
synonym for CATSTR. TEXTEQU is normally used for single-string assignments,
while CATSTR is used for multistring concatenations.

The following example that pushes and pops one set of registers illustrates
several uses of string directives and functions:

    ; SaveRegs - Macro to generate a push instruction for each
    ; register in argument list. Saves each register name in the
    ; regpushed text macro.
    regpushed TEXTEQU <>                    ;; Initialize empty string

    SaveRegs MACRO regs:VARARG
        FOR reg, <regs>                     ;; Push each register
            push reg                        ;;  and add it to the list
            regpushed CATSTR   <reg>, <,>, regpushed
        ENDM                                ;; Strip off last comma
        regpushed CATSTR <!<>, regpushed    ;; Mark start of list with
    <
        regpushed SUBSTR regpushed, 1, @SizeStr( regpushed )
        regpushed CATSTR regpushed, <!>>    ;; Mark end with >
    ENDM

    ; RestoreRegs - Macro to generate a pop instruction for registers
    ; saved by the SaveRegs macro. Restores one group of registers.

    RestoreRegs MACRO
        LOCAL regs
        %FOR reg, regpushed                  ;; Pop each register        pop
    reg
        ENDM
    ENDM

Notice how the  SaveRegs  macro saves its result in the  regpushed  text
macro for later use by the  RestoreRegs  macro. In this case, a text macro
is used as a global variable. By contrast, the  regs  text macro is used
only in RestoreRegs. It is declared LOCAL so that it won't take the name
regs  from the global name space. The MACROS.INC file provided with MASM 6.0
includes expanded versions of these same two macros.


9.6  Returning Values with Macro Functions

A macro function returns a text string.

A macro function is a named group of statements that returns a value. When a
macro function is called, its argument list must be enclosed in parentheses,
even if the list is empty. The value returned is always text.

Macro functions are new to MASM 6.0, as are several predefined macro
functions for common tasks. The predefined macros include @Environ (see
Section 1.2.3) and the string functions @SizeStr, @CatStr, @SubStr, and
@InStr (discussed in the preceding section).

Macro functions are defined in exactly the same way as macro procedures,
except that a value must always be returned using the EXITM directive. Here
is an example:

    DEFINED MACRO   symbol:REQ
        IFDEF symbol
            EXITM <-1>              ;; True
        ELSE
            EXITM <0>               ;; False
        ENDIF
    ENDM

This macro works like the defined operator in the C language. You can use it
to test the defined state of several different symbols with a single
statement, as shown below:

    IF DEFINED( DOS ) AND NOT DEFINED( XENIX )
        ;; Do something
    ENDIF

Notice that the macro returns integer values as strings of digits, but the
IF statement evaluates numeric values or expressions. There is no conflict
because the value returned by the macro function is seen in the statement
exactly as if the user had typed the values directly into the program:

    IF -1 AND NOT 0


Returning Values with EXITM

The return value must be text, a text equate name, or the result of another
macro function. If a function must return a numeric value (such as a
constant, a numeric equate, or the result of a numeric expression), it must
first convert the value to text using angle brackets or the expansion
operator (%). The defined macro, for example, could have returned its value
as

    EXITM   %-1

Although macro functions can include any legal statement, they seldom need
to include instructions. This is because a macro function is expanded and
its value returned at assembly time, while instructions are executed at run
time.

Here is another example of a macro function. It uses the WHILE directive to
calculate factorials:

    factorial   MACRO   num:REQ
        LOCAL   i, factor
        factor  =   num
        i       =   1
        WHILE   factor GT 1
            i       =   i * factor
            factor  =   factor - 1
        ENDM
        EXITM   %i
    ENDM

The integer result of the calculation is changed to a text string with the
expansion operator (%). The  factorial  macro can be used to define data, as
shown below:

    var     WORD    factorial( 4 )

The effect of this statement is to initialize  var  with the number 24 (the
factorial of 4).


Using Macro Functions with Variable-Length Parameter Lists

Macro functions can enhance FOR loops.

You can use the FOR directive to handle macro parameters with the VARARG
attribute. Section 9.4.3 explains how to do this in simple cases where the
variable parameters are handled sequentially, from first to last. However,
you may sometimes need to process the parameters in reverse order or
nonsequentially. Macro functions make these techniques possible.

You may need to know the number of arguments in a VARARG parameter. The
following macro functions handle this.

    @ArgCount MACRO arglist:VARARG
        LOCAL count
        count = 0
        FOR arg, <arglist>
            count = count + 1       ;; Count the arguments
        ENDM
        EXITM %count
    ENDM

You could use this inside a macro that has a VARARG parameter, as shown
below:

    work    MACRO args:VARARG
    %   ECHO Number of arguments is: @ArgCount( args )
    ENDM

Another useful task might be to select an item from an argument list using
an index to indicate which item. The following macro simplifies this.

    @ArgI MACRO index:REQ, arglist:VARARG
        LOCAL count, retstr
        retstr TEXTEQU <>            ;; Initialize count
        count  = 0                   ;; Initialize return string
        FOR arg, <arglist>
            count = count + 1
            IF count EQ index        ;; Item is found
                retstr TEXTEQU <arg> ;; Set return string
                EXITM                ;;  and exit IF
            ENDIF
        ENDM
        EXITM retstr                 ;; Exit function
    ENDM

This function can be used as shown below:

    work    MACRO args:VARARG
    %   ECHO Third argument is: @ArgI( 3, args )
    ENDM

Finally, you might need to process arguments in reverse order. The following
macro returns a new argument list in reverse order.

    @ArgRev MACRO arglist:REQ
        LOCAL txt, arg
        txt TEXTEQU <>
    %   FOR arg, <arglist>
            txt CATSTR <arg>, <,>, txt      ;; Paste each onto list
        ENDM
                                            ;; Remove terminating comma
        txt SUBSTR  txt, 1, @SizeStr( %txt ) - 1
        txt CATSTR  <!<>, txt, <!>>         ;; Add angle brackets
        EXITM txt
    ENDM

You could call this function as shown below:

    work    MACRO   args:VARARG
    %   FOR  arg, @ArgRev( <args> )   ;; Process in reverse order
            ECHO    arg
        ENDM
    ENDM

These three macro functions are provided on the MASM distribution disk in
the MACROS.INC include file.


Macro Operators and Macro Functions

This list summarizes the behavior of the expansion operator with macro
functions.


    ■   If a macro function is not preceded by a %, it will be expanded.
        However, if it expands to a text macro or a macro function call, the
        result will not be expanded further.

    ■   If you use a macro function call as an argument for another macro
        function call, a % is not needed.

    ■   If a macro function expands to a text macro (or another macro
        function), the macro function will be recursively expanded.

    ■   If a macro function is called inside angle brackets and is preceded by
        %, it will be expanded.



9.7  Advanced Macro Techniques

The concept of replacing macro names with predefined macro text is simple in
theory, but it has many implications and complications. Here is a brief
summary of some advanced techniques you can use in macros.


9.7.1  Nesting Macro Definitions

Macros can define other macros or can be redefined. MASM does not process
nested definitions until the outer macro has been called. Therefore, the
inner macros cannot be called until the outer macro has been called. The
nesting of macro definitions is limited only by memory.

    shifts  MACRO   opname                  ;; Macro generates macros
        opname&s    MACRO operand:REQ, rotates:=<1>
            IF rotates LE 2                 ;; One at a time is faster
                REPEAT rotate               ;;  for 2 or less
                    opname  operand, 1
                ENDM
            ELSE                            ;; Using CL is faster for
                mov     cl, rotates         ;;  more than 2
                opname  operand, cl
            ENDIF
        ENDM
    ENDM

    ; Call macro to make new macros
            shifts  ror                     ; Generates rors
            shifts  rol                     ; Generates rols
            shifts  shr                     ; Generates shrs
            shifts  shl                     ; Generates shls
            shifts  rcl                     ; Generates rcls
            shifts  rcr                     ; Generates rcrs
            shifts  sal                     ; Generates sals
            shifts  sar                     ; Generates sars

This macro generates enhanced versions of the shift and rotate instructions.
The macros could be called like this:

    shrs    ax, 5
            rols    bx, 3

The macro versions handle multiple shifts by generating different code,
depending on how many shifts are specified. The example above is optimized
for the 8088 and 8086 processors. If you want to enhance for other
processors, you can simply change the outer macro; it automatically changes
all the inner macros. Code that uses the inner macros benefits from the
enhancements but does not change so long as the macro interface doesn't
change.


9.7.2  Testing for Argument Type and Environment

Macros can check the type of arguments and generate different code depending
on what they find. For example, you can use the OPATTR operator to determine
if an argument is a constant, a register, or a memory operand.

If you discover a constant value, you can often optimize the code. In some
cases, you can generate better code for 0 or 1 than for other constants. If
the argument is a memory operand, you know nothing about the value of the
operand, since it may change at run time. However, you may want to generate
different code depending on the operand size and on whether it is a pointer.
Similarly, if the operand is a register, you know nothing of its contents,
but you may be able to optimize if you can identify a particular register
with the IFDIFI or IFIDNI directives.

The following example illustrates some of these techniques. It loads a
specified address into a specified offset register. The segment register is
assumed to be DS.

    load    MACRO reg:REQ, adr:REQ
        IF (OPATTR (adr)) AND 00010000y    ;; Register
            IFDIFI reg, adr                ;; Don't load register
                mov     reg, adr           ;;  onto itself
            ENDIF
        ELSEIF (OPATTR (adr)) AND 00000100y
            mov     reg, adr               ;; Constant
        ELSEIF (TYPE (adr) EQ BYTE) OR (TYPE (adr) EQ SBYTE)
            mov    reg, OFFSET adr         ;; Bytes
        ELSEIF (SIZE (TYPE (adr)) EQ 2
            mov    reg, adr                ;; Near pointer
        ELSEIF (SIZE (TYPE (adr)) EQ 4
            mov    reg, WORD PTR adr[0]    ;; Far pointer
            mov    ds,  WORD PTR adr[2]
        ELSE
            .ERR <Illegal argument>
        ENDIF
    ENDM

A macro may also generate different code depending on the assembly
environment. The predefined text macro @Cpu can be used to test for
processor type. The following example uses the more efficient constant
variation of the PUSH instruction if the processor is an 80186 or higher.

    IF  @Cpu AND 00000010y
        pushc  MACRO op             ;; 80186 or higher
            push op
        ENDM
    ELSE
        pushc  MACRO op             ;; 8088/8086
            mov  ax, op
            push ax
        ENDM
    ENDIF

Note that the example generates a completely different macro for the two
cases. This is more efficient than testing the processor inside the macro
and conditionally generating different code. With this macro, the
environment is checked only once; if the conditional were inside the macro
it would be checked every time the macro is called.

You can test the language and operating system using the @Interface text
macro. The memory model can be tested with the @Model, @DataSize, or
@CodeSize text macros.

You can save the contexts inside macros with PUSHCONTEXT and POPCONTEXT. The
options for these keywords are:

Option            Description
────────────────────────────────────────────────────────────────────────────
RADIX             Saves segment register information
LIST              Saves listing and CREF information
CPU               Saves current CPU and processor
ALL               All of the above


9.7.3  Using Recursive Macros

Macros can call themselves. In previous versions of MASM, recursion is an
important technique for handling variable arguments. With MASM 6.0, you can
do this much more cleanly using the FOR directive and the VARARG attribute,
as described in Section 9.4.3. However, recursion is still available and may
be useful for some macros.


9.8  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help. From the "MASM 6.0 Contents"
screen:

╓┌─────────────────────────────────────┌─────────────────────────────────────╖
Topics                                Access
────────────────────────────────────────────────────────────────────────────
INCLUDE                               Choose "Directives," and then "Scope
                                        and
                                        Visibility"

GOTO, PURGE                           Choose "Directives," and then
Topics                                Access
────────────────────────────────────────────────────────────────────────────
GOTO, PURGE                           Choose "Directives," and then
                                        "Macros and Iterative Blocks"

.LISTMACRO                            Choose "Directives," and then
                                        "Listing
                                        Control"

IFB, IFNB, IFDIFI,                    Choose "Directives," and then
and IFIDNI                            "Conditional Assembly"

ECHO                                  Choose "Directives," and then
                                        "Miscellaneous"

OPATTR                                Choose "Operators," and then
                                        "Miscellaneous"

@Cpu, @Interface, @DataSize,          Choose "Predefined Symbols"
@Environ, and @CodeSize

Topics                                Access
────────────────────────────────────────────────────────────────────────────

PUSHCONTEXT,                          Choose "Directives" and then
POPCONTEXT                            "Iterative Blocks"








Chapter 10  Managing Projects with NMAKE
────────────────────────────────────────────────────────────────────────────

The Microsoft Program Maintenance Utility (NMAKE) is a sophisticated command
processor that saves time and simplifies project management. Once you
specify which project files depend on others, NMAKE automatically executes
the commands needed to update your project when any project file has
changed.

The advantage of using NMAKE instead of simple batch files is that NMAKE
recompiles only those files that need recompiling. NMAKE doesn't waste time
with files that haven't changed since the last build. NMAKE also has
advanced features (such as macros) that simplify managing complex projects.


This chapter includes examples that show how each feature of NMAKE works. In
addition, Section 10.9, "A Sample NMAKE Description File," shows how many of
these features work together.

If you are using the Microsoft Programmer's WorkBench (PWB) to build your
project, PWB automatically creates a description file (called a "makefile"
in the PWB documentation) and calls NMAKE to run the file. You may want to
read this chapter if you intend to build your program outside of PWB or if
you want to understand or modify a description file created by PWB.

A utility called NMK allows you to use NMAKE to manage your project under
DOS (or in a DOS session under OS/2). Section 10.11, "Using NMK," explains
when and how to use NMK.

If you are familiar with MAKE, the predecessor to NMAKE, be sure to read
Section 10.10, "Differences between NMAKE and MAKE." These utilities differ
in several important respects.


10.1  Overview of NMAKE

NMAKE works by looking at the last times and dates of modification for a
"target" file and its "dependents" and then comparing them. A target is
usually a file you want to create, such as an executable file. A dependent
is usually a file from which a target is created, such as a source file. A
target is "out-of-date" if any of its dependents has changed more recently
than the target.

────────────────────────────────────────────────────────────────────────────
WARNING

For NMAKE to work properly, the date and time setting on your system must be
consistent relative to previous settings. If you set the date and time each
time you start the system, be careful to set it accurately. If your system
stores a setting, be certain that the battery is working.
────────────────────────────────────────────────────────────────────────────

When you run NMAKE, it reads a "description file" that you supply. The
description file consists of one or more description blocks. Each
description block typically lists a target, the target's dependents, and the
commands that build the target. NMAKE compares the last time the targets
changed to the last time the dependents changed. If the modification time of
any dependents is the same or later than the time of the target, NMAKE
updates the target by executing the command or commands listed in the
description block.

NMAKE's main purpose is to help you update applications quickly and simply.
However, it can execute any DOS or OS/2 command, so it is not limited to
compiling and linking. NMAKE can also make backups, move files, and perform
other project-management tasks that you ordinarily do at the
operating-system prompt.


10.2  Running NMAKE

You invoke NMAKE with the following syntax:

    NMAKE [[options]] [[macros]]
    [[targets]]

The options field lists NMAKE options, which are described in Section 10.4,
"Command-Line Options."

The macros field lists macro definitions, which allow you to change text in
the description file. The syntax for macros is described in "User-Defined
Macros" in Section 10.3.4.1, "Macros."

The targets field lists targets to build. NMAKE rebuilds only the targets
listed on the command line. If you don't specify any targets, NMAKE builds
only the first target in the description file. (This behavior departs
significantly from that of MAKE. See Section 10.10, "Differences between
NMAKE and MAKE.")

NMAKE follows the instructions you specify in a description file.

NMAKE searches the current directory for the name of a description file you
specify with the /F option. It halts and displays an error message if the
file does not exist. If you do not use the /F option to specify a
description file, NMAKE searches the current directory for a description
file named MAKEFILE. If MAKEFILE does not exist, NMAKE checks the command
line for target files and tries to build them using predefined inference
rules (either default or defined in TOOLS.INI). This feature lets you use
NMAKE without a description file (as long as NMAKE has a predefined
inference rule for the target). If the command line does not specify any
target files, NMAKE halts and displays an error message.


Example

    NMAKE /S "program=sample" sort.exe search.exe

This command supplies four arguments: an option (/S), a macro definition
("program=sample"), and two target specifications (sort.exe  and
search.exe).

The command does not specify a description file, so NMAKE looks for the
default description file, MAKEFILE. The /S option tells NMAKE not to display
the commands as they are executed. (See Section 10.4, "Command-Line
Options.") The macro definition performs a text substitution throughout the
description file, replacing every instance of  program  with  sample. The
target specifications tell NMAKE to update the targets SORT.EXE and
SEARCH.EXE.


10.3  NMAKE Description Files

The most important parts of a description file are the description blocks,
which tell NMAKE how to build your project's target files. A description
file can also contain comments, macros, inference rules, and directives.
This section describes the elements of description files.


10.3.1  Description Blocks

Description blocks form the heart of the description file. Figure 10.1
illustrates a typical NMAKE description block, including the three sections:
targets, dependents, and commands.

(This figure may be found in the printed book.)


10.3.1.1  Targets

The target is the file that you want to build.

The targets section of the dependency line lists one or more files to build.
The line that lists targets and dependents is called the "dependency line."


The example in Figure 10.1 tells NMAKE how to build a single target,
MYAPP.EXE, if it is missing or out-of-date. Although single targets are
common, you can also list multiple targets in a single dependency line; you
must separate each target name with a space. If the name of the last target
before the colon (:) is one character long, put a space between the name and
the colon, so NMAKE won't interpret the character as a drive specification.


A target can appear in only one dependency line when specified as shown
above. To update a target using more than one description block, specify two
consecutive colons (::) between targets and dependents. For details, see
Section 10.3.1.8, "Specifying a Target in Multiple Description Blocks."

The target is usually a file, but it can also be a "pseudotarget," a name
that lets you build groups of files or execute a group of commands. For more
information, see Section 10.3.2, "Pseudotargets."


10.3.1.2  Dependents

A dependent is a file used to build a target.

The dependents section of the description block lists one or more files from
which the target is built. A colon (:) separates it from the targets
section. The example in Figure 10.1 lists three dependents after MYAPP.EXE:


    myapp.exe : myapp.obj another.obj myapp.def

You can also specify the directories in which NMAKE should search for a
dependent. Enclose one or more directory names in braces ( { } ). Separate
multiple directories with a semicolon ( ; ). The syntax for a directory
specification is

    {directory[[;directory...]]}dependent


Example

The following dependency line tells NMAKE to search the current directory
first, then the specified directories:

    forward.exe : {srcalpha;d:proj}pass.obj

In the line above, the target, FORWARD.EXE, has one dependent, PASS.OBJ. The
directory list specifies two directories:

    {srcalpha;d:proj}

NMAKE first searches for PASS.OBJ in the current directory. If PASS.OBJ
isn't there, NMAKE searches the  SRC  ALPHA directory, then the D: PROJ
directory. If NMAKE cannot find a dependent in the current directory or a
listed directory, it looks for a description block with a dependency line
containing PASS.OBJ as a target, and uses the commands in that description
block to create PASS.OBJ. If NMAKE cannot find such a description block, it
looks for an inference rule that describes how to create the dependent. (See
Section 10.3.5, "Inference Rules.")


10.3.1.3  Dependency Line

The dependency line in Figure 10.1 tells NMAKE to rebuild the target
MYAPP.EXE whenever MYAPP.OBJ, ANOTHER.OBJ, or MYAPP.DEF has changed more
recently than MYAPP.EXE.

The object files in the dependency list above would never be newer than the
executable file (unless you had recompiled the source code before running
NMAKE). So NMAKE checks to see if the object files themselves are targets in
other dependency lists, and if any dependents in those lists are targets
elsewhere, and so on.

NMAKE continues moving through all dependencies this way to build a
"dependency tree" that specifies all the steps required to fully update the
target. If NMAKE then finds any dependents in the tree that are newer than
the target, NMAKE updates the appropriate files and rebuilds the target.


10.3.1.4  Commands

The commands section can contain one or more commands.

The commands section of the description block lists the commands that NMAKE
should use to build the target. You can use any command that can be executed
from the command line. The example in Figure 10.1 tells NMAKE to build
MYAPP.EXE using the following LINK command:

        link myapp another.obj, , NUL, os2, myapp

Notice that the line is indented. NMAKE uses indentation to distinguish
between a dependency line and a command line. A command line must be
indented at least one space or tab. The dependency line must not be indented
(it cannot start with a space or tab).

Many targets are built with a single command, but you can place more than
one command after the dependency line, each on a separate line, as shown in
Figure 10.1.

A long command can span several lines if each line ends with a backslash ( 
). A backslash at the end of a line is equivalent to a space on the command
line. For example, the command

    echo abcd
    efgh

is equivalent to the command

    echo abcd efgh

You can also place a command at the end of a dependency line. Use a
semicolon (;) to separate the command from the rightmost dependent, as in

    project.exe : project.obj ; link project;

OS/2 allows multiple commands on one command line.

OS/2 allows you to combine two or more commands on a single command line
with an ampersand (&). For example, the following command line is legal in
an OS/2 description file:

    DIR & COPY sample.exe backup.exe

A slight restriction is imposed on the use of the CD, CHDIR, and SET
commands in OS/2 description files. NMAKE executes these commands itself
rather than passing them to OS/2. Therefore, if any of these commands is the
first command on a line, the remaining commands are not executed because
they aren't passed to OS/2.

The following multiple-command line does not display the directory listing
because DIR is preceded by a CD command:

        CD mydir & DIR

To use CD, CHDIR, or SET in a description block, place these commands on
separate lines:

    CD mydir
        DIR

NMAKE interprets a percent symbol (%) within a command line as the start of
a file specifier. To use a literal percent symbol in a command line, specify
it as a double percent symbol (%%). (See Section 10.3.8, "Extracting
Filename Components.")


10.3.1.5  Wild Cards

You can use DOS and OS/2 wild-card characters (* and ?) to specify target
and dependent filenames. NMAKE expands the wild cards when analyzing
dependencies and when building targets. For example, the following
description block links all files having the .OBJ extension in the current
directory:

    project.exe : *.obj
        LINK $*.obj;


10.3.1.6  Command Modifiers

Command modifiers are special prefixes attached to the command. They provide
extra control over the commands in a description block. You can use more
than one modifier for a single command. Table 10.1 describes the three NMAKE
command modifiers.

Table 10.1  Command Modifiers

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Character                         Action
────────────────────────────────────────────────────────────────────────────
@                            Prevents NMAKE from displaying the
                                    command as it executes. In the example
                                    below, the at sign (@) suppresses
                                    display of the ECHO command line:

                                    sort.exe : sort.obj
                                        @ECHO Now sorting.

                                    The output of the ECHO command is not
                                    suppressed.

Character                         Action
────────────────────────────────────────────────────────────────────────────

-«number»                         Turns off error checking for the command.
                                    Spaces and tabs can appear before the
                                    command. If the dash is followed by a
                                    number, NMAKE checks the exit code
                                    returned by the command and stops if the
                                    code is greater than the number. No
                                    space or tab can appear between the dash
                                    and number. (See Section 10.12, "Using
                                    Exit Codes with NMAKE.")

                                    In the following example, if the program
                                    sample  returns an exit code, NMAKE
                                    does not stop but continues to execute
                                    commands; if sort  returns an exit code
                                    greater than 5, NMAKE stops:

                                    light.lst : light.txt
                                    -sample light.txt
Character                         Action
────────────────────────────────────────────────────────────────────────────
                                    -sample light.txt
                                        -5 sort light.txt

!                                 Executes the command for each dependent
                                    file if the command preceded by the
                                    exclamation point uses the predefined
                                    macros $** or $?. (See Section 10.3.4,
                                    "Macros.") The $** macro refers to all
                                    dependent files in the description block.
                                    The $? macro refers to all dependent
                                    files in the description block that have
                                    a more recent modification time than the
                                    target. For example,

                                    print : one.txt two.txt three.txt
                                        !print $** lpt1:

                                    generates the following commands:

Character                         Action
────────────────────────────────────────────────────────────────────────────

                                    print one.txt lpt1:
                                    print two.txt lpt1:
                                    print three.txt lpt1:

────────────────────────────────────────────────────────────────────────────




10.3.1.7  Using Special Characters as Literals

You may need to specify as a literal character one of the characters that
NMAKE uses for a special purpose. These characters are

: ; # ( ) $ ^  { } ! @  ─

To use one of these characters literally, place a caret (^) in front of it.
For example, suppose you define a macro that ends with a backslash:

    exepath=c:bin

The line above is intended to define a macro named  exepath  with the value
c:bin. But the second backslash has an unintended side effect. Since the
backslash is NMAKE's line-continuation character, the line actually defines
exepath  as  c:bin, followed by whatever appears on the next line of the
description file. You can avoid this problem by placing a caret in front of
the second backslash:

    exepath=c:bin^

You can also use a caret to insert a literal newline character in a string
or macro:

    XYZ=abc^
    def

The caret tells NMAKE to interpret the newline character as part of the
macro, not a line break. Note that this effect differs from using a
backslash (  ) to continue a line. A newline character that follows a
backslash is replaced with a space.

NMAKE ignores carets that precede characters other than the special
characters listed above. The line

    ign^ore : these ca^rets

is interpreted as

    ignore : these carets

A caret within a quoted string is treated as a literal caret character.


10.3.1.8  Specifying a Target in Multiple Description Blocks

You can specify a target in more than one description block by placing two
colons (::) after the target. This feature is useful for building a complex
target, such as a library, that contains components created with different
commands. For example,

    target.lib :: a.asm b.asm c.asm
        ML a.asm b.asm c.asm
        LIB target -+a.obj -+b.obj -+c.obj;
    target.lib :: d.c e.c
        CL /c d.c e.c
        LIB target -+d.obj -+e.obj;

Both description blocks update the library named TARGET.LIB. If any of the
assembly-language files have changed more recently than the library, NMAKE
executes the commands in the first block to assemble the source files and
update the library. Similarly, if any of the C-language files have changed,
NMAKE executes the second group of commands to compile the C files and
update the library.

If you use a single colon in the example above, NMAKE issues an error
message. It is legal, however, to use single colons if the target appears in
only one block. In this case, dependency lines are cumulative. For example,


    target : jump.bas
    target : up.c
        echo Building target...

is equivalent to

    target : jump.bas up.c
        echo Building target...

No commands can appear between cumulative dependency lines, but blank lines,
comment lines, macro definitions, and directives can appear.


10.3.2  Pseudotargets

A "pseudotarget" is similar to a target, but it is not a file. It is a name
used as a label for executing a group of commands. In the following example,
    UPDATE  is a pseudotarget.

    UPDATE : *.*
        !COPY $** a:product

NMAKE always considers the pseudotarget to be out-of-date. In the previous
example, NMAKE copies all the dependent files to the specified drive and
directory.

Like target names, pseudotarget names are not case sensitive.


10.3.3  Comments

You can place comments in a description file by preceding them with a number
sign (#):

    # Comment on line by itself
    OPTIONS = /MAP  # Comment on macro's line
    all.exe : one.obj two.obj  # Comment on dependency line
        link $(OPTIONS) one.obj two.obj;

A comment extends to the end of the line in which it appears. Command lines
(and dependency lines containing commands) cannot contain comments.

To specify a literal #, precede it with a caret (^ ), as in the following:

    DEF=^#define #Macro representing a C preprocessing directive


10.3.4  Macros

Macros offer a convenient way to replace a particular string in the
description file with another string. Macros are useful for a variety of
tasks, including the following:


    ■   Creating a single description file that works for several projects.
        You can define a macro that replaces a dummy filename in the
        description file with the specific filename for a particular project.

    ■   Controlling the options NMAKE passes to the compiler or linker. When
        you specify options in a macro, you can change options throughout the
        description file in a single step.


You can define your own macros or use predefined macros. This section
describes user-defined macros first.


10.3.4.1  User-Defined Macros

You can define a macro with this syntax:

    macroname=string

The macroname can be any combination of letters, digits, and the underscore
( _ ) character. Macro names are case sensitive. NMAKE interprets  MyMacro
and  MYMACRO  as different macro names.

The string can be any sequence of zero or more characters. (A string of zero
characters is called a "null string." A string consisting only of spaces,
tabs, or both is also considered a null string.) For example,

    linkcmd=LINK /map

defines a macro named  linkcmd  and assigns it the string  LINK /map.

You can define macros in the description file, on the command line, in a
command file (see Section 10.5, "NMAKE Command File"), or in TOOLS.INI (see
Section 10.6, "The TOOLS.INI File"). Each macro defined in the description
file must appear on a separate line. The line cannot start with a space or
tab.

When you define a macro in the description file, NMAKE ignores spaces on
either side of the equal sign. The string itself can contain embedded
spaces. You do not need to enclose string in quotation marks (if you do,
they become part of the string).

Slightly different rules apply when you define a macro on the command line
or in a command file. The command-line parser treats spaces as argument
delimiters. Therefore, the string itself, or the entire macro, must be
enclosed in double quotation marks if it contains embedded spaces. All three
forms of the following command-line macro are legal and equivalent:

    NMAKE program=sample
    NMAKE "program=sample"
    NMAKE "program = sample"

The macro  program  is passed to NMAKE, with an assigned value of  sample.

If the string contains spaces, either the string or the entire macro must
appear within quotes. Either form of the following command-line macro is
allowed:

    NMAKE linkcmd="LINK /map"
    NMAKE "linkcmd=LINK /map"

However, the following form of the same macro is not allowed. It contains
spaces that are not enclosed by quotation marks:

    NMAKE linkcmd = "LINK /map"

A macro name can be given a null value. Both of the following definitions
assign a null value to the macro  linkoptions:

    NMAKE linkoptions=
    NMAKE linkoptions="    "

A macro name can be "undefined" with the !UNDEF preprocessing directive (see
Section 10.3.7, "Preprocessing Directives"). Assigning a null value to a
macro name does not undefine it; the name is still defined, but with a null
value.

A macro can be followed by a comment, using the syntax described in the
preceding section on comments.


10.3.4.2  Using Macros

Use a macro by enclosing its name in parentheses preceded by a dollar sign
($). For example, you can use the  linkcmd  macro defined above by
specifying

    $(linkcmd)

NMAKE replaces every occurrence of  $(linkcmd)  with  LINK /map.

The following description file defines and uses three macros:

    program=sample
    L=LINK
    options=

    $(program).exe : $(program).obj
        $(L)  $(options)  $(program).obj;

NMAKE interprets the description block as

    sample.exe : sample.obj
        LINK sample.obj;

NMAKE replaces every occurrence of  $(program)  with  sample, every instance
of  $(L)  with  LINK, and every instance of  $(options)  with a null string.


An undefined macro is replaced by a null string.

If you use as a macro a name that has never been defined, or was undefined,
NMAKE treats that name as a null string. No error occurs.

To use the dollar sign ($) as a literal character, specify two dollar signs
($$).

The parentheses are optional if macroname is a single character. For
example,  $L  is equivalent to  $(L). However, parentheses are recommended
for consistency.


10.3.4.3  Special Macros

NMAKE provides several special macros to represent various filenames and
commands. One use for these macros is in predefined inference rules. (See
Section 10.3.5.4.) Like user-defined macro names, special macro names are
case sensitive. For example, NMAKE interprets  CC  and  cc  as different
macro names.

Tables 10.2 through 10.5 summarize the four categories of special macros.
The filename macros offer a convenient representation of filenames from a
dependency line; these are listed in Table 10.2. The recursion macros,
listed in Table 10.3, allow you to call NMAKE from within your description
file. Tables 10.4 and 10.5 describe the command macros and options macros
that make it convenient for you to invoke the Microsoft language compilers.


The filename macros conveniently represent filenames from the dependency
line.

Table 10.2 lists macros that are predefined to represent file names. As with
all one-character macros, these do not need to be enclosed in parentheses.
(The $$@ and $** macros are exceptions to the parentheses rule for macros;
they do not require parentheses even though they contain two characters.)
Note that the macros in Table 10.2 represent filenames as you have specified
them in the dependency line, and not the full specification of the filename.


Table 10.2  Filename Macros

╓┌────────────────┌──────────────────────────────────────────────────────────╖
Macro
Reference        Meaning
────────────────────────────────────────────────────────────────────────────
$@          The current target's full name, as currently specified.
                    This is not necessarily the full path name.

Macro
Reference        Meaning
────────────────────────────────────────────────────────────────────────────

$*               The current target's full name minus the file extension.

$**              The dependents of the current target.

$?               The dependents that have a more recent modification time
                    than the current target.

$$@         The target that NMAKE is currently evaluating. You can
                    use this macro only to specify a dependent.

$<               The dependent file that has a more recent modification
                    time than the current target (evaluated only for
                    inference rules).

────────────────────────────────────────────────────────────────────────────



The example below uses the $? macro, which represents all dependents that
are more recent than the target. The ! command modifier causes NMAKE to
execute a command once for each dependent in the list (see Table 10.1). As a
result, the LIB command is executed up to three times, each time replacing a
module with a newer version.

    trig.lib : sin.obj cos.obj arctan.obj
        !LIB trig.lib -+$?;

In the next example, NMAKE updates files in another directory by replacing
them with files of the same name from the current directory. The $@ macro is
used to represent the current target's full name:

    #Files in objects directory depend on versions in current directory
    DIR=c:objects
    $(DIR)globals.obj : globals.obj
        COPY globals.obj $@
    $(DIR)types.obj : types.obj
        COPY types.obj $@
    $(DIR)macros.obj : macros.obj
        COPY macros.obj $@

Macro modifiers specify parts of the predefined filename macros.

You can append one of the modifiers in the following list to any of the
filename macros to extract part of a filename. If you add one of these
modifiers to the macro, you must enclose the macro name and the modifier in
parentheses.

Modifier                          Resulting Filename Part
────────────────────────────────────────────────────────────────────────────
D                                 Drive plus directory

B                                 Base name

F                                 Base name plus extension

R                                 Drive plus directory plus base name

For example, assume that $@ has the value C:SOURCEPROGSORT.OBJ. The
following list shows the effect of combining each modifier with $@:

Macro Reference                   Value
────────────────────────────────────────────────────────────────────────────
$(@D)                             C:SOURCEPROG

$(@F)                             SORT.OBJ

$(@B)                             SORT

$(@R)                             C:SOURCEPROGSORT

If $@ has the value SORT.OBJ without a preceding directory, the value of
$(@R) is just SORT, and the value of $(@D) is a dot (.) to represent the
current directory.

Recursion macros let you use NMAKE to call NMAKE.

Table 10.3 lists three macros that you can use when you want to call NMAKE
recursively from within a description file.

Table 10.3  Recursion Macros

Macro
Reference        Meaning
────────────────────────────────────────────────────────────────────────────
$(MAKE)          The name used to call NMAKE recursively. The line on
                    which it appears is executed even if the /N command-line
                    option is specified.

$(MAKEDIR)       The directory from which NMAKE is called.

$(MAKEFLAGS)     The NMAKE options currently in effect. This macro is
                    passed automatically when you call NMAKE recursively. You
                    cannot redefine this macro. Use the preprocessing
                    directive !CMDSWITCHES to update the MAKEFLAGS macro.
                    (See Section 10.3.7, "Preprocessing Directives.")

────────────────────────────────────────────────────────────────────────────


To call NMAKE recursively, use the command

    $(MAKE) /$(MAKEFLAGS)

The MAKE macro is useful for building different versions of a program. The
following description file calls NMAKE recursively to build targets in the
VERS1 and VERS2 directories.

    all : vers1 vers2

    vers1 :
        cd vers1
        $(MAKE)
        cd ..

    vers2 :
        cd vers2
        $(MAKE)
        cd ..

The example changes to the VERS1 directory and then calls NMAKE
recursively, causing NMAKE to process the file MAKEFILE in that directory.
Then it changes to the VERS2 directory and calls NMAKE again, processing
the file MAKEFILE in that directory.

You can add options to the ones already in effect for NMAKE by following the
MAKE macro with the options in the same syntax as you would specify them on
the command line. You can also pass the name of a description file with the
/F option instead of using a file named MAKEFILE.

Deeply recursive build procedures can exhaust NMAKE's run-time stack,
causing an error. If this occurs, use the EXEHDR utility to increase NMAKE's
run-time stack. The following command, for example, gives NMAKE.EXE a stack
size of 16,384 (0x4000) bytes:

    exehdr /stack:0x4000 nmake.exe

Command macros are shortcut calls to Microsoft compilers.

NMAKE defines several macros to represent commands for Microsoft products.
(See Table 10.4.) You can use these macros as commands in a description
block, or invoke them using a predefined inference rule. (See Section
10.3.5, "Inference Rules.") You can redefine these macros to represent part
or all of a command line, including options.

Table 10.4  Command Macros

╓┌────────────────┌─────────────────────────────────────────┌────────────────►
Macro Reference  Command Action                            Predefined Value
─────────────────────────────────────────────────────────────────────────────
$(AS)            Invokes the Microsoft Macro               AS=ml
                    Assembler

$(BC)            Invokes the Microsoft Basic               BC=bc
                    Compiler

$(CC)            Invokes the Microsoft C Compiler          CC=cl

$(COBOL)         Invokes the Microsoft COBOL Compiler      COBOL=cobol

$(FOR)           Invokes the Microsoft FORTRAN             FOR=fl
                    Compiler

$(PASCAL)        Invokes the Microsoft Pascal              PASCAL=pl
                    Compiler
Macro Reference  Command Action                            Predefined Value
─────────────────────────────────────────────────────────────────────────────
                    Compiler

$(RC)            Invokes the Microsoft Resource Compiler   RC=rc

─────────────────────────────────────────────────────────────────────────────



Options macros pass preset options to Microsoft compilers.

The macros in Table 10.5 are used by NMAKE to represent options to be passed
to the commands for Microsoft languages. By default, these macros are
undefined. You can define them to mean the options you want to pass to the
commands. Whether or not they are defined, the macros are used automatically
in the predefined inference rules. If the macros are undefined, or if they
are defined to be null strings, a null string is generated in the command
line. (See Section 10.3.5.4, "Predefined Inference Rules.")

Table 10.5  Options Macros

╓┌─────────────────────────┌─────────────────────────────────────────────────╖
Macro Reference           Passed to
────────────────────────────────────────────────────────────────────────────
$(AFLAGS)                 Microsoft Macro Assembler
$(BFLAGS)                 Microsoft Basic Compiler
$(CFLAGS)                 Microsoft C Compiler
$(COBFLAGS)               Microsoft COBOL Compiler
$(FFLAGS)                 Microsoft FORTRAN Compiler
$(PFLAGS)                 Microsoft Pascal Compiler
$(RFLAGS)                 Microsoft Resource Compiler
────────────────────────────────────────────────────────────────────────────



10.3.4.4  Substitution within Macros

You can replace text in a macro as well as in the description file.

Just as macros allow you to substitute text in a description file, you can
also substitute text within a macro itself. The substitution is temporary;
it applies only to the current use of the macro and does not modify the
original macro definition. Use the following form:

    $(macroname:string1=string2)

Every occurrence of string1 is replaced by string2 in the macro macroname.
Do not put any spaces or tabs between macroname and the colon. Spaces
between the colon and string1 or between string1 and the equal sign are part
of string1. Spaces between the equal sign and string2 or between string2 and
the right parenthesis are part of string2. If string2 is a null string, all
occurrences of string1 are deleted from the macroname macro.

Macro substitution is case sensitive. This means that the case as well as
the characters in string1 must exactly match the target string in the macro,
or the substitution is not performed. It also means that the string2
substitution is exactly as specified.


Example 1

The following description file illustrates macro substitution:

    SOURCES = project.for one.for two.for

    project.exe : $(SOURCES:.for=.obj)
        LINK  $**;

    COPY : $(SOURCES)
        !COPY $** c:backup

The predefined macro $** stands for the names of all the dependent files
(see Table 10.2).

If you invoke the example file with a command line that specifies both
targets,

    NMAKE project.exe copy

NMAKE executes the following commands:

    LINK project.obj one.obj two.obj;
    COPY project.for c:backup
    COPY one.for c:backup
    COPY two.for c:backup

The macro substitution does not alter the  SOURCES  macro definition.
Rather, it replaces the listed characters. When NMAKE builds the target
PROJECT.EXE, it gets the definition for the predefined macro $** (the
dependent list) from the dependency line, which specifies the macro
substitution in  SOURCES.

The same is true for the second target,  COPY. In this case, however, no
macro substitution is requested, so  SOURCES  retains its original value,
and $** represents the names of the FORTRAN source files. (In the example
above, the target  COPY  is a pseudotarget; Section 10.3.2 describes
pseudotargets.)


Example 2

If the macro OBJS is defined as

    OBJS=ONE.OBJ TWO.OBJ THREE.OBJ

with exactly one space between each object name, you can replace each space
in the defined value of OBJS with a space, followed by a plus sign, followed
by a newline, by using

    $(OBJS: = +^
    )

The caret (^) tells NMAKE to treat the end of the line as a literal newline
character. This example is useful for creating response files.


10.3.4.5  Substitution within Predefined Macros

You can also substitute text in any predefined macro except $$@. The
principle is the same as for other macros. The command in the following
description block substitutes within a predefined macro. Note that even
though $@ is a singlecharacter macro, the substitution makes it a
multi-character macro invocation, so it must be enclosed in parentheses.

    target.abc : depend.xyz
        echo $(@:targ=blank)

If dependent  depend.xyz  has a later modification time than target
target.abc, then NMAKE executes the command

    echo blanket.abc

The example uses the predefined macro $@, which equals the full name of the
current target (target.abc). It substitutes  blank  for  targ  in the
target, resulting in  blanket.abc.


10.3.4.6  Inherited Macros

When NMAKE executes, it inherits macro definitions equivalent to every
environment variable. The inherited macro names are converted to uppercase.


Inherited macros can be used like other macros. You can also redefine them.
The following example redefines the inherited macro  PATH:

    PATH = c:toolsbin

    sample.exe : sample.obj
        LINK sample;

Inherited macros take their definitions from environment variables.

No matter what value the environment variable PATH had before, it has the
value  c:toolsbin  when NMAKE executes the LINK command in this
description block. Redefining the inherited macro does not affect the
original environment variable; when NMAKE terminates, PATH still has its
original value.

Inherited macros have one restriction: in a recursive call to NMAKE, the
only macros that are preserved are those defined on the command line or in
environment variables. Macros defined in the description file are not
inherited when NMAKE is called recursively. To pass a macro to a recursive
call:


    ■   Use the SET command before the recursive call to set the variable for
        the entire NMAKE session.

    ■   Define the macro on the command line for the recursive call.


The /E option causes macros inherited from environment variables to override
any macros with the same name in the description file.


10.3.4.7  Precedence among Macro Definitions

If you define the same macro name in more than one place, NMAKE uses the
macro with the highest precedence. The precedence from highest to lowest is
as follows:


    1.  A macro defined on the command line

    2.  A macro defined in a description file or include file

    3.  An inherited environment-variable macro

    4.  A macro defined in the TOOLS.INI file

    5.  A predefined macro such as CC and AS



10.3.5  Inference Rules

Inference rules are templates that define how a file with one extension is
created from a file with a different extension. When NMAKE encounters a
description block that has no commands, it searches for an inference rule
that matches the extensions of the target and dependent files. Similarly, if
a dependent file doesn't exist, NMAKE looks for an inference rule that shows
how to create the missing dependent from another file with the same base
name.

Inference rules tell NMAKE how to create files with a specific extension.

Inference rules provide a convenient shorthand for common operations. For
instance, you can use an inference rule to avoid repeating the same command
in several description blocks. You can define your own inference rules or
use predefined inference rules.

────────────────────────────────────────────────────────────────────────────
NOTE
An inference rule is useful only when a target and dependent have the same
base name, and have a one-to-one correspondence. For example, you cannot
define an inference rule that replaces several modules in a library, because
the modules would have different base names than the target library.
────────────────────────────────────────────────────────────────────────────

Inference rules can exist only for dependents with extensions that are
listed in the .SUFFIXES directive. (For information on the .SUFFIXES
directive, see Section 10.3.6, "Directives.") NMAKE searches in the current
or specified directory for a file whose base name matches the target and
whose extension is listed in the .SUFFIXES list. If it finds such a file, it
applies the inference rule that matches the extensions of the target and the
located file.

The .SUFFIXES list specifies an order of priority for NMAKE to use when
searching for files. If more than one file is found, and thus more than one
rule matches a dependency line, NMAKE searches the .SUFFIXES list and uses
the rule whose extension appears earlier in the list. For example, the
dependency line

    project.exe :

can be matched to several predefined inference rules and possibly one or
more user-defined rules, all of which describe a command for creating an
.EXE file. NMAKE uses the inference rule corresponding to the first matching
file it finds.


10.3.5.1  Inference Rule Syntax

An inference rule has the following syntax:

    .fromext.toext:
        commands

The first line lists two extensions: fromext extension represents the
filename extension of a dependent file, and toext represents the extension
of a target file. Extensions are not case sensitive.

The second line of the inference rule gives the command to create a target
file of toext from a dependent file of fromext. Use the same rules for
commands in inference rules as in description blocks. (See Section 10.3.1,
"Description Blocks.")


10.3.5.2  Inference Rule Search Paths

The inference-rule syntax described above tells NMAKE to look for the
specified files in the current directory. You can also specify directories
to be searched by NMAKE when it looks for files with the extensions fromext
and toext. An inference rule that specifies paths has the following syntax:


    {frompath}.fromext {topath}.toext:
        commands

NMAKE searches in the frompath directory for files with the fromext
extension. It uses commands to create files with the toext extension in the
topath directory, if the fromext file has a later modification time than the
toext file.

The paths in the inference rule must exactly match the paths explicitly
specified in the dependency line of a description block.

If you use a path on one element of the inference rule, you must use paths
on both. You can specify the current directory for either element by using
the operating system notation for the current directory, which is a dot (.),
or by specifying an empty pair of braces.

You can specify only one path for each element in an inference rule. To
specify more than one path, repeat the inference rule with the alternate
path.


10.3.5.3  User-Defined Inference Rules

You can define inference rules in the description file or in TOOLS.INI (see
Section 10.6, "The TOOLS.INI File"). An inference rule lists two file
extensions and one or more commands.


Example 1

The following inference rule tells NMAKE how to build a .OBJ file from a .C
file:

    .c.obj:
        CL /c $<

In this example, the predefined macro $< represents the name of a dependent
that has a more recent modification time than the target.

NMAKE applies this inference rule to the following description block:

    sample.obj :

The description block lists only a target, SAMPLE.OBJ. Both the dependent
and the command are missing. However, given the target's base name and
extension, plus the inference rule, NMAKE has enough information to build
the target.

NMAKE first looks for a file with the same base name as the target and with
one of the extensions in the .SUFFIXES list. If SAMPLE.C exists (and no
files with higher-priority extensions exist), NMAKE compares its time to
that of SAMPLE.OBJ. If SAMPLE.C has changed more recently, NMAKE compiles it
using the CL command listed in the inference rule:

    CL /c sample.c


Example 2

The following inference rule compares a .C file in the current directory
with the corresponding .OBJ file in another directory:

    {.}.c{c:objects}.obj:
        cl /c $<;

The path for the .C file is represented by a dot. A path for the dependent
extension is required because one is specified for the target extension.

This inference rule matches a dependency line containing the same
combination of paths, such as:

    c:objectstest.obj : test.c

This rule does not match a dependency line such as:

    test.obj : test.c

In this case, NMAKE uses the predefined inference rule .c.obj when building
the target.


10.3.5.4  Predefined Inference Rules

NMAKE provides predefined inference rules containing commands for creating
object, executable, and resource files. Table 10.6 describes the predefined
inference rules.

Table 10.6  Predefined Inference Rules

╓┌──────────┌─────────────────────────────────────┌──────────────────────────╖
Rule       Command                               Default Action
────────────────────────────────────────────────────────────────────────────
.asm.obj   $(AS) $(AFLAGS) /c $*.asm             ML /c $*.ASM
.asm.exe   $(AS) $(AFLAGS) $*.asm                ML $*.ASM
.bas.obj   $(BC) $(BFLAGS) $*.bas;               BC $*.BAS;
.c.obj     $(CC) $(CFLAGS) /c $*.c               CL /c $*.C
.c.exe     $(CC) $(CFLAGS) $*.c                  CL $*.C
.cbl.obj   $(COBOL) $(COBFLAGS) $*.cbl;          COBOL $*.CBL;
.cbl.exe   $(COBOL) $(COBFLAGS) $*.cbl, $*.exe;  COBOL $*.CBL, $*.EXE;
.for.obj   $(FOR) /c $(FFLAGS) $*.for            FL /c $*.FOR
.for.exe   $(FOR) $(FFLAGS) $*.for               FL $*.FOR
.pas.obj   $(PASCAL) /c $(PFLAGS) $*.pas         PL /c $*.PAS
.pas.exe   $(PASCAL) $(PFLAGS) $*.pas            PL $*.PAS
.rc.res    $(RC) $(RFLAGS) /r $*                 RC /r $*
────────────────────────────────────────────────────────────────────────────


For example, assume you have the following description file:

    sample.exe :

This description block lists a target without any dependents or commands.
NMAKE looks at the target's extension (.EXE) and searches for an inference
rule that describes how to create an .EXE file. Table 10.6 shows that more
than one inference rule exists for building an .EXE file. NMAKE looks for a
file in the current or specified directory that has the same base name as
the target  sample  and one of the extensions in the .SUFFIXES list. For
example, if a file called SAMPLE.FOR exists, NMAKE applies the  .for.exe
inference rule. If more than one file with the base name SAMPLE is found,
NMAKE applies the inference rule for the extension listed earliest in the
.SUFFIXES list. In this example, if both SAMPLE.C and SAMPLE.FOR exist,
NMAKE uses the  .c.exe inference rule to compile SAMPLE.C and links the
resulting file SAMPLE.OBJ to create SAMPLE.EXE.

────────────────────────────────────────────────────────────────────────────
NOTE

By default, the options macros such as CFLAGS shown in Table 10.5 are
undefined. As explained in Section 10.3.4.2, "Using Macros," this causes no
problem; NMAKE replaces an undefined macro with a null string. Because the
predefined options macros are included in the inference rules, you can
define these macros and have their assigned values passed automatically to
the predefined inference rules. The predefined inference rules are listed in
Table 10.6.
────────────────────────────────────────────────────────────────────────────


10.3.5.5  Precedence among Inference Rules

If the same inference rule is defined in more than one place, NMAKE uses the
rule with the highest precedence. The precedence from highest to lowest is


    1.  An inference rule defined in the description file. If more than one,
        the last one applies.

    2.  An inference rule defined in the TOOLS.INI file. If more than one, the
        last one applies.

    3.  A predefined inference rule.


User-defined inference rules always override predefined inference rules.
NMAKE uses a predefined inference rule only if no user-defined inference
rule exists for a given target and dependent.

If two inference rules could produce a target with the same extension, NMAKE
uses the inference rule whose dependent's extension appears first in the
.SUFFIXES list. See Table 10.7 in the next section, "Directives."


10.3.6  Directives

The directives in Table 10.7 provide additional control of NMAKE operations.
You can use them in a description file outside of a description block or in
the TOOLS.INI file. The four directives listed in the table are case
sensitive and must appear in all uppercase letters. (Preprocessing
directives are not case sensitive; see Section 10.3.7, "Preprocessing
Directives.")

Table 10.7  Directives

Directive                         Action
────────────────────────────────────────────────────────────────────────────
.IGNORE :                         Ignores exit codes returned by programs
                                    called from the description file. This
                                    directive has the same effect as
                                    invoking NMAKE with the /I option.

.PRECIOUS : target...             Tells NMAKE not to delete targets if the
                                    commands that build them quit or are
                                    interrupted. Overrides the NMAKE default,
                                    which is to delete the target if
                                    building was interrupted by CTRL+C or
                                    CTRL+BREAK.

.SILENT :                         Does not display lines as they are
                                    executed. This directive has the same
                                    effect as invoking NMAKE with the /S
                                    option.

.SUFFIXES : list                  Lists file suffixes for NMAKE to try
                                    when building a target file for which no
                                    dependents are specified. This list is
                                    used together with inference rules. See
                                    Section
                                    10.3.5, "Inference Rules."

────────────────────────────────────────────────────────────────────────────


The .IGNORE and .SILENT directives affect the file from their location
onward. Location within the file does not matter for the .PRECIOUS and
.SUFFIXES directives; they affect the entire description file.

NMAKE refers to the value of the .SUFFIXES directive when using inference
rules. When NMAKE finds a target without dependents, it searches the current
directory for a file with the same base name as the target and a suffix from
list. If NMAKE finds such a file, and if an inference rule applies to the
file, then NMAKE treats the file as a dependent of the target. The order of
the suffixes in the list defines the order in which NMAKE searches for the
file. The list is predefined as follows:

    .SUFFIXES : .exe .obj .asm .c .bas .cbl .for .pas .res .rc

To add additional suffixes to the end of the list, specify  .SUFFIXES :
followed by the additional suffixes. To clear the list, specify  .SUFFIXES :
    by itself. To change the list order or to specify an entirely new list,
clear the list and specify a new  .SUFFIXES :  setting.


10.3.7  Preprocessing Directives

NMAKE preprocessing directives are similar to compiler preprocessing
directives. You can use the !IF, !IFDEF, !IFNDEF, !ELSE, and !ENDIF
directives to conditionally process the description file. With other
preprocessing directives you can display error messages, include other
files, undefine a macro, and turn certain options on or off. NMAKE reads and
executes the preprocessing directives before processing the description file
as a whole.

Preprocessing directives (listed in Table 10.8) begin with an exclamation
point (!), which must appear at the beginning of the line. You can place
spaces between the exclamation point and the directive keyword. These
directives are not case sensitive.

Table 10.8  Preprocessing Directives

╓┌─────────────────────────┌─────────────────────────────────────────────────╖
Directive                 Description
────────────────────────────────────────────────────────────────────────────
!CMDSWITCHES              Turns on or off NMAKE options /D, /I, /N, and /S.
{+| -}opt...              (See Section 10.4, "Command-Line Options.") Do
                            not specify the slash ( / ). If !CMDSWITCHES is
                            specified with no options, all options are reset
                            to the values they had when NMAKE was started.
                            This directive updates the MAKEFLAGS macro. Turn
                            an option on by preceding it with a plus sign (+
                            ), or turn it off by preceding it with a minus
                            sign (-).

!ERROR text               Prints text, then stops execution.

!IF constantexpression    Reads the statements between the !IF keyword and
                            the next !ELSE or !ENDIF keyword if
                            constantexpression evaluates to a nonzero value.

Directive                 Description
────────────────────────────────────────────────────────────────────────────

!IFDEF macroname          Reads the statements between the !IFDEF keyword
                            and the next !ELSE or !ENDIF keyword if
                            macroname is defined. NMAKE considers a macro
                            with a null value to be defined.

!IFNDEF macroname         Reads the statements between the !IFNDEF keyword
                            and the next !ELSE or !ENDIF keyword if
                            macroname is not defined.

!ELSE                     Reads the statements between the !ELSE and
                            !ENDIF keywords if the preceding !IF, !IFDEF, or
                            !IFNDEF statement evaluated to zero. Anything
                            following !ELSE on the same line is ignored.

!ENDIF                    Marks the end of an !IF, !IFDEF, or !IFNDEF
                            block. Anything following !ENDIF on the same
                            line is ignored.

Directive                 Description
────────────────────────────────────────────────────────────────────────────


!INCLUDE filename         Reads and evaluates the description file
                            filename before continuing with the current
                            description file. If filename is enclosed by
                            angle brackets (< >), NMAKE searches for the
                            file first in the current directory and then in
                            the directories specified by the INCLUDE macro.
                            Otherwise, it looks only in the current
                            directory. The INCLUDE macro is initially set to
                            the value of the INCLUDE environment variable.

!UNDEF macroname          Marks macroname as undefined in NMAKE's symbol
                            table.

────────────────────────────────────────────────────────────────────────────




10.3.7.1  Expressions in Preprocessing

The constantexpression used with the !IF directive can consist of integer
constants, string constants, or program invocations. Integer constants can
use the unary operators for numerical negation (-), one's complement (~),
and logical negation (!). They can also use any binary operator listed in
Table 10.9.

Table 10.9  Preprocessing-Directive Binary Operators

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Operator                          Description
────────────────────────────────────────────────────────────────────────────
+                                 Addition

-                                 Subtraction

*                                 Multiplication

/                                 Division
Operator                          Description
────────────────────────────────────────────────────────────────────────────
/                                 Division

%                                 Modulus

&                                 Bitwise AND

|                                 Bitwise OR

^                                 Bitwise XOR

&&                                Logical AND

||                                Logical OR

<<                                Left shift

>>                                Right shift

==                                Equality
Operator                          Description
────────────────────────────────────────────────────────────────────────────
==                                Equality

!=                                Inequality

<                                 Less than

>                                 Greater than

<=                                Less than or equal to

>=                                Greater than or equal to

────────────────────────────────────────────────────────────────────────────



You can group expressions by enclosing them in parentheses. NMAKE treats
numbers as decimal unless they start with 0 (octal) or 0x (hexadecimal). Use
the equality (==) operator to compare two strings for equality, or the
inequality (!=) operator to compare for inequality. Enclose strings in
double quotation marks.


Example

The following example shows how preprocessing directives can be used to
control whether the linker inserts CodeView information into the .EXE file:


    !INCLUDE <infrules.txt>
    !CMDSWITCHES +D
    winner.exe : winner.obj
    !IFDEF debug
    !   IF "$(debug)"=="y"
            LINK /CO winner.obj;
    !  ELSE
            LINK winner.obj;
    !   ENDIF
    !ELSE
    !   ERROR Macro named debug is not defined.
    !ENDIF

In this example, the !INCLUDE directive inserts the INFRULES.TXT file into
the description file. The !CMDSWITCHES directive sets the /D option, which
displays the times of the files as they are checked. The !IFDEF directive
checks to see if the macro  debug  is defined. If it is defined, the !IF
directive checks to see if it is set to  y. If it is, NMAKE reads the LINK
command with the /CO option; otherwise, NMAKE reads the LINK command without
/CO. If the  debug  macro is not defined, the !ERROR directive prints the
specified message and NMAKE stops.


10.3.7.2  Executing a Program in Preprocessing

NMAKE can invoke programs and check their status.

You can invoke any program from within NMAKE by placing the program's name
or path name within square brackets ( [ ] ). The program is executed during
preprocessing, and its exit code replaces the program specification in the

description file. A nonzero exit code usually indicates an error. You can
use this value to control execution, as in the following example:

    !IF [c:utilcheckdsk] != 0
    !    ERROR Not enough disk space; NMAKE terminating.
    !ENDIF


10.3.8  Extracting Filename Components

"Special Macros," Section 10.3.4.3, showed how qualifiers could be added to
macros that represented filenames in order to select components of the name
or path. This feature is especially useful when creating a general-purpose
description block that works with the name of any dependent.

Besides these macro modifiers, NMAKE offers another feature that allows you
to extract components of the name of the first dependent file as you have
specified it in the description file or on the command line (not the full
filename specification on disk). The components can then be recombined with
specific paths, extensions, or directories to create the particular name or
path you need, without having to specify the exact name or path when you
write the description block.

The first dependent file is the first file listed to the right of the colon
on a dependency line. If a dependent is implied from an inference rule,
NMAKE considers it to be the first dependent file. If more than one
dependent is implied from inference rules, the .SUFFIXES list determines
which dependent is first.

You can use either of the following syntaxes:

    %s

    %|«parts»F

where parts can be one or more of the following letters, or can be omitted:


Letter                    Description
────────────────────────────────────────────────────────────────────────────
No letter                 Complete name
d                         Drive
p                         Path
f                         File base name
e                         File extension

You can specify more than one letter. The order of the letters is not
significant; NMAKE constructs the filename that meets (or comes closest to
meeting) all the specifications. The letters are case sensitive.

The  %s  option substitutes the complete name; it is equivalent to both  %|F
    and  %|dpfeF.

NMAKE interprets any percent symbol (%) within a command line (either in a
description block or an inference rule) as the start of a file specifier
using this syntax. Therefore, if you need to use a literal percent symbol
within a command line, you must specify it as a double percent symbol (%%).



Example

The following example demonstrates this special syntax:

    sample.exe : c:projectsample.obj
        LINK %|dpfF, a:%|pfF.exe;

This example represents the following command:

    LINK c:projectsample, a:projectsample.exe;

In this example, the sequence  %|dpfF  represents the same drive, path, and
base name as the dependent on the dependency line, while the sequence  %|pfF
    represents only the path and base name of the dependent. The command tells
the LINK utility to build the executable file on another drive in a
directory of the same name.


10.4  Command-Line Options

NMAKE accepts a number of options, listed in Table 10.10. You can specify
options in uppercase or lowercase and use either a slash or dash. For
example, -A, /A, -a, and /a all represent the same option. This book uses a
slash and uppercase letters.

Table 10.10  NMAKE Options

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Option                            Action
────────────────────────────────────────────────────────────────────────────
/A                                Forces execution of all commands in
                                    description blocks in the description
                                    file even if targets are not out-of-date
                                    with respect to their dependents. Does
                                    not affect the behavior of incremental
                                    commands such as ILINK; using /A does
                                    not force a full link.

/C                                Suppresses nonfatal error or warning
                                    messages and the NMAKE copyright message.

/D                                Displays the modification time of each
                                    file.

/E                                Causes environment variables to override
                                    macro definitions in description files.
Option                            Action
────────────────────────────────────────────────────────────────────────────
                                    macro definitions in description files.
                                    See Section 10.3.4, "Macros."

/F filename                       Specifies filename as the name of the
                                    description file. If you supply a dash (
                                    -) instead of a filename, NMAKE gets
                                    description-file input from the standard
                                    input device. (Terminate keyboard input
                                    with either F6 or CTRL+Z.) If you omit
                                    /F, NMAKE searches the current directory
                                    for a file called
                                    MAKEFILE and uses it as the description
                                    file. If MAKEFILE doesn't exist, NMAKE
                                    uses inference rules for the
                                    command-line targets.

/HELP                             Calls the QuickHelp utility. If NMAKE
                                    cannot locate the help file or QuickHelp,
                                    it displays a brief summary of NMAKE
Option                            Action
────────────────────────────────────────────────────────────────────────────
                                    it displays a brief summary of NMAKE
                                    command-line syntax and exits to the
                                    operating system.

/I                                Ignores exit codes from commands listed
                                    in the description file. NMAKE processes
                                    the whole description file even if
                                    errors occur.

/N                                Displays but does not execute the
                                    description file's commands. This option
                                    is useful for debugging description
                                    files and checking which targets are
                                    out-of-date.

/NOLOGO                           Suppresses the NMAKE copyright message.

/P                                Displays all macro definitions,
                                    inference rules, target descriptions,
Option                            Action
────────────────────────────────────────────────────────────────────────────
                                    inference rules, target descriptions,
                                    and the .SUFFIXES list on the standard
                                    output device.

/Q                                Checks modification times for
                                    command-line targets (or first target in
                                    description file if no command-line
                                    targets are specified). NMAKE returns a
                                    zero exit code if all such targets are
                                    up-to-date and a nonzero exit code if
                                    any target is out-of-date. Only
                                    preprocessing commands in the
                                    description file are executed. This
                                    option is useful when running NMAKE from
                                    a batch file.

/R                                Ignores inference rules and macros that
                                    are defined in the TOOLS.INI file or
                                    that are predefined.
Option                            Action
────────────────────────────────────────────────────────────────────────────
                                    that are predefined.

/S                                Suppresses the display of commands
                                    listed in the description file.

/T                                Changes modification times for
                                    command-line targets (or first target in
                                    description file if no command-line
                                    targets are specified). Only
                                    preprocessing commands in the
                                    description file are executed. Contents
                                    of target files are not modified.

/X filename                       Sends all error output to filename,
                                    which can be a file or a device. If you
                                    supply a dash (-) instead of a filename,
                                    error output is sent to the standard
                                    output device.

Option                            Action
────────────────────────────────────────────────────────────────────────────

/Z                                Used for internal communication between
                                    NMAKE (or NMK) and PWB.

/?                                Displays a brief summary of NMAKE
                                    command-line syntax and exits to the
                                    operating system.

────────────────────────────────────────────────────────────────────────────




Example

The following command line specifies two NMAKE options:

    NMAKE /F sample.mak /C targ1 targ2

The /F option tells NMAKE to read the description file SAMPLE.MAK. The /C
option tells NMAKE not to display nonfatal error messages and warnings. The
command specifies two targets (targ1  and  targ2) to update.

In the following example, NMAKE updates the target  targ1:

    NMAKE /D /N targ1

Since no description file is specified, NMAKE searches the current directory
for a description file named MAKEFILE. The /D option displays the
modification time of each file; the /N option displays the commands in
MAKEFILE without executing them.


10.5  NMAKE Command File

If you find yourself repeatedly using the same sequence of command-line
arguments, you can place them in a text file and pass the file's name as a
command-line argument to NMAKE. NMAKE opens the command file and reads the
arguments. This feature is especially useful if the argument list exceeds
the maximum length of a command line (128 characters in DOS, 256 in OS/2).

To provide input to NMAKE with a command file, type

NMAKE @commandfile

In the commandfile field, enter the name of a file containing the
information NMAKE expects on the command line. You can split input between
the command line and a command file. Use the name of the command file
(preceded by @) in place of the input information on the command line.


Example 1

Assume you have created a filenamed UPDATE containing this line:

    /S "program = sample" sort.exe search.exe

If you start NMAKE with the command

    NMAKE @update

then NMAKE reads its command-line arguments from UPDATE. The at sign (@)
tells NMAKE to read arguments from the file. The effect is the same as if
you typed the arguments directly on the command line:

    NMAKE /S "program = sample" sort.exe search.exe

NMAKE treats the file as if it were a single set of arguments and replaces
each line break with a space. Macro definitions that contain spaces must be
enclosed in quotation marks, just as if you had typed them on the command
line.

The quotation marks that delimit a macro force all characters between them
to be interpreted literally. Therefore, if you split a macro between lines,
an unwanted line break is inserted into the macro. Macros that span multiple
lines must be continued by ending each line except the last with a backslash
(  ):

    /S "program 
    = sample" sort.exe search.exe

This file is equivalent to the first example. The backslash allows the macro
definition ("program = sample") to span two lines.


Example 2

If the command-file UPDATE contains this line:

    /S "program = sample" sort.exe

you can give NMAKE the same command-line input as in the example above by
specifying the command

    NMAKE @update search.exe


10.6  The TOOLS.INI File

You can customize NMAKE by placing commonly used macros, inference rules,
and description blocks in the TOOLS.INI initialization file. Settings for
NMAKE must follow a line that begins with [NMAKE]. This section of the
initialization file can contain macro definitions, .SUFFIXES lists, and
inference rules. For example, if TOOLS.INI contains the following section:

    [NMAKE]
    CC=qcl
    CFLAGS=/Gc /Gs /W3 /Oat
    .c.obj:
        $(CC) /c $(CFLAGS) $*.c

NMAKE reads and applies the lines following  [NMAKE]. The example redefines
the macro CC to invoke the Microsoft QuickC (R) Compiler, defines the macro
CFLAGS, and redefines the inference rule for making .OBJ files from .C
sources. (Note that macros are case sensitive; a macro called cc is not
substituted in a rule that uses $(CC).)

NMAKE looks for TOOLS.INI in the current directory. If it isn't there, NMAKE
searches the directory specified by the INIT environment variable.

Macros and inference rules appearing in TOOLS.INI can be overridden. See
Section 10.3.4.7, "Precedence among Macro Definitions," and Section
10.3.5.5, "Precedence among Inference Rules."


10.7  Inline Files

NMAKE can create "inline files" which contain any text you specify. One use
of inline files is to write a response file for another utility such as LINK
or LIB. This eliminates the need to maintain a separate response file and
removes the restraint on the maximum length of a command line.

Use this syntax to create an inline file called filename:

target : dependents  command << «filename» inlinetext <<«KEEP | NOKEEP»

All inlinetext between the two sets of double angle brackets (<<) is placed
in the inline file. The filename is optional. If you don't supply filename,
NMAKE gives the inline file a unique name. NMAKE places the inline file in
the directory specified by the TMP environment variable. If TMP is not
defined, the inline file is placed in the current directory.

Directives are not allowed in an inline file. NMAKE treats a directive in an
inline file as literal text.

The inline file can be temporary or permanent. If you don't specify the
option, or if you specify NOKEEP, the file is temporary. Specify KEEP to
retain the file after the build ends.


Example

The following description block creates a LIB response file named LIB.LRF:

    OBJECTS=add.obj sub.obj mul.obj div.obj
    math.lib : $(OBJECTS)
        LIB @<<lib.lrf
    $*.lib
    -+$(OBJECTS: = &^
    -+)
    listing;
    <<KEEP

The resulting response file tells LIB which library to use, the commands to
execute, and the name of the listing file to produce:

    math.lib
    -+add.obj &
    -+sub.obj &
    -+mul.obj &
    -+div.obj
    listing;

The file MATH.LIB must exist beforehand for this example to work.


Multiple Inline Files

The inline file specification can create more than one inline file. For
instance,

    target.abc : depend.xyz
        cat <<file1 <<file2
    I am the contents of file1.
    <<KEEP
    I am the contents of file2.
    <<KEEP

The example creates the two inline files, FILE1 and FILE2. All inline text
is written to the files sequentially. Therefore, the text

    I am the contents of file1.

goes into FILE1, not FILE2, even though the text is nested between the angle
brackets for FILE2 and the  <<KEEP  statement which follows. NMAKE then
executes the command

    cat file1 file2

The KEEP keywords tell NMAKE not to delete FILE1 and FILE2 when done.


10.8  Sequence of NMAKE Operations

When you are writing a complex description file, it can be helpful to know
the sequence in which NMAKE performs operations. This section describes
those operations and their order.

NMAKE first looks for a description file.

When you run NMAKE from the command line, NMAKE's first task is to find the
description file:


    1.  If the /F option is used, NMAKE searches for the filename specified in
        the option. If NMAKE cannot find that file, it returns an error.

    2.  If the /F option is not used, NMAKE looks for a file named MAKEFILE in
        the current directory. If there are targets on the command line, NMAKE
        builds them according to the instructions in MAKEFILE. If there are no
        targets on the command line, NMAKE builds only the first target it
        finds in MAKEFILE.

    3.  If NMAKE cannot find MAKEFILE, NMAKE looks for target files on the
        command line and attempts to build them using inference rules (either
        defined by the user in TOOLS.INI or predefined by NMAKE). If no target
        is specified, NMAKE returns an error.


Macro definitions follow a priority.

NMAKE then assigns macro definitions with the following precedence (highest
first):


    1.  Macros defined on the command line

    2.  Macros defined in a description file or include file

    3.  Inherited macros

    4.  Macros defined in the TOOLS.INI file

    5.  Predefined macros (such as CC and RFLAGS)


Macro definitions are assigned in order of priority, not in the order in
which NMAKE encounters them. For example, a macro defined in an include file
overrides a macro with the same name from the TOOLS.INI file. Note that a
macro within a description file can be redefined; the most recent definition
in the description file is used.

Inference rules also follow a priority.

NMAKE also assigns inference rules, using the following precedence (highest
first):


    1.  Inference rules defined in a description file or include file

    2.  Inference rules defined in the TOOLS.INI file

    3.  Predefined inference rules (such as .c.obj)


You can use command-line options to change some of these precedences.


    ■   The /E option allows macros inherited from the environment to override
        macros defined in the description file.

    ■   The /R option tells NMAKE to ignore macros and inference rules that
        are defined in TOOLS.INI or are predefined.


NMAKE preprocesses directives before running the description-file commands.


Next, NMAKE evaluates any preprocessing directives. If an expression for
conditional preprocessing contains a program in square brackets ( [ ] ), the
program is invoked during preprocessing, and the program's exit code is used
in the expression. If an !INCLUDE directive is specified for a file, NMAKE
preprocesses the included file before continuing to preprocess the rest of
the description file. Preprocessing determines the final description file
that NMAKE reads.

NMAKE updates targets in the description file.

NMAKE is now ready to update the targets. If you specified targets on the
command line, NMAKE updates only those targets. If you did not specify
targets on the command line, NMAKE updates just the first target it finds in
the description file. (This behavior differs from the MAKE utility's
default; see Section 10.10, "Differences between NMAKE and MAKE.") If you
specify a pseudotarget, NMAKE always updates the target. If you use the /A
option, NMAKE always updates the target, even if the file is not
out-of-date.

If the dependents of the targets are themselves out-of-date or do not exist
yet, NMAKE updates them first. If the target has no explicit dependent,
NMAKE looks in the current directory for one or more files with the same
base name as the target and whose extensions are in the .SUFFIXES list. (See
Section 10.3.6, "Directives," for a description of the .SUFFIXES list.) If
it finds such files, NMAKE treats them as dependents and updates the target
according to the commands.

Errors usually stop the build.

NMAKE normally stops processing the description file when a command returns
a nonzero exit code. In addition, if NMAKE cannot tell whether the target
was built successfully, it deletes the target. If you use the /I
command-line option, NMAKE ignores error codes and attempts to continue
processing. The .IGNORE directive has the same effect as the /I option. To
prevent NMAKE from deleting the partially created target if you interrupt
the build with CTRL+C or CTRL+BREAK, specify the target name in the
.PRECIOUS directive.

Alternatively, you can use the dash (-) command modifier to ignore the error
code for an individual command. An optional number after the dash tells
NMAKE to continue if the command returns an exit code that is less than or
equal to the number, and to stop if the exit code is greater than the
number.

You can document errors by using the !ERROR directive to print descriptive
text. The directive causes NMAKE to print some text, then stop, even if you
use /I, .IGNORE, or the dash (-) modifier.


10.9  A Sample NMAKE Description File

The following example illustrates many of NMAKE's features. The description
file creates an executable file from C-language source files:

    #  This description file builds SAMPLE.EXE from SAMPLE.C,
    #  ONE.C, and TWO.C, then deletes intermediate files.

    CFLAGS   = /c /AL /Od $(CODEVIEW)  # controls compiler options
    LFLAGS   = /CO                     # controls linker options
    CODEVIEW = /Zi                     # controls CodeView data

    OBJS = sample.obj one.obj two.obj
    all : sample.exe

    sample.exe : $(OBJS)
        link $(LFLAGS) @<<sample.lrf
    $(OBJS: =+^
    )
    sample.exe
    sample.map;
    <<KEEP

    sample.obj : sample.c sample.h common.h
        CL $(CFLAGS) sample.c

    one.obj : one.c one.h common.h
        CL $(CFLAGS) one.c

    two.obj : two.c two.h common.h
        CL $(CFLAGS) two.c

    clean :
        -del *.obj
        -del *.map
        -del *.lrf

Assume that this description file is named SAMPLE.MAK. To invoke it, enter

    NMAKE /F SAMPLE.MAK all clean

NMAKE then builds SAMPLE.EXE and deletes intermediate files.

Here is how the description file works. The CFLAGS, CODEVIEW, and LFLAGS
macros define the default options for the compiler, linker, and inclusion of
CodeView information. You can redefine these options from the command line
to alter or delete them. For example,

    NMAKE /F SAMPLE.MAK CODEVIEW= CFLAGS= all clean

creates an .EXE file that does not contain CodeView information.

The OBJS macro specifies the object files that make up SAMPLE.EXE, so they
can be reused without having to type them again. Their names are separated
by exactly one space so that the space can be replaced with a plus sign (+)
and a carriage return in the link response file. (This is illustrated in the
second example in Section 10.3.4.4, "Substitution within Macros.")

The  all  pseudotarget points to the real target,  SAMPLE.EXE. If you do not
specify any target on the command line, NMAKE ignores the  clean
pseudotarget but still builds  all, since  all  is the first target in the
description file.

The dependency line containing the target  sample.exe  makes the object
files specified in OBJS the dependents of SAMPLE.EXE. The command section of
the block contains only link instructions. No compilation instructions are
given, since they are given explicitly later in the file. (You could also
define an inference rule to specify how an object file is to be created from
a C source file.)

The link command is unusual in that the link parameters and options are not
passed directly to LINK. Rather, an inline response file is created
containing these elements. This eliminates the need to maintain a separate
link response file. It also allows the LINK command line to exceed the
normal limit on the length of a command line (128 characters in DOS, 256
characters in OS/2).

The next three dependencies define the relationship of the source code to
the object files. The .H (header or include) files are also dependents,
since any changes to them would require recompilation.

The  clean  pseudotarget deletes unneeded files after a build. The dash
modifier (-) tells NMAKE to ignore errors returned by the deletion commands.
If you want to save any of these files, don't specify  clean  on the command
line; NMAKE then ignores the  clean  pseudotarget.


10.10  Differences between NMAKE and MAKE

NMAKE replaces the Microsoft MAKE program. NMAKE differs from MAKE in the
following ways:


    ■   NMAKE does not evaluate targets sequentially. Instead, NMAKE updates
        the targets you specify when you invoke it, regardless of their
        positions in the description file. If no targets are specified, NMAKE
        updates only the first target in the file.

    ■   NMAKE requires a special syntax when specifying a target in more than
        one dependency line. (See Section 10.3.1.8, "Specifying a Target in
        Multiple Description Blocks.")

    ■   NMAKE accepts command-line arguments from a file.

    ■   NMAKE provides more command-line options.

    ■   NMAKE provides more predefined macros.

    ■   NMAKE permits substitutions within macros.

    ■   NMAKE supports directives placed in the description file.

    ■   NMAKE allows you to specify include files in the description file.


The first item in the list deserves special emphasis. While MAKE updates
every target, working from beginning to end of the description file, NMAKE
expects you to specify targets on the command line. If you do not, NMAKE
builds only the first target in the description file.

This difference is clear if you run NMAKE using a typical MAKE description
file, which lists a series of subordinate targets followed by a higher-level
target that depends on the following subordinates:

    pmapp.obj : pmapp.c
        CL /c /G2sw /W3 pmapp.c

    pmapp.exe : pmapp.obj pmapp.def
        LINK pmapp, /align:16, NUL, os2, pmapp

MAKE builds both targets (PMAPP.OBJ and PMAPP.EXE), but NMAKE builds only
the first target (PMAPP.OBJ).

Because of these performance differences, you may want to convert MAKE files
to NMAKE files. MAKE description files are easy to convert. One way is to
create a new description block at the beginning of the file. Give this block
a pseudotarget named  all  and list the top-level target as a dependent of
all. To build  all, NMAKE must update every file upon which the target  all
depends:

    all : pmapp.exe

    pmapp.obj : pmapp.c
        CL /c /G2sw /W3 pmapp.c

    pmapp.exe : pmapp.obj pmapp.def
        LINK pmapp, /align:16, NUL, os2, pmapp

If the above file is named MAKEFILE, you can update the target PMAPP.EXE
with the command

    NMAKE

or the command

    NMAKE all

It is not necessary to list PMAPP.OBJ as a dependent of  all. NMAKE builds a
dependency tree for the entire description file and builds whatever files
are needed to update PMAPP.EXE. If PMAPP.C has a later modification time
than PMAPP.OBJ, NMAKE compiles PMAPP.C to create PMAPP.OBJ, then links
PMAPP.OBJ to create PMAPP.EXE.

The same technique is suitable for description files with more than one
top-level target. List all the top-level targets as dependents of  all:

    all : pmapp.exe second.exe another.exe

The example updates the targets PMAPP.EXE, SECOND.EXE, and ANOTHER.EXE.

If the description file lists a single, top-level target, you can use an
even simpler technique. Move the top-level block to the beginning of the
file:

    pmapp.exe : pmapp.obj pmapp.def
        LINK pmapp, /align:16, NUL, os2, pmapp
    pmapp.obj : pmapp.c
        CL /c /G2sw /W3 pmapp.c

NMAKE updates the second target (PMAPP.OBJ) whenever needed to keep the
first target (PMAPP.EXE) current.


10.11  Using NMK

When you maintain a project under DOS or in a DOS session under OS/2, you
will probably need to use the NMK utility. NMK uses only 5K of memory,
leaving room for the programs called during the build. You run NMK the same
way you run NMAKE, using the same command-line syntax and the same
description-file syntax. NMK calls NMAKE to read the description file and
perform the build.

The behavior of NMK is slightly different from that of NMAKE. The
fundamental difference is that NMAKE rechecks the update status of all files
after each build step, whereas NMK checks file status only once, at the
start of the build process. If your description file simply compiles a
series of files and then links them, this difference never causes a problem.
But consider the following example, which uses a pseudotarget to clean up
old files during the build:

    all : clean example.exe

    example.exe : example.asm
        ML example

    clean :
        del example.obj
        del example.exe

This description file erases EXAMPLE.OBJ and EXAMPLE.EXE, then recompiles.
Under NMAKE, it works as intended; that is, it


    1.  Erases files

    2.  Checks the status of EXAMPLE.EXE

    3.  Rebuilds EXAMPLE.EXE because EXAMPLE.EXE is no longer present


However, NMK checks the status of the environment only at the beginning of
the build. Since EXAMPLE.EXE exists when the build starts, the preceding
description file


    1.  Erases files

    2.  Stops execution, because EXAMPLE.EXE was present and up-to-date at the
        beginning of the process


PWB never generates a description file that requires dynamic status checking
to run correctly, so you can use PWB-created description files with either
NMAKE or NMK.


10.12  Using Exit Codes with NMAKE

NMAKE stops execution if a program executed by one of the commands in the
NMAKE description file encounters an error. The exit code returned by the
program is displayed as part of the error message.

Assume the NMAKE description file  TEST  contains the following lines:

    TEST.OBJ : TEST.FOR
        FL /c TEST.FOR

If the source code in  TEST.FOR  causes an error (but not a warning), you
would see the following message the first time you use NMAKE with the NMAKE
description file  TEST:

    NMAKE : fatal error U1077: 'FL /c TEST.FOR' - return code '2'

This error message indicates that the command  FL /c TEST.FOR  in the NMAKE
description file returned exit code 2.

You can cause NMAKE to ignore an exit code for a command by preceding the
command with a dash modifier (-). If you specify a number after the dash
modifier (-n), NMAKE stops only if the exit code is greater than the
specified number. (See Table 10.1.) You disable this behavior for the entire
description file by invoking NMAKE with the /I option.

You can also test exit codes in NMAKE description files with the !IF
preprocessing directive. See Section 10.3.7.2, "Executing a Program in
Preprocessing."

If you prefer to use DOS batch files instead of NMAKE description files, you
can test the code returned with the IF command. See a DOS manual for more
information.

NMAKE returns an exit code to the operating system or the calling program. A
value of 0 indicates execution of NMAKE with no errors. Warnings return exit
code 0.

Code               Meaning
────────────────────────────────────────────────────────────────────────────
0                  No error
2                  Program error
4                  System error─out of memory


10.13  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topics                                Access
────────────────────────────────────────────────────────────────────────────
Syntax and procedural information on  From the list of Utilities on the
NMAKE                                 "Microsoft Advisor Contents" screen,
                                        choose "NMAKE"

Using TOOLS.INI                       From the "Microsoft Advisor Contents"
                                        screen, choose "Programmer's
                                        WorkBench"; then choose "Using
                                        TOOLS.INI" from the list of topics
                                        relating to customizing PWB







Chapter 11  Creating Help Files with HELPMAKE
────────────────────────────────────────────────────────────────────────────

If you've used the Programmer's WorkBench (PWB) or one of the Microsoft
Quick languages, you already know the advantages of online help, or the
Microsoft Advisor. The Microsoft Help File Maintenance utility (HELPMAKE)
lets you extend these advantages by customizing the help files supplied with
Microsoft language products, or by creating your own help files for them.

HELPMAKE translates help text files into a help database accessible within
these environments:


    ■   Microsoft Programmer's WorkBench (PWB)

    ■   Microsoft QuickHelp utility

    ■   Microsoft CodeView debugger

    ■   Microsoft Editor version 1.02

    ■   Microsoft QuickC compiler versions 2.0 and later

    ■   Microsoft QuickBasic(tm) versions 4.5 and later

    ■   Microsoft QuickPascal(tm) version 1.0

    ■   Microsoft Word version 5.5


This chapter describes how to create and modify help files using the
HELPMAKE utility.


11.1  Structure and Contents of a Help Database

HELPMAKE creates a help database from one or more input files that contain
information formatted for the help system. This section defines some of the
terms involved in formatting and outlines the formats that HELPMAKE can
process.


11.1.1  Contents of a Help File

Each help input file consists of one or more help "topics." A topic is the
fundamental unit of help information. It is usually a screenful of
information about a particular subject. You identify the subject by one or
more "context strings," which are the words and phrases for which you want
to be able to request help. When help is requested on a context string, the
topic is displayed.

The .context command defines a context string for the topic that follows it.
In the source file for C help, for example, this line introduces help for
the #include directive:

    .context #include

The .context command and other formatting elements are described in Section
11.5, "Help Text Conventions."

Whether a context string contains one word or several words depends on the
application. For example, because Microsoft QuickBasic considers spaces to
be delimiters, a context string in QuickBasic help files is limited to a
single word. Other applications, such as PWB, can handle context strings
that span several words. In either case, the application hands the context
string to an internal "help engine" that searches the database for
information.

Often, especially with library routines, the same information applies to
more than one subject. For example, the C-language string-to-number
functions strtod, strtol, and strtoul share the same help text. The help
file lists all three function names as contexts for one block of topic text.
The converse, however, is not true. You cannot associate a single context
string with several blocks of topic text located at different places in the
help file.

Cross-references help you navigate a help database.

Cross-references make it possible to view information about related topics,
including header files and code examples. The help for the C-language open
function, for example, references the access function. Cross-references can
point to other contexts in the same help database, to contexts in other help
databases, or even to ASCII files outside the database.

Help files can have two kinds of cross-references:


    ■   Implicit

    ■   Explicit, or hyperlinks


Implicit cross-references are coded with an ordinary .context command.

The word "open" is an implicit cross-reference throughout Microsoft C help,
and introduces help for the open function. If you select the word "open"
anywhere in C help, the help system displays information on the open
function. The context for open begins with an ordinary .context command. As
a result, anywhere that you select "open," the help system references this
context.

Hyperlinks are explicit cross-references marked by invisible text.

A "hyperlink" is an explicit cross-reference tied to a word or phrase at a
specific location in the help file. You create hyperlinks when you write the
help text. The hyperlink consists of a word or phrase followed by invisible
text that gives the context to which the hyperlink refers.

For example, to cause an instance of the word "formatting" to display help
on the printf function, you would create an explicit cross-reference from
the word "formatting" to the context "printf." Elsewhere in the file,
"formatting" has no special significance, but at that one position, it
references the help for printf. For details on how to create hyperlinks, see
Section 11.5.4.

Formatting flags let you change the appearance of text.

Help text can also include formatting attributes to control the appearance
of the text on the screen. Using these attributes, you can make certain
words appear in various colors, inverse video, and so forth, depending on
the application displaying help and the graphics capabilities of your
computer.


11.1.2  Help File Formats

You can create sources for help text files in any of three formats:


    ■   QuickHelp format

    ■   Rich Text Format (RTF)

    ■   Minimally formatted ASCII


In addition, you can reference unformatted ASCII files, such as include
files, from within a help database.

An entire help system (such as the ones supplied with Microsoft C, FORTRAN,
MASM, or QuickBasic) can use any combination of files formatted with
different format types. With C, for example, the README.DOC information file
is encoded as minimally formatted ASCII; the help files for the PWB, C
language, and run-time library are written in QuickHelp format before being
compressed by HELPMAKE. The database also cross-references the header
(include) files, which are unformatted ASCII files stored outside the
database.


QuickHelp

QuickHelp format is the default format into which HELPMAKE decodes help
databases. Any text editor can create a QuickHelp-format help text file.
QuickHelp format also lends itself to a relatively easy automated
translation from other document formats.

QuickHelp files can contain any kind of cross-reference or formatting
attribute. Typically, you use QuickHelp format when modifying a
Microsoft-supplied database.

QuickHelp format makes use of dot commands (such as .context─see the
description of QuickHelp dot commands in Section 11.6.1). To use dot
commands other than .context and .comment, the / T option is required for
encoding and decoding. For details, see Section 11.3, "Helpmake Options."


Rich Text Format

Rich Text Format (RTF) is a Microsoft word-processing format that several
word processors support, including Microsoft Word version 5.0 and later, and
Microsoft Word for Windows. You can use RTF as an intermediate format to
simplify transferring help files from one format to another. Like QuickHelp
files, RTF files can contain formatting attributes and cross-references.

An RTF word processor provides the easiest way to create an RTF file, but
you can manually insert RTF codes with an ordinary text editor. There are
also utility programs that convert text files in other formats to RTF
format.

See Section 11.6.2, "Rich Text Format," for more information.


Minimally Formatted ASCII

Minimally formatted ASCII files define contexts and their topic text; they
cannot contain screen-formatting commands or explicit cross-references.
(Implicit cross-references work the same way they do in the other formats.)
Minimally formatted ASCII files are often used to display text in a
README.DOC or small help files that do not require compression. See Section
11.6.3, "Minimally Formatted ASCII Format," for more information.


Unformatted ASCII

Unformatted ASCII files are exactly what their name implies: regular ASCII
files with no formatting commands, context definitions, or special
information. HELPMAKE does not process unformatted ASCII files in any
special way. An unformatted ASCII file does not become part of the help
database; only its name is used as the object of a cross-reference.
Unformatted ASCII files are useful for storing program examples. Any word
that is an implicit cross-reference in other help files is also an implicit
cross-reference in unformatted ASCII files.


11.2  Invoking HELPMAKE

The HELPMAKE program can encode to create new help files or decode to modify
existing ones. Encoding converts a text file to a compressed help database.
HELPMAKE can encode text files written in QuickHelp, RTF, and minimally
formatted ASCII format. Decoding converts a help database to a text file for
editing. Regardless of the source format, HELPMAKE always decodes a help
database into a QuickHelp-format text file.

You invoke HELPMAKE with the following syntax:

    HELPMAKE {/E«n» | /D«c» |
    / H| /?} [[options]] sourcefiles

The options modify the action of HELPMAKE; they are described in Section
11.3, "HELPMAKE Options."

You must supply either the /E (encode) or the /D (decode) option. When
encoding, you must also use the /O option to specify the file name of the
database.

The sourcefiles field is required. It specifies the input file(s) for
HELPMAKE. If you use the /D (decode) option, sourcefiles can be one or more
help database files (such as PWB.HLP). HELPMAKE decodes the database files
to the standard output device. If you use the /E (encode) option,
sourcefiles can be one or more help text files (such as PWB.SRC). File names
are separated with a space. You can use standard wild-card characters to
specify a group of related files.

The example below invokes HELPMAKE with the /V, /E, and /O options (see
Section 11.3.1, "Options for Encoding"). HELPMAKE reads input from the text
file  my.txt  and writes the compressed help database in the file  my.hlp.
The /E option, without a compression specification, maximizes compression.
Note that the DOS or OS/2 redirection symbol (>) sends a log of HELPMAKE
activity to the file  my.log. You may want to redirect the log file because,
in its verbose mode (given by /V), HELPMAKE can generate a lengthy log.

    HELPMAKE /V /E /Omy.hlp my.txt > my.log

The example below invokes HELPMAKE to decode the help database  my.hlp into
the text file  my.src, given with the /O option. Once again, the /V option
results in verbose output, and the output is directed to the log file
my.log. Section 11.3.2 describes additional options for decoding.

    HELPMAKE /V /D /Omy.src my.hlp > my.log


11.3  HELPMAKE Options

HELPMAKE accepts the command-line options described below. You can specify
options in uppercase or lowercase letters and precede them with either a
forward slash ( / ) or a dash ( - ). Most options apply only to encoding,
others apply only to decoding, and a few apply to both. The /T option is
required if you want to use dot commands with the QuickHelp format (which is
the default format).


11.3.1  Options for Encoding

When you encode a file─that is, when you build a help database─you must
specify the /E option. HELPMAKE also accepts other options to control
encoding. The encoding options are listed below:

╓┌───────────┌───────────────────────────────┌───────────────────────────────╖
Option      Action
────────────────────────────────────────────────────────────────────────────
Option      Action
────────────────────────────────────────────────────────────────────────────
/Ac         Specifies c as an
            application-specific control
            character for the help
            database file. The character
            marks a line that contains
            special information for
            internal use by the
            application. For example, the
            Microsoft Advisor uses the
            colon (:).

/C          Makes context strings for this
            help file case sensitive.

/E«n»       Creates (encodes) a help
            database from a specified text
            file. The n specifies the
            type(s) of compression. If n
            is omitted, HELPMAKE
Option      Action
────────────────────────────────────────────────────────────────────────────
            is omitted, HELPMAKE
            compresses the file as much as
            possible (about 50%). The
            value of n is in the range 0
            -15. It is the sum of
            successive integral powers of
            2 representing various
            compression techniques:

            Value                           Technique

            0                               No compression

            1                               Run-length compression

            2                               Keyword compression

            4                               Extended keyword compression

Option      Action
────────────────────────────────────────────────────────────────────────────

            8                               Huffman compression

            Add values to combine
            compression techniques. For
            example, use / E3 to get
            run-length and keyword compres-

            sion. Use / E0 in the testing
            stages of help database
            creation where you need to
            create the database quickly
            and are not yet concerned with
            size.

/Kfilename  Optimizes keyword compression
            by supplying a list of
            characters that act as word
            separators. The filename is a
Option      Action
────────────────────────────────────────────────────────────────────────────
            separators. The filename is a
            file containing your list of
            separator characters.


            The / E2 and / E3 options tell
            HELPMAKE to identify
            "keywords"─words occurring
            often enough to justify
            replacing them with shorter
            character sequences. A word is
            any series of characters that
            do not appear in the separator
            list. The default separator
            list includes all ASCII
            characters from 0 to 32, ASCII
            character 127, and the
            following characters:

Option      Action
────────────────────────────────────────────────────────────────────────────

            ! " # & ` ' ( ) * + - , / : ;
            < = > ? @ [  ] ^ _ { | } ~

            You can improve keyword
            compression by designing a
            separator list tailored to a
            specific help file. If your
            help file contains #include
            directives, #include is
            encoded (by default) as
            include. To encode #include as
            a keyword, create a separator
            list that omits the #:

            !   " & ` ' ( ) * + - , / : ;
            < = > ? @ [  ] ^ _ { | } ~

            Characters in the range 0 -31
Option      Action
────────────────────────────────────────────────────────────────────────────
            Characters in the range 0 -31
            are always separators, so you
            need not include them. A
            customized list must include
            all other separators, however,
            including the space (which
            follows ! in the list above).
            If you omit the space,
            HELPMAKE encodes sequences of
            words as keywords.

/L          Locks the generated file so
            that it cannot later be
            decoded.

/NOLOGO     Suppresses the HELPMAKE
            copyright message.

/Ooutfile   Specifies outfile as the name
Option      Action
────────────────────────────────────────────────────────────────────────────
/Ooutfile   Specifies outfile as the name
            of the help database.

/Sn         Specifies the type of input
            file, according to the
            following n values:

            Option                          File Type

            /S1                             Rich Text Format (RTF)

            /S2                             QuickHelp (default)

            /S3                             Minimally formatted ASCII

/T          Translates dot commands into
            internal format. If your help
            file contains dot commands
            other than .context and
Option      Action
────────────────────────────────────────────────────────────────────────────
            other than .context and
            .comment, you must supply this
            option when encoding it. Dot
            commands are described in
            Section 11.6.1,"QuickHelp
            Format," and in later sections.
            The /T option causes the
            option /A: to be assumed.


/V«n»       Controls verbosity of
            diagnostic and informational
            output. Larger values of n add
            more information. Omitting n
            produces a full listing. The
            values of n are listed below:

            Option                          Output

Option      Action
────────────────────────────────────────────────────────────────────────────

            /V                              Maximum diagnostic output

            /V0                             No diagnostic output and no
                                            banner

            /V1                             HELPMAKE banner only

            /V2                             Pass names

            /V3                             Contexts on first pass

            /V4                             Contexts on each pass

            /V5                             Any intermediate steps within
                                            each pass

            /V6                             Statistics on help file and
                                            compression
Option      Action
────────────────────────────────────────────────────────────────────────────
                                            compression

/Wwidth     Indicates the fixed width of
            the resulting help text in
            number of characters. The
            value of width can range from
            11 to 255. If the /W option is
            omitted, the default is 76.
            When encoding an RTF source
            (/S1), HELPMAKE automatically
            formats the text to width.
            When encoding QuickHelp (/S2)
            or minimally formatted ASCII
            (/S3) files, HELPMAKE
            truncates lines to this width.




11.3.2  Options for Decoding

The /D option decodes a help database into QuickHelp files. HELPMAKE also
accepts other options to control decoding. The decoding options are listed
below:

╓┌────────────┌──────────────────────────────┌───────────────────────────────╖
Option       Action
────────────────────────────────────────────────────────────────────────────
/D«c»        Decodes the input file into
                its original text or
                component parts. If a
                destination file is not
                specified with the /O option,
                the help file is decoded to
                the standard output device.
                The form of decoding is
                controlled by the form of /D«
                c» specified:

                Form                           Effect
Option       Action
────────────────────────────────────────────────────────────────────────────
                Form                           Effect

                /D                             Fully decodes the help
                                            database, leaving all
                                            cross-references and
                                            formatting information intact.

                /DS                            Splits a concatenated help
                                            database into its components
                                            using their original names. If
                                            the database was not created
                                            by concatenation, HELPMAKE
                                            copies it to a file with its
                                            original name. The database is
                                            not decompressed.

                /DU                            Decompresses the database and
                                            removes all screen formatting
                                            and cross-
Option       Action
────────────────────────────────────────────────────────────────────────────
                                            and cross-
                                            references. The output can be
                                            used later for input and
                                            recompression, but all screen
                                            formatting and
                                            cross-references are lost.

                /NOLOGO                        Suppresses the HELPMAKE
                                            copyright message.

/O«outfile»  Specifies outfile for the
                decoded output from HELPMAKE.
                If outfile is omitted, the
                help database is decoded to
                the standard output device.
                HELPMAKE always decodes help
                database files into QuickHelp
                format.

Option       Action
────────────────────────────────────────────────────────────────────────────

/T           Translates dot commands from
                internal format into
                dot-command format. You must
                always supply this option
                when decoding a help database
                that contains dot commands
                other than .context and
                .comment.




/V«n»        Controls verbosity of
                diagnostic and informational
                output. Larger values of n
                add more information.
                Omitting n produces a full
                listing. The values of n are
Option       Action
────────────────────────────────────────────────────────────────────────────
                listing. The values of n are
                listed below:

                Option                         Output

                /V                             Maximum diagnostic output

                /V0                            No diagnostic output and no
                                            banner

                /V1                            HELPMAKE banner only

                /V2                            Pass names

                /V3                            Contexts on first pass




11.3.3  Options for Help

The following are the options for help.

Option                            Action
────────────────────────────────────────────────────────────────────────────
/ ?                               Displays a brief summary of HELPMAKE
                                    command-line syntax and exits without
                                    encoding or decoding any files. All
                                    other information on the command line is

                                    ignored.

/ «HELP»                          Calls the QuickHelp utility and displays
                                    help about HELPMAKE. If HELPMAKE cannot
                                    find QuickHelp or the help file, it
                                    displays the same information as with
                                    the /? option. No files are encoded or
                                    decoded. All other information on the
                                    command line is ignored.



11.4  Creating a Help Database

There are two ways to create a Microsoft-compatible help database.

The first method is to decompress an existing help database, modify the
resulting help text file, and recompress the help text file to form a new
database.

The second method is to append a new help database to an existing help
database. This method involves the following steps:


    1.  Create a help text file in QuickHelp format, RTF, or minimally
        formatted ASCII.

    2.  Use HELPMAKE to create a help database file. The example below invokes
        HELPMAKE, using  yourhelp.txt  as the input file and producing a help
        database file named  yourhelp.hlp:

        HELPMAKE /V /E /Oyourhelp.hlp yourhelp.txt > yourhelp.log


    3.  Back up the existing database.

    4.  Append the new help database file to the existing database. The
        example below appends the new database  yourhelp.hlp  to the
        alang.hlp  database. (In the example, the / b modifier for the DOS
        COPY command combines the files as binary files.)

        COPY alang.hlp /b + yourhelp.hlp /b


    5.  Test the database. Assume  yourhelp.hlp  contains the context  sample.
        If you type  sample  in PWB and request help on it, the help window
        should display the text associated with the context  sample.


────────────────────────────────────────────────────────────────────────────
WARNING

The PWB editor truncates lines longer than about 250 characters. Some
databases contain lines longer than this. To edit or create database files
with extremely long lines, you must either use an editor (such as Microsoft
Word) that does not restrict line length, or extend long lines using the
backslash () line-continuation character.
────────────────────────────────────────────────────────────────────────────


11.5  Help Text Conventions

The source text that HELPMAKE uses to create Microsoft help databases must
follow specific organizational conventions. The following sections explain
these conventions.


11.5.1  Structure of the Help Text File

The Microsoft help system is simply a data-retrieval tool. It imposes no
restrictions on the content or organization of help data. However, the
HELPMAKE utility and the data-display routines in the help system expect a
help file to follow a standard format. This section explains how to create
correctly formatted help text files.

In all three help text formats, the help text source file is a sequence of
topics, each preceded by one or more context definitions. The following
table lists the various formats and the corresponding context definition
statements:

Format                            Context Definition
────────────────────────────────────────────────────────────────────────────
QuickHelp                         .context context

RTF                                par >>context  par

Minimally formatted ASCII         >>context

Unformatted ASCII                 None

In QuickHelp format, each topic begins with one or more .context statements.
These statements link the context string to its topic text. The topic text
consists of all subsequent lines up to the next .context statement.

In RTF format, each context definition must be in a paragraph of its own
(denoted by  par), beginning with the help delimiter (>>). As in QuickHelp,
the topic text consists of all subsequent paragraphs up to the next context
definition.

In minimally formatted ASCII, each context definition must be on a separate
line, and each must begin with the help delimiter (>>). As in RTF and
QuickHelp files, all subsequent lines up to the next context definition
constitute the topic text.

See Section 11.6, "Using Help Database Formats," for detailed information
about these three formats.

────────────────────────────────────────────────────────────────────────────
WARNING

HELPMAKE warns you if it encounters a duplicate context string definition
within a given help source file. Each context string must be unique.
────────────────────────────────────────────────────────────────────────────


11.5.2  Local Contexts

Context strings beginning with the "at" sign (@) are "local." Making a
context local saves file space and speeds access. However, local contexts
cannot be cross-referenced with an implicit link, and they have no meaning
outside the local file.

When you use a local context, HELPMAKE does not generate a global context
string (a context string that is known throughout the help system). Instead,
it embeds an encoded cross-reference that has meaning only within the
current context. For example,

    .context normal
    This is a normal topic, accessible by the context string "normal".
    [buttonv@localv] is a cross-reference to the following topic.

    .context @local

    This topic can be reached only by the explicit cross-reference
    in the previous topic (or by browsing the file sequentially).

In the example above, the text  buttonv@localv  references  local  as a
local context. If the user selects the text  button  or scrolls through the
file, the help system displays the topic text that follows the context
definition for  local. Because  local  is defined with the "at" sign @, it
can be accessed only by a hyperlink within the same help file or by
sequentially browsing the file.

If you want a topic to be accessible in both local and global contexts, you
simply mark the topic text with both global and local .context statements.
For example, to make  topic  both global and local, add the following
statements:

    .context topic
    .context @topic

Naturally, both .context statements must appear immediately before the topic
text to which they point.

To create a context that begins with a literal @, precede it with a
backslash (  ).


11.5.3  Context Prefixes

Microsoft help databases use several "context prefixes." A context prefix is
a single letter followed by a period. It appears before a context string
with a predefined meaning. These contexts may appear in the resulting text
file when you decode a Microsoft help database.

Context prefixes are used internally by Microsoft.

Except for the h. prefix described below, the context prefixes are used by
Microsoft to mark environment- or product-specific features. You would not
normally add them to the help files you write.

You can use the h. prefix to identify standard help-file contexts. For
instance, h.default identifies the default help screen (the screen that
normally appears when you select top-level help). Table 11.1 lists the
standard h. contexts.

Table 11.1  Standard h. Contexts

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Context                           Description
────────────────────────────────────────────────────────────────────────────
h.contents                        The table of contents for the help file.
                                    You should also define the string
                                    "contents" for direct reference to this
                                    context.

h.default                         The default help screen, typically
                                    displayed when the user presses SHIFT+F1
                                    at the "top level" in some applications.

h.index                           The index for the help file. You can
                                    also define the string "index" for
                                    direct reference to this context.

h.notfound                        The help text displayed by some
                                    applications when the help system cannot
                                    find information about the requested
                                    context. The text could be an index of
                                    contexts, a topical list, or general
Context                           Description
────────────────────────────────────────────────────────────────────────────
                                    contexts, a topical list, or general
                                    information about using help.

h.pg#                             A specific page within the help file.
                                    This is used in response to a "go to
                                    page #" request.

h.pg$                             The help text that is logically last in
                                    the file. This is used by some
                                    applications in response to a "go to the
                                    end" request made within the help window.

h.pg1                             The help text that is logically first in
                                    the file. This is used by some
                                    applications in response to a "go to the
                                    beginning" request made within the help
                                    window.

h.title                           The title of the help database.
Context                           Description
────────────────────────────────────────────────────────────────────────────
h.title                           The title of the help database.

────────────────────────────────────────────────────────────────────────────



The context prefixes in Table 11.2 are internal to Microsoft products. They
appear in decompressed databases, but you do not need to use them.

Table 11.2  Microsoft Product Context Prefixes

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Prefix                            Purpose
────────────────────────────────────────────────────────────────────────────
d.                                Dialog box. Each dialog box is assigned
                                    a number. Its help context string is d.
                                    followed by the number (for example,
                                    d.12).

Prefix                            Purpose
────────────────────────────────────────────────────────────────────────────

e.                                Error number. If a product supports the
                                    error-numbering scheme used by Microsoft
                                    languages, it displays help for each
                                    error using this prefix. For example,
                                    the context  e.P0105  refers to the
                                    Microsoft QuickPascal Compiler error
                                    message number P0105.

h.                                Help item. Prefixes miscellaneous help
                                    context strings that may be constructed
                                    or otherwise hidden from the user. For
                                    example, most applications look for the
                                    context string h.contents when Contents
                                    is chosen from the Help menu.

m.                                Menu item. Contexts that relate to
                                    product menu items are defined by their
                                    shortcut keys. For example, the Exit
Prefix                            Purpose
────────────────────────────────────────────────────────────────────────────
                                    shortcut keys. For example, the Exit
                                    selection on the File menu item is
                                    accessed by ALT+F, X and is referenced
                                    in help by  m.f.x.

n.                                Message number. Each message box is
                                    assigned a number. Its help context
                                    string is n. plus the number (for
                                    example,  n.5).

────────────────────────────────────────────────────────────────────────────




11.5.4  Hyperlinks

Explicit cross-references, or hyperlinks, are marked with invisible text in
the help text file. A hyperlink is a word or phrase followed by invisible
text that names the context to which the hyperlink refers.

The keystroke that activates the hyperlink depends on the application.
Consult the documentation for each product for the specific keystroke.

When the user activates the hyperlink, the help system displays the topic
referenced by the invisible text. The invisible cross-reference text is
formatted as one of the following:

Hidden Text                       Action
────────────────────────────────────────────────────────────────────────────
contextstring                     Displays the topic associated with
                                    contextstring. For example,  exeformat
                                    displays the topic text for the context
                                    exeformat.

filename!                         Treats filename as a single topic to be
                                    displayed. For example,
                                    $INCLUDE:stdio.h!  searches the
                                    directories in the INCLUDE environment
                                    variable for file  stdio.h  and displays
                                    it as a single help topic.

filename!contextstring            Works the same as contextstring, except
                                    only the help file filename is searched
                                    for the context. If the file is not
                                    already open, the help system finds it
                                    (by searching either the current path or
                                    an explicit environment variable) and
                                    opens it. For example,
                                    $BIN:readme.doc!patches  searches for
                                    readme.doc  in the BIN environment
                                    variable and displays the topic
                                    associated with  patches.

!command                          Executes the command specified after the
                                    exclamation point (!).

In the following example, the word  Example  is a hyperlink. The b,p, and
v formatting flags mark hyperlinks in the help text. (The formatting flags
are listed later in this chapter, in Table 11.4.)

    bSee also:p    Examplevopen.exv

The hyperlink refers to  open.ex. If you select any of the letters of
Example, the help system displays the topic whose context is  open.ex. On
the screen, this line appears as follows:

    See also: Example

An application might display  See also:  and  Example  in different colors
or character types, depending on factors such as your default color
selection and type of monitor.

When a hyperlink needs to cross-reference more than one word, you must use
an anchor, as in the following example:

    bSee also:p   uExamplepvprintf.exv, fprintf, scanf, sprintf,
    vfprintf, vprintf, vsprintf
                aformatting tablevprintf.tablev

This part of the example is an anchored hyperlink:

    aformatting tablevprintf.tablev

The anchor must fit on one line.

The  a flag creates an anchor for the cross-reference. In the example, the
phrase following the  a flag (formatting table) is the hyperlink. It refers
to the context  printf.table. The first v flag marks both the end of the
hyperlink and the beginning of the invisible text. The name  printf.table
is invisible; it does not appear on the screen when the help is displayed.
The second v flag ends the invisible text.


11.6  Using Help Database Formats

A database can be written in any of three text formats. The list below
briefly describes these types. Sections 11.6.1-11.6.3 describe the
formatting types in detail.

An entire help system (such as the one supplied with PWB or QuickC) can
handle any combination of formats. For example, the help files for Microsoft
C are written in QuickHelp format, and the README.DOC file is unformatted
ASCII.

Type                              Characteristics
────────────────────────────────────────────────────────────────────────────
QuickHelp                         Uses dot commands and embedded
                                    formatting characters (the default
                                    formatting type expected by HELPMAKE);
                                    supports highlighting, color, and
                                    cross-references. Files in this format
                                    must be compressed before use.

RTF                               Uses a subset of standard RTF; supports
                                    highlighting, color, and
                                    cross-references; supports some dot
                                    commands. Files in this format must be
                                    compressed before use.

Minimally formatted ASCII         Uses a help delimiter (>>) to define
                                    help contexts; does not support
                                    highlighting, color, or crossreferences.
                                    Files in this format can be compressed,
                                    but compression is not required.


11.6.1  QuickHelp Format

The QuickHelp format uses a dot command and embedded formatting flags to
convey information to HELPMAKE.


11.6.1.1  QuickHelp Dot Commands

QuickHelp provides a number of dot commands that identify topics and convey
other topic-related information to the help system. If your help file
contains dot commands other than .context or .comment, you must supply the /
T option when encoding and decoding with HELPMAKE.

You can define more than one context for a single topic.

The most important dot command is the .context command. Every topic in a
QuickHelp file begins with one or more .context commands. Each .context
command defines a context string for the topic text. You can define more
than one context for a single topic, as long as you do not place any topic
text between them.

Typical .context commands are shown below. The first defines a context for
the  #include C preprocessor directive. The second set illustrates multiple
contexts for one block of topic text. In this case, the same topic text
explains all of the string-to-number conversion routines in C.

    .context #include
            .
            . description of #include goes here
            .
    .context strtod
    .context strtol
    .context strtoul
            .
            . description of string-to-number functions goes here
            .

The QuickHelp format includes several other dot commands. Table 11.3 lists
the dot commands available in QuickHelp format.

Table 11.3  QuickHelp Dot Commands

╓┌─────────────────────────────────────┌─────────────────────────────────────╖
Command                               Action
────────────────────────────────────────────────────────────────────────────
.category string                      Lists the category in which the
                                        current topic appears and its
                                        position in the list of topics. The
                                        category name is used by the
                                        QuickHelp Categories command, which
                                        displays the topics list. Supported
                                        only by QuickHelp.

.command                              Indicates that the topic text is not
                                        a displayable help topic. Use this
                                        command to hide hyperlink topics and
                                        other internal information.

.comment string                       The string is a comment that appears
.. string                             only in the help source file.
Command                               Action
────────────────────────────────────────────────────────────────────────────
.. string                             only in the help source file.
                                        Comments are not inserted in the
                                        help database, so they cannot be
                                        restored when you decompress a help
                                        file.

.context string                       The string introduces a topic.

.end                                  Ends a paste section. See the .paste
                                        command below. Supported only by
                                        QuickHelp.

.freeze numlines                      Locks the first numlines lines at
                                        the top of the screen. This can be
                                        used to preserve a bar of
                                        cross-reference buttons for a help
                                        topic and prevent it from being
                                        scrolled.

Command                               Action
────────────────────────────────────────────────────────────────────────────

.length topiclength                   Indicates the default window size,
                                        in topiclength lines, of the topic
                                        about to be displayed.

.line number                          Tells HELPMAKE to reset the line
                                        number to begin at number for
                                        subsequent lines of the input file.
                                        Line numbers appear in HELPMAKE
                                        error messages. HELPMAKE does not
                                        put the .line command into the help
                                        database, so it is not restored
                                        during decompression. See .source.

.list                                 Indicates that the current topic
                                        contains a list of topics. QuickHelp
                                        displays a highlighted line; you can
                                        choose a topic by moving the
                                        highlighted line over the desired
Command                               Action
────────────────────────────────────────────────────────────────────────────
                                        highlighted line over the desired
                                        topic and pressing ENTER. Help
                                        searches for the first word of the
                                        line. Supported only by QuickHelp.

.mark name «column»                   Defines a mark immediately preceding
                                        the following line of text. The
                                        marked line shows a script command
                                        where the display of a topic begins.
                                        The name identifies the mark. The
                                        column is an integer value
                                        specifying a column location within
                                        the marked line. Supported only by
                                        QuickHelp.




.next context                         Tells the help system to look up the
Command                               Action
────────────────────────────────────────────────────────────────────────────
.next context                         Tells the help system to look up the
                                        next topic using
                                        context instead of the topic that
                                        physically follows it in the file.
                                        You can use this command to skip
                                        large blocks of .command or .popup
                                        topics.

.paste pastename                      Begins a paste section. The
                                        pastename appears in the QuickHelp
                                        Paste menu. Supported only by
                                        QuickHelp.

.popup                                Tells the help system to display the
                                        current topic as a popup instead of
                                        a normal, scrollable topic.
                                        Supported only by QuickHelp.

.previous context                     Tells the help system to look up the
Command                               Action
────────────────────────────────────────────────────────────────────────────
.previous context                     Tells the help system to look up the
                                        previous topic using context instead
                                        of the topic that physically
                                        precedes it in the file. You can use
                                        this command to skip large blocks of
                                        .command or .popup topics.

.raw                                  Turns off special processing of
                                        certain characters by the
                                        application.

.ref topic «, topic» ...              Tells the help system to display the
                                        topic in the Reference menu. You can
                                        list as many topics as needed;
                                        separate each additional topic with
                                        a comma. A .ref command is formatted
                                        without regard to the /W option.
                                        Supported only by QuickHelp.

Command                               Action
────────────────────────────────────────────────────────────────────────────

                                        If no topic is specified, QuickHelp
                                        searches the line immediately
                                        following for a See: or See Also:
                                        reference; if present, the reference
                                        must be the first non-white-space
                                        characters on the line.

.source filename                      Tells HELPMAKE that subsequent
                                        topics come from filename. By
                                        default, when an error occurs, the
                                        error message contains the name and
                                        line number of the input file. The
                                        .source command tells HELPMAKE to
                                        use filename in the error message
                                        instead of the name of the input
                                        file and to reset the line number to
                                        1. This is useful when you
                                        concatenate several sources to form
Command                               Action
────────────────────────────────────────────────────────────────────────────
                                        concatenate several sources to form
                                        the input file. HELPMAKE does not
                                        put the .source command into the
                                        help database, so it is not restored
                                        during decompression. See .line.

.topic text                           Defines text as the name or title to
                                        be displayed in place of the context
                                        string if the application help
                                        displays a title. This command is
                                        always the first line in the context
                                        unless you also use the .length or
                                        .freeze commands.

────────────────────────────────────────────────────────────────────────────




11.6.1.2  QuickHelp Formatting Flags

The QuickHelp format provides a number of formatting flags that are used to
highlight parts of the help database and to mark hyperlinks in the help
text.

Each formatting flag consists of a backslash (  ) followed by a character.
Table 11.4 lists the formatting flags.

Table 11.4  QuickHelp Formatting Flags

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Formatting Flag                   Action
────────────────────────────────────────────────────────────────────────────
 a                               Anchors text for cross-references

 b,  B                          Turns boldface on or off

 i,  I                          Turns italics on or off

 p,  P                          Turns off all attributes
Formatting Flag                   Action
────────────────────────────────────────────────────────────────────────────
 p,  P                          Turns off all attributes

 u,  U                          Turns underlining on or off

 v, V                           Turns invisibility on or off
                                    (hides cross-references in text)

\                                Inserts a single backslash in text

────────────────────────────────────────────────────────────────────────────



On monochrome monitors, text labeled with the bold, italic, and underline
attributes appears in various ways, depending on the application (for
example, high intensity and reverse video are commonly displayed). On color
monitors, these attributes are translated by the application into suitable
colors, depending on the user's default color selections.

The  b,  i,  u, and v options are toggles, turning on and off their
respective attributes. You can use several of these on the same text. Use
the  p attribute to turn off all attributes. Use the v attribute to hide
cross-references and hyperlinks in the text.

HELPMAKE truncates the lines in QuickHelp files to the width specified with
the / W option. Only visible characters count toward the character-width
limit. Lines that begin with an application-specific control character are
truncated to 255 characters regardless of the width specification. See
Section 11.3.1, "Options for Encoding," for more information on truncation
and application-specific control characters.

In the example below, the  b flag initiates boldface text for  Returns:,
and the  p flag changes the remaining text to plain text.

    bReturns:p    a handle if successful, or -1 if not.
                errno:  EACCES, EEXIST, EMFILE, ENOENT

In the example below, the  a flag anchors text for the hyperlink  Example.
The v flags define the cross-reference  sample_prog  and make the text
between the v flags invisible. Cross-references are described in the
following section.

    aExample vsample_progv


11.6.1.3  QuickHelp Cross-References

Help databases contain two types of cross-references, implicit and explicit.
They are described in Section 11.1.1, "Contents of a Help File."

Any word that appears as a global context is implicitly cross-referenced.
For example, any time you request help in PWB on close, the help window
displays information about that function. You do not code implicit
cross-references into your help text files.

Insert formatting flags to mark explicit cross-references.

Explicit cross-references (hyperlinks) are words or phrases on the screen
that point to a context. For example, almost every "See:" and "See also:"
reference in online help has a hyperlink pointing to the appropriate
context. You can view the cross-referenced material immediately by
activating the hyperlink, without having to search the help system's menus
for the topic. You must insert formatting flags in your help text files to
mark explicit cross-references.

If the hyperlink consists of a single word, you can use invisible text to
flag it in the source file. The v formatting flag creates invisible text,
as follows:

    hyperlinkvcontextv

Put the first v flag immediately following the word you want to be the
hyperlink. Following the flag, insert the context that the hyperlink points
to. The second v flag marks the end of the context; that is, the end of the
invisible text. HELPMAKE generates a cross-reference whose context is the
invisible text and whose hyperlink is the word.

If the hyperlink consists of a phrase, rather than a single word, you must
use anchored text to create explicit cross-references. Use the  a and v
flags to create anchored text as follows:

    ahyperlink-wordsvcontextv

The  a flag marks an anchor for the cross-reference. The text that follows
the  a flag is the hyperlink. The hyperlink must fit entirely on one line.
The first v flag marks both the end of the hyperlink and the beginning of
the invisible text that contains the cross-reference context. The second v
flag marks the end of the invisible text.

The C functions abs, cabs, and fabs in the following examples are implicit
cross-references because they have a global context in the help system.

    See also: abs, cabs, fabs

The next example shows the encoding for an explicit cross-reference to an
example program and a function template from the help database for the
Microsoft C run-time library:

    See also: Examplevopen.exv, Templatevopen.tmv, close

Here, the hyperlinks are  Example  and  Template, which reference the
contexts  open.ex  and  open.tm. The example also contains an implicit
cross-reference to the close function.

The final example shows the encoding for an explicit cross-reference to an
entire family of functions:

    See also: ais... functionsvis_functionsv, atoi

The cross-reference uses anchored text to associate a phrase, rather than
just a word, with a context. In this example, the hyperlink is the anchored
phrase  is... functions, and it cross-references the context  is_functions.
In addition, the example contains an implicit cross-reference to the
C-language atoi routine.


11.6.1.4  QuickHelp Example

The code below is an example in QuickHelp format that contains a single
entry:

    .context open
    .length 13
    bInclude:p   <fcntl.h>, <io.h>, <sys\types.h>, <sys\stat.h>

    bPrototype:p  int open(char *path, int flag[, int mode]);
            oflag:  O_APPEND O_BINARY O_CREAT O_EXCL O_RDONLY
                    O_RDWR    O_TEXT    O_TRUNC  O_WRONLY
                    (can be joined by |)
            pmode:  S_IWRITE  S_IREAD   S_IREAD | S_IWRITE

    bReturns:p    a handle if successful, or -1 if not.
                errno:  EACCES, EEXIST, EMFILE, ENOENT

    bSee also:p  uExamplepvopen.exv, uTemplatepvopen.tpv,
                access, chmod, close, creat, dup, dup2, fopen, sopen,
    umask

The .length command near the beginning of the example specifies the size of
the initial window for the help text. Here, the initial window displays 13
lines.

The manifest constants (such as O_WRONLY and EEXIST), the C keywords (such
as int and char), and the other functions (such as access and sopen) are
implicit cross-references. The words  Example  and  Template  are explicit
cross-references to the example  open.ex  and to the open template  open.tp,
respectively. Note the use of double backslashes in the include file names.



11.6.2  Rich Text Format

Rich Text Format (RTF) is a Microsoft word-processing format supported by
several word processors, including Microsoft Word 5.0 and Microsoft Word for
Windows. RTF allows documents to be transferred between applications without
loss of formatting. The HELPMAKE utility recognizes a subset of the full RTF
syntax. If your file contains RTF codes that are not part of the subset,
HELPMAKE discards them.

To create an RTF-formatted file, enter the text and format it as you want it
to appear: bold, underlined, hidden, italic, and so forth. (You can combine
attributes.) You can also format paragraphs, selecting body and first-line
indenting. The only items you need to insert into an RTF file manually are
the help delimiter (>>) and the context string that start each entry.

When you have entered and formatted the text, save it in RTF format. In
Microsoft Word 5.0, for example, this means choosing Transfer Save, then
highlighting RTF in the format: field.

You do not see the RTF formatting codes when you load an RTF file into a
compatible word processor; the word processor removes them and displays the
text with the specified attribute(s). However, you can view these codes by
loading an RTF file into a plain-text word processor.

HELPMAKE recognizes the subset of RTF codes listed in Table 11.5.

Table   11.5 RTF Formatting Codes

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
RTF Code
────────────────────────────────────────────────────────────────────────────
 b                               Boldface. The application decides how to
                                    display this; often it is
                                    intensified text.

 fin                             Paragraph first-line indent, n columns.

RTF Code
────────────────────────────────────────────────────────────────────────────

 i                               Italic. The application decides how to
                                    display this; often it is reverse video.

 lin                             Paragraph indent from left margin, n
                                    columns.

 line                            New line (not new paragraph).

 par                             End of paragraph.

 pard                            Default paragraph formatting.

 plain                           Default attributes. On most screens,
                                    this is nonblinking normal
                                    intensity.

 tab                             Tab character.

RTF Code
────────────────────────────────────────────────────────────────────────────

 ul                              Underline. The application decides how
                                    to display this; some adapters that do
                                    not support underlining display it as
                                    blue text.

 v                               Hidden text. Hidden text is used for
                                    cross-reference information and for some
                                    application-specific communications; it
                                    is not
                                    displayed.

────────────────────────────────────────────────────────────────────────────



When HELPMAKE compresses the file, it formats the text to the width given
with the / W option, ignoring the paragraph formats.

As with the other text formats, each entry in the database source consists
of one or more context strings, followed by topic text. An RTF file can
contain QuickHelp dot commands.

The help delimiter (>>) at the beginning of any paragraph marks the
beginning of a new help entry. The text that follows on the same line is
defined as a context for the topic. If the next paragraph also begins with
the help delimiter, it also defines a context string for the same topic
text. You can define any number of contexts for a block of topic text. The
topic text comprises all subsequent paragraphs up to the next paragraph that
begins with the help delimiter.

The example below is a help database containing a single entry using subset
RTF text. Note that RTF uses curly braces ( { } ) for nesting. Thus, the
entire file is enclosed in curly braces, as is each specially formatted text
item.

    {rtf1
    pard >>openpar
    {b Include:}    <fcntl.h>, <io.h>, <sys\types.h>, <sys\stat.h>par
    par
    {b Syntax:}     int open( char * filename, int oflag[, int pmode
    ] );par
                oflag:  O_APPEND  O_BINARY  O_CREAT  O_EXCL  O_RDONLYpar

                        O_RDWR    O_TEXT    O_TRUNC  O_WRONLYpar
                        (may be joined by |)par
                pmode:  S_IWRITE  S_IREAD   S_IREAD | S_IWRITEpar
    par
    {b Returns:}    a handle if successful, or -1 if not.par
                errno:  EACCES, EEXIST, EMFILE, ENOENTpar
    par
    {b See also:}  Examples{v open.ex}, access, chmod, close, creat,
    dup,par
                dup2, fopen, sopen, umaskpar
    >>open.expar
    To build this help file, use the following command:par
    par
    HELPMAKE /S1 /E15 /OOPEN.HLP OPEN.RTFpar
    par

            < Back >{v !B}
    }

RTF files normally contain additional information that is not visible to the
user; HELPMAKE ignores this extra information.


11.6.3  Minimally Formatted ASCII Format

A minimally formatted ASCII text file comprises a sequence of topics, each
preceded by one or more unique context definitions. Each context definition
must be on a separate line beginning with a help delimiter (>>). Subsequent
lines up to the next context definition constitute the topic text.

Minimally formatted ASCII files cannot contain highlighting.

There are two ways to use a minimally formatted ASCII file. You can compress
it with HELPMAKE, creating a help database, or an application can access the
uncompressed file directly. Compressing minimally formatted ASCII files
increases search speed. Uncompressed files are somewhat larger and slower to
search. Minimally formatted ASCII files have a fixed width, and they cannot
contain highlighting (or other nondefault attributes) or explicit
cross-references.

The following example, coded in minimally formatted ASCII, shows the same
text as the QuickHelp example presented earlier in this section. The first
line of the example defines  open  as a context string. The minimally
formatted ASCII help file must begin with the help delimiter (>>), so that
HELPMAKE or the application can verify that the file is indeed an ASCII help
file.

    >>>>open

    Include:    <fcntl.h>, <io.h>, <systypes.h>, <sysstat.h>

    Prototype:  int open(char *path, int flag[, int mode]);
            oflag:  O_APPEND  O_BINARY  O_CREAT  O_EXCL  O_RDONLY
                    O_RDWR    O_TEXT    O_TRUNC  O_WRONLY
                    (can be joined by |)
            pmode:  S_IWRITE  S_IREAD   S_IREAD | S_IWRITE

    Returns:    a handle if successful, or -1 if not.
                errno:  EACCES, EEXIST, EMFILE, ENOENT

    See also:  access, chmod, close, creat, dup, dup2, fopen, sopen,
    umask

When displayed, the help information appears exactly as it is typed into the
file. Any formatting codes are treated as ASCII text.


11.7  Related Topics in Online Help

Information on the following related topics can be found in online help.

Topic       Access
────────────────────────────────────────────────────────────────────────────
HELPMAKE    Choose "HELPMAKE" from the "Microsoft Advisor Contents" screen
QuickHelp   Choose "QH" from the "Microsoft Advisor Contents" screen






Chapter 12  Linking Object Files with LINK
────────────────────────────────────────────────────────────────────────────

This chapter describes the Microsoft Segmented-Executable Linker (LINK),
which combines compiled or assembled object files into an executable file.
It explains LINK's input syntax and fields and tells how to use options to
control LINK. It discusses overlays in DOS programs and concludes with
background information about LINK.


12.1  Overview

LINK combines 80x86 object files into either an executable file or a
dynamic-link library (DLL). The object-file format is the Microsoft
Relocatable Object-Module Format (OMF), based on the Intel 8086 OMF. LINK
uses library files in Microsoft library format.

LINK creates "relocatable" executable files and DLLs─that is, the operating
system can load and execute these files in any unused section of memory.
LINK can create DOS executable files with up to 1 megabyte of code and data
(or up to 16 megabytes when using overlays), or OS/2 and Microsoft Windows
programs with up to 16 megabytes.

For more information on OMF, executable-file format, and the linking
process, see the MS-DOS Encyclopedia.

Use BIND to create an OS/2 program that also runs under DOS.

The linker produces programs that run under DOS only or under OS/2 only, but
not both. However, if an OS/2 program limits its OS/2 function calls to the
Family API subset, you can use the Microsoft Bind Utility (BIND) to modify
the OS/2 executable file so that it runs under both OS/2 and DOS. For more
information, see online help.

Use EXEHDR to examine the finished file.

When the file (either executable or DLL) is created, you can examine the
information that LINK puts in the file's header by using the Microsoft EXE
File Header Utility (EXEHDR). For more information, see online help.

Other programs can call LINK automatically.

The Programmer's WorkBench (PWB) invokes LINK to create the final executable
file or DLL. Therefore, if you develop your software with PWB, you might not
need to read this chapter. However, the detailed explanations of LINK
options might be helpful when you use the LINK Options dialog box in PWB.
This information is also available in online help.

The compiler or assembler supplied with your language (CL with C, FL with
FORTRAN, ML with MASM) also invokes LINK. You can use most of the LINK
options described in this chapter with this utility. Online help has more
information about the compilers and assembler: select help for the
appropriate language from the Compiler box of the help Contents screen.

────────────────────────────────────────────────────────────────────────────
NOTE

Unless otherwise noted, all references to "library" in this chapter refer to
a static library, either a standard library created by the Microsoft Library
Manager (LIB) or an import library created by the Microsoft Import Library
Manager (IMPLIB), and not a DLL.
────────────────────────────────────────────────────────────────────────────


12.2  LINK Output Files

LINK is a bound application that runs under both DOS and OS/2 and can create
executable files for DOS, OS/2, or Windows. You do not have to run LINK
under OS/2 to create OS/2 applications, or under DOS to create DOS programs.
The kind of file produced is determined by the way the source code is
compiled and the information supplied to LINK, not the operating system LINK
runs under.

A program that runs under DOS is called an executable file or application. A
program or DLL that runs under Windows or OS/2 is called a segmented
executable file. LINK creates the appropriate file according to the
following rules:


    ■   If a module-definition file or import library is not specified and the
        object files and libraries do not contain export definitions, LINK
        creates an application that runs under DOS.

    ■   If a module-definition file containing a LIBRARY statement is
        specified, LINK creates a DLL for Windows or OS/2.

    ■   If any other form of module-definition file is specified, or if any of
        the object files contains an exported definition, LINK creates an
        application to run under Windows or OS/2.


LINK looks for the default run-time libraries named in the object files.
Default libraries can be real or protected mode. (The mode is usually set
when the language product is installed.) Protected-mode libraries contain
export definitions. If LINK finds protected-mode default libraries, the
output file will be a segmented executable file rather than a DOS file.

The file OS2.LIB is an import library. Linking with OS2.LIB produces an OS/2
application or DLL. When you use a Microsoft high-level language to compile
for protected mode, the compiler automatically specifies OS2.LIB as a
default library.

LINK's output is either an executable file or a DLL. For simplicity, this
chapter sometimes refers to this output as the "main file" or "main output."


Map files list the segments and symbols in a program.

LINK also creates a "map" file, which lists the segments in the executable
file. The /MAP option adds public symbols to the map file, and the /LINE
option adds line numbers.

LINK produces other files when certain options are used.

Other options tell LINK to create other kinds of output files. The /INCR
option creates .ILK and .SYM files for incremental linking with ILINK. LINK
produces a .COM file instead of an .EXE file when the /TINY option is
specified. The combination of /CO and /TINY puts debugging information into
a .DBG file. A Quick library results when the /Q option is specified. For
more information on these and other options, see Section 12.5, "LINK
Options."


12.3  LINK Syntax and Input

The LINK command has the following syntax:

    LINK objfiles«, «exefile» «,
    «mapfile»«, «libraries»«, deffile»
    » » »«;»

The LINK fields perform the following functions:


    ■   The objfiles field is a list of the object files that are to be linked
        into an executable file or DLL. It is the only required field.

    ■   The exefile field lets you change the name of the output file from its
        default.

    ■   The mapfile field gives the map file a name other than its default
        name.

    ■   The libraries field specifies additional (or replacement) libraries to
        search for unresolved references.

    ■   The deffile field gives the name of a description file needed to
        create Windows and OS/2 applications and DLLs.


Fields are separated by commas. You can specify all the fields or leave one
or more fields (including objfiles) blank; LINK will then prompt you for the
missing input. (For an explanation of how to use LINK prompts, see Section
12.4, "Running LINK.") To leave a field blank, enter only the field's
trailing comma.

Options can be specified in any field. For descriptions of each of LINK's
options, see Section 12.5, "LINK Options."

The fields must be entered in the order shown, whether they contain input or
are left blank. A semicolon (;) at the end of the LINK command line
terminates the command and suppresses prompting for any missing fields. LINK
then assumes the default values for the missing fields.

If your file appears in or is to be created in another directory or device,
you must supply the full pathname. Filenames are not case sensitive.

The next five sections explain how to use each of the LINK fields.


12.3.1  The objfiles Field

The objfiles field specifies one or more object files to be linked. At least
one filename must be entered. If you do not supply an extension, LINK
assumes a default .OBJ extension. If the filename has no extension, add a
period (.) at the end of its name.

If you name more than one object file, separate the names with a plus sign
(+) or a space. To extend objfiles to the following line, type a plus sign
(+) as the last character on the current line, press ENTER, and continue. Do
not split a name across lines.


12.3.1.1  Load Libraries

The objfiles field can also specify library files. A library specified this
way becomes a "load library." You must specify the library's filename
extension; otherwise, LINK assumes an .OBJ extension.

LINK treats load libraries as any other object file: it puts every object
module from a load library in the executable file, regardless of whether a
module satisfies an unresolved external reference. The effect is the same as
if you had specified all the library's object-module names in the objfiles
field.

Specifying a load library can therefore create an executable file or DLL
that is larger than it needs to be. (A library named in the libraries field
adds only those modules required to resolve external references.) However,
loading an entire library can be useful when


    ■   Repeatedly specifying the same group of object files

    ■   Placing a library in an overlay

    ■   Debugging, so you can call library routines that would not be included
        in the release version of the program



12.3.1.2  How LINK Searches for Object Files

When searching for object (and load-library) files, LINK looks in the
following locations in the order specified:


    1.  The directory specified for the file (if a path is included). If the
        file is not in that directory, the search terminates.

    2.  The current directory.

    3.  Any directories specified in the LIB environment variable.


If LINK cannot find an object file, and a floppy drive is associated with
that object file, LINK pauses and prompts you to insert a disk containing
the object file.

If you specify a library in the objfiles field, LINK treats it like any
other object file. LINK therefore does not search for load libraries in
directories named in the libraries field.


12.3.1.3  Overlays

A special syntax for the objfiles field lets you create DOS programs that
use overlay modules. For more information about overlays, see Section 12.7,
"Using Overlays under DOS."


12.3.2  The exefile Field

The exefile field is used to specify a name for the main output file. If you
do not supply an extension, LINK assumes a default extension, either .EXE,
.COM (when using the /TINY option), .DLL (when using a module-definition
file containing a LIBRARY statement), or .QLB (when using the /Q option).

If you do not specify an exefile, LINK gives the main output a default name.
This name is the base name of the first file listed in the objfiles field,
plus the extension appropriate for the type of executable file being
created.

LINK creates the main file in the current directory unless you specify an
explicit path with the filename.


12.3.3  The mapfile Field

The mapfile field is used to specify a filename for the map file or to
suppress creation of a map file. A map file lists the segments in the
executable file or DLL.

You can specify a path with the filename. The default extension is .MAP.
Specify  NUL  to suppress the creation of a map file. The default for the
mapfile field is one of the following:


    ■   If this field is left blank on the command line or in a response file,
        LINK creates a map file with the base name of the exefile (or the
        first object file if no exefile is specified) and the extension .MAP.

    ■   When using LINK prompts, LINK assumes either the default described
        above (if an empty mapfile field is specified) or  NUL.MAP, which
        suppresses creation of a map file.


To add line numbers to the map file, use the /LINE option. To add public
symbols, use the /MAP option. Both /LINE and /MAP force a map file to be
created unless NULL is explicitly specified.


12.3.4  The libraries Field

You can specify one or more standard or import libraries (not DLLs) in the
libraries field. If you name more than one library, separate the names with
a plus sign (+) or a space. To extend libraries to the following line, type
a plus sign (+) as the last character on the current line, press ENTER, and
continue. Do not split a name across lines. If you specify the base name of
a library without an extension, LINK assumes a default .LIB extension.

If no library is specified, LINK searches only the default libraries named
in the object files to resolve unresolved references. If one or more
libraries are specified, LINK searches them in the order named before
searching the default libraries.

You can tell LINK to search additional directories for specified or default
libraries by giving a drive name or path specification in the libraries
field; end the specification with a backslash (  ). (If you don't include
the backslash, LINK assumes the last element of the path is a library file.)
LINK looks for files ending in .LIB in these directories.

You can specify a total of 32 paths or libraries in the field. If you give
more than 32 paths or libraries, LINK ignores the additional specifications
without warning you.

You might need to specify library names when you want to


    ■   Use a default library that has been renamed.

    ■   Specify a library other than the default named in the object file (for
        example, a library that handles floating-point arithmetic differently
        from the default library).

    ■   Search additional libraries.

    ■   Find a library not in the current directory and not in a directory
        specified by the LIB environment variable.



12.3.4.1  Overriding Default-Library Searches

Most compilers insert the names of the required language libraries in the
object files. LINK searches for these default libraries automatically; you
do not need to specify them in the libraries field. The libraries must
already exist with the name expected by LINK. Default-library names usually
refer to combined libraries built and named during setup; consult your
compiler documentation for more information about default libraries.

To make LINK ignore the default libraries, use the /NOD option. This leaves
unresolved references in the object files, so you must use the libraries
field to specify the alternative libraries that LINK is to search.


12.3.4.2  Import Libraries

You can specify import libraries created by the IMPLIB utility anywhere you
can specify standard libraries. You can also use the LIB utility to combine
import libraries and standard libraries. These combined libraries can then
be specified in the libraries field.


12.3.4.3  How LINK Resolves References

LINK searches static libraries to resolve external references. A static
library is either a standard library created by the LIB utility or an import
library created by the IMPLIB utility. The linker searches first in the
libraries and library directories you specify (in the order you specify
them), then in the default libraries. If a default library is explicitly
specified, it is searched in the order it is given.

LINK uses only those library modules needed to resolve external references,
not the entire library. However, if you enter a library as a load library in
the objfiles field, all the modules of a load library are added to the main
output.


12.3.4.4  How LINK Searches for Library Files

When searching for libraries, LINK looks in the following locations in this
order:


    1.  The directory specified for the file (if a path is included). If the
        file is not in that directory, the search terminates. (The default
        libraries named in object files by Microsoft compilers do not include
        path specifications.)

    2.  The current directory.

    3.  Any directories in the libraries field.

    4.  Any directories specified in the LIB environment variable.


If LINK cannot locate a library file, it prompts you to enter the location.
The /BATCH option disables this prompting.


Example

The following is a specification in the libraries field:

    C:TESTLIB NEWLIBV3 C:MYLIBSSPECIAL

LINK searches NEWLIBV3.LIB first for unresolved references. Since no
directory is specified for NEWLIBV3.LIB, LINK searches the following
locations in this order:


    1.  The current directory

    2.  The C:TESTLIB directory

    3.  The directories in the LIB environment variable


If LINK still cannot find NEWLIBV3.LIB, it prompts you with the message

    Enter new file spec

You can then enter either a path to the library or a full pathname for
another library.

If unresolved references remain after searching NEWLIBV3.LIB, LINK then
searches the library C:MYLIBSSPECIAL.LIB. If LINK cannot find this
library, it prompts you as described above for NEWLIBV3.LIB. If there are
still unresolved references, LINK searches the default libraries.


12.3.5  The deffile Field

Use the deffile field to specify a module-definition file when you are
linking a segmented executable file, which is an application or DLL for OS/2
or Windows. A module-definition file is optional for an application but
required for a DLL. If you specify a base name with no extension, LINK
assumes a .DEF extension. If the filename has no extension, put a period (.)
at the end of the name.

By default, LINK assumes that no deffile needs to be specified. If you are
linking for DOS, use a semicolon to terminate the command line before the
deffile field (or accept the default NUL.DEF at the  Definitions File
prompt).


12.3.5.1  How LINK Searches for Module-Definition Files

LINK searches for the module-definition file in the following order:


    1.  The directory specified for the file (if a path is included). If the
        file is not in that directory, the search terminates.

    2.  The current directory.


For information on module-definition files, see Chapter 13.


12.3.6  Examples

The following examples illustrate various uses of the LINK command line.


Example 1

    LINK FUN+TEXT+TABLE+CARE, , FUNLIST, XLIB.LIB;

This command line links the object files FUN.OBJ, TEXT.OBJ, TABLE.OBJ, and
CARE.OBJ. By default, the executable file is named FUN.EXE, because the base
name of the first object file is  FUN, and no name is specified for the
executable file. The map file is named FUNLIST.MAP. LINK searches for
unresolved external references in the library XLIB.LIB before searching in
the default libraries. LINK does not prompt for a .DEF file because a
semicolon appears before the deffile field.


Example 2

    LINK FUN, , ;

This command produces a map file named FUN.MAP because a comma appears as a
placeholder for the mapfile field on the command line.


Example 3

    LINK FUN, ;
    LINK FUN;

Neither of these commands produces a map file, because commas do not appear
as placeholders for the mapfile field. The semicolon (;) terminates the
command line and accepts all remaining defaults without prompting; the
prompting default for the map file is not to create one.


Example 4

    LINK MAIN+GETDATA+PRINTIT, , MAIN ;

This command links the files MAIN.OBJ, GETDATA.OBJ, and PRINTIT.OBJ into a
DOS executable file because no module-definition file is specified. The map
file MAIN.MAP is created.


Example 5

    LINK GETDATA+PRINTIT, , , , MODDEF

This command links GETDATA.OBJ and PRINTIT.OBJ into a DLL if MODDEF.DEF
contains a LIBRARY statement. Otherwise, it links them into a segmented
executable file for OS/2 or Windows. LINK creates a map file named
GETDATA.MAP.


12.4  Running LINK

The simplest use of LINK is to combine one or more object files with a
run-time library to create an executable file. You type  LINK  at the
command-line prompt, followed by the names of the object files and a
semicolon (;). LINK combines the object files with language libraries
specified in the object files to create an executable file. By default, the
executable file takes the name of the first object file in the list.

To interrupt LINK and return to the operating-system prompt, press CTRL+C at
any time.

LINK expects you to supply at least one input field (the objfiles field),
and as many as five. There are several ways to supply the input fields LINK
expects:


    ■   Enter all the required input directly on the command line.

    ■   Omit one or more of the input fields and respond when LINK prompts for
        the missing fields.

    ■   Put the input in a response file and enter the response-file name in
        place of the expected input.


These methods can be used in combination. The LINK command line was
discussed in Section 12.3. The following sections explain the other two
methods.


12.4.1  Specifying Input with LINK Prompts

If any field is missing from the LINK command line and the line does not end
with a semicolon, or if any of the supplied fields are invalid, LINK prompts
you for the missing or incorrect information. LINK displays one prompt at a
time and waits until you respond:

    Object Modules [.OBJ]:
    Run File [basename.EXE]:
    List File [NUL.MAP]:
    Libraries [.LIB]:
    Definitions File [NUL.DEF]:

The LINK prompts correspond to the command-line fields described earlier in
this chapter. If you want LINK to prompt you for every input field,
including objfiles, type the command  LINK  by itself.

Options can be entered anywhere in any field, before the semicolon if
specified.


12.4.1.1  Defaults

The default values for each field are shown in brackets. Press ENTER to
accept the default, or type in the filename(s) you want. The basename is the
base name of the first object file you specified. To select the default
responses for all the remaining prompts and terminate prompting, type a
semicolon (;) and press ENTER.

If you specify a filename without giving an extension, LINK adds the
appropriate default extension. To specify a filename that does not have an
extension, type a period (.) after the name.

Use a space or plus sign (+) to separate multiple filenames in the objfiles
and libraries fields. To extend a long objfiles or libraries response to a
new line, type a plus sign (+) as the last character on the current line and
press ENTER. You can continue entering your response when the same prompt
appears on a new line. Do not split a filename or a pathname across lines.


12.4.2  Specifying Input in a Response File

You can supply input to LINK in a response file. A response file is a text
file containing the input LINK expects on the command line or in response to
prompts. Response files can be used to hold frequently used options or
responses, or to overcome the 128-character limit on the length of a DOS
command line.


12.4.2.1  Usage

Specify the name of the response file in place of the expected command-line
input or in response to a prompt. Precede the name with an at sign (@), as
in @responsefile. You must specify an extension if the response file has
one; there is no default extension. You can specify a path with the
filename.

You can specify a response file in any field (either on the command line or
when responding to prompts) to supply input for one or more consecutive
fields or all remaining fields. Note that LINK assumes nothing about the
contents of the response file; LINK simply reads the fields from the file
and applies them, in order, to the fields for which it has no input. LINK
ignores any fields in the response file or on the command line after the
five expected fields are satisfied or a semicolon (;) appears.


Example

The following command invokes LINK and supplies all input in a response
file, except the last input field:

    LINK @input.txt, mydefs


12.4.2.2  Contents of the Response File

Each input field must appear on a separate line or be separated from other
fields on the same line by a comma. You can extend a field to the following
line by adding a plus sign (+) at the end of the current line. A blank field
can be represented by either a blank line or a comma.

Options can be entered anywhere in any field, before the semicolon if
specified.

If a response file does not specify all the fields, LINK prompts you for the
rest. Use a semicolon (;) to suppress prompting and accept the default
responses for all remaining fields.


Example

    FUN TEXT TABLE+
    CARE
    /MAP
    FUNLIST
    GRAF.LIB ;

If the response file above is named  FUN.LNK, the command

    LINK @FUN.LNK

causes LINK to


    ■   Link the four object files FUN.OBJ, TEXT.OBJ, TABLE.OBJ, and CARE.OBJ
        into an executable file named FUN.EXE.

    ■   Include public symbols and addresses in the map file.

    ■   Make the name of the map file FUNLIST.MAP.

    ■   Link any needed routines from the library file GRAF.LIB.

    ■   Assume no module-definition file.



12.5  LINK Options

This section explains how to use options to control LINK's behavior and
modify LINK's output. It contains a description of each option following a
brief introduction on how to specify options.


12.5.1  Specifying Options

The following paragraphs discuss rules for using options.


12.5.1.1  Syntax

All options begin with a slash ( / ). You can specify an option by using the
shortest sequence of characters that uniquely identifies the option. The
description for each option shows the minimum legal abbreviation with the
optional part enclosed in double brackets. No gaps or transpositions of
letters are allowed. For example,

    /B«ATCH»

indicates that either /B or /BATCH can be used, as can /BA, /BAT, or /BATC.
Option names are not case sensitive, so you can also specify /batch or
/Batch. This chapter uses meaningful yet legal forms of the option names.


12.5.1.2  Usage

LINK options can appear on the command line, in response to a prompt, or as
part of a field in a response file. They can also be specified in the LINK
environment variable. (For more information, see Section 12.6, "Setting
Options with the LINK Environment Variable.") Options can appear in any
field before the last input, except as noted in the descriptions.

If an option appears more than once (for example, on the command line and in
the LINK variable), the effect is the same as if the option was given only
once. If two options conflict, the most recently specified option takes
effect. This means that a command-line option or one given in response to a
prompt overrides one specified in the LINK environment variable. For
example, the command-line option /SEG:512 cancels the effect of the
environment-variable option /SEG:256.


12.5.1.3  Numeric Arguments

Some LINK options take numeric arguments. You can enter numbers either in
decimal format or in standard C-language notation.


12.5.2  The /ALIGN Option


Option

    /A«LIGNMENT»:size

The /ALIGN option aligns segments in a segmented executable file at the
boundaries specified by size. The size argument must be an integer power of
two. For example,

    /ALIGN:16

indicates an alignment boundary of 16 bytes. The default alignment is 512
bytes.

This option reduces the size of the disk file by reducing the size of gaps
between segments. It has no effect on the size of the file when loaded in
memory.


12.5.3  The /BATCH Option


Option

    /B«ATCH»

The /BATCH option suppresses prompting for libraries or object files that
LINK cannot find. By default, the linker prompts for a new pathname whenever
it cannot find a library that it has been directed to use. It also prompts
you if it cannot find an object file that it expects to find on a floppy
disk. When /BATCH is used, the linker generates an error or warning message
(if appropriate). The /BATCH option also suppresses the LINK copyright
message and echoed input from response files.

Using this option can cause unresolved external references. It is intended
primarily for users who use batch files or makefiles for linking many
executable files with a single command and who wish to prevent linker
operation from halting.

────────────────────────────────────────────────────────────────────────────
NOTE

This option does not suppress prompts for input fields. Use a semicolon (;)
at the end of the LINK input to suppress input prompting.
────────────────────────────────────────────────────────────────────────────


12.5.4  The /CO Option


Option

    /CO«DEVIEW»

The /CO option adds line numbers and symbolic data to the executable file
for use with the Microsoft CodeView debugger. The /CO option has no effect
if the object files do not contain CodeView debugging information.

You can run the resulting executable file outside CodeView; the debugging
data in the file is ignored. However, it increases file size and slows
execution slightly. You should link a separate release version without the
/CO option after the program has been debugged.

When /CO is used with the /TINY option, debug information is put in a
separate file with the same base name as the .COM file and with the .DBG
extension.

The /CO option is not compatible with the /EXEPACK option for DOS executable
files.


12.5.5  The /CPARM Option


Option

    /CP«ARMAXALLOC»:number

The /CPARM option sets the maximum number of 16-byte paragraphs needed by
the program when it is loaded into memory. The operating system uses this
value to allocate space for the program before loading it. This option is
useful when you want to execute another program from within your program and
you need to reserve memory for the program. The /CPARM option is valid only
when linking DOS programs.

LINK normally requests the operating system to set the maximum number of
paragraphs to 65,535. Since this is more memory than DOS can supply, the
operating system always denies the request and allocates the largest
contiguous block of memory it can find. If the /CPARM option is used, the
operating system allocates no more space than the option specified. Any
memory in excess of that required for the program loaded is free for other
programs.

The number can be any integer value in the range 1 to 65,535. If number is
less than the minimum number of paragraphs needed by the program, LINK
ignores your request and sets the maximum value equal to whatever the
minimum value happens to be. The minimum number of paragraphs needed by a
program is never less than the number of paragraphs of code and data in the
program. To free more memory for programs compiled in the medium and large
models, link with /CPARM:1. This leaves no space for the near heap.

────────────────────────────────────────────────────────────────────────────
NOTE

You can change the maximum allocation after linking by using the EXEHDR
utility, which modifies the executable-file header.
────────────────────────────────────────────────────────────────────────────


12.5.6  The /DOSSEG Option


Option

    /DO«SSEG»

The /DOSSEG option forces segments to be ordered as follows:


    1.  All segments with a class name ending in CODE

    2.  All other segments outside DGROUP

    3.  DGROUP segments, in the following order:

        a.  Any segments of class BEGDATA. (This class name is reserved for
            Microsoft use.)

        b.  Any segments not of class BEGDATA, BSS, or STACK.

        c.  Segments of class BSS.

        d.  Segments of class STACK.



In addition, /DOSSEG option defines the following two labels:

    _edata = DGROUP : BSS
    _end   = DGROUP : STACK

The variables  _edata  and  _end  have special meanings for Microsoft
compilers, so you should not define program variables with these names.
Assembly-language programs can reference these variables but should not
change them.

The /DOSSEG option also inserts 16 null bytes at the beginning of the _TEXT
segment (if this segment is defined). This behavior of the option is
overridden by the /NONULLS option when both are used; use /NONULLS to
override the DOSSEG comment record commonly found in standard Microsoft
libraries.

This option is principally for use with assembly-language programs. When you
link high-level-language programs, a special object-module record in the
Microsoft language libraries automatically enables the /DOSSEG option. This
option is also enabled by assembly modules that use MASM directive .DOSSEG.



12.5.7  The /DSALLOC Option


Option

    /DS«ALLOCATE»

The /DSALLOC option tells LINK to load all data starting at the high end of
the data segment. At run time, the data segment (DS) register is set to the
lowest data-segment address that contains program data.

By default, LINK loads all data starting at the low end of the data segment.
At run time, the DS register is set to the lowest possible address to allow
the entire data segment to be used.

The /DSALLOC option is most often used with the /HIGH option to take
advantage of unused memory within the data segment. These options are valid
only for assembly-language programs that create DOS .EXE files.


12.5.8  The /EXEPACK Option


Option

    /E«XEPACK»

The /EXEPACK option directs LINK to remove sequences of repeated bytes
(usually null characters) and to optimize the load-time relocation table
before creating the executable file. (The load-time relocation table is a
table of references relative to the start of the program, each of which
changes when the executable image is loaded into memory and an actual
address for the entry point is assigned.)

The /EXEPACK option does not always produce a significant saving in disk
space and may sometimes actually increase file size. Programs that have a
large number of load-time relocations (about 500 or more) and long streams
of repeated characters are usually shorter if packed. LINK notifies you if
the packed file is larger than the unpacked file. The time required to
expand a packed file may cause it to load more slowly than a file linked
without this option.

You cannot debug packed files with CodeView, because the /EXEPACK option
removes symbolic information. A LINK warning message notifies you of this.

The /EXEPACK option is not compatible with the /INCR option or with Windows
programs.


12.5.9  The /FARCALL Option


Option

    /F«ARCALLTRANSLATION»

The /FARCALL option directs the linker to optimize far calls to procedures
that lie in the same segment as the caller. This can result in slightly
faster code; the gain in speed is most apparent on 80286-based machines and
later. The /PACKC option can be used with /FARCALL when linking for OS/2.
/PACKC is not recommended when linking Windows applications with /FARCALL.

The /FARCALL option is off by default. If an environment variable (such as
LINK or FL) includes /FARCALL, you can use the /NOFARCALL option to override
it.

FARCALL optimizes by creating more efficient code.

A program that has multiple code segments may make a far call to a procedure
in the same segment. Since the segment address is the same (for both the
code and the procedure it calls), only a near call is necessary. Far calls
appear in the relocation table; a near call does not require a table entry.
By converting far calls to near calls in the same segment, the /FARCALL
option both reduces the size of the relocation table and increases execution
speed, since only the offset needs to be loaded, not a new segment. The
/FARCALL option has no effect on programs that make only near calls, since
there are no far calls to convert.

When /FARCALL is specified, the linker optimizes code by removing the
instruction  call FAR label  and substituting the following sequence:

    nop
            push    cs
            call    NEAR label

During execution, the called procedure still returns with a far-return
instruction. However, because both the code segment and the near address are
on the stack, the far return is executed correctly. The  nop  (no-op)
instruction is added so that exactly five bytes replace the five-byte
far-call instruction.

In rare cases, /FARCALL should be used with caution.

There is a small risk with the /FARCALL option. If LINK sees the far-call
opcode (9A hexadecimal) followed by a far pointer to the current statement,
and that segment has a class name ending in  CODE, it interprets that as a
far call. This problem can occur when using  _based (segname  ("CODE")) in a
C program. If a program linked with /FARCALL fails for no apparent reason,
try using /NOFARCALL.

Object modules produced by Microsoft high-level languages are safe from this
problem because little immediate data is stored in code segments.
Assemblylanguage programs are generally safe for use with the /FARCALL
option if they do not involve advanced system-level code, such as might be
found in operating systems or interrupt handlers.


12.5.10  The /HELP Option


Option

    /HE«LP»

The /HELP option calls the QuickHelp utility. If LINK cannot find the help
file or QuickHelp, it displays a brief summary of LINK command-line syntax
and options. Do not give a filename when using the /HELP option.


12.5.11  The /HIGH Option


Option

    /HI«GH»

At load time, the executable file can be placed either as low or as high in
memory as possible. The /HIGH option causes DOS to place the executable file
as high as possible in memory. Without the /HIGH option, DOS places the
executable file as low as possible. This option is usually used with the
/DSALLOC option. These options are valid only for assembly-language programs
that create DOS .EXE files.


12.5.12  The /INCR Option


Option

    /INC«REMENTAL»

The /INCR option must be used to prepare for subsequent linking with ILINK.
This option produces a .SYM file and an .ILK file, each containing
additional information needed by ILINK.

When /INCR is specified, LINK creates the main output file as a segmented
executable file. If the main output is a DOS application, LINK adds a stub
loader so that the program can run under DOS. The file is slightly larger
than it would be without /INCR.

The /PADC and /PADD options are often used with the /INCR option to increase
buffer size and thereby increase the likelihood that incremental linking
will be successful. The /TINY and /EXEPACK options are not compatible with
/INCR.

You should not use /INCR or ILINK for the release version of a product.
ILINK is intended to speed linking during development and debugging. In rare
cases, linking with /INCR causes warning  L4001  to be generated. If this
occurs, do not use this option or ILINK.


12.5.13  The /INFO Option


Option

    /INF«ORMATION»

The /INFO option displays to the standard output information about the
linking process, including the phase of linking and the names of the object
files being linked. This option is a useful way to determine the locations
of the object files being linked, the number of segments, and the order in
which they are linked.


12.5.14  The /LINE Option


Option

    /LI«NENUMBERS»

The /LINE option adds the line numbers and associated addresses from source
files to the map file. The object file must contain line-number information
for it to appear in the map file. If the object file has no line-number
information, the /LINE option has no effect. (Use the /Zd or /Zi option with
Microsoft compilers such as CL, FL, and ML to add line numbers to the object
file.) If you also want to add public symbols to the map file, use the /MAP
option.

The /LINE option causes a map file to be created even if you did not
explicitly tell the linker to do so. By default, the map file is given the
same base name as the executable file with the extension .MAP. You can
override the default name by specifying a new map filename in the mapfile
field or in response to the  List File  prompt.


12.5.15  The /MAP Option


Option

    /M«AP»

The /MAP option adds to the map file all public (global) symbols defined in
object files. When /MAP is specified, the map file contains a list of all
the symbols sorted by name and a list of all the symbols sorted by address.
If you do not use this option, the map file contains only a list of
segments. If you also want to add line numbers to the map file, use the
/LINE option.

The /MAP option causes a map file to be created even if you did not
explicitly tell the linker to do so. By default, the map file is given the
same base name as the executable file with the extension .MAP. You can
override the default name by specifying a new map filename in the mapfile
field or in response to the  List File  prompt.

Under some circumstances, adding symbols slows the linking process. If this
is a problem, do not use /MAP.


12.5.16  The /NOD Option


Option

    /NOD«EFAULTLIBRARYSEARCH»«:libraryname»

The /NOD option tells LINK not to search default libraries named in object
files. Specifying libraryname tells LINK to search all libraries named in
the object files except libraryname. If you want LINK to ignore more than
one library, specify /NOD once for each library. To tell LINK to ignore all
default libraries, specify /NOD without a libraryname.

High-level-language object files usually must be linked with a run-time
library to produce an executable file. Therefore, if you use the /NOD
option, you must also use the libraries field to specify an alternate
library that resolves the external references in the object files.


12.5.17  The /NOE Option


Option

    /NOE«XTDICTIONARY»

The /NOE option prevents the linker from searching extended dictionaries,
which are lists of symbol locations in libraries created with LIB. The
linker consults extended dictionaries to speed up library searches.

Using /NOE slows the linker. Use this option when you are redefining a
symbol or function defined in a library and you get the error

    L2044 symbol multiply defined, use /NOE


12.5.18  The /NOFARCALL Option


Option

    /NOF«ARCALLTRANSLATION»

The /NOFARCALL option turns off far-call optimization (translation).
Far-call optimization is off by default. However, if an environment variable
(such as LINK or FL) includes the /FARCALL option, you can use /NOFARCALL to
override /FARCALL.


12.5.19  The /NOGROUP Option


Option

    /NOG«ROUPASSOCIATION»

The /NOGROUP option ignores group associations when assigning addresses to
data and code items. It is provided primarily for compatibility with
previous versions of the linker (2.02 and earlier) and early versions of
Microsoft compilers. This option is valid only for assembly-language
programs that create DOS .EXE files.>


12.5.20  The /NOI Option


Option

    /NOI«GNORECASE»

This option preserves case in identifiers. By default, LINK treats uppercase
and lowercase letters as equivalent. Thus  ABC,  Abc, and  abc  are
considered the same name. When you use the /NOI option, the linker
distinguishes between uppercase and lowercase, and considers these
identifiers to be three different names.

In most high-level languages, identifiers are not case sensitive, so this
option has no effect. However, case is significant in C. It's a good idea to
use this option with C programs to catch misnamed identifiers.


12.5.21  The /NOLOGO Option


Option

    /NOL«OGO»

The /NOLOGO option suppresses the copyright message displayed when LINK
starts. This option has no effect if not specified first on the command line
or in the LINK environment variable.


12.5.22  The /NONULLS Option


Option

    /NON«ULLSDOSSEG»

The /NONULLS option arranges segments in the same order they are arranged by
the /DOSSEG option. The only difference is that the /DOSSEG option inserts
16 null bytes at the beginning of the _TEXT segment (if it is defined), but
/NONULLS does not insert the extra bytes.

If both the /DOSSEG and /NONULLS options are given, the /NONULLS option
takes precedence. You can therefore use /NONULLS to override the DOSSEG
comment record found in run-time libraries. This option is for segmented
executable files.


12.5.23  The /NOPACKC Option


Option

    /NOP«ACKCODE»

This option turns off code-segment packing. Code-segment packing is normally
off by default. However, if an environment variable (such as LINK or FL)
includes the /PACKC option to turn on code-segment packing, you can use
/NOPACKC to override /PACKC.


12.5.24  The /OV Option


Option

    /O«VERLAYINTERRUPT»:number

This option sets an interrupt number for passing control to overlays. By
default, the interrupt number used for passing control to overlays is 63 (3F
hexadecimal). The /OV option allows you to select a different interrupt
number. This option is valid only when linking DOS programs.

The number can be any number from 0 to 255, specified in decimal format or
in C-language notation. Numbers that conflict with DOS interrupts can be
used; however, their use is not advised. You should use this option only
when you want to use overlays with a program that already reserves interrupt
63 for some other purpose.


12.5.25  The /PACKC Option


Option

    /PACKC«ODE»«:number»

The /PACKC option turns on code-segment packing. The linker packs code
segments by grouping neighboring code segments that have the same
attributes. Segments in the same group are assigned the same segment
address; offset addresses are adjusted accordingly. All items have the same
physical address whether or not the /PACKC option is used. However, /PACKC
changes the segment and offset addresses so that all items in a group share
the same segment.

The number specifies the maximum size of groups formed by /PACKC. The linker
stops adding segments to a group when it cannot add another segment without
exceeding number; then it starts a new group. The default segment size
without /PACKC (or when /PACKC is specified without number) is 65,500 bytes
(64K - 36 bytes).

The /PACKC option produces slightly faster and more compact code. It affects
only programs with multiple code segments. This option is off by default
and, if specified in an environment variable, can be overridden with the
/NOPACKC option.

Code-segment packing provides more opportunities for far-call optimization
(which is enabled with the /FARCALL option). The /FARCALL and /PACKC options
together produce faster and more compact code. However, this combination is
not recommended for Windows applications.

Use caution when packing assembly-language programs.

Object code created by Microsoft compilers can safely be linked with the
/PACKC option. This option is unsafe only when used with assembly-language
programs that make assumptions about the relative order of code segments.
For example, the following assembly code attempts to calculate the distance
between CSEG1  and  CSEG2. This code produces incorrect results when used
with /PACKC, because /PACKC causes the two segments to share the same
segment address. Therefore, the procedure would always return zero.

    CSEG1      SEGMENT PUBLIC 'CODE'
    .
    .
    .
    CSEG1      ENDS

    CSEG2      SEGMENT PARA PUBLIC 'CODE'
                ASSUME  cs:CSEG2

    ; Return the length of CSEG1 in AX

    codesize   PROC  NEAR
                mov   ax, CSEG2  ; Load para address of CSEG1
                sub   ax, CSEG1  ; Load para address of CSEG2
                mov   cx, 4      ; Load count
                shl   ax, cl     ; Convert distance from paragraphs
                                ;  to bytes
    codesize   ENDP

    CSEG2      ENDS


12.5.26  The /PACKD Option


Option

    /PACKD«ATA»«:number»

The /PACKDoption turns on data-segment packing. The linker considers any
segment definition with a class name that does not end in  CODE  as a data
segment. Adjacent data-segment definitions are combined into the same
physical segment. The linker stops adding segments to a group when it cannot
add another segment without exceeding number bytes; then it starts a new
group. The default segment size without /PACKD (or when /PACKD is specified
without number) is 65,536 bytes (64K).

The /PACKD option produces slightly faster and more compact code. It affects
only programs with multiple data segments and is valid for OS/2 and Windows
programs only. It might be necessary to use the /PACKD option to get around
the limit of 255 physical data segments per executable file imposed by OS/2
and Windows. Try using /PACKD if you get the following LINK error:

    L1073 file-segment limit exceeded

This option may not be safe with other compilers that do not generate fixup
records for all far data references.


12.5.27  The /PADC Option


Option

    /PADC«ODE»«:padsize»

The /PADC option adds filler bytes to the end of each code segment for use
when later linking with ILINK. If you use /PADC, you must also specify the
/INCR option.

The padsize is optional; the default is 0 bytes. If incremental linking
fails, you can specify a padsize in decimal format or C-language notation.
For example,  /PADC:256  adds an additional 256 bytes to each code segment.
(You can also use  0400  or  0x100  to specify 256 bytes.)

The linker recognizes code segments as segment definitions with class names
that end in  CODE. Microsoft high-level languages automatically use this
declaration for code segments. Code padding is not usually necessary for
programs with multiple code segments but is recommended for mixed-model
programs, programs with one code segment, and assembly-language programs in
which code segments are grouped.


12.5.28  The /PADD Option


Option

    /PADD«ATA»«:padsize»

The /PADD option adds filler bytes to the end of each data segment to permit
subsequent linking with ILINK. If you use /PADD, you must also specify the
/INCR option.

The padsize is optional; the default is 16 bytes. The /INCR option itself
adds 16 bytes. This default padding is usually sufficient for successful
incremental linking. If incremental linking fails, you can specify a padsize
in decimal format or C-language notation. (If you specify too large a
padsize, you might exceed the 64K limitation on the size of the default data
segment.) For example,  /PADD:32  adds an additional 32 bytes to each data
segment. (You can also use  040  or  0x20  to specify 32 bytes.)


12.5.29  The /PAUSE Option


Option

    /PAU«SE»

The /PAUSE option pauses the session before LINK writes the executable file
or DLL to disk. This option is supplied for compatibility with machines that
have two floppy drives but no hard disk. It allows you to swap floppy disks
before LINK writes the executable file.

If you specify the /PAUSE option, LINK displays the following message before
it creates the main output:

    About to generate .EXE file
    Change diskette in drive letter and press <ENTER>

The letter is the current drive. LINK resumes processing when you press
ENTER.

Do not remove a disk that contains either the map file or the temporary
file. If LINK creates a temporary file on the disk you plan to remove,
terminate the LINK session and rearrange your files so that the temporary
file is on a disk that does not need to be removed. For more information on
how LINK determines where to put the temporary file, see Section 12.9, "LINK
Temporary Files."


12.5.30  The /PM Option


Option

    /PM«TYPE»:type

This option specifies the type of Windows or OS/2 application being
generated. The /PM option is equivalent to including a type specification in
the NAME statement in a module-definition file.

The type field can take one of the following values:

Value                             Description
────────────────────────────────────────────────────────────────────────────
PM                                Presentation Manager (PM) or Windows
                                    application. The application uses the
                                    API provided by PM or Windows and must
                                    be executed in the PM or Windows
                                    environment. This is equivalent to NAME
                                    WINDOWAPI.

VIO                               Character-mode application to run in a
                                    text window in the
                                    PM or Windows session. This is
                                    equivalent to NAME
                                    WINDOWCOMPAT.

NOVIO                             The default. Character-mode application
                                    that must run full screen and cannot run
                                    in a text window in PM or in Windows.
                                    This is equivalent to NAME
                                    NOTWINDOWCOMPAT.



12.5.31  The /Q Option


Option

    /Q«UICKLIBRARY»

The /Q option directs the linker to produce a "Quick library" instead of an
executable file. A Quick library is similar to a standard library in that
both contain routines that can be called by a program. However, a standard
library is linked with a program at link time; in contrast, a Quick library
is linked with a program at run time.

When /Q is specified, the exefile field refers to a Quick library instead of
an application. The default extension for this field is then .QLB instead of
.EXE.

Quick libraries can be used only with programs created with Microsoft
QuickBasic or early versions of Microsoft QuickC. These programs have the
special code that loads a Quick library at run time.


12.5.32  The /SEG Option


Option

    /SE«GMENTS»«:number»

The /SEG option sets the maximum number of program segments. The default
without /SEG or number is 128. You can specify number as any value from 1 to
16,384 in individual format or C-language notation. However, the number of
segment definitions is constrained by available memory.

LINK must allocate some memory to keep track of information for each
segment; the larger the number you specify, the less free memory LINK has to
run in. A relatively low segment limit (such as the 128 default) reduces the
chance LINK will run out of memory. For programs with fewer than 128
segments, you can minimize LINK's memory requirements by setting number to
reflect the actual number of segments in the program. If a program has more
than 128 segments, however, you must set a higher value.

If the number of segments allocated is too high for the amount of memory
available while linking, LINK displays the error message

    L1054 requested segment limit too high

When this happens, try linking again after setting /SEG to a smaller number.



12.5.33  The /STACK Option


Option

    /ST«ACK»:number

The /STACK option lets you change the stack size from its default value of
2,048 bytes. The number is any positive value in decimal or C-language
notation, up to 64K.

Programs that pass large arrays or structures by value or with deeply nested
subroutines may need additional stack space. In contrast, if your program
uses the stack very little, you might be able to save space by decreasing
the stack size. If a program fails with a stack-overflow message, try
increasing the size of the stack.

────────────────────────────────────────────────────────────────────────────
NOTE

You can also use the EXEHDR utility to change the default stack size by
modifying the executable-file header.
────────────────────────────────────────────────────────────────────────────


12.5.34  The /TINY Option


Option

    /T«INY»

The /TINY option produces a .COM file instead of an .EXE file. The default
extension of the output file is .COM. When the /CO option is used with
/TINY, debug information is put in a separate file with the same base name
as the .COM file and with the .DBG extension.

Not every program can be linked in the .COM format. The following
restrictions apply:


    ■   The program must consist of only one physical segment. You can declare
        more than one segment in assembly-language programs; however, the
        segments must be in the same group.

    ■   The code must not use far references.

    ■   Segment addresses cannot be used as immediate data for instructions.
        For example, you cannot use the following instruction:

        mov     ax, CODESEG


    ■   Windows and OS/2 programs cannot be converted to a .COM format.



12.5.35  The /W Option


Option

    /W«ARNFIXUP»

The /W option issues the  L4000  warning when LINK uses a displacement from
the beginning of a group in determining a fixup value. This option is
provided because early versions of the Windows linker (LINK4) performed
fixups without this displacement. This option is for linking segmented
executable files.


12.5.36  The /? Option


Option

    /?

The /? option displays a brief summary of LINK command-line syntax and
options.


12.6  Setting Options with the LINK Environment Variable

You can use the LINK environment variable to set options that will be in
effect each time you link. (Microsoft compilers such as CL, FL, and ML also
use the options in the LINK environment variable.)


12.6.1  Setting the LINK Environment Variable

You set the LINK environment variable with the following operating-system
command:

    SET LINK=options

LINK expects to find options listed in the variable exactly as you would
type them in fields on the command line, in response to a prompt, or in a
response file. It does not accept input for other fields; filenames in the
LINK variable cause an error.


Example

    SET LINK=/NOI /SEG:256 /CO
    LINK TEST;
    LINK /NOD PROG;

In the example above, the commands are specified at the system prompt. The
file TEST.OBJ is linked using the options  /NOI,  /SEG:256, and  /CO. The
file PROG.OBJ is then linked with the option  /NOD, in addition to  /NOI,
/SEG:256, and  /CO.


12.6.2  Behavior of the LINK Environment Variable

You can specify options on the LINK command line or in a response file in
addition to those in the LINK environment variable. If an option appears
both in an input field and in the LINK variable, the input-field option
overrides any environment-variable option it conflicts with. For example,
the command-line option /SEG:512 overrides the environment-variable option
/SEG:256.


12.6.3  Clearing the LINK Environment Variable

You must reset the LINK environment variable to prevent LINK from using its
options. To clear the LINK variable, use the operating-system command

    SET LINK=

To see the current setting of the LINK variable, type  SET  at the
operatingsystem prompt.


12.7  Using Overlays under DOS

LINK can create DOS programs with "overlays." Overlays allow sections of a
program to be loaded into memory only as needed. This permits running a
program that would otherwise be too large to fit in available memory.
Overlay programs execute more slowly, however, since the various program
modules must be swapped into and out of memory.

The CodeView debugger is compatible with overlaid modules. If you use
CodeView to debug a program that has an overlay containing more than one
code segment, you will see only the identifiers contained in the first
segment of the overlay.


12.7.1  Restrictions on Overlays

Not all programs can use overlays. You will probably need to reorganize the
code to accommodate the limitations explained in this section. Even after
reorganization, some programs might not be convertible to overlay form or
might not show a significant reduction in the amount of memory needed to
execute them.

Consider the following restrictions before trying to overlay a program:


    ■   You can use overlays only in programs with multiple code segments,
        because separate segment names are needed for overlays. Only code is
        overlaid, not data. The data becomes part of the "root" section of the
        program that is always in memory.

    ■   Only 255 overlays can be specified. The program can define only 255
        logical segments (segments with different names). This limits the
        total size of an overlaid program to 16 megabytes.

    ■   Only one overlay (in addition to the root) can be in memory at any one
        time. You must structure your program accordingly.

    ■   Duplicate names for different overlays are not supported; each module
        can appear only once in a program.

    ■   You must use far call/return instructions to transfer control between
        overlaid files. You cannot overlay files containing near routines if
        other overlays call those routines.

    ■   You cannot jump out of or into overlaid files using the longjmp
        C-library function. You can, however, use long jumps within an
        overlaid file.

    ■   You cannot use a function pointer to call a routine out of or into
        overlaid files. You can, however, use a function pointer to call a
        routine within an overlaid file.

    ■   You cannot use the same public name in different overlays.

    ■   The code required to manage overlays adds about 2K to 3K to the size
        of the root module.


────────────────────────────────────────────────────────────────────────────
WARNING

Never rename an executable program file containing overlays if it is to run
under DOS 2.x and earlier. LINK records the .EXE filename in the program
file. If you rename the file, the overlay manager may not be able to locate
the proper file. You can rename an .EXE file that will run under DOS 3.x and
later.
────────────────────────────────────────────────────────────────────────────


12.7.2  Specifying Overlays

Specify overlays by enclosing object-file (and possibly load-library) names
in parentheses in the objfiles field. Each group of object files bracketed
by parentheses represents one overlay. Overlays cannot be nested.

The remaining modules (those not in parentheses), and any drawn from the
run-time libraries, constitute the resident (or root) part of your program.
The entry point to the program (for example,  main()  in a C program, or
PROGRAM  in a FORTRAN program) must be in the root.


Example

The following list of files contains three overlays:

    a + (b+c) + (d+e) + f + (g)

In this example, the groups  (b+c),  (d+e), and  (g)  are overlays. The
remaining files  a  and  f  and any modules from libraries in the libraries
field remain memory-resident throughout the execution of the program.

It is important to remember that whichever object file first defines a
segment gets all contributions to that segment. In the example above, if
D.OBJ and F.OBJ both define the same segment, the contribution from F.OBJ to
that segment goes into the  (d+e)  overlay rather than into the root.


12.7.3  How Overlays Work

Programs that use overlays require the overlay-manager code to handle module
swapping. This code is included as part of the standard libraries for
Microsoft high-level languages. If you specify overlays during linking, the
code for the overlay manager is automatically linked with the rest of your
program.

LINK produces only one .EXE file. The overlay manager searches for this file
whenever another overlay needs to be loaded. It first searches in the
current directory. If the file is not there, the manager then searches the
directories in the PATH environment variable. If the overlay manager still
cannot find the file, it prompts for the pathname.


Example

Assume that an executable program called PAYROLL.EXE uses overlays and does
not exist in either the current directory or the directories specified by
PATH. If you run PAYROLL.EXE by entering a complete path specification, the
overlay manager displays the following message when it attempts to load an
overlay file:

    Cannot find PAYROLL.EXE
    Please enter new program spec:

You can then enter the drive or directory, or both, where PAYROLL.EXE is
located. For example, if the file is located in directory EMPLOYEEDATA on
drive B, enter  B:EMPLOYEEDATA; if the current drive is B, you can enter
just  EMPLOYEEDATA.

If you later remove the disk in drive B and the overlay manager needs the
overlay again, it does not find PAYROLL.EXE and displays the following
message:

    Please insert diskette containing B:EMPLOYEEDATAPAYROLL.EXE
    in drive B: and strike any key when ready.

After the overlay file has been read from the disk, the overlay manager
displays the following message:

    Please restore the original diskette.
    Strike any key when ready.


12.7.4  Overlay Interrupts

LINK replaces far calls to routines in overlays with interrupts (followed by
the module identifier and offset). By default, the interrupt number is 63
(3F hexadecimal). You can use the /OV option to change the interrupt number.



12.8  Linker Operation under DOS

LINK performs the following steps to produce a DOS executable file:


    1.  Reads the object modules submitted

    2.  Searches the given libraries, if necessary, to resolve external
        references

    3.  Assigns addresses to segments

    4.  Assigns addresses to public symbols

    5.  Reads code and data in the segments

    6.  Reads all relocation references in object modules

    7.  Performs fixups

    8.  Outputs an executable file (executable image and relocation
        information)


Steps 5, 6, and 7 are performed iteratively─that is, LINK repeats these
steps as many times as required before it progresses to step 8.

The "executable image" contains the code and data that constitute the
executable file. The "relocation information" is a list of references
relative to the start of the program, each of which changes when the
executable image is loaded into memory and an actual address for the entry
point is assigned.

The following sections explain the process LINK uses to concatenate segments
and resolve references to items in memory.


12.8.1  Segment Alignment

LINK uses each segment's alignment type to set the starting address for the
segment. The alignment types are BYTE, WORD, DWORD, PARA, and PAGE. These
correspond to starting addresses at byte, word, doubleword, paragraph, and
page boundaries, representing addresses that are multiples of 1, 2, 4, 16,
and 256, respectively. The default alignment is PARA.

When LINK encounters a segment, it checks the alignment type before copying
the segment to the executable file. If the alignment is WORD, DWORD, PARA,
or PAGE, LINK checks the executable image to see if the last byte copied
ends at an appropriate boundary. If not, LINK pads the image with extra null
bytes.


12.8.2  Frame Number

LINK computes a starting address for each segment in a program. The starting
address is based on a segment's alignment and the sizes of the segments
already copied to the executable file. The address consists of an offset and
a "canonical frame number." The canonical frame number specifies the address
of the first paragraph in memory containing one or more bytes of the
segment. (A paragraph is 16 bytes of memory; therefore, to compute a
physical location in memory, multiply the frame number by 16 and add the
offset.) The offset is the number of bytes from the start of the paragraph
to the first byte in the segment. For BYTE, WORD, and DWORD alignments, the
offset may be nonzero. The offset is always zero for PARA and PAGE
alignments. (An offset of zero means that the physical location is an exact
multiple of 16.)

The frame number of a segment can be obtained from the map file created by
LINK. The first four digits of the start address give the frame number in
hexadecimal. For example, a start address of  0C0A6  gives a frame number of
    0C0A.


12.8.3  Segment Order

LINK copies segments to the executable file in the same order that it
encounters them in the object files. This order is maintained throughout the
program unless LINK encounters two or more segments having the same class
name. Segments having identical class names belong to the same class type
and are copied as a contiguous block to the executable file.

The /DOSSEG option might change the way in which segments are ordered.


12.8.4  Combined Segments

LINK uses combine types to determine whether two or more segments sharing
the same segment name should be combined into one large segment. The valid
combine types are PUBLIC, STACK, COMMON, and PRIVATE.

If a segment has combine type PUBLIC, LINK automatically combines it with
any other segments having the same name and belonging to the same class.
When LINK combines segments, it ensures that the segments are contiguous and
that all addresses in the segments can be accessed using an offset from the
same frame address. The result is the same as if the segment were defined as
a whole in one source file.

LINK preserves each individual segment's alignment type. This means that
even though the segments belong to a single large segment, the code and data
in the segments do not lose their original alignment. If the combined
segments exceed 64K, LINK displays an error message.

If a segment has combine type STACK, LINK carries out the same combine
operation as for PUBLIC segments. The only exception is that STACK segments
cause LINK to copy an initial stack-pointer value to the executable file.
This stack-pointer value is the offset to the end of the first stack segment
(or combined stack segment) encountered.

If a segment has combine type COMMON, LINK automatically combines it with
any other segments having the same name and belonging to the same class.
When LINK combines COMMON segments, however, it places the start of each
segment at the same address, creating a series of overlapping segments. The
result is a single segment no larger than the largest segment combined.

A segment has combine type PRIVATE only if no explicit combine type is
defined for it in the source file. LINK does not combine private segments.


12.8.5  Groups

Groups allow segments to be addressed relative to the same frame address.
When LINK encounters a group, it adjusts all memory references to items in
the group so that they are relative to the same frame address.

Segments in a group do not have to be contiguous, belong to the same class,
or have the same combine type. The only requirement is that all segments in
the group fit within 64K.

Groups do not affect the order in which the segments are loaded. Unless you
use class names and enter object files in the right order, there is no
guarantee the segments will be contiguous. In fact, LINK may place segments
that do not belong to the group in the same 64K of memory. LINK does not
explicitly check that all segments in a group fit within 64K of memory;
however, LINK is likely to encounter a fixup-overflow error if this
requirement is not met.


12.8.6  Fixups

Once the starting address of each segment in a program is known and all
segment combinations and groups have been established, LINK can "fix up" any
unresolved references to labels and variables. To fix up unresolved
references, LINK computes an appropriate offset and segment address and
replaces the temporary values generated by the assembler with the new
values.

LINK carries out fixups for the types of references shown in Table 12.1.

The size of the value to be computed depends on the type of reference. If
LINK discovers an error in the anticipated size of a reference, it displays
a fixupoverflow message. This can happen, for example, if a program attempts
to use a 16-bit offset to reach an instruction which is more than 64K away.
It can also occur if all segments in a group do not fit within a single 64K
block of memory.

Table 12.1  LINK Fixups

Type              Location of Reference    LINK Action
────────────────────────────────────────────────────────────────────────────
Short             In JMP instructions      Computes a signed, eight-bit
                    that attempt to pass     number for the reference and
                    control to labeled       displays an error message if
                    instructions in the      the target instruction belongs
                    same segment or group.   to a different segment or group
                    The target instruction   (has a different frame address),
                    must be no more than     or if the target is more than
                    128 bytes from the       128 bytes away in either
                    point of reference.      direction.

Near              In instructions that     Computes a 16-bit offset for
self-relative     access data relative to  the reference and displays an
                    the same segment or      error if the data are not in
                    group.                   the same segment or group.

Near              In instructions that     Computes a 16-bit offset for
segment-relative  attempt to access data   the reference and displays an
                    in a specified segment   error message if the offset of
                    or group, or relative    the target within the specified
                    to a specified segment   frame is greater than 64K or
                                            less than 0, or if the
                    register.                beginning of the canonical
                                            frame of the target is not
                                            addressable.

Long              In CALL instructions     Computes a 16-bit frame address
                    that attempt to access   and 16-bit offset for this
                    an instruction in        reference, and displays an
                    another segment or       error message if the computed
                    group.                   offset is greater than 64K or
                                            less than 0, or if the
                                            beginning of the canonical
                                            frame of the target is not
                                            addressable.

────────────────────────────────────────────────────────────────────────────



12.9  LINK Temporary Files

LINK uses available memory during the linking session. If LINK runs out of
memory, it creates a disk file to hold intermediate files. LINK deletes this
file when it finishes.

When the linker creates a temporary disk file, you see the message

    Temporary file tempfile has been created.
    Do not change diskette in drive, letter.

In the message displayed above, tempfile is the name of the temporary file
and letter is the drive containing the temporary file. (The second line
appears only for a floppy drive.)

After this message appears, do not remove the disk from the drive specified
by letter until the link session ends. If the disk is removed, the operation
of LINK is unpredictable, and you might see the following message:

    Unexpected end-of-file on scratch file

If this happens, run LINK again.


Location of the Temporary File

If the TMP environment variable defines a temporary directory, LINK creates
temporary files there. If the TMP environment variable is undefined or the
temporary directory doesn't exist, LINK creates temporary files in the
current directory.


Name of the Temporary File

When running under OS/2 or DOS version 3.0 or later, LINK asks the operating
system to create a temporary file with a unique name in the temporary-file
directory.

Under DOS versions earlier than 3.0, LINK creates a temporary file named
VM.TMP. Do not use this name for your files. LINK generates an error message
if it encounters an existing file with this name.


12.10  LINK Exit Codes

LINK returns an exit code (also called return code or error code) that you
can use to control the operation of batch files or makefiles.

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Code                              Meaning
────────────────────────────────────────────────────────────────────────────
0                                 No error.

2                                 Program error. Commands or files given
                                    as input to the linker produced the
                                    error.

4                                 System error. The linker

                                    Ran out of space on output files

                                    Was unable to reopen the temporary file

Code                              Meaning
────────────────────────────────────────────────────────────────────────────

                                    Experienced an internal error

                                    Was interrupted by the user




12.11  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topic                                 Access
────────────────────────────────────────────────────────────────────────────
Syntax and procedural information on  Choose these topics from the
LINK, BIND, and LIB                   "Microsoft Advisor Contents" screen

Syntax and procedural information on  Choose "Miscellaneous" from the list
EXEHDR                                of utilities on the "Microsoft
                                        Advisor Contents" screen







Chapter 13  Module-Definition Files
────────────────────────────────────────────────────────────────────────────

This chapter describes the contents of a module-definition file. It begins
with a brief overview of the purpose of module-definition files. The rest of
the chapter discusses each statement in a module-definition file and
describes syntax rules, argument fields, attributes, and keywords for each
statement.


13.1  Overview

A module-definition file is a text file that describes the name, attributes,
exports, imports, system requirements, and other characteristics of an
application or dynamic-link library (DLL) for OS/2 or Microsoft Windows.
This file is required for DLLs and is optional (but desirable) for OS/2 and
Windows applications.

You use module-definition files in two situations:


    ■   You can specify a module-definition file in LINK's deffile field. The
        module-definition file gives LINK the information it needs to
        determine how to set up the application or DLL it creates.

    ■   You can provide LINK with the needed information when creating an
        application by using the Microsoft Import Library Manager utility
        (IMPLIB) to create an import library from a module-definition file (or
        from the DLL created by a module-definition file). You then specify
        the import library in LINK's libraries field.


For more information about IMPLIB, see online help.


13.2  Module Statements

A module-definition file contains one or more "module statements." Each
module statement defines an attribute of the executable file, such as its
name, the attributes of program segments, and the number and names of
exported and imported functions and data. Table 13.1 summarizes the purpose
of the module statements and shows the order in which they are discussed in
this chapter.

Table 13.1  Module Statements

╓┌─────────────┌─────────────────────────────────────────────────────────────╖
Statement     Purpose
────────────────────────────────────────────────────────────────────────────
NAME          Names the application (no library created)
LIBRARY       Names the DLL (no application created)
DESCRIPTION   Embeds text in the application or DLL
STUB          Adds a DOS executable file to the beginning of the file
EXETYPE       Identifies the target operating system
Statement     Purpose
────────────────────────────────────────────────────────────────────────────
EXETYPE       Identifies the target operating system
PROTMODE      Specifies a protected-mode application or DLL
REALMODE      Supported for compatibility
STACKSIZE     Sets stack size in bytes
HEAPSIZE      Sets local heap size in bytes
CODE          Sets default attributes for all code segments
DATA          Sets default attributes for all data segments
SEGMENTS      Sets attributes for specific segments
OLD           Preserves ordinals from a previous DLL
EXPORTS       Defines exported functions
IMPORTS       Defines imported functions
────────────────────────────────────────────────────────────────────────────



13.2.1  Syntax Rules

The syntax rules in this section apply to all statements in a
module-definition file. Other rules specific to each statement are described
in the sections that follow.


    ■   Statement and attribute keywords are not case sensitive. A statement
        keyword can be preceded by spaces and tabs.

    ■   A NAME or LIBRARY statement, if used, must precede all other
        statements.

    ■   Most statements appear at most once in a file and accept one
        specification of parameters and attributes. The specification follows
        the statement keyword on the same or subsequent line(s). If repeated
        with a different specification later in the file, the later statement
        overrides the earlier one.

    ■   The SEGMENTS, EXPORTS, and IMPORTS statements can appear more than
        once in the file and take multiple specifications, each on its own
        line. The statement keyword must appear once before the first
        specification and can be repeated before each additional
        specification.

    ■   Comments in the file are designated by a semicolon (;) at the
        beginning of each comment line. A comment cannot share a line with
        part or all of a statement but can appear between lines of a multiline
        statement.

    ■   Numeric arguments can be specified in decimal or in C-language
        notation.

    ■   Name arguments cannot match a reserved word.



Example

The sample module-definition file below gives a description for a DLL. This
sample file includes one comment and five statements.

    ; Sample module-definition file

    LIBRARY

    DESCRIPTION 'Sample dynamic-link library'

    CODE       PRELOAD

    STACKSIZE  1024

    EXPORTS
        Init   @1
        Begin  @2
        Finish @3
        Load   @4
        Print  @5


13.2.2  Reserved Words

The following words are reserved by the linker for use in module-definition
files. These names cannot be used as arguments in module-definition
statements.

(This figure may be found in the printed book.)

* DOS4 and HUGE are obsolete but are still reserved by the linker.

In addition to the words listed above, the following words are reserved for
use by future or other versions of the linker and should be avoided.

(This figure may be found in the printed book.)


13.3  The NAME Statement

The NAME statement identifies the executable file as an application (rather
than a DLL). It can also specify the name and application type. The NAME or
LIBRARY statement must precede all other statements. If NAME is specified,
the LIBRARY statement cannot be used. If neither is used, the default is
NAME and LINK creates an application.


Syntax

    NAME «appname» «apptype» «NEWFILES»


Remarks

The fields can appear in any order.

If appname is specified, it becomes the name of the application as it is
known by OS/2 or Windows. This name can be any valid filename. If appname
contains a space, begins with a nonalphabetic character, or is a reserved
word, surround appname with double quotation marks. The name cannot exceed
255 characters (not including surrounding quotation marks). If appname is
not specified, the base name of the executable file becomes the name of the
application.

If apptype is specified, it defines the type of application. This
information is kept in the executable-file header. The apptype field can
take one of the following values:

Value                             Description
────────────────────────────────────────────────────────────────────────────
WINDOWAPI                         Presentation Manager (PM) or Windows
                                    application. The application uses the
                                    API provided by PM or Windows and must
                                    be executed in the PM or Windows
                                    environment. This is equivalent to the
                                    LINK option /PM:PM.

WINDOWCOMPAT                      Character-mode application to run in a
                                    text window in the PM or Windows session.
                                    This is equivalent to the LINK option
                                    /PM:VIO.

NOTWINDOWCOMPAT                   The default. Character-mode application
                                    that must run full screen and cannot run
                                    in a text window in PM or Windows. This
                                    is equivalent to the LINK option
                                    /PM:NOVIO.


Specify NEWFILES to tell the operating system that the application supports
long filenames and extended file attributes (available under OS/2 version
1.2 and later). The synonym LONGNAMES is supported for compatibility.


Example

The example below assigns the name  calendar  to an application that can run
in a text window in PM or Windows:

    NAME calendar WINDOWCOMPAT


13.4  The LIBRARY Statement

The LIBRARY statement identifies the executable file as a DLL. It can also
specify the name of the library and the type of library-module
initialization required. The NAME or LIBRARY statement must precede all
other statements. If LIBRARY is specified, the NAME statement cannot be
used. If neither is used, the default is NAME.


Syntax

    LIBRARY «libraryname» «initialization»
    «PRIVATELIB»


Remarks

The fields can appear in any order.

If libraryname is specified, it becomes the name of the library as it is
known by OS/2 or Windows. This name can be any valid filename. If
libraryname contains a space, begins with a nonalphabetic character, or is a
reserved word, surround the name with double quotation marks. The name
cannot exceed 255 characters. If libraryname is not given, the base name of
the DLL file becomes the name of the library.

If initialization is specified, it determines the type of initialization
required. The initialization field can take one of the following values:

Value                             Description
────────────────────────────────────────────────────────────────────────────
INITGLOBAL                        The default. The library-initialization
                                    routine is called only when the library
                                    is initially loaded into memory.

INITINSTANCE                      The library-initialization routine is
                                    called each time a new process gains
                                    access to the DLL. This keyword applies
                                    only to OS/2.


If PRIVATELIB is specified, it tells Windows that only one application may
use the DLL.


Example

The following example assigns the name  calendar  to the DLL being defined
and specifies that library initialization is performed each time a new
process gains access to  calendar:

    LIBRARY calendar INITINSTANCE


13.5  The DESCRIPTION Statement

The DESCRIPTION statement inserts specified text into the application or
DLL. This statement is useful for embedding source-control or copyright
information into a file.


Syntax

    DESCRIPTION 'text'


Remarks

The text is a string of up to 255 characters enclosed in single or double
quotation marks (' or "). To include a literal quotation mark in the text,
either specify two consecutive quotation marks of the same type or enclose
the text with the other type of quotation mark. If a DESCRIPTION statement
is not specified, the default text is the name of the main output file as
specified in LINK's exefile field. You can view this string by using the
Microsoft EXE File Header Utility (EXEHDR).

The DESCRIPTION statement is different from a comment. A comment is a line
that begins with a semicolon (;). Comments are not placed in the application
or library.


Example

The following example inserts the text  Tester's Version, Test "A",
including a literal single quotation mark and a pair of literal double
quotation marks, into the application or DLL being defined:

    DESCRIPTION "Tester's Version, Test ""A"""


13.6  The STUB Statement

The STUB statement adds a DOS executable file to the beginning of an OS/2 or
Windows application or DLL. The stub is invoked whenever the file is
executed under DOS. Usually, the stub displays a message and terminates
execution. By default, LINK adds a standard stub for this purpose. Use the
STUB statement when creating a dual-mode program.


Syntax

    STUB {'filename' | NONE}


Remarks

The filename specifies the DOS executable file to be added. LINK searches
for filename first in the current directory and then in directories
specified with the PATH environment variable. The filename must be
surrounded by single or double quotation marks (' or ").

The alternate specification NONE prevents LINK from adding a default stub.
This saves space in the application or DLL, but the resulting file will hang
the system if loaded in DOS.


Example

The following example inserts the DOS executable file STOPIT.EXE at the
beginning of the application or DLL:

    STUB 'STOPIT.EXE'

The file STOPIT.EXE is executed when you attempt to run the application or
DLL under DOS.


13.7  The EXETYPE Statement

The EXETYPE statement specifies under which operating system the application
or DLL is to run. This statement is optional and provides an additional
degree of protection against the program being run under an incorrect
operating system.


Syntax

    EXETYPE «OS2 | WINDOWS« version» |
    UNKNOWN»


Remarks

The EXETYPE keyword is followed by a descriptor of the operating system,
either OS2 (for OS/2 applications and DLLs), WINDOWS (for WINDOWS
applications and DLLs), or UNKNOWN (for other applications). The default
without a descriptor or an EXETYPE statement is OS2.

EXETYPE sets bits in the header which identify the operating system.
Operating-system loaders can check these bits.


Windows Programming

The WINDOWS descriptor takes an optional version number. Windows reads this
number to determine the minimum version of Windows needed to load the
application or DLL. For example, if 3.0 is specified, the resulting
application or DLL

can run under Windows versions 3.0 and higher. If version is not specified,
the default is 3.0. The syntax for version is

number«.«number» »

where each number is a decimal integer.

In Windows programming, use the EXETYPE statement with a PROTMODE statement
to specify an application or DLL that runs only under protected-mode
Windows.


13.8  The PROTMODE Statement

The PROTMODE statement specifies that the application or DLL runs only under
OS/2 or under Windows 3.0 standard mode and 386 enhanced mode. PROTMODE lets
LINK optimize to reduce both the size of the file on disk and its loading
time. However, an OS/2 program created with PROTMODE cannot be bound using
BIND. Use PROTMODE in combination with an EXETYPE WINDOWS statement to
define an application or DLL that runs only under protected-mode Windows.


Syntax

    PROTMODE


Example

The following statement combination defines an application that runs only
under protected-mode (standard or 386 enhanced) Windows version 3.0:

    EXETYPE WINDOWS 3.0
    PROTMODE





13.9  The REALMODE Statement

The REALMODE statement specifies that the application runs only in real
mode. This statement is supported for compatibility with existing
module-definition files. Use EXETYPE instead.


Syntax

    REALMODE


13.10  The STACKSIZE Statement

The STACKSIZE statement specifies the size of the stack in bytes. It
performs the same function as LINK's /STACK option. If both are specified,
the STACKSIZE statement overrides the /STACK option.


Syntax

    STACKSIZE number


Remarks

The number must be a positive integer, in decimal or C-language notation, up
to 64K.


Example

The following example allocates 4,096 bytes of stack space:

    STACKSIZE 4096


13.11  The HEAPSIZE Statement

The HEAPSIZE statement defines the size of the application or DLL's local
heap in bytes. This value affects the size of the default data segment
(DGROUP). The default without HEAPSIZE is no local heap.


Syntax

    HEAPSIZE {bytes | MAXVAL}


Remarks

The bytes field accepts a positive integer in decimal or C-language
notation. The limit is MAXVAL; if bytes exceeds MAXVAL, the excess is not
allocated.

MAXVAL is a keyword that sets the heap size to 64K minus the size of DGROUP.
This is useful in bound applications when you want to force a 64K
requirement for DGROUP for the program in DOS. The bound program fails to
load if 64K of memory is not available.


Example

The following example sets the local heap to 4,000 bytes:

    HEAPSIZE 4000


13.12  The CODE Statement

The CODE statement defines the default attributes for all code segments
within the application or DLL. The SEGMENTS statement can override this
default for one or more specific segments.


Syntax

    CODE «attribute...»


Remarks

This statement accepts several optional attribute fields: conforming,
discard, executeonly, iopl, load, movable, and shared. Each can appear once,
in any order. These fields are described in Section 13.15, "CODE, DATA, and
SEGMENTS Attributes."


Example

The following example sets defaults for the program's code segments. No code
segments in the program are loaded until accessed, and all require I/O
hardware privilege.

    CODE LOADONCALL IOPL


13.13  The DATA Statement

The DATA statement defines the default attributes for all data segments
within the application or DLL. The SEGMENTS statement can override this
default for one or more specific segments.


Syntax

    DATA «attribute...»


Remarks

This statement accepts several optional attribute fields: instance, iopl,
load, movable, readonly, and shared. Each can appear once, in any order.
These fields are described in Section 13.15, "CODE, DATA, and SEGMENTS
Attributes."


Example

The example below defines the application's data segment so that it cannot
be shared by multiple copies of the program and cannot be written to. By
default, the data segment can be read and written to and a new DGROUP is
created for each instance of the application.

    DATA NONSHARED READONLY


13.14  The SEGMENTS Statement

The SEGMENTS statement defines the attributes of one or more individual
segments in the application or DLL. The attributes specified for a specific
segment override the defaults set in the CODE and DATA statements (except as
noted below). The total number of segment definitions cannot exceed the
number set using LINK's /SEG option. (The default without /SEG is 128.)

The SEGMENTS keyword marks the beginning of the segment definitions, where
each definition is on its own line. The SEGMENTS statement must appear once
before the first specification (on the same or preceding line) and can be
repeated before each additional specification. SEGMENTS statements can
appear more than once in the file.


Syntax

    SEGMENTS
            «'»segmentname«'» «CLASS 'classname'»
    «attribute...»


Remarks

Each segment definition begins with segmentname, optionally enclosed in
single or double quotation marks (' or "). The quotation marks are required
if segmentname is a reserved word.

The CLASS keyword optionally specifies the class of the segment. Single or
double quotation marks (' or ") are required around classname. If you do not
use the CLASS argument, the linker assumes that the class is CODE.

This statement accepts several optional attribute fields: conforming,
discard, executeonly, iopl, load, movable, readonly, and shared. Each can
appear once, in any order. These fields are described in the next section,
"CODE, DATA, and SEGMENTS Attributes."


Example

The following example specifies segments named  cseg1,  cseg2, and  dseg.
The first segment is assigned the class  mycode  and the second is assigned
CODE by default. Each segment is given different attributes.

    SEGMENTS
        cseg1 CLASS 'mycode' IOPL
        cseg2    EXECUTEONLY PRELOAD CONFORMING
        dseg  CLASS 'data'   LOADONCALL READONLY


13.15  CODE, DATA, and SEGMENTS Attributes

The following attribute fields apply to the CODE, DATA, and SEGMENTS
statements previously described. Refer to "Remarks" in each of the previous
sections for the attribute fields that are used by each statement. Most
fields are used by all three statements; others are used as noted. Each
field can appear once, in any order.

Listed with each attribute field below are keywords that are legal values
for the field, along with descriptions of the field and values. The defaults
are noted. If two segments with different attributes are combined into the
same group, LINK makes decisions to resolve any conflicts and assumes a set
of attributes.

╓┌───────────────────┌───────────────────────────────────────────────────────╖
Attribute           Description
────────────────────────────────────────────────────────────────────────────
conforming          {CONFORMING | NONCONFORMING}

                    For CODE and SEGMENTS statements only. Determines
                    whether a code segment is an 80286 "conforming"
                    segment for device drivers and system-level code. The
                    conforming attribute is for OS/2 only.

                    CONFORMING specifies that the segment executes at the
                    caller's privilege level. When IOPL=YES is specified
                    in CONFIG.SYS, no call gates are generated for calls
                    or jumps.

                    NONCONFORMING (the default) specifies that the segment
                    can be accessed from Ring 2. When IOPL=YES is
                    specified in CONFIG.SYS, call gates are generated.

                    For more information, refer to Intel documentation for
                    the 80286 processor and later.
Attribute           Description
────────────────────────────────────────────────────────────────────────────
                    the 80286 processor and later.

discard             {DISCARDABLE | NONDISCARDABLE}

                    For CODE and SEGMENTS statements only. Determines
                    whether a code segment can be discarded from memory
                    to fill a different memory request. If the discarded
                    segment is accessed later, it is reloaded from disk.
                    NONDISCARDABLE is the default. The discard attribute
                    is for Windows only.




executeonly         {EXECUTEONLY | EXECUTEREAD}

                    For CODE and SEGMENTS statements only. Determines
                    whether a code segment can be read as well as executed.

Attribute           Description
────────────────────────────────────────────────────────────────────────────

                    EXECUTEONLY specifies that the segment can only be
                    executed. The keyword EXECUTE-ONLY is an alternate
                    spelling.

                    EXECUTEREAD (the default) specifies that the segment
                    is both executable and readable. This attribute is
                    necessary for a program to run under the Microsoft
                    CodeView debugger.

instance            {NONE | SINGLE | MULTIPLE}

                    For the DATA statement only. Affects the sharing
                    attributes of the default data segment (DGROUP). This
                    attribute interacts with the shared attribute.

                    NONE tells the loader not to allocate DGROUP. Use NONE
                    when a DLL has no data and uses an application's
                    DGROUP.
Attribute           Description
────────────────────────────────────────────────────────────────────────────
                    DGROUP.

                    SINGLE (the default for DLLs) specifies that one
                    DGROUP is shared by all instances of the DLL or
                    application.

                    MULTIPLE (the default for applications) specifies that
                    DGROUP is copied for each instance of the DLL or
                    application.

iopl                {IOPL | NOIOPL}

                    Determines whether a segment has I/O privilege. OS/2
                    only.

                    IOPL specifies that a code segment has I/O privilege
                    and that a data segment can be accessed only from an
                    IOPL code segment.

Attribute           Description
────────────────────────────────────────────────────────────────────────────

                    NOIOPL (the default) specifies that there is no I/O
                    privilege for code and no protection for data.

load                {PRELOAD | LOADONCALL}

                    Determines when a segment is loaded.



(load,              PRELOAD specifies that the segment is loaded when the
continued)          program starts.

                    LOADONCALL (the default) specifies that the segment is
                    not loaded until accessed and only if not already
                    loaded.

movable             {MOVABLE | FIXED}

Attribute           Description
────────────────────────────────────────────────────────────────────────────

                    Determines whether a segment can be moved in memory.
                    Windows only. FIXED is the default. An alternative
                    spelling for MOVABLE is MOVEABLE.

readonly            {READONLY | READWRITE}

                    For DATA and SEGMENTS statements only. Determines
                    access rights to a data segment.

                    READONLY specifies that the segment can only be read.

                    READWRITE (the default) specifies that the segment is
                    both readable and writeable.

shared              {SHARED | NONSHARED}

                    For real-mode Windows and for READWRITE data segments
                    under OS/2 only. Determines whether all instances of
Attribute           Description
────────────────────────────────────────────────────────────────────────────
                    under OS/2 only. Determines whether all instances of
                    the program can share EXECUTEREAD and READWRITE
                    segments. (Under OS/2, all code segments and READONLY
                    data segments are shared.)

                    SHARED (the default for DLLs) specifies that one copy
                    of the segment is loaded and shared among all
                    processes accessing the application or DLL. This
                    attribute saves memory and can be used for code that
                    is not self-modifying. An alternate keyword is PURE.

                    NONSHARED (the default for applications) specifies
                    that the segment must be loaded separately for each
                    process. An alternate keyword is IMPURE.

                    This attribute and the instance attribute interact for
                    data segments. The instance attribute has the keywords
                    NONE, SINGLE, and MULTIPLE. If  DATA SINGLE  is
                    specified, LINK assumes SHARED; if  DATA MULTIPLE  is
Attribute           Description
────────────────────────────────────────────────────────────────────────────
                    specified, LINK assumes SHARED; if  DATA MULTIPLE  is
                    specified, LINK assumes NONSHARED. Similarly,  DATA
                    SHARED  forces SINGLE, and  DATA NONSHARED  forces
                    MULTIPLE.




13.16  The OLD Statement

The OLD statement directs the linker to search another DLL for export
ordinals. This statement preserves ordinal values used from older versions
of a DLL. For more information on ordinals, see the sections below on the
EXPORTS and IMPORTS statements.

Exported names in the current DLL that match exported names in the old DLL
are assigned ordinal values from the earlier DLL unless


    ■   The name in the old module has no ordinal value assigned, or

    ■   An ordinal value is explicitly assigned in the current DLL.


Only one DLL can be specified; ordinals can be preserved from only one DLL.
The OLD statement has no effect on applications.


Syntax

    OLD 'filename'


Remarks

The filename specifies the DLL to be searched. It must be enclosed in single
or double quotation marks (' or ").


13.17  The EXPORTS Statement

The EXPORTS statement defines the names and attributes of the functions and
data made available to other applications and DLLs, and of the functions
that run with I/O privilege. By default, functions and data are hidden from
other programs at run time. A definition is required for each function or
data item being exported.

The EXPORTS keyword marks the beginning of the export definitions, each on
its own line. The EXPORTS keyword must appear once before the first
definition (on the same or preceding line) and can be repeated before each
additional definition. EXPORTS statements can appear more than once in the
file.

Some languages offer a way to export without using an EXPORTS statement. For
example, in C the _exports keyword makes a function available from a DLL.


Syntax

    EXPORTS
    entryname«=internalname» «@ord«
    RESIDENTNAME» » «NODATA» «pwords»


Remarks

The entryname defines the function or data-item name as it is known to other
programs. The optional internalname defines the actual name of the exported
function or data item as it appears within the exporting program; by
default, this name is the same as entryname.

The optional ord field defines a function's ordinal position within the
moduledefinition table as an integer from 1 to 65,535. If ord is specified,
the function can be called by either entryname or ord. Use of ord is faster
and can save space.

The optional keyword RESIDENTNAME specifies that entryname be kept resident
in memory at all times. This keyword is applicable only if ord is used. (If
ord is not used, the name entryname is always kept in memory.)

The optional keyword NODATA specifies that there is no static data in the
function.

The pwords field specifies the total size of the function's parameters in
words. This field is required only if the function executes with I/O
privilege. When a function with I/O privilege is called, OS/2 consults
pwords to determine how many words to copy from the caller's stack to the
I/O-privileged function's stack.


Example

The following EXPORTS statement defines the three exported functions
SampleRead,  StringIn, and  CharTest. The first two functions can be called
either by their exported names or by an ordinal number. In the application
or DLL where they are defined, these functions are named  read2bin  and
str1, respectively. The first and last functions run with I/O privilege and
therefore are given with the total size of the parameters.

    EXPORTS
            SampleRead = read2bin @8              24
            StringIn   = str1     @4 RESIDENTNAME
            CharTest                              6


13.18  The IMPORTS Statement

The IMPORTS statement defines the names and locations of functions and data
items to be imported (usually from a DLL) for use in the application or DLL.
A definition is required for each function or data item being imported. This
statement is an alternative to resolving references through an import
library created by the IMPLIB utility; functions and data items listed in an
import library do not require an IMPORTS definition.

The IMPORTS keyword marks the beginning of the import definitions, each on
its own line. The IMPORTS keyword must appear once before the first
definition on the same or preceding line and can be repeated before each
additional definition. IMPORTS statements can appear more than once in the
file.


Syntax

    IMPORTS
            «internalname=»modulename.entry


Remarks

The internalname specifies the function or data-item name as it is used in
the importing application or DLL. Thus, internalname appears in the source
code of the importing program, while the function may have a different name
in the program where it is defined. By default, internalname is the same as
the entry name. An internalname is required if entry is an ordinal value.

The modulename is the filename of the exporting application or DLL that
contains the function or data item.

The entry field specifies the name or ordinal value of the function or data
item as defined in the modulename application or DLL. If entry is an ordinal
value, internalname must be specified. (Ordinal values are set in an EXPORTS
statement.)

────────────────────────────────────────────────────────────────────────────
NOTE

A given symbol (function or data item) has a name for each of three
different contexts. The symbol has a name used by the exporting program
(application or DLL) where it is defined, a name used as an entry point
between programs, and a name used by the importing program where the symbol
is used. If neither program uses the optional internalname field, the symbol
has the same name in all three contexts. If either of the programs uses the
internalname field, the symbol may have more than one distinct name.
────────────────────────────────────────────────────────────────────────────


Example

The following IMPORTS statement defines three functions to be imported:
SampleRead,  SampleWrite, and a function that has been assigned an ordinal
value of 1. The functions are found in the  Sample,  SampleA, and  Read
applications or DLLs, respectively. The function from  Read  is referred to
as  ReadChar  in the importing application or DLL. The original name of the
function, as it is defined in  Read, may or may not be known and is not
included in the IMPORTS statement.

    IMPORTS
                    Sample.SampleRead
                    SampleA.SampleWrite
        ReadChar = Read.1


13.19  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topic                                 Access
────────────────────────────────────────────────────────────────────────────
Syntax and procedural information on  Choose "LIB" from the list of
LIB                                   utilities on the "Microsoft Advisor
                                        Contents" screen

Module-definition files and IMPLIB    Choose "LINK" from the list of
                                        utilities on the "Microsoft Advisor
                                        Contents" screen









Chapter 14  Customizing the Microsoft Programmer's WorkBench
────────────────────────────────────────────────────────────────────────────

The Microsoft Programmer's WorkBench (PWB) is not just a text editor, but
also a full-featured platform for program development. It is both flexible
(you can customize it to match your working habits) and extensible (you can
add your own functions and features).

This chapter explains three ways to customize the Programmer's WorkBench:


    ■   Setting switches

    ■   Assigning keystrokes

    ■   Writing macros


While this chapter explains customizing techniques, it does not document
every customizable feature. Please consult online help for detailed
information about these and other PWB features.

This chapter assumes you are familiar with basic PWB operation and
terminology. If not, please read "Using the Programmer's WorkBench" in
Installing and Using the Microsoft Macro Assembler Professional Development
System. The Programmer's WorkBench is supplied with both the Macro Assembler
and Microsoft C so that you can customize one copy of PWB to work with these
and other languages.


14.1  Setting Switches

The Programmer's WorkBench has a number of "switches," or user-configurable
options, that control features such as how many lines the screen scrolls or
whether you are prompted to save a file when you exit. Each switch has a
name and can be assigned a value.

There are two ways to set PWB switches. The easiest way is to choose Editor
Settings from the Options menu. Saving the changes made to Editor Settings
updates your TOOLS.INI initialization file. You can also directly edit
TOOLS.INI. Either method can be used for more elaborate customizations, such
as writing macros.


14.1.1  Changing Current Assignments and Switch Settings

You can change the current editor switches and key assignments. Choose
Editor Settings or Key Assignments from the Options menu. PWB displays these
settings in a new window labeled Current Assignments and Switch Settings.

The <ASSIGN> pseudofile is associated with the Current Assignments and
Switch Settings window. A pseudofile exists only in memory; it has no
counterpart on disk until you explicitly save it. Saving the <ASSIGN>
pseudofile automatically saves any changes you make in the Current
Assignments and Switch Settings window.

To change a switch, edit the line on which it appears. For instance, the
vscroll switch controls how many lines PWB scrolls vertically; its default
setting is 1. To change it, move to the corresponding line:

    vscroll:1

Change the 1 to 3 and move the cursor to another line. PWB highlights the
line to indicate that the change has been executed. (If you make an illegal
change, PWB signals an error.) The change takes effect immediately: PWB now
scrolls text three lines at a time.

When you save <ASSIGN>, PWB updates your TOOLS.INI file.

PWB discards all changes at the end of a session unless you explicitly save
them. You save changes by saving <ASSIGN> as you would any other file.
Select Save from the File menu, or press SHIFT+F2.

You can also use this method for more elaborate customizations, such as
writing macros (see Section 14.3, "Writing Macros"). Simply insert a few
blank lines in the Current Assignments and Switch Settings window and enter
the new information in them.

If you add or modify a line of the Current Assignments and Switch Settings
window, PWB immediately alters its behavior accordingly; the new or changed
lines are saved in TOOLS.INI when you save the <ASSIGN> file. However,
deleting a line has no effect, either on PWB's behavior or the contents of
TOOLS.INI; you must edit TOOLS.INI to remove an assignment.


14.1.2  Editing the TOOLS.INI Initialization File

Another way to customize PWB is by editing TOOLS.INI, the initialization
file used by PWB and other Microsoft language utilities. This is the most
convenient way to perform extensive customizing.

While the Current Assignments and Switch Settings window displays every
customizable PWB item, the TOOLS.INI file contains lines only for items you
have customized. PWB sets any items you omit from TOOLS.INI to a default
value.

TOOLS.INI is made up of sections that start with tags.

Since TOOLS.INI can initialize a number of Microsoft tools, the file is
divided into sections, one for each tool. Each section begins with a tag
consisting of the tool's base name enclosed in square brackets:  [PWB]  for
PWB.EXE,  [NMAKE]  for NMAKE.EXE, and so on.

For example, assume you set the vscroll switch to 3 and saved the change,
but you have not customized PWB in any other way. Your TOOLS.INI file will
contain this section:

    [PWB]
    vscroll:3

PWB reads TOOLS.INI at start-up and loads the settings from the  [PWB]
section.

You can also create sections of TOOLS.INI that configure PWB for specific
programming languages or operating systems. For instance, your TOOLS.INI
file could contain a section beginning with the tag

    [PWB-.C]

for C source files, and

    [PWB-.ASM]

TOOLS.INI sections contain customization information.

for assembly-language (.ASM) source files. Each time you load a file with
the designated extension, PWB reads the appropriate section of TOOLS.INI.
You can have a different set of macros and other customizations for each
file type.

TOOLS.INI can also contain sections specific to an operating system. The
following tag introduces a section specific to DOS version 3.31, for
instance:

    [PWB-3.31]

You can combine tags as needed. For example, the tag

    [PWB-3.0 PWB-10.10R]

applies to DOS version 3.0 and OS/2 version 1.1 real mode.


14.2  Assigning Functions to Keystrokes

You can assign any PWB function to almost any keystroke. Keystroke
assignments, like switches, are displayed in the Current Assignments and
Switch Settings window (choose Key Assignments from the Options menu) and
can be

changed there. Suppose you want to assign the home cursor function to
SHIFT+HOME. The default keystroke assignment for home is

    home:Goto

If you change the assignment to

    home:Shift+Home

SHIFT+HOME moves the cursor to the home (upper left) window position.

You can assign the same function to more than one keystroke. For example,
many keystrokes invoke the select function, which selects a text region. The
preceding example adds a new keystroke (SHIFT+HOME) for the home function,
but it does not remove the previous assignment (GOTO, the 5 key on the
keypad).

If you aren't sure whether a keystroke is already assigned, select the
Current Assignments and Switch Settings window and press PGDN until you
reach the Available Keys table. All unassigned keystrokes are displayed;
once a keystroke is assigned, it no longer appears in this table.

There are two limitations on keystroke assignments:


    ■   You should not reassign a keystroke that PWB assigns to a menu. For
        instance, ALT+F displays the File menu; PWB ignores any attempt to
        reassign ALT+F.

    ■   You should not reassign the ALT plus number keys 1- 6 (ALT+1, ALT+2,
        and so on). These keystrokes are reserved for the file history menu
        items.


PWB uses the most recent duplicate key assignment.

A keystroke can invoke only one function. If you accidentally assign a
keystroke to more than one function, PWB uses the most recent assignment.
For example,

    home:Ctrl+A
    setfile:Ctrl+A

assigns the CTRL+A keystroke to two different functions, home and setfile.
The second assignment overrides the first, assigning CTRL+A to setfile.

You might occasionally want to "unassign," or disable, a keystroke. This is
done by assigning the unassigned function to the keystroke. For example,

    unassigned:Ctrl+A

disables CTRL+A. PWB signals an error when you press any unassigned key.

As the list of assigned keystrokes shows, you can use SHIFT+CTRL as a
prefix. For PWB to recognize this key combination, SHIFT must come first.
For example, to use SHIFT+CTRL with M, you must type SHIFT+CTRL+M, not
CTRL+SHIFT+M.


14.3  Writing Macros

If you need a feature or function that is not a part of PWB, the quickest
way to create it is by writing a macro in the TOOLS.INI file. A macro can do
something as simple as inserting a line of text, or it can perform complex
operations by invoking PWB functions and other macros.


14.3.1  Macro Syntax

A macro can consist of any combination of PWB functions, literal text, and
calls to previously defined macros. You can define up to 1,024 macros at one
time.

Anything inside quotation marks is literal text. Within literal text,
quotation marks are represented by a backslash followed by quotation marks
( ") and a backslash is represented by two consecutive backslashes ( ).
Only literal text is case sensitive; PWB ignores the case of everything
else.

The following macro "comments out" a line of MASM source code:

    comment:=begline "; "
    comment:alt+c

The first line names the macro (comment); the macro commands follow the
assignment operator ( := ). The begline editor function moves the cursor to
the beginning of the current line. The text inside quotation marks (the MASM
comment delimiter) is then inserted. The second line assigns a keystroke
(ALT+C) to the macro.

Macros can extend over one line.

If a macro definition takes up more space than you have on one line (about
250 characters in PWB), you can use the backslash (  ) to continue the
definition on the next line. Consider, for instance, the following macro,
which comments out a line of C source code:

    comment:=begline "/* " endline " */"

It could be written as

    comment:=begline  
    "/* " endline  
    " */"

Notice the extra space before each backslash. If you want a space between
the end of one line and the beginning of the next, you must precede the
backslash with two spaces.

You can pass arguments to PWB macros.

You can use the arg function to pass arguments to functions. For example,
the following macro passes the argument  15  to the plines function (which
scrolls text down):

    movedown:=arg "15" plines

Because arg precedes the literal text, the text isn't written to the screen.
Instead, it is passed as an argument to the next function, plines. The macro
scrolls the current text down 15 lines.

Arguments can also use regular-expression syntax (regular expressions are
documented in online help):

    endword:=arg arg "([ .,;:()[\»!$)" psearch cancel

The arg arg sequence directs the psearch function to treat the text argument
as a regular-expression search pattern. This search pattern tells PWB to
search for the next space, period, comma, semicolon, colon, parentheses, and
square brackets. (Note that a backslash must precede any character that has
a special meaning in regular expressions─in this case, the right bracket.)

A macro can invoke other macros:

    lcomment:= "/* "
    rcomment:= " */"
    commentout:=begline lcomment endline rcomment
    commentout:ctrl+o

The  commentout  macro invokes the previously defined macros  lcomment  and
rcomment.

In addition to standard PWB functions, PWB macros can invoke user-defined
macro functions. See Section 9.6, "Returning Values with Macro Functions."


14.3.2  Macro Responses

Some PWB functions ask you for confirmation. For example, the meta exit
(quit without saving) function normally asks if you really want to exit.
Such questions always take the answer "yes" (Y) or "no" (N).

When you invoke such a function in a macro, the function assumes an answer
of yes and does not ask for confirmation. For example, the macro definition


    quit:=meta exit
    quit:alt+x

The meta prefix modifies the action of a function.

invokes meta exit when you press ALT+X. Because the meta exit function is
invoked from a macro, PWB exits without asking for confirmation.

The following operators allow you to restore normal prompting or change the
default responses:

Operator                          Description
────────────────────────────────────────────────────────────────────────────
<                                 Asks for confirmation; if not followed
                                    by another
                                    < operator, prompts for all further
                                    questions

<y                                Assumes a response of "yes"

<n                                Assumes a response of "no"


A response operator applies to the function immediately preceding it. For
example, you can add the < operator to the  quit  macro definition to
restore the usual prompt:
────────────────────────────────────────────────────────────────────────────
    quit:=meta exit <
    quit:alt+x

Now the macro prompts for a response before it exits.


14.3.3  Macro Arguments

If you enter an argument in PWB and then invoke a macro, the argument is
passed to the first function in the macro that takes an argument:

    tripleit:=copy paste paste

The  tripleit  macro invokes the copy and paste editing functions. When you
highlight a text area and then invoke the macro, your highlighted argument
is passed to the copy function, which copies the argument to the clipboard.
The macro then invokes paste twice. The effect is to insert two copies of
the highlighted text.

You cannot pass more than one argument from PWB to a macro.

You cannot pass more than one argument from PWB to a macro, even if the
macro invokes more than one function that can accept an argument. The
argument always goes to the first function in the macro that takes an
argument.

You can also prompt for input inside a macro and pass the input as an
argument using the prompt function as shown below:

    newfile:=arg "Next file: " prompt setfile <
    newfile:alt+n

The  newfile  macro prompts for a file name and then switches to the
specified file. The sequence  arg "Next file: "  passes the text argument
Next file:  to prompt, which prints it in the text-argument dialog box and
waits for the user to respond. The response is passed as a text argument to
the setfile function, which switches to that file.


14.3.4  Macro Conditionals

Macros can take different actions depending on certain conditions. Such
macros take advantage of the fact that PWB editing functions return values─
a TRUE (nonzero) value if successful or FALSE (zero) if unsuccessful.

Macros can use four conditional operators:

Operator    Description
────────────────────────────────────────────────────────────────────────────
:>label     Defines a label that can be targeted by other operators
=>label     Jumps to label
+>label     Jumps to label if the previous function returns TRUE
->label     Jumps to label if the previous function returns FALSE

For example, the  leftmarg  macro moves the cursor to the left margin of
the editing window:
────────────────────────────────────────────────────────────────────────────
    leftmarg:=:>leftmore left +>leftmore

The macro above invokes the left function repeatedly (jumping to the label
leftmore) until it returns FALSE, indicating the cursor has reached the left
margin.

Macro execution depends on the status of conditionals.

The label must appear immediately after the conditional operator, with no
intervening spaces. A conditional operator without a label exits the macro
immediately if the condition is satisfied. If the condition is not
satisfied, the macro continues execution. The following example demonstrates
this:

    turnon:=insertmode +> insertmode

This macro turns on insert mode regardless of whether insert mode is
currently on or off. If insert mode is off, the first invocation of
insertmode toggles the mode on and returns TRUE, causing the +> operator to
terminate the macro. If insert mode is currently on, the first invocation of
insertmode turns insert mode off and returns FALSE. The macro then invokes
insertmode a second time, turning insert mode back on.


14.3.5  Recording Macros

You can also create a macro by recording a procedure as you perform it. The
keystroke sequence is saved and can be replayed, like any other macro. To
record a macro:


    1.  Choose Set Record from the Edit menu. The Set Macro Record dialog box
        appears.

    2.  Type the name you want the macro to have in the Name text box.

    3.  Tab to the Key Assignment text box and press the key to which you are
        assigning the macro. (For example, press ALT+T to assign the macro to
        ALT+T. The name of the keystroke appears in the text box.) If the
        keystroke (such as ENTER, TAB, or ESC) would normally exit the dialog
        box or move to the next field, type in the keystroke's name.

    4.  Click the OK button.

    5.  Choose Record On from the Edit menu to start the recording.

    6.  Type the text or perform the actions you want to record. (You can
        select text or fields with the mouse as well as the keyboard. Mouse
        selections are automatically converted into equivalent keystrokes.)

    7.  Choose Record On again to end the recording.


You have now created a named macro available through the assigned keystroke.
Pressing this key replays the actions you recorded.

────────────────────────────────────────────────────────────────────────────
WARNING

If you do not select a name for your macro, it is assigned the default name
recordvalue. Unless you plan to discard the macro when exiting, do not let a
recorded macro's name default to recordvalue. Any subsequent macro recorded
with the  recordvalue default name will overwrite the first recordvalue
macro.
────────────────────────────────────────────────────────────────────────────

A recorded macro is temporary; PWB discards it when you exit. To save a
recorded macro:


    1.  Choose Edit Macro from the Edit menu. This opens the <RECORD>
        pseudofile and displays the macros you recorded.

    2.  Make any changes required. For example, you might want to change the
        macro's name or modify the keystroke sequence.

    3.  Save the macro using the Save command from the File menu.


The macros defined in the <RECORD> pseudofile are added to your TOOLS.INI
file when you save the <RECORD> file. PWB automatically reloads them at the
next session.

You can append functions to an existing macro without having to record the
original steps again:


    1.  Choose Set Record from the Edit menu. The Set Macro Record dialog box
        appears.

    2.  Type the macro's name in the Name text box.

    3.  Tab to the Clear First check box and cancel selection. This causes any
        new actions to be appended to the original macro, rather than
        replacing (clearing) it.

    4.  Click the OK button.

    5.  Choose Record On from the Edit menu to start the recording.

    6.  Perform the actions you want added to the macro.

    7.  Choose Record On again to end the recording.


Remember to save the modified macro before exiting, or the new version will
be discarded.

You can record a series of actions without executing them.

You can make a "silent" recording, which records a series of actions without
executing them. This allows you to create a macro without altering or
damaging the file. Start the recording with a meta record command (press F9,
SHIFT+CTRL+R). When the macro is complete, terminate recording with record
(press SHIFT+CTRL+R).

PWB gives no visual feedback during silent recording. If you need to see the
macro being created, open the <RECORD> pseudofile in a second window as
described above. This is an excellent way to get a better understanding of
macros and editor functions.


14.3.6  Temporary Macros

You can use the assign function to create a macro that lasts only until the
end of the current session. For example, the following steps create the
comment  macro described above:


    ■   Press ALT+A

    ■   Type  comment:=begline "; "

    ■   Press ALT+=


This key sequence tells PWB to open dialog boxes where the macro and key
assignments are to be typed. To assign ALT+C to the macro,


    ■   Press ALT+A

    ■   Type  comment:alt+c

    ■   Press ALT+=


The macro is available immediately and is discarded when you exit PWB.


14.4  Related Topics in Online Help

Information on the following related topics can be found in online help. All
the topics listed below are found by choosing "Programmer's WorkBench" from
the "Microsoft Advisor's Help System Contents" screen.

Topic                             Access
────────────────────────────────────────────────────────────────────────────
Writing macros                    Choose "Writing and Using Macros"

TOOLS.INI                         Choose "Using TOOLS.INI"

Regular expressions               Choose "Writing and Using Macros;" then
                                    choose "Regular Expressions" from under
                                    the "Building Macros" subhead

The prompt and meta functions     Choose "Using PWB Functions," and from
                                    the next screen, choose "Alphabetical
                                    List"

Assigning keystrokes              Choose "Setting PWB Switches" and then
                                    "Assign Function"






Chapter 15  Debugging Assembly-Language Programs with CodeView
────────────────────────────────────────────────────────────────────────────

You can diagnose software problems and locate programming errors quickly
with the CodeView debugger. This chapter explains how to


    ■   Display and modify variables and memory

    ■   Control the flow of execution

    ■   Use advanced CodeView debugging techniques

    ■   Modify CodeView's behavior with command-line switches and the
        TOOLS.INI file


CodeView supports the Microsoft mouse (or any fully compatible pointing
device). This chapter first describes CodeView operations with the mouse,
then with function keys. Command-window commands are not generally
discussed, except when there is no comparable mouse or function-key command.
Unless a specific mouse button is named, "clicking" means pressing and
quickly releasing the left mouse button.


15.1  Understanding Windows in CodeView

CodeView divides the screen into logically separate sections called windows.
Windows permit a large amount of information to be displayed in an organized
and easy-to-read fashion.

Each window displays a different type of data.

Each CodeView window has a distinct function and operates independently of
the others. The name of each window described below appears in the top of
the window's frame:


    ■   The Source window displays the source code. You can open a second
        source window to view an include file, another source file, or the
        same source file at a different location. Any ASCII text file can be
        viewed in the Source window.

    ■   The Command window accepts debugging commands from the keyboard.

    ■   The Watch window displays the current values of selected variables.

    ■   The Local window lists the values of all variables local to the
        current procedure.

    ■   The Memory window shows the contents of memory. You can open a second
        Memory window to view a different section of memory.

    ■   The Register window displays the contents of the microprocessor's
        registers, as well as the processor flags.

    ■   The 8087 window displays the registers of the coprocessor or its
        software emulator.


Figure 15.1 shows all CodeView windows.

(This figure may be found in the printed book.)

The first time you run CodeView, it displays three windows. The Local window
is at the top, the Source window fills the middle of the screen, and the
Command window is at the bottom. CodeView records which windows were open
and how they were positioned at the time you exit. These settings become the
default the next time you run CodeView.

There are two ways to open windows. You can choose the desired window from
the View menu or press its shortcut key. In addition, some operations (such
as selecting a Watch variable) automatically open the appropriate window if
it isn't already open.

All displays are updated automatically.

CodeView continually and automatically updates the contents of all windows.
However, if you want to interact with a particular window (such as entering
a command, setting a breakpoint, or modifying a variable), you must first
select that window.

The selected window is called the "active" window. The active window is
marked in three ways:


    ■   The window's name is highlighted.

    ■   The text cursor appears in the window.

    ■   The vertical and horizontal scroll bars move into the window.


Figure 15.2 shows the Source window as the active window.

(This figure may be found in the printed book.)

To select a new active window, click that window (position the mouse pointer
in the window and press the left mouse button). You can also press F6 or
SHIFT+F6 to move from one window to the next.

Windows often contain more information than can be displayed in the area
allotted to the window. There are several ways to view these additional
contents.

To view additional contents with the mouse:


    ■   Drag the scroll box on the horizontal or vertical scroll bars.
        (Position the mouse pointer on the scroll box and, while holding down
        the left mouse button, move the mouse in the appropriate direction.)

    ■   Click the arrows at the top and bottom of the scroll bars.

    ■   Click the gray area to either side of the scroll box in a scroll bar.


To view additional contents with the keyboard:


    ■   Press the direction keys (LEFT, RIGHT, UP, DOWN) to move the cursor.

    ■   Press PGUP, PGDN, CTRL+PGUP (page left), and CTRL+PGDN (page right) to
        move the cursor to a different page of the window's contents.

    ■   Press CTRL+HOME to move the cursor to the beginning of the window's
        contents.

    ■   Press CTRL+END to move the cursor to the end of the window's contents.


Typing commands when the Source window is active causes CodeView to
temporarily shift its focus to the Command window. Whatever you type is
appended to the last line in the Command window. If the Command window is
closed, CodeView beeps in response to your entry and ignores the input.


Adjusting the Windows

Although you can't reposition the windows, you can change their size or
close them. The Maximize, Size, and Close commands from the View menu
perform these functions, or you can press CTRL+F10, CTRL+F8, and CTRL+F4,
respectively. Window manipulation is especially easy with a mouse:


    ■   To maximize a window (enlarge it so it fills the screen), click the up
        arrow at the right end of the window's top border, or double-click the
        window's title. (Position the mouse pointer anywhere on the title and
        press the left mouse button twice, rapidly.) To restore the window to
        its original size, click the double arrow at the right end of the top
        border or press CTRL+F10.

    ■   To change the size of a window, position the mouse pointer anywhere
        along the line at the top of the window. Press and hold down the left
        mouse button, then drag the mouse to enlarge or reduce the window. The
        same action on a vertical border widens or narrows the window.

    ■   To close a window, click the dot at the left end of the top border.
        The adjacent windows automatically expand to recover the unused space.
        You can also close any window whose View menu name has a dot next to
        it: choose that window from the menu or press the window's shortcut
        key.


CodeView remembers the last debugging session.

CodeView stores session information in a file called CURRENT.STS, which is
created in the directory pointed to by the INIT environment variable (or in
the current directory, if there is no INIT variable). The session
information includes such items as the name of the program being debugged,
the CodeView windows that were open, breakpoint locations, and other status.
This information becomes the default status the next time you run CodeView.



15.2  Overview of Debugging Techniques

There is no single best approach to debugging. CodeView offers a variety of
debugging tools that let you select a method appropriate for the program or
for your work habits. This section describes some approaches to solving
debugging problems.

Broadly speaking, two things can go wrong in a program:


    ■   The program doesn't manipulate the data the way you expected it to.

    ■   The flow of execution is incorrect.


These problems usually overlap. Incorrect execution can corrupt the data,
and bad data can cause execution to take an unexpected turn. Because
CodeView allows you to trace program execution while simultaneously
displaying whatever combination of variables you want, you don't have to
know ahead of time whether the problem is bad data manipulation, a bad
execution path, or some combination of both.

CodeView has specific features that deal with the problems of bad data and
incorrect execution:


    ■   You can view and modify any program variable, any section of memory,
        or any processor register. These features are explained in Section
        15.3, "Viewing and Modifying Program Data."

    ■   You can monitor the path of execution and precisely control where
        execution pauses. These features are explained in Section 15.4,
        "Controlling Execution."



15.3  Viewing and Modifying Program Data

CodeView offers a variety of ways to display the values of program
variables, processor registers, and memory. You can also modify the values
of all these items as the program executes. This section shows how to
display and modify variables, registers, and memory.


15.3.1  Displaying Variables in the Watch Window

To add a variable to the Watch window, position the cursor on the variable's
name, using the mouse or the direction keys (LEFT, RIGHT, UP, DOWN). Then
choose the Add Watch command from the Watch menu, or press CTRL+W.

A dialog box appears with the selected variable's name displayed in the
Expression field. If you don't want to watch the variable shown, type in the
name of another variable. Click the OK button or press ENTER to add this
variable to the Watch window.

The Watch window appears at the top of the screen. Selecting a Watch
variable automatically opens the Watch window if the window isn't already
open.

A newly added variable may be followed by the message:

    <Watch Expression Not in Context>

This message appears when execution has not yet reached the procedure where
a local variable is defined. Global variables (those declared outside
procedures) never cause CodeView to display this message; they can be
watched from anywhere in the program.

To remove a variable from the Watch window, choose the Delete Watch command
from the Watch menu or press CTRL+U. Then select the variable to be removed
from the list in the dialog box. You can also position the cursor on any
line in the Watch window and press CTRL+Y to delete that line.

You can watch an unlimited number of variables.

You can place as many variables as you like in the Watch window; the
quantity is limited only by available memory. You can scroll the Watch
window to position it at those variables you want to view. CodeView
automatically updates all Watch window variables as the program runs,
including those not currently visible within the Watch window frame.

A variable can be specified by its address as well as its name. You can give
its address in segment:offset form, where either component can be a register
name or a number. You can extract a variable's address by prefixing the &
operator to its name. Prefixing a variable's address (or any address) with
the BY, WO, or DW operator displays the byte, word, or doubleword value
starting at that address.

There are several ways to display a variable's value.

By default, CodeView displays variables as decimal values. You can select
the radix by typing  n8,  n10, or  n16  in the Command window for an octal,
decimal, or hexadecimal display. CodeView remembers the current radix when
you exit; it becomes the default radix the next time you run CodeView.


15.3.2  Displaying Expressions in the Watch Window

The Watch window is not limited to variables. You can enter an expression
(that is, any valid combination of variables, constants, and operators) for
CodeView to evaluate and display. You can also select the format in which
CodeView displays the expression.

MASM expressions are evaluated using C rules.

CodeView does not include an expression evaluator specifically for MASM. It
uses the C expression evaluator instead. This means you must enter MASM
variables or expressions in a form the C evaluator recognizes, which is not
always the way they appear in a MASM program. (Online help describes the
operators and precedence order for C expressions. The last part of this
section also gives examples of some of the more commonly used expression
forms.)

The Language command from the Options menu offers a choice of Auto, C,
Basic, or FORTRAN expression evaluators. However, the Basic and FORTRAN
expression evaluators do not support address evaluation, pointer
conversions, type casting, or other operations needed when debugging
assembly-language code.

Besides arithmetic and memory-reference expressions, CodeView can also
display Boolean expressions. For example, if a variable is never supposed to
be larger than 100 or less than 25, the expression

    (var < 25 || var > 100)

evaluates to one (TRUE) if  var  goes out of bounds.


Changing Display Format

By default, CodeView displays expression values in decimal form. You can
change the display radix to octal or hexadecimal with the Radix (N) command
described at the end of the previous section.

Another way to change the display format is to append a comma and a
single-digit format specifier to any watched variable, expression, or
address. For example, to display  varname  in octal form, type  varname,o
in the Watch expression box. (If  varname  is already in the Watch window,
simply append a comma and the octal specifier  ,o  and then move the cursor
off the line.) The following list describes the use of each specifier:

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Specifier                         Form Displayed
────────────────────────────────────────────────────────────────────────────
c                                 Least-significant byte of the variable
                                    displayed as a single character

d                                 Decimal value

e or E                            Eight bytes displayed as a
                                    double-precision exponential
                                    number
Specifier                         Form Displayed
────────────────────────────────────────────────────────────────────────────
                                    number

f                                 Four bytes displayed as a
                                    single-precision floating-point
                                    number

g or G                            Eight bytes displayed as a
                                    double-precision exponential
                                    number

i                                 Signed integer value

o                                 Unsigned octal value

s                                 String; all following bytes displayed as
                                    ASCII characters, up to next null
                                    character (ASCII 0)

u                                 Unsigned decimal value
Specifier                         Form Displayed
────────────────────────────────────────────────────────────────────────────
u                                 Unsigned decimal value

x or X                            Hexadecimal value, without leading  0x




Displaying MASM Expressions

Expressions using registers or indexes are more complex. The following
sections show how to substitute CodeView expressions using the C expression
evaluator for MASM expressions.

Register Indirection - The C expression evaluator does not recognize
brackets to indicate the memory location pointed to by a register. Instead,
use the BY, WO, or DW operator to reference the corresponding byte, word, or
doubleword value.

MASM Expression              CodeView Equivalent
────────────────────────────────────────────────────────────────────────────
BYTE PTR [bx]                BY bx
WORD PTR [bp]                WO bp
DWORD PTR [bp]               DW bp

Register Indirection with Displacement - To perform based, indexed, or
based-indexed indirection with a displacement, use the BY, WO, or DW
operator combined with addition.

MASM Expression                 CodeView Equivalent
────────────────────────────────────────────────────────────────────────────
BYTE PTR [di+6]                 BY di+6
BYTE PTR Test [bx]              BY &Test+bx
WORD PTR [si] [bp+6]            WO si+bp+6
DWORD PTR [bx] [si]             DW bx+si

Address of a Variable - Use the address operator (&) instead of the OFFSET
operator.

MASM Expression              CodeView Equivalent
────────────────────────────────────────────────────────────────────────────
OFFSET Var                   &Var

PTR Operator - Use C type casts, or the BY, WO, and DW operators in
conjunction with the address operator (&), to replace the PTR operator.

MASM Expression                   CodeView Equivalents
────────────────────────────────────────────────────────────────────────────
BYTE PTR Var                      BY &Var
                                    *(unsigned char*)&Var

WORD PTR Var                      WO &Var
                                    *(unsigned *)&Var

DWORD PTR Var                     DW &Var
                                    *(unsigned long*)&Var


Strings - Add a comma and the string specifier  ,s  after the variable name.

MASM Expression              CodeView Equivalent
────────────────────────────────────────────────────────────────────────────
Stringvar                    Stringvar,s

Because CodeView uses the C expression evaluator and C strings end with an
ASCII null (zero), CodeView displays all characters up to the next null in
memory when you request a string display. If you intend to debug a MASM
program, you should terminate string variables with a null.

Array and Structure Elements - The C expression evaluator equates an array
name with the address of its first element. Therefore, you should prefix an
array name with the address operator (&), then add the desired offset. The
offset can be added directly, or it can appear within parentheses. It can be
a number, a register name, or a variable.

The following examples (using byte, word, and doubleword arrays) show how
this is done:

MASM Expression                   CodeView Equivalents
────────────────────────────────────────────────────────────────────────────
String[12]                        BY &String+12
                                    *(&String+12)

aWords[bx+di]                     WO &aWords+bx+di
                                    *(unsigned*)(&aWords+bx+di)

aDWords[bx+4]                     DW &aDWords+bx+4
                                    *(unsigned long*)(&aDWords+bx+4)


Pointers - MASM 6.0 lets you define pointer-type variables. Since these are
the same as C pointers, the C expression evaluator works as it does with C
programs.

You dereference a pointer simply by typing its name in the Watch window. The
pointer's address is displayed, followed by all the elements of the variable
to which the pointer refers. Multiple levels of indirection (that is,
pointers referencing other pointers) can be displayed simultaneously.


15.3.3  Displaying Local Variables

When your program is executing within the scope of a procedure, the Local
window automatically displays the variables local to that procedure (stack
variables). This includes arguments declared in PROC directives and
variables explicitly declared as LOCAL within the procedure.

Note that variables you create on the stack are not displayed in the Local
window, since CodeView is aware only of the assembler-created stack. You can
display user-defined stack variables in the Watch window by specifying their
address in segment:offset form.


15.3.4  Using Pointers to Display Arrays and Strings

Unlike high-level-language compilers, MASM does not provide symbolic
information for arrays. Consequently, CodeView cannot distinguish between a
simple variable and an array, and therefore cannot directly display an
assemblylanguage array in expanded form. (See Section 15.3.2, "Displaying
Expressions in the Watch Window," to display individual array elements.)

A user-defined pointer lets you view an expanded array.

For debugging purposes, you can overcome MASM's lack of array information by
using the TYPEDEF directive to define a pointer type, and from that a
pointer variable for the array. (Place the directive and pointer definition
within a conditional-assembly block, so the pointer won't be added to your
release code.) You can then view the array from CodeView by placing the
pointer in the Watch window. For example:

    array   BYTE    20 DUP (0)      ; array of 20 bytes

    IF debug
        PBYTE   TYPEDEF PTR BYTE     ; PBYTE type is pointer to bytes
        parray PBYTE array           ; parray points to array
    ENDIF

If you declare multiple levels of pointers (pointers to pointers to
pointers, and so on), multiple levels of indirection can be displayed
simultaneously by expanding each subpointer.

If it is inconvenient to view a character array in hexadecimal form, cast
the variable's name to a character pointer by placing (char *) in front of
the name. The character array is then displayed as a string delimited by
apostrophes. You can also append the string-format specifier  ,s  to the
expression.

Note that the C expression evaluator expects a string to terminate with the
ASCII null character (0). If you do not include a terminating null in the
string's definition, the evaluator continues displaying memory as characters
until it encounters a null. The Memory window is an effective way to view
nonterminated strings.


15.3.5  Displaying Structures

MASM adds structure and union information to the debugging table. You can
display MASM structures in expanded form, just as you would in C, Basic,
Pascal, or FORTRAN.

Structures contain multiple data values, often of different data types,
arranged in one or more layers. Therefore, they are often referred to as
"aggregate" data items. CodeView lets you control how much of a structure is
shown; that is, whether all, part, or none of its components are displayed.


The following example defines a structure and pointer types to implement a
simple linked list:

    PTRLINKEDLIST TYPEDEF PTR LINKEDLIST
    PTRDATAWORD   TYPEDEF PTR WORD

    LINKEDLIST STRUCT
        ptrNext PTRLINKEDLIST 0
        ptrData PTRDATAWORD   0
    LINKEDLIST ENDS

    rootNode linkedList < >

Once  rootNode  has been defined, the program calls the MALLOC function
(which is available from the libraries of Microsoft high-level languages) to
allocate memory for a structure pointer and a data pointer. The addresses of
each are assigned to the corresponding pointers in  rootNode, readying the
list for its first entry.

The program stores a list item at the memory location specified by the
preceding pointer, then calls MALLOC to allocate memory for the next list
item. This process is repeated for each new list item, creating a linked
list of data structures.

To display the linked list of structures, add  rootNode  to the Watch
window. It initially appears in the form:

    +rootnode = {...}

The brackets indicate that this is an aggregate variable (since it's a
structure). The plus sign (+) indicates that the structure has not yet been
expanded to display its components.

To expand  rootnode, double-click its display line. (Position the mouse
pointer anywhere on the line and press the left mouse button twice,
rapidly.) You can also move the cursor to the line and press ENTER. The
Watch window display changes to

    -rootnode
        +ptrnext  = 0F00:1111
        ptrdata  = 0x0032  "2"

The address and data values shown here are arbitrary. They depend on the
data values stored and on the memory location from where MALLOC obtained
free space. The minus sign (-) indicates that  rootnode  has been fully
expanded; no further expansion is possible. The plus sign (+) indicates that
    ptrnext  points to another structure that has not been expanded.

Any structure element can be independently expanded or contracted. To expand
the next structure, double-click  ptrnext, or press ENTER when the cursor is
on that line. The Watch window display changes to

    -rootnode
        -ptrnext  = 0F00:1111
        +ptrnext  = 0F00:2222
        ptrdata  = 0x0034  "4"
        ptrdata  = 0x0032  "2"

Note that both the data value and its ASCII equivalent are displayed. To
contract the structure, double-click its line a second time or position the
cursor on the line and press ENTER.

The process of expanding structures pointed to by  ptrnext  may be repeated
indefinitely until you reach the last structure in the list. Its identifier
will be prefixed with a minus sign, indicating that no more space for
structures has been allocated.

You can view individual elements instead of the entire structure.

If you want to view only one or two elements of a large structure, indicate
the specific structure elements in the Expression field of the Add Watch
dialog box. Structure elements are separated by a dot (.), so you would type


    rootnode.ptrnext.ptrnext

to view the pointer from the third structure in the list.


15.3.6  Using Quick Watch

Choose the Quick Watch command from the Watch menu (or press SHIFT+F9) to
display the Quick Watch dialog box. If the cursor is in the Source, Local,
or Watch window, the variable at the current cursor position appears in the
dialog box. If it isn't the item you want to display, type in the desired
expression or variable; then press ENTER. The Quick Watch window immediately
displays the specified item.

The Quick Watch display automatically expands structures and pointers to
their first level. You can expand or contract an element just as you would
in the Watch window: position the cursor on the appropriate line and press
ENTER. If the array needs more lines than the Quick Watch window can
display, drag the scroll box with the mouse, or press DOWN or PGDN to view
the rest of the array.

You can add Quick Watch variables to the Watch window.

Choose the Add Watch button to add a Quick Watch item to the Watch window.
Structures and pointers appear in the Watch window expanded as they were
displayed in the Quick Watch dialog box.

Quick Watch is a convenient way to take a quick look at a variable or
expression. Since only one Quick Watch variable can be viewed at a time, you
would not use Quick Watch for most of the variables you want to view.


15.3.7  Displaying Memory

Choosing the Memory command from the View menu opens a Memory window. Two
Memory windows can be open at one time.

By default, memory is displayed as hexadecimal byte values, with 16 bytes
per line. At the end of each line is a second display of the same memory in
ASCII form. Values that correspond to printable ASCII characters (decimal 32
to 127) are displayed in that form. Values outside this range are shown as
dots (.).

You can display memory values in any form.

Byte values are not always the most convenient way to view memory. If the
area of memory you're examining contains character strings or floating-point
values, you might prefer to view them in a directly readable form. Choosing
the Memory Window command from the Options menu displays a dialog box with a
variety of display options:


    ■   ASCII characters

    ■   Byte, word, or doubleword binary values

    ■   Signed or unsigned integer decimal values

    ■   Short (32-bit), long (64-bit), or ten-byte (80-bit) floating-point
        values


Figures 15.3 and 15.4 show two of these different displays.

(This figure may be found in the printed book.)

(This figure may be found in the printed book.)

Another way to choose a display format is to cycle through the formats by
repeatedly pressing SHIFT+F3.

Not every four-byte or eight-byte sequence represents a valid floating-point
number. If a section of memory cannot be displayed in the floating-point
format you select, the number displayed includes the characters NAN─"not a
number."

You can change the contents of the memory by simply overtyping new values in
the Memory window. See Section 15.3.9 for more information on modifying
values.


Displaying Variables with a Live Expression

Section 15.3.4 explained how to display a specific array element by adding
the appropriate expression to the Watch window. You can also watch a
particular array element or structure element in the Memory window. This
CodeView display feature is called a "live expression." The term "live"
means that CodeView dynamically displays memory starting at the current
value of the address expression you specify.

To create a live expression, choose the Memory Window command from the
Options menu; then select the Live Expression check box. Type the element
you want to view in the Address Expression field. For example, if  array  is
a variable whose current value is being indexed by the value in the BI
register and you wish to view it, type  array [bi]. Then choose the OK
button or press ENTER.

If no memory windows are open, a new Memory window opens. The first memory
location in the window is the first memory location of the live expression.
The section of memory displayed changes to the section the live expression
currently references.

You can use the Memory Window command from the Options menu to display the
memory in a directly readable form. This is especially convenient when the
live expression represents strings or floating-point values, which are
difficult to interpret in hexadecimal form.

It is usually more convenient to view an item in the Watch window than as a
live expression. However, some items are more easily viewed as live
expressions. For example, you can examine what is currently on top of the
stack by entering SS:SP as the live expression. In fact, any legal
combination of register values (such as ES:DI or DS:SI) can be entered in
segment:offset form.


15.3.8  Displaying the Processor Registers

Choosing the Register command from the View menu (or pressing F2) opens a
window on the right side of the screen. The microprocessor's current
register values appear in this window. At the bottom of the window is a
group of mnemonics representing the processor flags. Pressing F2 a second
time closes the window.

Video intensity shows changed values.

When you first open the Register window, all register and flag values are
shown in normal text. When you change a register or flag, the changed value
is highlighted. For example, suppose the overflow flag is not set when the
Register window is first opened. The corresponding mnemonic is NV and
appears in light gray. If the overflow flag is subsequently set, the
mnemonic changes to OV and appears in bright white. If your computer uses an
80386/486 processor and you are running the real-mode version of CodeView
choosing the 386 Instructions command from the Options menu displays the
registers as 32-bit values. Choosing this command a second time returns to
the 16-bit display.

You can also display the registers of an 8087-80387 coprocessor (or the
built-in coprocessor of the 80486) in a separate window by choosing the 8087
command from the View menu. If your program uses the coprocessor emulator,
the emulated registers are displayed instead.

The Register values reveal program status.

The Register window is a valuable debugging tool. Almost every assembly
instruction alters a register or flag. As each line of code is executed, the
register values and flags that change are highlighted, so you can see
whether each instruction does what you intended it to.

Also, when you execute an instruction whose operand has a memory location
(such as a variable), the effective address of the operand, as well as the
value stored at that address, is displayed at the bottom of the Register
window.


15.3.9  Modifying the Values of Variables, Memory, and Registers

You can easily change the values of variables, memory locations, or
registers displayed in the Watch, Local, Memory, Register, or 8087 windows.
Simply position the cursor at the value you want to change and edit it to
the appropriate value. In the Watch and Local windows, the change is
accepted by CodeView when you move the cursor off the line. If you change
your mind, press ALT+BKSP to undo the last change you made.

You can also alter expressions in the Watch window by adding an operator or
changing the variable displayed. When you have altered the expression and
moved the cursor off the line, CodeView will immediately show the new value
of the modified expression.

The starting address of each line of memory displayed is shown at the left
of the Memory window in segment:offset form. Altering the address
automatically shifts the display to the corresponding section of memory.
Under OS/2, if your program does not own that section of memory, memory
values are displayed as double question marks (??).

It's easy to change memory values...

You can also change the values of memory locations by modifying the right
side of the memory display (where memory values are shown in ASCII form).
For example, to change a byte from decimal 75 to decimal 85, place the
cursor over the letter K, which corresponds to the position where the memory
value is 75 (K is ASCII 75), and type in U (ASCII 85).

...or flags.

To toggle a processor flag, double-click its mnemonic. You can also position
the cursor on a mnemonic, then press any key (except ENTER, TAB, or SPACE).
Press ALT+BKSP (undo) to restore the flag to its previous setting.

Be cautious when modifying memory or a register.

The effect of changing a register, flag, or memory location can vary from no
effect at all to crashing the operating system. Be cautious when altering
these values.


15.4  Controlling Execution

There are two forms of program execution under CodeView:


    ■   Continuous; the program executes until either a previously specified
        breakpoint has been reached or the program terminates.

    ■   Single-step; the program pauses after each line of code has been
        executed.


Sections 15.4.1 and 15.4.2 explain how each form of execution works and the
most effective way to use each.

As you are debugging, you can display the program in source-code form or
assembly form. Section 15.4.3 explains the advantages of each.


15.4.1  Continuous Execution

Continuous execution lets you quickly execute the bug-free sections of code
which would otherwise take a long time to execute one instruction at a time.


The simplest form of continuous execution is to click the line of code you
want to debug or examine in more detail with the right mouse button. The
program executes up to the start of this line, then pauses. An alternative
method is to position the cursor on this line, then press F7.

You can also pause execution at a specific line of code with a "breakpoint."
There are several types of breakpoints. Breakpoints are explained in the
following section.


Selecting Breakpoint Lines

Breakpoints can be tied to lines of code.

You can skip over those parts of the program that you don't want to examine
by specifying one or more lines as breakpoints. The program executes up to
the first breakpoint, then pauses. Pressing F5 continues program execution
up to the next breakpoint, and so on. (You can halt execution at any time by
pressing CTRL+C.)

There is no limit to the number of breakpoints.

You can set as many breakpoints as you like (limited only by available
memory). There are several ways to set breakpoints:


    ■   Double-click anywhere on the desired breakpoint line. The selected
        line is highlighted to show that it is a breakpoint. To remove the
        breakpoint, double-click the line a second time.

    ■   Position the cursor anywhere on the line at which you want execution
        to pause. Press F9 to select the line as a breakpoint and highlight
        it. Press F9 a second time to remove the breakpoint and highlighting.

    ■   Display the Set Breakpoint dialog box by choosing Set Breakpoint from
        the Watch menu. Select one of the breakpoint options that permits a
        line ("location") to be specified. The line at the cursor is the
        default breakpoint line in the Location field. If this line is not the
        desired location, enter the line number desired. (You must place a
        period in front of the line number, or CodeView will interpret the
        number as an absolute address.) To remove the breakpoint, use F9 or
        choose Edit Breakpoints from the Watch menu to display the Edit
        Breakpoints dialog box.


Not every line can be a breakpoint.

A breakpoint line must be a program line that represents executable code.
You cannot select a blank line, a comment, or a declaration (such as a
variable declaration or a segment specifier) as a breakpoint.

A breakpoint can also be set at an address. Type the address in
segment:offset form in the Set Breakpoint dialog box. (Address breakpoints,
unlike line breakpoints, are not saved in CodeView's status file, and
therefore are not restored when you restart a debugging session.)

A breakpoint can be set to the name of a procedure if the procedure was
declared with the PROC directive. If not, the procedure must contain a
labeled line. Type the procedure's name or the line's label in the Set
Breakpoint dialog box.

Once execution has paused, you can continue execution by clicking the F5=Go
button in the display or by pressing F5. Execution continues to the next
breakpoint. If there are no more breakpoints, execution continues to the end
of the program, or until a fatal error occurs.

────────────────────────────────────────────────────────────────────────────
NOTE

The Set Breakpoint dialog box contains a Commands text box. You can type
Command-window commands in this box, separated by semicolons. These commands
are executed when the breakpoint is reached. See the Command Window section
of CodeView online help for a full description of Command-window commands.
────────────────────────────────────────────────────────────────────────────


Conditional Breakpoints

Breakpoints are not limited to specific lines of code. CodeView can also
pause when a variable reaches a particular value or just changes value. This
is a "conditional breakpoint." In previous versions of CodeView, conditional
breakpoints are called "watchpoints" and "tracepoints."

You can associate a conditional breakpoint with a specific line of code, so
that execution pauses at that line only if the variable has simultaneously
reached a particular value or changed value. The check boxes in the Set
Breakpoint dialog box select these other breakpoint types.

To pause execution when a variable reaches a particular value, type an
expression that is usually false in the Expression field of the Set
Breakpoint dialog box. For example, if you want to pause when the variable
looptest  equals 17, type  looptest == 17.

To pause execution when a variable changes value, you need to type only the
name of the variable in the Expression field. For large variables (such as
arrays or character strings), you can specify the number of bytes you want
checked (up to 32K) in the Length field. Execution pauses when any one of
these values changes.

────────────────────────────────────────────────────────────────────────────
NOTE

CodeView checks every conditional breakpoint after executing each line of
source code. Unless you have enabled the use of the debug registers with the
CodeView /R command-line option, this computational overhead greatly slows
execution. (Execution is even slower if you are executing in Mixed mode or
Assembly mode, because conditional breakpoints are checked after each
machine instruction.)

For maximum speed when debugging, either associate conditional breakpoints
with specific lines, or set conditional breakpoints only after you have
reached the section of code that needs to be debugged. You can also use the
Disable button in the Edit Breakpoints dialog box to temporarily suspend
evaluation of a previously set conditional breakpoint.
────────────────────────────────────────────────────────────────────────────


Using Breakpoints

One of the most common bugs is a loop that executes too many or too few
times. If you set a breakpoint on the statement that controls the loop
statements, the program pauses after each iteration. With the loop variable
or critical program variables in the Watch or Local windows, it should be
easy to see what's going wrong in the loop.

You can specify how many times a breakpoint is reached before stopping.

You do not have to pause at a breakpoint the first time execution reaches
it. CodeView lets you specify the number of times you want to ignore the
breakpoint condition before pausing. Type the number in the Pass Count field
of the Set Breakpoint dialog box. This feature can eliminate a lot of
tedious singlestepping.

Another programming error is erroneously assigning a value to a variable
that should not change. Type the variable in the Expression field of the Set
Breakpoint dialog box. Execution breaks whenever this variable changes─even
unintentionally.

You can assign new values to variables while execution is paused.

Breakpoints are a convenient way to pause the program so you can assign new
values to variables. For example, if a limit value is set by a variable, you
can change the value to see whether program execution is affected.


15.4.2  Single-Stepping

In single-stepping, CodeView pauses after each line of code is executed. The
next line to be executed is highlighted.

There are two ways to single-step.

You can single-step through a program with the Step and Trace commands. Step
(executed by pressing F10) steps over procedure calls. All the code in the
procedure is executed, but it appears to you as if the procedure executed in
a single step. Trace (executed by pressing F8) traces through every step of
all procedures. Each line of the procedure is executed as a separate step.

You can alternate between Trace and Step as you like. The method you use
depends only on whether you want to see what happens within a particular
procedure. (Note that interrupt calls are always stepped over; you do not
see individual steps of the execution.)

If CodeView cannot locate the source code for a procedure in the current
directory, it pauses and asks for the name of the file that contains the
source. If you cannot supply a source file, CodeView disassembles the
executable code and displays that instead. (If you are executing in Source
mode, and the source code for a procedure is not available, CodeView steps
over the procedure, even if you use the Trace command.)

Note that breakpoints are active during both step and trace mode. If the
procedure you step over contains a breakpoint, execution stops at the
breakpoint.

You can trace through the program continuously (without having to press F8
at each step), using the Animate command from the Run menu. The speed of
execution is controlled by the Trace Speed command from the Options menu.
You can halt animated execution at any time by pressing any key.


15.4.3  Changing the Program Display Mode

The F3 function switches the display between Source mode, Mixed mode, and
Assembly mode. You can also switch display modes by choosing the Source
Window command from the Options menu and then selecting a display mode in
the Source Window Options dialog box. (If the source-code text file cannot
be located, CodeView automatically disassembles the executable file and
displays it in assembly-language form.)

The Source mode shows the program as you wrote it. The Mixed mode and
Assembly mode each expand macros and code-generating directives (such as
.STARTUP) into assembly-language instructions. You can execute these
instructions one at a time (rather than as a single item), and verify that
the assembler has created the correct instructions from the macro or the
directive.

Figures 15.5 and 15.6 show Mixed mode and Assembly mode, respectively, for
the same code.

(This figure may be found in the printed book.)

(This figure may be found in the printed book.)


15.5  Replaying a Debug Session

CodeView can automatically create a "tape" (a disk file) with the debugging
instructions and input data you entered when testing a program. The tape can
then be "replayed" to repeat the debugging process. You initiate recording
by choosing the History On command from the Run menu. Choosing History On a
second time terminates recording. The recording is saved in the .CVH file in
the current directory.

Dynamic replay has several uses. The most obvious is repeating a debug
session for the corrected version of a program. Dynamic replay usually works
with slightly modified programs. However, the more you change the program,
the less likely the new version will replay reliably.

You can also use the recording as a bookmark. You can quit after a long
debugging session, then pick up the session later in the same place.

Dynamic replay makes it easy to correct a mistake.

Most importantly, dynamic replay allows you to back up when you make an
error or overshoot the section of code with the bug. This feature is
important because not all bugs appear on the first path of execution you
try.

For example, you might have to manually execute a procedure many times
before its bug appears. If you then enter a command that alters the
machine's or program's status, thereby losing the information you need to
find the cause of the bug, you would have to restart the program and
manually repeat every debugging step to return to that point. Even worse, if
you don't remember the exact sequence of events that exposed the bug, it
could take hours to reproduce them.

Dynamic replay of a recorded tape eliminates this problem. Choose the Undo
command from the Run menu to automatically restart the program and
continuously execute every command up to (but not including) the last one
you entered. You can repeat this process as many times as you like until you
return to the desired point in execution.

You can add additional steps to an existing tape. Choose History On, then
choose Replay. When replay has completed, perform whatever new debugging
steps you want, then choose History On a second time to terminate recording.
The new tape contains both the original and the added commands.

────────────────────────────────────────────────────────────────────────────
NOTE

CodeView records only those mouse commands that apply to CodeView. Mouse
commands recognized by the application being debugged are not recorded.
────────────────────────────────────────────────────────────────────────────


Replay Limitations under OS/2

There are some limitations to dynamic replay when debugging under OS/2:


    ■   The program must not respond to asynchronous events. Replay under
        Presentation Manager is not currently supported because of this
        restriction.

    ■   Breakpoints must be specified at specific source lines or for specific
        symbols (rather than by absolute addresses), or replay may fail.

    ■   Single-thread programs behave normally during replay. However, one of
        the threads in a multithread program may cause an asynchronous event,
        violating the first restriction in this list. Multithread programs are
        therefore more likely to fail during replay.

    ■   Multiprocess replay will fail. Each new process invokes a new CodeView
        session. The existence of multiple sessions makes it impractical to
        record the sequence of events if you execute commands in a session
        other than the original session.



15.6  Advanced CodeView Techniques

Once you are comfortable displaying and changing variables, stepping through
the program, and using dynamic replay, you might want to experiment with the
advanced techniques explained below.


Debugging OS/2 Programs

You can debug protected-mode and bound programs under CodeView. See the
Debug Multiple Processes and Debug Multiple Threads sections of CodeView
online help for information about executing threads and multiple processes.



Setting Command-Line Arguments

If your program retrieves command-line arguments, you can specify them with
the Set Runtime Arguments command from the Run menu. Type the arguments in
the Command Line field before you begin execution. (Arguments entered after
execution begins cause an automatic restart.)


Opening Multiple Source Windows

You can open two Source windows at the same time. The windows can display
two different sections of the same program, or one window can show the
calling program and the other a procedure file. You can move freely between
the windows, executing lines of code as you like.


Calling Procedures

Any procedure in your program (whether user-written or from a library) can
be called from the Command window or the Watch window. In the Command
window, use the Display Expression command as follows:

    ?procname (arglist)

The procedure procname is evaluated with the arglist arguments and the
returned value is displayed in the Command window. (Note that CodeView
cannot evaluate a function that returns an aggregate type.) In the Watch
window, simply enter the procedure call. If the procedure does not return a
value, the value displayed is the value of the AX register upon return from
the procedure.

You can evaluate any procedure, not just those called by your program. All
object code specified to the linker is linked into the program. Any public
functions in this code can be evaluated from the Command window.

You can use this feature to call functions from within CodeView that you
would not normally include in the final version of your program. For
example, you could include the OS/2 API functions that control semaphores,
then execute them from the Command window to manipulate the run-time
environment at any point in the debugging process. (Remember that altering
the environment during program execution may have unexpected side effects.)



Executing Faster when Using Breakpoints

Breakpoints can slow execution. You can increase CodeView's speed with the
/R command-line option if you have an 80386/486-based computer and are
running CodeView under DOS. This option enables the four debug registers,
which support breakpoint-checking in hardware rather than in software. (The
CodeView options are described in Section 15.7.)


Printing Selected Items

You can print all or part of the contents of any window with the Print
command from the File menu. In the Print dialog box, a check box lets you
print selected text from the window, the material currently displayed in the
window, or the complete contents of the window. Select text by dragging the
mouse across it, or by holding down the SHIFT key and pressing the direction
keys (LEFT, RIGHT, UP, DOWN).

By default, print output is to the file CODEVIEW.LST in the current
directory. You can choose whether the new material is appended to an
existing file or overwrites it, using the Append/Overwrite check box. If you
want print output to go to a different file, type its name in the To File
Name field. If you want the output to go to a printer, enter the appropriate
device name such as LPT1 or COM2.


Redirecting CodeView Input and Output

The Command window accepts DOS-like commands that redirect input and output.
These commands can also be included on the command line that invokes
CodeView. Whatever items follow the /C option on the command line are
treated as CodeView commands to be immediately executed at start-up.

    CV /c "<infile; t>outfile" myprog

In the example above, input is redirected from  infile, which can contain
start-up commands for CodeView. When CodeView exhausts all commands in the
input file, focus automatically shifts to the Command window. Output is sent
to  outfile  and echoed to the Command window. The  t  must precede the  >
command for output to be sent to the Command window.

Redirection is a useful way to automate CodeView start-up. It also lets you
keep a viewable record of command-line input and output, a feature not
available with dynamic replay. No record is kept of mouse operations. Some
applications (particularly interactive ones) may need modification to allow
for redirection of input to the application itself.


Executing Faster with Additional Memory

If you are running DOS and your computer uses expanded or extended memory,
you can increase CodeView's execution speed by selecting the /X or /E
option. CodeView moves as much as it can of itself and the symbolic CodeView
information to higher memory (above the first megabyte).

The /X option uses extended memory and gives the greatest speed increase.
This option requires the HIMEM.SYS driver, which is included on your
distribution disks. Add  DEVICE = HIMEM.SYS  to your CONFIG.SYS file to load
HIMEM.SYS at boot time.

The /E option uses expanded memory. The speed increase is not as great as
that supplied by the /X option. The expanded memory manager (EMM) must be
LIM 4.0, and no single module's debug information can exceed 48K. If the
symbol table exceeds this limit, try reducing file-name information by not
specifying full path names at compile time and by specifying CodeView
information (/Zi) only with those program modules that need debugging.

If you do not specify either /X or /E (or the /D disk-overlay option),
CodeView automatically searches for the HIMEM.SYS driver and extended memory
so it can implement the /X option. If it fails, CodeView searches for
expanded memory to implement the /E option. If that search fails, CodeView
uses a default disk overlay of 64K. (See the description of the /D option in
the next section.)


15.7  CodeView Command-Line Options

The following options can be added to the command line that invokes
CodeView. The Starting Up CodeView section of CodeView online help contains
more information about these options.

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Option                            Description
Option                            Description
────────────────────────────────────────────────────────────────────────────
/2                                Two-monitor debugging. The display
                                    adapters must be configured for
                                    different addresses, such as Hercules (R)
                                    and VGA. The application is displayed on
                                    the primary monitor (the monitor the
                                    operating system normally directs output
                                    to), while CodeView's output appears on
                                    the secondary monitor.

/25                               Display in 25-line mode.

/43                               Display in 43-line mode.

/50                               Display in 50-line mode.

/B                                Display in black and white. This assures
                                    that the display is readable when a
                                    color display is not used. You should
                                    also specify this option along with the
Option                            Description
────────────────────────────────────────────────────────────────────────────
                                    also specify this option along with the
                                    /2 option when the secondary monitor is
                                    black and white.

/Ccommands                        Execute commands immediately on start-up.
                                    The commands must be separated with a
                                    semicolon. If any commands require a
                                    space, enclose the entire list in double
                                    quotation marks.

/D«buffersize»                    Use disk overlays to increase the size
                                    of the program that can be debugged,
                                    where buffersize is the decimal size of
                                    the overlay buffer, in kilobytes.
                                    Smaller buffers leave more room for the
                                    program being debugged, while larger
                                    buffers increase the speed of execution.
                                    The acceptable range is 16K to 128K. The
                                    default size is 64K. (DOS only.)
Option                            Description
────────────────────────────────────────────────────────────────────────────
                                    default size is 64K. (DOS only.)


/E                                Use expanded memory for symbolic
                                    information and CodeView overlays. (DOS
                                    only.)

/F                                Flip screen video pages (rather than
                                    swap). When your application does not
                                    use graphics, eight video screen pages
                                    are available. Switching from CodeView
                                    to the output screen is accomplished by
                                    directly selecting the appropriate video
                                    page. Cannot be used with /S. (DOS only.)

/G                                Suppress "snow" on a CGA display. (DOS
                                    only.)

/I«0 | 1»                         Control trapping of nonmaskable
Option                            Description
────────────────────────────────────────────────────────────────────────────
/I«0 | 1»                         Control trapping of nonmaskable
                                    interrupts and 8259 interrupts. A value
                                    of 0 forces interrupt trapping on
                                    machines CodeView doesn't recognize as
                                    IBM-
                                    compatible. A value of 1 (the default)
                                    disables interrupt trapping. (DOS only.)

/K                                Disable keyboard monitors (under OS/2)
                                    and keyboard interrupts (under DOS).
                                    This allows you to regain control of the
                                    computer under deadlock conditions, but
                                    prevents CodeView from recording
                                    keyboard entries when recording a debug
                                    session.

/Ldll                             Load symbolic information for the
                                    specified dynamic-link libraries (DLL).
                                    (OS/2 only.) This option is required
Option                            Description
────────────────────────────────────────────────────────────────────────────
                                    (OS/2 only.) This option is required
                                    only for DLLs loaded with DOSLOADMODULE.
                                    CodeView automatically loads debug
                                    information for statically linked DLLs.

/M                                Disable CodeView's use of the mouse.
                                    This simplifies debugging programs that
                                    accept mouse commands.

/N«0 | 1»                         Identical to /I, but applies only to
                                    nonmaskable interrupts. (DOS only.)

/O                                Debug child processes ("offspring").
                                    (OS/2 only.)

/R                                Use 80386/486 hardware debug registers
                                    to speed execution. (DOS only.)


Option                            Description
────────────────────────────────────────────────────────────────────────────

/S                                Swap screen in buffers (rather than
                                    flip). When your program uses graphics,
                                    all eight video pages must be used.
                                    Switching from CodeView to the output
                                    screen is accomplished by saving the
                                    previous screen in a buffer. Cannot be
                                    used with /F. (DOS only.)

/TSF                              Toggle (invert) the sense of the
                                    Statefileread switch in TOOLS.INI. If
                                    Statefileread is set to no (do not read
                                    the status file), the status file is
                                    read, and vice-versa.

/X                                Use extended memory for CodeView and
                                    symbolic information. (DOS only.)




15.8  Customizing CodeView with the TOOLS.INI File

The TOOLS.INI file customizes the behavior and user interface of several
Microsoft products. The TOOLS.INI file is a plain ASCII text file. You
should place it in a directory pointed to the INIT environment variable. (If
you do not use the INIT environment variable, CodeView looks for TOOLS.INI
only in the CodeView source directory.)

The CodeView section of TOOLS.INI is preceded by the following line:

    [cv]

If you run the protected-mode version of CodeView, use [cvp] instead. If you
run both versions, include both: [cv cvp]. You can have separate sections
for  cv  and  cvp  if you want different customizations.

Most of the TOOLS.INI customizations for CodeView control screen colors, but
you can also specify such things as start-up commands or the default name of
the file that receives CodeView output. See the Configure CodeView section
of CodeView online help for full information about all TOOLS.INI switches
that control CodeView.


15.9  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topic                             Access
────────────────────────────────────────────────────────────────────────────
CodeView information              Choose "CodeView Debuggers" from the
                                    "Microsoft Advisor Contents" screen

ML command-line options           Choose "Macro Assembler" from the
                                    "Command Line" section of the "Microsoft
                                    Advisor Contents" screen









Chapter 16  Converting C Header Files to MASM Include Files
────────────────────────────────────────────────────────────────────────────

The H2INC utility translates C header files into MASM-compatible include
files. C header files normally have the extension .H; MASM include files
normally have the extension .INC. This is the origin of the program's name:
"H to INC."

H2INC simplifies porting data structures from your C programs to MASM
programs. This is especially useful when you have


    ■   A program that mixes C code and MASM code with globally accessible
        data structures

    ■   A program prototyped in C that you're translating to MASM for
        compactness and fast execution


The H2INC program translates data declarations, function prototypes, and
type definitions. H2INC does not convert C code into MASM code. When H2INC
encounters a C statement that would compile into executable code, H2INC
ignores the statement and issues a warning message to the standard output.

H2INC accepts C source code compatible with Microsoft C 6.0 and creates
include files suitable for MASM 6.0. These include files will not work with
versions of MASM prior to 6.0.

H2INC is designed to translate project header files that you have written
specifically for translation to MASM 6.0 include files. It is not designed
to translate header files such as PM.H and WINDOWS.H.

This chapter explains how H2INC performs the C code translation and how the
command-line options control the conversions.


16.1  Basic H2INC Operation

H2INC is designed to provide automatic translation of C declarations that
you need to include in the MASM portions of an application. However, the set
of C statements processed by H2INC must be those needed by and interpretable
by MASM. H2INC converts only function prototypes, some preprocessor
directives,

and C declarations outside the scope of procedures. For example, H2INC
translates the C statement

    #define MAX_EMPLOYEES 400

into this MASM statement:

    MAX_EMPLOYEES EQU 400t

The t specifies the decimal radix.

H2INC does not translate C code into MASM code. Statements such as the
following are ignored:

    printf( "This is an executable statement.n" );

H2INC translates declarations, not executable code.

By default, H2INC creates a single .INC file. If the C header file includes
other header files, the statements from the original and nested files are
translated and combined into one .INC file. This behavior can be changed
with the /Ni option (see Section 16.2).

The program also preprocesses some statements, just as the C preprocessor
would. For example, given the following statements, if  VERSION  is not
defined, H2INC ignores the #ifdef block.

    #ifdef VERSION
    #define BOX_VALUE 4
    #endif

If  VERSION  is defined, H2INC translates the statements inside the block
from C syntax to MASM syntax.

H2INC normally discards comments. If you use the /C option, C comments are
passed to the output file. If the line starts with a  /*  or  // , the
comment specifier is converted to a semicolon (;). If the line is part of a
multiline comment, a semicolon is prefixed to each line.

H2INC ignores anything that is not a comment or that cannot be translated.
These items do not appear in the output file. If H2INC encounters an error,
it stops translating and deletes the resulting .INC file.


16.2  H2INC Syntax and Options

To run H2INC, type  H2INC  at the command-line prompt, followed by the
options desired and the names of the .H files you want to convert:

    H2INC [[options]] file.H ...

You can specify more than one file.H. File names are separated by a space.
The contents of each file.H are translated into a single file in the current
directory with the name file.INC. The original file.H is not altered.

The following lists describe the available options. You can specify more
than one option. Note that the options are case sensitive except for /HELP.


H2INC recognizes /? to display a summary of H2INC syntax, and /HELP to
invoke QuickHelp for H2INC. If QuickHelp is not available, H2INC displays a
short list of H2INC options. This option is not case sensitive.

H2INC recognizes but ignores C 6.0 options that aren't specified in the
following two lists.


Options Directly Affecting H2INC Output

This first list describes the options that directly affect the H2INC output:


Option                            Action
────────────────────────────────────────────────────────────────────────────
/C                                Passes comments in the .H file to the
                                    .INC file.

/Fa «filename»                    Specifies that the output file contain
                                    only equivalent MASM statements. This is
                                    the default. If specified, the filename
                                    overrides the default, keeping the base
                                    name of the C header files and adding
                                    the .INC extension.

/Fc «filename»                    Specifies that the output file contain
                                    equivalent MASM statements plus original
                                    C statements converted to comment lines.

/Mn                               Assumes the .MODEL directive is not
                                    specified for the MASM source or the
                                    generated .INC files. Instructs H2INC to
                                    declare explicitly the distances for all
                                    pointers and functions.

/Ni                               Suppresses the expansion of nested
                                    include files.

/Zu                               Makes all structure and union tag names
                                    unique.


Options Indirectly Affecting H2INC Output

This second list describes the options that indirectly affect the H2INC
output:

Option                            Action
────────────────────────────────────────────────────────────────────────────
/AT                               Specifies tiny memory model (.COM).

/AS                               Specifies small memory model, the
                                    default.

/AC                               Specifies compact memory model.

/AM                               Specifies medium memory model.

/AL                               Specifies large memory model.

/AH                               Specifies huge memory model.

/D«const«=value» »                Defines a constant or macro.

/G0                               Enables 8086/8088 instructions (default).

/G1                               Enables 80186/80188 instructions.

/G2                               Enables 80286 instructions.

/G3                               Enables 80386 instructions. Changes the
                                    default word size to DWORD.

/G4                               Enables 80486 instructions. Changes the
                                    default word size to DWORD.

/Gc                               Specifies Pascal as the default calling
                                    convention.

/Gd                               Specifies C as the default calling
                                    convention for functions (default).

/Gr                               Specifies the _fastcall calling
                                    convention for functions. Generates a
                                    warning since H2INC does not translate
                                    _fastcall functions and prototypes.

/Ht                               Enables generation of text equates. By
                                    default, text items are not translated.

/Ipaths                           Searches named paths for include files
                                    before searching the paths in the
                                    INCLUDE environment variable. Paths are
                                    separated with a semicolon (;).

/J                                Changes default character type from
                                    signed char to unsigned char.

/nologo                           Suppresses display of the sign-on banner.

Option                            Action
────────────────────────────────────────────────────────────────────────────
/Tc «filename»                    Enables the processing of files whose
                                    name does not end in .H.

/uident                           "Undefines" one of the predefined
                                    identifiers. (See Section 16.3.1.)

/U                                "Undefines" all predefined identifiers.
                                    (See Section 16.3.1.)

/w                                Suppresses compiler warning messages;
                                    same as /W0.

/W0                               Suppresses all warning messages.

/W1                               Displays level 1 warning messages
                                    (default).

/W2                               Displays level 1 and level 2 warning
                                    messages.

/W3                               Displays level 1, 2, and 3 warning
                                    messages.

/W4                               Displays all warning messages.

/X                                Excludes search for include files in the
                                    standard places.

/Za                               Disables language extensions (allows
                                    ANSI standard only).

/Zc                               Causes functions declared as _pascal to
                                    be case insensitive.

/Ze                               Enables language extensions (default).

/Zn string                        Adds string to all names generated by
                                    H2INC. Used to eliminate name conflicts
                                    with other H2INC-generated include files.

/Zp{1 | 2 | 4}                    Packs structure on a 1-, 2-, or 4-byte
                                    boundary, following C packing rules.
                                    Default is /Zp2.


16.3  Converting Data and Data Structures

The primary use of H2INC is to convert data automatically from C format into
MASM format. This section shows how H2INC converts constants, variables,
pointers, and other C data structures to definitions recognizable to MASM.

Since the names of the items translated by H2INC may be distinguished only
by the case of the names, you should specify OPTION CASEMAP:NONE in any MASM
files that include .INC files generated with H2INC.


16.3.1  User-Defined and Predefined Constants

H2INC translates constants from C to MASM format. For example, C symbolic
constants of the form

    #define CORNERS 4

are translated to MASM constants of the form

    CORNERS EQU 4t

in cases where  CORNERS  is an integer constant or is preprocessed to an
integer constant. See Section 1.2.4, "Integer Constants and Constant
Expressions," for more information on integer constants in MASM.

TEXTEQU is new to MASM 6.0.

When the defined expression evaluates to a noninteger value, such as a
floating-point number or a string, H2INC defines the expression with TEXTEQU
and adds angle brackets to create text macros. By default, however, these
TEXTEQU expressions are not added to the include file. Set the /Ht option to
tell H2INC to generate TEXTEQU expressions.

    /* #define PI 3.1415 */
    PI TEXTEQU <3.1415>

H2INC uses this form when the expression is anything other than a constant
integer expression. H2INC does not check the constant or string for
validity. For example, although the following C definitions are valid, H2INC
creates invalid string equates without generating an error.

These C statements

    #define INT 6
    #define FOREVER for(;;)

generate these MASM statements:

    INT EQU 6t
    FOREVER TEXTEQU <for(;;)>

The first #define statement is invalid because INT is a MASM instruction; in
MASM 6.0, instructions are reserved and cannot be used as identifiers. The
for loop definition is invalid because MASM cannot assemble C code.

Predefined constants control the contents of .INC files.

You can make use of the following predefined constants in your C code to
conditionally generate the code in .INC files. The predefined constants and
the conditions under which they are defined are

Predefined Constant               When Defined
────────────────────────────────────────────────────────────────────────────
_H2INC                            Always defined

M_I86                             Always defined

MSDOS                             Always defined

_MSC_VER                          Defined as 600 for this release

M_I8086                           Defined if /G0 is specified

M_I286                            Defined if /G0 is not specified

NO_EXT_KEYS                       Defined if /Za is specified

_CHAR_UNSIGNED                    Defined if /J is specified

M_I86SM                           Defined if /AS is specified

M_I86MM                           Defined if /AM is specified

M_I86CM                           Defined if /AC is specified

M_I86LM                           Defined if /AL is specified

M_I86HM                           Defined if /AH is specified

For example, if your C header file includes definitions which are specific
to the C portion of the program or otherwise are not appropriate for
translation by H2INC, you can bracket the C-specific code with

    #ifndef _H2INC
        /* C-specific code */
    #endif

In this case, only the C compiler processes the bracketed code.

The /u and /U options affect these predefined constants. The /uarg option
undefines the constant specified as the argument. The /U option disables the
definition of all predefined constants. Neither /u or /U affects constants
defined by the /D option.

H2INC places an OPTION EXPR32 directive in the .INC file so that MASM
correctly handles long integers within expressions. This means that the .INC
files as well as all the .ASM files which include .INC files created with
H2INC will resolve integer expressions in 32 bits instead of 16 bits.


16.3.2  Variables

H2INC translates variables from C to MASM format. For example, this C
declaration

    int my_var;

is translated into the MASM declaration

    EXTERNDEF my_var:SWORD

H2INC converts C variable types to MASM types as follows:

C Type                            MASM Type
────────────────────────────────────────────────────────────────────────────
char                              BYTE or SBYTE (controlled by /J option)

signed char                       SBYTE

unsigned char                     BYTE

short                             SWORD

unsigned short                    WORD

int                               SWORD (SDWORD with /G3 or /G4 option)

unsigned int                      WORD (DWORD with /G3 or /G4 option)

long                              SDWORD

unsigned long                     DWORD

float                             REAL4

double                            REAL8

long double                       REAL10

H2INC assumes that a variable is external unless the variable is explicitly
declared as static. For example, the C declaration

    long big_data;

is converted to this MASM declaration:

    EXTERNDEF big_data:SDWORD

See Sections 1.2.6, "Data Types," and 4.1.1, "Allocating Memory for Integer
Variables," for more information on MASM data types, and Section 8.2.2,
"Declaring Symbols Public and External," for information on EXTERNDEF.

H2INC does not allocate space for arrays since all variables are assumed to
be external. For example, the C declaration

    int two_d[10][20];

translates to

    EXTERNDEF two_d:SWORD

H2INC does not translate static variables, since the scope of these
variables extends only to the file where they are declared.


16.3.3  Pointers

H2INC translates C pointer variables into their MASM equivalents. The C
declarations

    int *ptr_var;
    char NEAR *pCh;

are translated into these MASM statements:

    EXTERNDEF ptr_var:PTR SWORD
    EXTERNDEF pCh:NEAR PTR SBYTE

If you set the /Mn option, H2INC specifies all distances explicitly (for
example, NEAR PTR instead of PTR). If /Mn is not set, the distances are
generated only when they differ from the default values implied by the
memory model specified by the /A command-line option.

H2INC converts _segment and _based variables to type WORD in MASM.

See Sections 1.2.6, "Data Types," and 3.3, "Accessing Data with Pointers and
Addresses," for information about MASM pointers.


16.3.4  Structures and Unions

H2INC translates C structures and unions into their MASM equivalents. H2INC
modifies the C structure or union definition to account for differences from
MASM structure and union definitions. This list describes these
modifications.


    ■   C allows a structure or union variable to have the same name as the
        type name, but MASM does not. The H2INC /Zu option prevents the
        structure name from matching a variable or instance by prefixing every
        MASM structure name with  @tag_.

    ■   If a C structure or union definition does not have a name, H2INC
        supplies one for the MASM conversion. These generated structure names
        take the form  @tag_n, where n is an integer that starts at zero and
        is incremented for each structure name H2INC generates.

    ■   If the /Zn option is specified, H2INC inserts the given string between
        the underscore and the number in the generated structure names. This
        eliminates name conflicts with other H2INC-generated include files.

    ■   H2INC adds the alignment value to the converted structure definition.


The following examples show how these rules are applied when converting
structures. (Union conversions are not shown; they are handled identically.)
These examples assume that the C header file defines an alignment value of
2. (See Section 5.2.1, "Declaring Structure and Union Types," for
information on alignment values.)

The following named C structure definition

    struct file_info
    {
        unsigned char  file_addr;
        unsigned int   file_size;
    };

is converted to the following MASM form. Except for explicitly specifying
the alignment value, the conversion is direct:

    file_info          STRUCT 2t
    file_addr          BYTE          ?
    file_size          WORD          ?
    file_info          ENDS

If the same C structure definition is converted using the /Zu option, the
@tag_  prefix is added to the structure's name so that the name does not
duplicate the name of a structure component:

    @tag_file_info     STRUCT 2t
    file_addr          BYTE          ?
    file_size          WORD          ?
    @tag_file_info     ENDS

If the original C structure definition is modified to be an unnamed-type
declaration of a specific instance (myfile)

    struct
    {
        unsigned char  file_addr;
        unsigned int   file_size;
    } myfile ;

its MASM conversion looks like the following example. (The specific integer
added to the  @tag_  prefix is determined by the sequence in which H2INC
creates tag names.)

    @tag_7          STRUCT 2t
    file_addr       BYTE ?
    file_size       WORD ?
    @tag_7          ENDS
    EXTERNDEF       C myfile:@tag_7

Nested structures may have as many levels as desired; they are not limited
to one level. Nested structures are "unnested" (expanded) in the correct
hierarchical sequence, as shown with the C structure and H2INC-generated
code in this example.

    /* C code: */
    struct phone
    {
        int  areacode;
        long number;
    };

    struct person
    {
        char   name[30];
        char   sex;
        int    age;
        int    weight;
        struct phone;
    } Jim;

    ; H2INC generated code:
    phone           STRUCT 2t
    areacode        SWORD          ?
    number          SDWORD         ?
    phone           ENDS

    person          STRUCT 2t
    name            SBYTE          30t DUP (?)
    sex             SBYTE          ?
    age             SWORD          ?
    weight          SWORD          ?
    STRUCT
    areacode      SWORD          ?
    number        SDWORD         ?
    ENDS
    person          ENDS

    EXTERNDEF       C Jim:person

See Section 5.2 for information on MASM structures and unions.


16.3.5  Bit Fields

H2INC translates C bit fields into MASM records. H2INC looks at a structure
definition; if it consists only of bit fields of the same type and if the
total size of the bit fields does not exceed the type of the bit fields,
then H2INC outputs a RECORD definition with the name of the structure. All
bit-field names are modified to include the structure name for uniqueness,
since record fields have global scope in MASM.

For example,

    struct s
    {
        int i:4;
        int j:4;
        int k:4;
    }

becomes:

    s       RECORD  @tag_0:4,
                    k@s:4,
                    j@s:4,
                    i@s:4

The  @tag  variable pads out the record to the type size of the bit fields
so alignment of the structures will be correct.

If the bit fields are too large, are not of the same type, or are mixed with
fields that are not bit fields, H2INC generates a RECORD definition inside
the structure and then uses the definition.

For example,

    struct t
    {
        int i;
        unsigned char a:4;
        int j:9;
        int k:9;
        long l;
    }  m;

becomes:

    t         STRUCT 2t
    i         SWORD       ?
    rec@t_0   RECORD      @tag_1:4,
            a@t:4
    @bit_0    rec@t_0     <>
    rec@t_1   RECORD      @tag_2:7,
            j@t:9
    @bit_1    rec@t_1     <>
    rec@t_2   RECORD      @tag_3:7,
            k@t:9
    @bit_2    rec@t_2     <>
    l         SDWORD      ?
    t         ENDS

    EXTERNDEF C m:t

Notice that  j  and  k  are not packed because their total size exceeds the
16 bits of an integer in C.

Since the  @bit  field names are local to the structure, these begin with  0
    for each structure type; the  @rec  variables have global scope and so
their number always increases.

The C bit-field declaration

    struct SCREENMODE
    {
        unsigned int disp_mode : 4;
        unsigned int fg_color  : 3;
        unsigned int bg_color  : 3;
    };

is converted into the following MASM record:

    SCREENMODE      RECORD          disp_mode@SCREENMODE:4,
                                    fg_color@SCREENMODE:3,
                                    bg_color@SCREENMODE:3

See Section 5.3 for information about MASM records.


16.3.6  Enumerations

H2INC converts C enumeration declarations into MASM EQU definitions that are
treated as standard integer constants. If the C declaration is not assigned
a value, the H2INC generates an EQU statement that supplies a value
equivalent to its position in the list. For example, the C enumeration
declaration

    enum tagName
    {
        id1,
        id2,
        id3 = 42,
        id4
    };

is converted into the following EQU statements:

    id1     EQU     0t
    id2     EQU     1t
    id3     EQU     42t
    id4     EQU     43t

See Section 1.2.4 for information on MASM integer constants.


16.3.7  Type Definitions

All type definitions using C base types are translated directly. For
example, H2INC converts the C type definitions

    typedef int INTEGER;
    typedef float FLOAT;

to these MASM forms:

    INTEGER TYPEDEF SWORD
    FLOAT   TYPEDEF REAL4

Pointer types are converted in a similar fashion. The following declarations


    typedef int *PINT
    typedef int **PINT
    typedef int far *PINT

become (respectively)

    PINT TYPEDEF PTR SWORD
    PINT TYPEDEF PTR PTR SWORD
    PINT TYPEDEF FAR PTR SWORD

Addressing mode determines pointer size.

The number of bytes allocated for the pointer is set by the addressing mode
you have selected unless if is specifically overridden in the type
definition.

C statements using typedef which convert to a type with the same name as the
type do not generate errors, but are not converted. For example, H2INC does
not convert

    typedef int SWORD
    typedef unsigned char BYTE

since these typedef statements would generate these MASM statements:

    SWORD   TYPEDEF SWORD
    BYTE    TYPEDEF BYTE

See Section 3.3, "Accessing Data with Pointers and Addresses," for
information on using TYPEDEF in MASM 6.0.


16.4  Converting Function Prototypes

When H2INC converts C function prototypes into MASM function prototypes, the
elements of the C syntax are converted into the corresponding elements of
the MASM syntax.

The syntax of a C function prototype is

    [[storage]] [[distance]]
    [[ret_type]] [[langtype]]
    label ( [[parmlist»  )

In C syntax, storage can be STATIC or EXTERN. H2INC does not translate
static function prototypes because static functions are visible only within
the current source module, and standard include files do not contain
executable code.

Procedures for returning values depend on the langtype specified.

In C, the ret_type is the data type of the return value. Because the MASM
PROTO directive does not specify how to handle return values, H2INC does not
translate the return type. However, H2INC checks the langtype specified in
the C prototype to determine how particular languages return the
value─through the stack or through registers.

For the Pascal, FORTRAN, or Basic langtype specifications, H2INC appends an
additional parameter to the argument list if the return type is longer than
four bytes. This parameter is always a near pointer with the type of the
return value. If the value of the return value type is not supported, this
parameter is an untyped near pointer.

For the _cdecl langtype specification in the C prototype, all returned data
is passed in registers (AX or AX plus DX). There is no restriction on the
return type. Additional parameters are not necessary.

The langtype represents the naming and passing conventions for a language
type. H2INC accepts the following C language types and converts them to
their corresponding MASM language types:

C Language Type                   MASM Language Type
────────────────────────────────────────────────────────────────────────────
_cdecl                            C

_fortran                          FORTRAN

_pascal                           PASCAL

_stdcall                          STDCALL

_syscall                          SYSCALL

H2INC explicitly includes the langtype in every function prototype. If no
language type is specified in the .H file prototype, the default language is
_cdecl (unless the default is overridden by the /Gc command-line option).

In the MASM prototype syntax, the label is the name of the function or
procedure.

If you select the /Mn option, H2INC specifies the distance of the function
(near or far), whether or not the C prototype specifies the distance. If /Mn
is not set, H2INC specifies the distance only when it is different from the
default distance specified by the memory model.

If the C prototype's parameter list ends with a comma plus an ellipsis (,
...), the function can accept a variable number of arguments. H2INC converts
this to the MASM form: a comma followed by the :VARARG keyword (, :VARARG)
appended to the last parameter.

H2INC does not translate _fastcall functions. Functions explicitly declared
_fastcall (or invoking H2INC with the /Gr option) generate a warning
indicating that the function declaration has been ignored.

The following examples show how the preceding rules control the conversion
of C prototypes to MASM prototypes (when the memory model default is small).
The example function is  my_func. The TYPEDEF generated by H2INC for the
PROTO is given along with the PROTO statement.

    /* C prototype */
                my_func (float fNum, unsigned int x);
    ; MASM TYPEDEF
                @proto_0 TYPEDEF PROTO C :REAL4, :WORD
    ; MASM prototype
                my_func  PROTO   @proto_0

    /* C prototype */
                extern my_func1 (char *argv[]);
    ; MASM TYPEDEF
                @proto_1  TYPEDEF  PROTO C :PTR PTR SBYTE
    ; MASM prototype
                my_func1  PROTO    @proto_1

    /* C prototype */
                struct vconfig _far * _far pascal my_func2 (int, scri
    );
    ; MASM TYPEDEF
                @proto_2  TYPEDEF  PROTO FAR PASCAL :SWORD, :scri
    ; MASM prototype
                my_func2  PROTO    @proto_2

    /* C prototype */
                long pascal my_func3 (double y, struct vconfig vc);
    ; MASM TYPEDEF
                @proto_3  TYPEDEF  PROTO PASCAL :REAL8, :vconfig
    ; MASM prototype
                my_func3    PROTO    @proto_3

    /* C prototype */
                void _far _cdecl myfunc4 ( char _huge *, short);
    ; MASM TYPEDEF
                @proto_4  TYPEDEF  PROTO FAR C :FAR PTR SBYTE, :SWORD

    ; MASM prototype
                myfunc4  PROTO  @proto_4

    /* C prototype */
                short my_func5 (void *);
    ; MASM TYPEDEF
                @proto_5  TYPEDEF  PROTO C :PTR
    ; MASM prototype
                my_func5  PROTO  @proto_5

    /* C prototype */
                char my_func6 (int, ...);
    ; MASM TYPEDEF
                @proto_6  TYPEDEF  PROTO C :SWORD, :VARARG
    ; MASM prototype
                my_func6  PROTO  @proto_6

    /* C prototype */
                typedef char * ptrchar;
                ptrchar _cdecl my_func7 (char *);
    ; MASM TYPEDEF
                @proto_7  TYPEDEF  PROTO C :PTR SBYTE
    ; MASM prototype
                my_func7  PROTO  @proto_7

See Section 7.3.6, "Declaring Procedure Prototypes," for more information on
prototypes and Chapter 20, "Mixed-Language Programming," for information on
calling conventions and mixed-language programs.


16.5  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topic                             Access
────────────────────────────────────────────────────────────────────────────
INCLUDE Directive                 From the "MASM 6.0 Contents" screen,
                                    choose "Directives" and then
                                    "Miscellaneous"

Include files                     From the "MASM 6.0 Contents" screen,
                                    choose "Example Code"; then choose
                                    "INCLUDE Files" to see a list of the
                                    include files provided with MASM 6.0

MASM data types (constants,       From the "MASM 6.0 Contents" screen,
variables, structures, unions,    choose "Directives"; then choose "Data
real numbers, records)            Allocation" or "Complex Data Types"

TYPEDEF                           From the "MASM 6.0 Contents" screen,
                                    choose "Directives" and then "Complex
                                    Data Types"

Procedures and prototypes         From the "MASM 6.0 Contents" screen,
                                    choose "Directives"; then choose
                                    "Procedure and Code Labels"






Chapter 17  Writing OS/2 Applications
────────────────────────────────────────────────────────────────────────────

Microsoft Operating System/2 (OS/2) takes full advantage of 80286 and later
processors. It supports memory far beyond the DOS 640K limit and offers a
rich set of multitasking system calls. Although OS/2 is much more powerful
than DOS, you may ultimately find it easier to program for OS/2.

This chapter shows how to develop an OS/2 application and how to write
dual-mode programs to run under both OS/2 and DOS.

To write OS/2 applications, you must learn OS/2 system calls. While this
chapter mentions a few of these calls, you should consult the references
listed in the book's introduction to learn more about OS/2 system functions.


OS/2 supports two modes─real mode, which emulates the DOS environment, and
protected mode, which supports all the advanced features. For simplicity's
sake, the rest of this chapter equates OS/2 with protected mode.

────────────────────────────────────────────────────────────────────────────
NOTE

Examples in this chapter support OS/2 1.x. Future versions of OS/2 may
support different calling conventions.
────────────────────────────────────────────────────────────────────────────


17.1  OS/2 Overview

There are three steps in developing OS/2 or dual-mode applications:


    1.  Write the source code, using procedure calls rather than interrupts to
        call system functions.

    2.  Assemble and link the program with OS2.LIB.

    3.  Optionally, convert the program so that it can run under both OS/2 and
        DOS.


This chapter explains each of these steps, first looking at specific
differences in how you write DOS and OS/2 code. Then it illustrates the
development of a simple OS/2 program. Finally, the chapter discusses
register initialization and additional OS/2 utilities.


17.2  Differences between DOS and OS/2

Assembly language is assembly language. Most machine instructions you use in
a DOS program are the same instructions you use in an OS/2 program. When you
start making calls to the operating system, however, things change.

You should understand the following differences between the two operating
systems before attempting to write an OS/2 program.


System Calls

System calls control I/O and screen access.

OS/2 is similar to DOS in that it offers a series of system calls that
perform tasks such as opening or closing a disk file. The OS/2 system calls
that handle keyboard input (KbdCharIn, for example) correspond to the
interrupt 16h instructions in DOS. The OS/2 system calls for screen output
(VioScrollDn, for example) correspond to DOS interrupt 10h calls. And the
OS/2 disk and operating-system calls (DosGetDateTime, for example)
correspond to DOS interrupt 21h calls.

The effect is similar, but the way you actually make the calls is different.
In DOS, you issue an interrupt. In OS/2, you make the system call with the
INVOKE directive or the CALL instruction.


New Instructions

OS/2 is designed for advanced processors, and you may want to write programs
that take advantage of the new instructions available on the 80286-80486. To
use the new instructions and still target OS/2 1.x, place a .286 directive
at the beginning of your source code.

In general, you should avoid the directives that enable privileged
instructions (.286P, .386P, and .486P), unless you are writing system-level
code.

Many OS/2 programs can be converted to run under DOS as well. To write
programs to run on all DOS and OS/2 systems, use the default processor
setting (.8086).


The OS/2 Library

MASM 6.0 provides OS2.INC and OS2.LIB.

OS/2 programs must be linked to the system-call import library, OS2.LIB. The
best way to perform this task is to use the INCLUDELIB directive, as shown
in the example in the next section. In addition, you can include the OS2.INC
file as an alternative to adding the prototypes for the OS/2 functions to
your file.

The OS2.LIB file makes system calls possible; it contains import definitions
for all system calls. An import definition specifies the name of a procedure
and the dynamic-link library (DLL) where the procedure resides. You can
learn more about DLLs in Chapter 18, "Creating Dynamic-Link Libraries." To
create an OS/2 application, however, you need to know only that OS2.LIB is
required.


Start-Up Code

Unlike DOS, OS/2 automatically initializes all segment registers as required
by the standard segment model. No special start-up sequence is required,
although OS/2 places useful information in AX, BX, and CX (see Section 17.6,
"Register and Memory Initialization") that you may want to save.


Calling Conventions

OS/2 1.x uses the Pascal calling convention.

OS/2 system calls follow the Pascal calling and naming conventions. One way
to enforce these conventions is to specify PASCAL in the .MODEL directive,
then use the INVOKE directive to generate the correct code. Another is to
include the OS2.INC file, which uses the PROTO directive to prototype the
functions to follow the Pascal conventions. The prototypes specify Pascal as
the calling convention. OS/2 functions return a value in AX. A nonzero value
indicates an error. All registers except AX are preserved.

The OS/2 2.x operating system uses different calling conventions. See the
documentation provided with that product.


Exit Code

To exit an OS/2 program, call the OS/2 system function DosExit. If you use
the .EXIT directive and the OS_OS2 attribute of the .MODEL statement, the
assembler automatically generates the proper system call if you have a
prototype for DosExit.


Segment Restrictions

Although OS/2 makes some operations easier, it does impose restrictions on
the programmer. You cannot do segment arithmetic. That is, you cannot
attempt to measure the distance between segments by subtracting one segment
from another. In general, you also cannot add values to segment registers.
Either operation may cause a protection violation, which would immediately
terminate the program.

Under OS/2, segment registers do not hold physical addresses; they hold
"segment selectors." A segment selector is an index into the system's
descriptor tables that hold the actual addresses. You can copy the segment
selector or use it to access data, but you should not try to modify it.

Huge pointer arithmetic is therefore different under OS/2. Under DOS, you
can handle huge pointers easily by checking the OVERFLOW? flag after you
increment or add to an offset address. If the result overflows (exceeds
64K), then you increment the segment address. Under OS/2, manipulation of
huge pointers requires special techniques. See your OS/2 documentation for
more information.


17.3  A Sample Program

The following program prints  Hello, world. It runs under OS/2 protected
mode.

    ; HELLO.ASM
    ;
                .MODEL  small, pascal, OS_OS2
                .286

                INCLUDELIB  os2.lib
                INCLUDE     os2.inc

                .STACK
                .DATA
    message     BYTE    "Hello, world.", 13, 10  ; Message to print
    bytecount   DWORD   ?                        ; Holds number of
                                                ;  bytes written
                .CODE

                .STARTUP
                push        1                  ; Select standard output
                push        ds                 ; Pass address of message
                push        OFFSET message
                push        LENGTHOF message   ; Pass length of message
                push        ds                 ; Pass address of count
                push        OFFSET bytecount   ;  returned by function
                call        DosWrite           ; Call system write
                                                ;  function
                .EXIT       0                  ; Exit with 0 return code
                END

.STARTUP and .EXIT automatically generate code.

The .STARTUP and .EXIT directives are very useful because they automatically
produce correct code for the operating-system type specified with the .MODEL
directive (see Section 2.2, "Using Simplified Segment Directives"). As
described in Section 17.6, OS/2 initializes all segment registers;
therefore, .STARTUP does nothing but indicate the starting point. To
correctly exit an OS/2 program, you must call the DosExit function. The
DosExit prototype is always available to MASM programs.

In the example above, .EXIT automatically generates the following code under
OS/2:

    .EXIT     0
    0011  6A 01             *   push    +000000001h ; Action 1 ends
    all threads
    0013  6A 00             *   push    +000000000h ; Pass 0 return code
    0015  9A ---- 0000 E    *   call    DosExit     ; Call system function
                                        END

Between .STARTUP and .EXIT, the entire program consists of a single call to
the DosWrite function. The program pushes the parameters on the stack and
then makes the call. No POP or ADD instructions are needed to restore the
stack after DosWrite returns; DosWrite observes the Pascal calling
convention and restores the stack itself before returning.

The .MODEL statement helps ensure that the assembler produces correct code
for calling DosWrite:

    .MODEL  small, pascal, OS_OS2

When you run HELLO.EXE, OS/2 looks at the import definitions in the
executable-file header and makes sure that all needed DLLs are in memory. It
then loads any needed DLLs not already in memory.

The assembler must be informed that DosWrite and DosExit are far and observe
the Pascal calling convention. This information is in the prototype.

In the call to DosWrite, note that although  OFFSET message  is an immediate
operand, the program pushes it directly onto the stack. This operation is
legal on 80186-80486 processors but not on the 8086 or 8088:

    push    OFFSET message

The processors you want to target determine the instructions you should use.


Since OS/2 programs can execute only on the 80286 or later processors, it is
reasonable to use extended operations not supported by the 8086. However, if
you want to write a program that can be converted to run under both OS/2 and
DOS (as shown in Section 17.5), then you should write code that can run on
the 8086. For example,

    mov ax, OFFSET msg
            push    ax

The following revision of the sample program illustrates the usefulness of
the INVOKE directive. This version does everything the previous example did
with far fewer statements:

    ; HELLO.ASM

                .MODEL  small, pascal, OS_OS2

                INCLUDE     os2.inc
                INCLUDELIB  os2.lib

                .STACK
                .DATA
    message     BYTE   "Hello, world.", 13, 10  ; Message to print
    bytecount   DWORD   ?                       ; Holds number of
                                                ;  bytes written
                .CODE
                .STARTUP

    INVOKE  DosWrite,
                        1,
                        ADDR message,
                        LENGTHOF message,
                        ADDR bytecount

                .EXIT 0                   ; Exit with return code 0
                END

The INVOKE directive generates a call to the given procedure after first
pushing all other arguments on the stack. Like a call statement in a
high-level language, the INVOKE directive handles types in a sophisticated
way.


17.4  Building an OS/2 Application

The easiest way to assemble and link the program is from the Programmer's
WorkBench (PWB). From the Options Menu, select Link Options and choose OS/2
Application. When you select Build from the Make menu, PWB calls ML and
LINK, passing the proper options.

From the command line, type

    ML hello.asm

The next section discusses how to "bind" the program─that is, convert it so
that it runs under either DOS or OS/2.


17.5  Binding OS/2 MASM Programs

You can convert many OS/2 programs to run under both OS/2 and DOS 3.x. This
conversion is called "binding" because it binds system calls to the API.LIB
file provided with MASM 6.0. This file simulates OS/2 functions under DOS.
The program must use a restricted set of system calls or it cannot be bound.


OS/2 function calls are known collectively as the applications program
interface (API). If you restrict your system calls to a subset of these
functions known as the Family API, the program can be bound. See the
Microsoft Operating System/2 Programmer's Reference for a list of the Family
API functions.

Online help also provides information on these utilities.

If you use PWB, binding is easy. Select Bound Application from the LINK
Options command in the Options menu. PWB does the rest, calling the BIND.EXE
utility.

If you want to bind the program to run under either OS/2 or DOS, use this
command line:

    ML /Fb hello.asm

You can use system calls outside the Family API provided that you never use
them when running under DOS. The program can check the operating system and,
if running under OS/2, can execute system calls that do not belong to the
Family API. To follow this strategy, list OS/2-only calls with the BIND's /N
option. It is the program's responsibility to make sure these calls are
never made under DOS; otherwise, execution is terminated.


17.6  Register and Memory Initialization

When you execute an OS/2 program, OS/2 stores information about the program
directly in registers. With DOS programs, the information is kept in a
separate program segment prefix (PSP). The registers hold these values when
an OS/2 program begins:

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Register                          Contents at Program Start
────────────────────────────────────────────────────────────────────────────
AX                                Segment address of program's environment

BX                                Offset of command-line arguments within
                                    the
                                    environment

CX                                Length of near data area (DGROUP)

SP                                Offset of the top of the stack within
                                    the stack segment
Register                          Contents at Program Start
────────────────────────────────────────────────────────────────────────────
                                    the stack segment

CS:IP                             Program's entry point

DS                                Segment address of near data area
                                    (DGROUP)

SS                                Segment address of stack



Note that OS/2 automatically initializes SS:SP correctly. If the .MODEL
directive specifies FARSTACK, SS is initialized to its own segment address.
If the model is NEARSTACK, OS/2 sets SS to DGROUP and SP to the top of the
stack within DGROUP.

You may want to save the AX, BX, and CX registers at startup.

Upon start-up, AX, BX, and CX all contain information highly useful to some
programs. If you want to access the program's command-line arguments or know
the size of DGROUP, you must save the contents of these registers
immediately:

    FPBYTE TYPEDEF FAR PTR BYTE

            .DATA

    args    FPBYTE  0
    cmds    FPBYTE  0

            .CODE

    mov WORD PTR args[0], ax ; Save segment of args
            mov WORD PTR args[2], 0  ; Offset is 0
            mov WORD PTR cmds[0], ax ; Save segment of cmds
            mov WORD PTR cmds[2], bx ; Save offset of cmds

The AX register points to the segment value of the start of the program's
environment. AX:BX points to the starting address of arguments within the
environment, the first of which is the program name. This name is followed
by a null (zero) byte and the command-line arguments exactly as typed at the
command prompt. A second null marks the end of the arguments.

If you use simplified segments, .DATA is equivalent to DGROUP.

Under OS/2, the data segment register, DS, contains the segment of the near
data area, DGROUP. If you use simplified segment directives, this is the
.DATA segment. You must place one data segment in a group called DGROUP if
you do not use the simplified directives:

    _DATA  SEGMENT WORD PUBLIC 'DATA'
            .
            .
            .
    _DATA  ENDS

    DGROUP GROUP _DATA
            ASSUME DS:DGROUP

Calling the group anything other than DGROUP, or not having a DGROUP, causes
an error. Only the memory required by the program is allocated by OS/2. This
means that the system has space in reserve for later memory requests and for
other programs.


17.7  Other OS/2 Utilities

In addition to LINK and BIND, MASM 6.0 provides other utilities useful for
working with OS/2.


EXEHDR

The EXEHDR utility examines and can modify a DOS, Windows, or OS/2
executable file header. In the case of OS/2 and Windows, EXEHDR reports a
great deal more information: specifically, it displays the contents of
segment tables and lists the attributes of the individual segments.


IMPLIB

The IMPLIB utility creates an import library that you can use when linking
with a DLL or group of DLLs. Generally, there are three steps in using a
DLL:


    1.  Copy the DLL to a directory listed in your CONFIG.SYS LIBPATH setting.

    2.  Run IMPLIB on the DLL to create an import library, or write a
        moduledefinition file.

    3.  Link the import library or module-definition file with any application
        that uses the DLL.


An import library does not contain executable code but does contain the name
and location of dynamic-link calls. These calls are resolved during run
time.

Chapter 18 goes into more detail about how to write DLLs.


17.8  Module-Definition Files

You can create a module-definition file for an application. A
module-definition file is a text file that contains statements that give
directions to the linker. These statements can alter the attributes of
individual segments─for example, whether multiple instances of the program
share data. Module-definition files are optional. If you use one, begin the
file with the NAME statement. The following sample module-definition file
specifies an application,  MYPROG, that shares the  CONSTDAT  segment:

    NAME MYPROG

    SEGMENTS CONSTDAT SHARED


17.9  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help:

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Topic                             Access
Topic                             Access
────────────────────────────────────────────────────────────────────────────
BIND                              See the "Microsoft Advisor Contents"
                                    screen

OS/2 Include files                Choose from the "MASM 6.0 Contents"
                                    screen

PROTO, INVOKE                     From the "MASM 6.0 Contents" screen,
                                    choose "Directives" and then "Procedure
                                    and Code Labels"

INCLUDE, INCLUDELIB               From the "MASM 6.0  Contents" screen,
                                    select "Directives" and then
                                    "Miscellaneous Language Directives"

EXEHDR                            From the "Microsoft Advisor Contents"
                                    screen, select "Miscellaneous" under
                                    "Microsoft Utilities"

INCL_NOCOMMON                     Select "OS/2 Include Files" from the
Topic                             Access
────────────────────────────────────────────────────────────────────────────
INCL_NOCOMMON                     Select "OS/2 Include Files" from the
                                    "MASM 6.0 Contents" screen; from the
                                    next screen, select "Category Summary"

CALL                              From the "MASM 6.0 Contents" screen,
                                    choose "Processor Instruction" and then
                                    "Control Flow"

SHOW.EXE                          From the "MASM 6.0 Contents" screen,
                                    choose "Example Code" and then "SHOW
                                    (Text Viewer)"








Chapter 18  Creating Dynamic-Link Libraries
────────────────────────────────────────────────────────────────────────────

A "dynamic-link library" (DLL) links to the main program at run time (hence
the term dynamic link). The program that calls the DLL is known as the
"client program." One DLL can supply services for several clients
simultaneously.

The client program can choose to load the DLL into memory at the same time
the main program loads, or it can choose to load the DLL only when it is
needed.

DLLs are available only in OS/2 and Windows. In non-Windows DOS programs,
all object modules are statically linked to the program at link time. This
chapter discusses DLL programming for OS/2 1.x only.

After an overview of DLLs, this chapter describes the following stages in
developing a DLL:


    ■   Understanding general DLL programming considerations

    ■   Writing an interface to the DLL's exported procedures and data

    ■   Writing initialization and termination code

    ■   Building the DLL


The last step requires use of a module-definition file and an import
library.


18.1  DLL Overview

Like a standard (object-code) library, a DLL contains procedures that one or
more programs can call. Yet unlike standard-library procedures, DLL
procedures are never copied into an application's executable file. They
reside only on disk in the DLL file.

DLLs have several advantages:


    ■   Dynamic link libraries save significant space since the DLL's code and
        data exist in only one place, no matter how many different programs
        call the DLL. Applications that need a particular DLL can share it.

        In contrast, a standard library routine (the printf function in C, for
        example) becomes part of the executable code for each application that
        uses it. For example, if three different programs use the statically
        linked printf function, three copies of the printf code are on disk.
        Furthermore, if all three programs run at once, the printf code occurs
        three times in memory. If the same function were part of a DLL, it
        would exist in only one location on disk and in memory.

    ■   Dynamic linking makes applications and libraries more independent, and
        therefore they are easier to maintain. You can update a DLL without
        having to relink any of the programs that use it.

    ■   Applications link faster because the executable code for a dynamic
        link function is not copied into the application's .EXE file. Instead,
        only an import definition is copied.


The purpose of a DLL is to supply ("export") procedures and data to client
programs at run time. Items not exported are visible only within the DLL.

Exported procedures are visible to the client program.

The concept of exporting is analogous to the action of the PUBLIC directive,
but goes further. A public item is available only to other source modules
within the same program or DLL. An exported item is available to all
programs running on the system. In addition to global procedures and data, a
DLL can contain other procedures and data definitions to support the
operations of exported procedures.

Finally, a DLL can contain initialization and termination code to allocate
and release resources needed by the procedures. Resources are typically
files or dynamic memory. System services for OS/2 and Windows are provided
through DLLs.


18.2  DLL Programming Requirements

Four programming requirements arise from the nature of DLLs. These
requirements apply to all code used in a dynamic-link call─both in an
exported procedure and in any procedure it may call:


    ■   You cannot assume that the SS and DS registers hold the same value,
        unless you explicitly set SS equal to DS.

    ■   You should avoid using the math coprocessor or emulator routines
        unless you are certain a coprocessor or emulator library is available.

    ■   The DLL should be "re-entrant," because there is no guarantee that
        only one program will use the DLL. A re-entrant procedure is one that
        can be called by different programs concurrently. This creates
        problems for static data in the DLL, unless you declare data to be
        NONSHARED in the module-definitions file.

    ■   Be careful how you place data and code in segments. The location of
        data and code in different segments and the contents of the
        module-definition file also determine the content of the executable
        file.


This section discusses these requirements.


18.2.1  Separate Stack and Data Requirement

The separate stack and data requirement involves both assembler assumptions
and coding techniques. If you used the FARSTACK keyword as described in
Section 18.3.1, "Choosing Module Attributes," the assembler makes correct
assumptions about the contents of DS and SS.

Do not assume that SS equals DS.

In your own code, avoid any optimizing techniques that use SS to access
items in the data segment or DS to access stack data. For example, the
following code uses the ASSUME statement to be sure the correct stack is
accessed:

    ASSUME  DS:DGROUP
            .
            .
            .
            push    ds
            lds     si, sourcead  ; Load DS for string ops
    ASSUME  DS:NOTHING
            .
            .
            .
    ASSUME  SS:STACK
            mov     bx, ss:thing  ; Access near data thing through SS
    ASSUME  SS:NOTHING

Thread-specific variables can be stored on the stack, as shown in the
example above.


18.2.2  Floating-Point Math Requirement

Don't assume the math coprocessor is available to the DLL.

A stand-alone DLL─that is, a DLL created for general use by many programs─
can make few assumptions about the calling program. Therefore, the safest
way to perform floating-point calculations is to use alternate math
routines. If you link to a Microsoft high-level language, you can access
these routines through a language library. These routines give the fastest
results possible without a coprocessor. See Section 6.3, "Using Emulator
Libraries," for more information.

Floating-point operations in DLLs can use a coprocessor or emulator routines
if you are certain that a coprocessor or emulator libraries are available.


18.2.3  Re-entrance Requirement

A procedure may be called by any number of different programs concurrently.
That is, program A may call a DLL procedure while program B is still
executing the same procedure. The basic problem of re-entrance is how data
is shared.

Be aware that re-entering the DLL can modify its data.

For example, suppose you have a DLL that contains an accounting package; one
of the functions adds up an employee's salary for a whole year. First it
initializes the total to zero; then it increments this total one week at a
time. While program A is in the middle of this function, program B could
enter the procedure; its first action would be to initialize the total to
zero. Control could then pass back to program A, which would then have zero
total for salary. The problem is that two instances of the DLL share the
same variable for totals.

A procedure in a DLL must therefore follow this rule: it can access static
data items but must not alter them. Otherwise, one instance of a procedure
could corrupt data relied on by another instance of the procedure.

There are several exceptions to this rule. First, if data is declared
NONSHARED in the module-definitions file, each instance has its own copy of
the data segment, and there is no conflict. Second, you can use semaphores
to allow mutually exclusive access to data items. Finally, there may be some
items you deliberately want all instances to alter─such as a global counter
to keep track of number of instances.

Section 18.4.1, "Writing the Module-Definition File," explains how to
declare some data items as SHARED while declaring others to be NONSHARED.


18.2.4  Segment Strategy in a DLL

Be careful how you place different kinds of data and code in different
segments. When loading the DLL, OS/2 checks to see if the DLL is already in
memory. If so, it loads only new copies of NONSHARED segments; it does not
reload SHARED segments. Code segments are always SHARED.

Control of DLL data and code works at the segment level. The DATA statement
assigns default attributes for all data segments in the DLL, but the
moduledefinition SEGMENTS statement overrides these attributes for any given
segment.

You may want to create a DLL that has some data shared between all programs
that call the DLL and some data that is private to each instance. The
following module-definition statement specifies that all data in  GLOBDAT
is shared and all data in  PRIVDAT  is not:

    SEGMENTS
        GLOBDAT SHARED 'data'
        PRIVDAT NONSHARED 'data'

The segments have class `code' unless you specifically define the class as
shown in this example. See Section 18.4.1 for more information on
module-definition files.


18.3  Writing the DLL Code

When you write the code for the DLL module, you need to select the correct
module attributes, define the procedures and data in your DLL, and write the
initialization and termination code. This section discusses these tasks.


18.3.1  Choosing Module Attributes

As noted in Chapter 2, there are four fields for the .MODEL directive:
memory model, language type, operating system, and stack type. When you
write a DLL, you can choose the attributes you would normally use for the
first two fields. OS/2 system calls use the Pascal calling convention, so
you may find it convenient to make all your modules use this convention as
well.

DLLs use the OS_OS2 and FARSTACK attributes.

The operating system and stack fields should be OS_OS2 and FARSTACK,
respectively. You should use the NEARSTACK attribute only if you switch
execution to your own stack.

A usable declaration is therefore

    .MODEL  large, pascal, os_os2, farstack

If you are using full segment definitions, remember to generate an ASSUME
directive for DS but not for SS.

    ASSUME  DS:DGROUP ; Necessary with full segment definitions


18.3.2  Defining Procedures and Data

Procedures and data in DLLs can be either global (available to the client
process) or local (used only by the DLL). To create a global data item, make
sure that it is public:

    EXTERNDEF   dllvar
                .DATA
    dllvar      WORD    0

The variable must then be exported in a module-definition file, as shown in
Section 18.4.1, "Writing the Module-Definition File." When executable files
other than the DLL access the variable, they must treat it as far data, as
in the following example:

    mov     ax, SEG dllvar
    mov     es, ax
    mov     bx, es:dllvar

An exported procedure (often called a dynamic-link procedure) must follow
these rules:


    ■   It must be declared far and public. The MASM keyword EXPORT does both
        of these.

    ■   The procedure should initialize DS upon entry (unless you are not
        going to be accessing any static near data).

    ■   Data pointers in the parameter list should be far.


The easiest way to realize most of these requirements is to use the EXPORT
keyword and LOADDS in the procedure's prologuearg list (see Section 7.3.8).
LOADDS generates instructions to save DS and load it with the value of the
DLL's data segment. The EXPORT keyword makes the procedure FAR and PUBLIC,
overriding the memory model. You may also need to use FORCEFRAME, which
instructs the assembler to generate a stack frame even if there are no
parameters or locals.

The example DLL used in the chapter, CSTR.DLL, illustrates how DLLs can be
shared by several processes. The procedures in the DLL write a string and
keep track of the number of times the string is written. When more than one
process uses the DLL, they all increment the global variable  GCount, but
each process increments its own private instance of the  PCount  variable.

The only initialization code this DLL needs is code to set up the exit code.
The next section shows how to write a module-definition file to create an
import library and how to create a DLL from this code.

The code for the CSTR.DLL example looks like this:

    .MODEL  small, pascal, os_os2, farstack
            .286

    INCL_NOCOMMON   EQU     1
    INCL_DOSPROCESS EQU     1
    INCL_VIO        EQU     1

            INCLUDE    OS2.INC
            INCLUDELIB OS2.LIB

            .DOSSEG

    VioWrtCStr PROTO FAR PASCAL, pchString:PCH, hv:HVIO
    GetGCount  PROTO     PASCAL
    GetPCount  PROTO     PASCAL
    CStrExit   PROTO FAR

            .STACK
            .DATA               ; Default segment is SHARED

    GCount  WORD    0           ; Count of all calls

    @CurSeg ENDS

    PRIVDAT SEGMENT WORD     ; Private segment is NONSHARED

    PCount  WORD    0           ; Count of all this process
                                ;  calls to VioWrtCStr
    PRIVDAT ENDS

            .CODE
            .STARTUP

        pusha

            ; Initialization goes here. In this case, the only
            ;  initialization is setting up the exit behavior.

            INVOKE  DosExitList, EXLST_ADD, CStrExit
            INVOKE  DosExitList, EXLST_EXIT,0

            popa
            retf

    VioWrtCStr PROC FAR PASCAL EXPORT <LOADDS> USES cx di si,
            pchString:PCH,
            hv:HVIO

            sub     al, al         ; Search for zero
            mov     cx, 0FFFFh     ; Set maximum length
            les     di, pchString  ; Load pointer
            mov     si, di         ; Copy it
            repne   scasb          ; Find null
            .IF     zero?          ; Continue if found
            sub     di, si         ; Calculate length
            xchg    di, si         ; Restore address and save length

            INVOKE  VioWrtTTy,     ; Let OS/2 do output
                    es:di,         ; Address of string
                    si,            ; Calculated length
                    hv             ; Video handle

            inc     GCount         ; Count as one of total calls

    ASSUME  DS:PRIVDAT
            mov     ax, PRIVDAT
            mov     ds, ax
            inc     PCount         ; Count as one of process calls
            ASSUME  DS:DGROUP
            sub     ax, ax         ; Success
            .ELSE
            mov     ax, 1          ; Error
            .ENDIF
            ret
    VioWrtCStr ENDP

    GetGCount PROC  FAR PASCAL EXPORT <LOADDS, FORCEFRAME>
            mov     ax, GCount
            ret
    GetGCount ENDP

    GetPCount PROC  FAR PASCAL EXPORT <LOADDS, FORCEFRAME> USES ds
            ASSUME  DS:PRIVDAT
            mov     ax, PRIVDAT
            mov     ds, ax
            mov     ax, PCount
            ASSUME  DS:NOTHING
            ret
    GetPCount ENDP

            .DATA
    szOut   BYTE    13, 10, "Exiting DLL...", 13, 10, 0
            .CODE

    CStrExit PROC   FAR  <LOADDS, FORCEFRAME>
            INVOKE  VioWrtCStr,
                    ADDR szOut,
                    0
            INVOKE  DosExitList, EXLST_EXIT, 0
    CStrExit ENDP

            END

These generated code for the  VIOWrtCStr  procedure follows. The code marked
with asterisks is generated by the assembler.

    VioWrtCStr PROC FAR PASCAL EXPORT <LOADDS> USES cx di si,
            pchString:PCH,
            hv:HVIO
    0000  55        *         push   bp
    0001  8B EC     *         mov    bp, sp
    0003  1E        *         push   ds
    0004  B8 ---- R *         mov    ax, DGROUP
    0007  8E D8     *         mov    ds, ax
    0009  51        *         push   cx
    000A  57        *         push   di
    000B  56        *         push   si
            .
            .                      ; Procedure code here
            .
                                ret
    000C  5E        *         pop    si
    000D  5F        *         pop    di
    000E  59        *         pop    cx
    000F  1F        *         pop    ds
    0010  C9        *         leave
    0011  CA 0006   *         ret    00006h
    0014               VioWrtCStr ENDP

The DLL should establish its own data segment.

The DLL should change DS in this manner because each client program has its
own private version of DGROUP. When a program calls your dynamic-link
procedure, DS points to the program's data area, not yours. The solution is
to initialize DS so that it points to your own default data area.

However, one side effect of this approach is that it alters DS so that it no
longer is equal to SS. Consequently, all data pointers in the parameter list
must be far pointers, even if the data was stack data or near data.


18.3.3  Creating Initialization and Termination Code

Begin initialization code with the .STARTUP directive.

A DLL can contain procedures that require special resources, such as
temporary files or dynamic memory blocks. Resources allocated during
initialization exist for the lifetime of the client program and are removed
when the client program exits. Usually the best method for managing these
resources is to write initialization and termination code.

A DLL can have a starting point just as an application does. In the case of
a DLL, this starting point marks the beginning of the initialization code. A
DLL does not need a starting point if it has no need for initialization. Do
not use .EXIT, since .EXIT will terminate the client program.

Attributes of the initialization code are defined in the module-definition
file (see Section 18.4.1). Initialization code can have the INITGLOBAL or
INITINSTANCE attribute.

INITGLOBAL specifies that the initialization code executes only once─when
the DLL is first loaded into memory. INITINSTANCE specifies that
initialization code should execute once for each program that uses the DLL.
INITGLOBAL is the default. You should use termination code only for DLLs
that have been defined with INITINSTANCE unless you know that the first
process to use the DLL is the last to terminate.

To specify INITINSTANCE, place the LIBRARY statement in your
moduledefinition file:

    LIBRARY CSTR INITINSTANCE

In the statement above, CSTR is the name of the DLL.

To include a termination procedure, invoke DosExitList in the initialization
code. DosExitList is a system function that attaches a termination procedure
to a program. When the program terminates, OS/2 executes the procedure as
part of the program exit sequence. In the termination procedure itself,
release any system resources (such as memory or files) allocated during
initialization.

This is the termination code for the CSTR.DLL module:

    CStrExit PROC   FAR  <LOADDS, FORCEFRAME>
            INVOKE  VioWrtCStr,
                    ADDR szOut,
                    0
            INVOKE  DosExitList, EXLST_EXIT, 0
    CStrExit ENDP

The termination code in CSTR.DLL uses the INVOKE directive to set up a call
to the DosExitList function. You can perform a similar operation by simply
pushing arguments on the stack and observing the correct calling convention.


The effect of DosExitList in the initialization code is to make OS/2 call
the termination procedure when the current process exits. The "current
process" in this case is the client program, not the DLL or the DLL
initialization code.


18.4  Building the DLL

To create a DLL, you need to assemble the DLL code, write a
module-definition file, use LINK to create the DLL, generate an import
library, and then link the DLL to the client program.


18.4.1  Writing the Module-Definition File

A module-definition file is required for DLLs.

The module-definition file is an ASCII text file that lists attributes of a
library or application (in the case of an application, this file is
optional). The moduledefinition file gives directions to the linker that
supplement the information on the command line.

This module-definition file tells the linker to create a DLL called CSTR.DLL
with INITINSTANCE data. The library has exported procedure  VioWrtCStr,
GetPCount, and  GetGCount, and the data segment  PRIVDAT  is not shared
between programs:

    LIBRARY CSTR INITINSTANCE

    EXPORTS
        VioWrtCstr
        GetGCount
        GetPCount

    DATA SINGLE NONSHARED

The LIBRARY statement need not specify a name. If the name is omitted, the
linker gives the library the base filename of the module-definition file.
The default file extension is .DLL. The INITINSTANCE attribute is optional
and is significant only if you have initialization code. If you specify
INITINSTANCE, then the library initialization is called each time a new
process gains access to the library. Otherwise, it will be called once only.


    At least one procedure must be listed after EXPORTS.

The EXPORTS statement lists identifiers (procedures and variables) that can
be accessed directly by client programs. Note that if you give a procedure
the EXPORTS attribute from within the source code, you do not need to list
the procedure here. The EXPORTS keyword automatically exports the procedure
by name, so putting the names of the procedures in the module-definition
file is not required. However, exported variables must be listed in a
module-definition file.

The DATA statement lists attributes for data segments (DGROUP) in the DLL.
The default for DLLs, SINGLE, specifies that one DGROUP is shared by all
instances of the DLL. NONSHARED specifies that all other data segments are
not to be shared. See Section 13.15, "CODE, DATA, and SEGMENTS Attributes."



18.4.2  Generating an Import Library with IMPLIB

The DLL exports a procedure; the client program imports it.

Just as a procedure is exported by a DLL, it must be imported by an
application. An application's EXE header must indicate what dynamic-link
procedures are used and where they reside. The easiest way to specify this
information is with an "import library," which is a .LIB file that contains
the import information in object-record form. The IMPLIB utility automates
this process for you.

To create an import library, run the IMPLIB utility on the module-definition
file:

    IMPLIB MYDYNLIB.LIB MYDYNLIB.DEF

The result is the import library, MYDYNLIB.LIB, which you then link to any
program that calls CSTR.DLL. You would then list MYDYNLIB.LIB in the
libraries field (the fourth field) of the LINK command. Or, in
assembly-language programs, you can link to this library automatically by
just adding the following statement to the source code of your program:

    INCLUDELIB MYDYNLIB.LIB


18.4.3  Creating and Using the DLL

Now you can use LINK to create the DLL. The LINK utility uses the object
module of the DLL code and the module definition to create the CSTR.DLL:

    LINK CSTR.OBJ , , , , MYDYNLIB.DEF

If linking is successful, the linker creates a file with a .DLL extension.

You can link several modules together to create a DLL. The following command
line links several object modules and an object-code library (BIGLIB.LIB) to
form a DLL. The module-definition file is MYDYNLIB.DEF:

    LINK  MOD1 MOD2 MOD3,,, BIGLIB, MYDYNLIB

To use the DLL, copy the .DLL file to a directory listed in the LIBPATH
setting in your CONFIG.SYS file.

To create an executable file using the DLL, link the client program with the
import library as shown:

    LINK CALLDLL.OBJ , , , MYDYNLIB.LIB

By running CALLDLL.EXE in separate OS/2 windows, you can see that both
client programs access the DDL at the same time. When the last process exits
the DLL, the DLL is removed from memory.


18.5  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topic                             Access
────────────────────────────────────────────────────────────────────────────
LINK                              From the "Microsoft Advisor Contents"
                                    screen, select LINK

Module-definition files           Select Module-Definition Files from the
                                    "LINK Contents" screen

EXPORT                            Select from the MASM Language Index

EXTERNDEF                         From the "MASM 6.0 Contents" screen,
                                    select "Directives"; then select "Scope
                                    and Visibility" from the next screen

LOADDS,                           Choose "Proc" from the MASM Language
FORCEFRAME                        Index

IMPLIB                            Select "IMPLIB Summary" from the "LINK
                                    Contents" screen






Chapter 19  Writing Memory-Resident Software
────────────────────────────────────────────────────────────────────────────

Through its memory-management system, DOS allows a program to remain
resident in memory after terminating. The resident program can later regain
control of the processor to perform tasks such as background printing or
"popping up" a calculator on the screen. Such a program is commonly called a
TSR, from the Terminate-and-Stay-Resident function it uses to return to DOS.


This chapter explains the techniques of writing memory-resident software.
The first two sections present introductory material. Following sections
describe important DOS and BIOS interrupts and focus on how to write safe,
compatible, memory-resident software. Two example programs illustrate the
techniques described in the chapter. These programs are also available as
sample programs on the MASM 6.0 disks.


19.1  Terminate-and-Stay-Resident Programs

DOS maintains a pointer to the beginning of unused memory. Programs load
into memory at this position. They terminate execution by returning control
to DOS. Normally, the pointer remains unchanged, allowing DOS to reuse
memory when loading other programs.

A terminating program can, however, prevent other programs from loading on
top of it. It does this by returning to DOS through the
terminate-and-stay-resident function, which resets the free-memory pointer
to a higher position. This leaves the program resident in a protected block
of memory, even though it is no longer running.

The terminate-and-stay-resident function (Function 31h) is one of the DOS
services invoked through Interrupt 21h. The following fragment shows how a
TSR program terminates using Function 31h and remains resident in a
1000h-byte block of memory:

    mov     ah, 31h          ; Request DOS Function 31h
            mov     al, err          ; Set return code
            mov     dx, 100h         ; Reserve 100h paragraphs
                                    ;  (1000h bytes)
            int     21h              ; Terminate-and-stay-resident

────────────────────────────────────────────────────────────────────────────
NOTE

In current versions of DOS, Interrupt 27h also provides a
terminate-and-stayresident service. However, Microsoft cannot guarantee
future support for Interrupt 27h and does not recommend its use.
────────────────────────────────────────────────────────────────────────────


19.1.1  Structure of a TSR

TSRs consist of two distinct parts that execute at different times. The
first part is the installation section, which executes only once, when DOS
loads the program. The installation code performs any initialization tasks
required by the TSR and then exits through the terminate-and-stay-resident
function.

A TSR consists of an installation section and a resident section.

The second part of the TSR, called the resident section, consists of code
and data left in memory after termination. Though often identified with the
TSR itself, the resident section makes up only part of the entire program.

The TSR's resident code must be able to regain control of the processor and
execute after the program has terminated. Methods of executing a TSR are
classified as either passive or active.


19.1.2  Passive TSRs

The simplest way to execute a TSR is to transfer control to it explicitly
from another program. Because the TSR in this case does not solicit
processor control, it is said to be passive. If the calling program can
determine the TSR's memory address, it can grant control via a far jump or
call. More commonly, a program activates a passive TSR through a software
interrupt. The installation section of the TSR writes the address of its
resident code to the proper position in the interrupt vector table (see
Section 7.4, "DOS Interrupts"). Any subsequent program can then execute the
TSR by calling the interrupt.

Passive TSRs often replace existing software interrupts. For example, a
passive TSR might replace Interrupt 10h, the BIOS video service. By
intercepting calls that read or write to the screen, the TSR can access the
video buffer directly, increasing display speed.

Passive TSRs allow limited access since they can be invoked only from
another program. They have the advantage of executing within the context of
the calling program, and thus run no risk of interfering with another
process, which could happen with active TSRs.


19.1.3  Active TSRs

The second method of executing a TSR involves signaling it through some
hardware event, such as a predetermined sequence of keystrokes. This type of
TSR is called active because it must continually search for its start-up
signal. The advantage of active TSRs lies in their accessibility. They can
take control from any running application, execute, and return, all on
demand.

An active TSR, however, must not seize processor control blindly. It must
contain additional code that determines the proper moment at which to
execute. The extra code consists of one or more routines called "interrupt
handlers," described in the following section.


19.2  Interrupt Handlers in Active TSRs

The memory-resident portion of an active TSR consists of two parts. One part
contains the body of the TSR─the code and data that perform the program's
main tasks. The other part contains the TSR's interrupt handlers.

An interrupt handler is a routine that takes control when a specific
interrupt occurs. Although sometimes called an "interrupt service routine,"
a TSR's handler usually does not service the interrupt. Instead, it passes
control to the original interrupt routine, which does the actual interrupt
servicing.

Collectively, interrupt handlers ensure that a TSR operates compatibly with
the rest of the system. Individually, each handler fulfills at least one of
the following functions:


    ■   Auditing hardware events that may signal a request for the TSR

    ■   Monitoring system status

    ■   Determining whether a request for the TSR should be honored, based on
        current system status



19.2.1  Auditing Hardware Events for TSR Requests

Active TSRs commonly use a special keystroke sequence or the timer as a
request signal. A TSR invoked through one of these channels must be equipped
with handlers that audit keyboard or timer events.

A keyboard handler receives control at every keystroke. It examines each
key, searching for the proper signal or "hot key." Generally, a keyboard
handler should not attempt to call the TSR directly when it detects the hot
key. If the TSR cannot safely interrupt the current process at that moment,
the keyboard handler is forced to exit to allow the process to continue.
Since the handler cannot regain control until the next keystroke, the user
has to press the hot key repeatedly until the handler can comply with the
request.

Instead, the handler should merely set a request flag when it detects a
hot-key signal and then exit normally. Examples in the following paragraphs
illustrate this technique.

For computers other than the IBM PS/2 (R) series, an active TSR audits
keystrokes through a handler for Interrupt 09, the keyboard interrupt:

    Keybrd  PROC    FAR
            sti                   ; Interrupts are okay
            push    ax            ; Save AX register
            in      al, 60h       ; AL = scan code of current key
            call    CheckHotKey   ; Check for hot key
            .IF     !carry?       ; If not hot key:
    ; Hot key pressed. Reset the keyboard to throw away keystroke.
            cli                   ; Disable interrupts while resetting
            in      al, 61h       ; Get current port 61h state
            or      al, 10000000y ; Turn on bit 7 to signal clear keybrd
            out     61h, al       ; Send to port
            and     al, 01111111y ; Turn off bit 7 to signal break
            out     61h, al       ; Send to port
            mov     al, 20h       ; Reset interrupt controller
            out     20h, al
            sti                   ; Reenable interrupts
            pop     ax            ; Recover AX
            mov     cs:TsrRequestFlag, TRUE ; Raise request flag
            iret                  ; Exit interrupt handler
            .ENDIF                ; End hot-key check

    ; No hot key was pressed, so let normal Int 09 service
    ; routine take over

            pop     ax            ; Recover AX and fall through
            cli                   ; Interrupts cleared for service
    KeybrdMonitor LABEL FAR       ; Installed as Int 09 handler for
                                ;  PS/2 or for time-activated TSR
                                ; Signal that interrupt is busy
            mov     cs:intKeybrd.Flag, TRUE
            pushf                 ; Simulate interrupt by pushing flags,
                                ;  far-calling old Int 09 routine
            call    cs:intKeybrd.OldHand
            mov     cs:intKeybrd.Flag, FALSE
            iret
    Keybrd  ENDP

A TSR running on a PS/2 computer cannot reliably read key-scan codes using
the above method. Instead, the TSR must search for its hot key through a
handler for Interrupt 15h (Miscellaneous System Services). The handler
determines the current keypress from the AL register when AH equals 4Fh, as
shown here:

    MiscServ PROC   FAR
            sti                   ; Interrupts okay
            .IF     ah == 4Fh     ; If Keyboard Intercept Service:
            push    ax            ; Preserve AX
            call    CheckHotKey   ; Check for hot key
            pop     ax
            .IF     !carry?       ; If hot key:
            mov     cs:TsrRequestFlag, TRUE ; Raise request flag
            clc                   ; Signal BIOS not to process the key
            ret     2             ; Simulate IRET without popping flags
            .ENDIF                ; End carry flag check
            .ENDIF                ; End Keyboard Intercept check
            cli                   ; Disable interrupts and fall through
    SkipMiscServ LABEL FAR        ; Interrupt 15h handler if PC/AT
            jmp     cs:intMisc.OldHand
    MiscServ ENDP

The example program in Section 19.8 demonstrates how a TSR tests for a PS/2
machine and then sets up a handler for either Interrupt 09 or Interrupt 15h
to audit keystrokes.

Setting a request flag in the keyboard handler allows other code, such as
the timer handler (Interrupt 08), to recognize a request for the TSR. The
timer handler gains control at every timer interrupt; the interrupts occur
an average of 18.2 times per second. The following fragment shows how a
timer handler tests the request flag and continually polls until it can
safely execute the TSR.

    TestFlag PROC FAR
            .
            .
            .
            cmp     TsrRequestFlag, FALSE ; Has TSR been requested?
            je      exit                  ; If not, exit
            call    CheckSystem           ; Can system be interrupted
                                        ;  safely?
            jc      exit                  ; If not, exit
            call    ActivateTsr           ; If okay, call TSR

Figure 19.1 illustrates the process. It shows a time line for a typical TSR
signaled from the keyboard. When the keyboard handler detects the proper hot
key, it sets a request flag called  TsrRequestFlag. Thereafter, the timer
handler continually checks the system status until it can safely call the
TSR.

The timer itself can serve as the start-up signal if the TSR executes
periodically. Screen clocks that continuously show seconds and minutes are
examples of TSRs that use the timer this way. ALARM.ASM, a program described
in the next section, shows another example of a timer-driven TSR.

(This figure may be found in the printed book.)


19.2.2  Monitoring System Status

A TSR that uses a hardware device such as the video or disk must not
interrupt while the device is active. A TSR monitors a device by handling
the device's interrupt. Each interrupt handler need only set a flag to
indicate that the device is in use and then clear the flag when the
interrupt finishes.

The following shows a typical monitor handler:

    NewHandler PROC    FAR
            mov     ActiveFlag, TRUE  ; Set active flag
            pushf                     ; Simulate interrupt by
                                    ;  pushing flags,
            call    OldHandler        ;  then calling original routine
            mov     ActiveFlag, FALSE ; Clear active flag
            iret                      ; Return from interrupt
    NewHandler ENDP

Only hardware used by the TSR requires monitoring. For example, a TSR that
performs disk input/output (I/O) must monitor disk use through Interrupt
13h. The disk handler sets an active flag that prevents the TSR from
executing during a read or write operation. Otherwise, the TSR's own I/O
would move the disk head. This would cause the suspended disk operation to
continue with the head incorrectly positioned when the TSR returned control
to the interrupted program.

In the same way, an active TSR that displays to the screen must monitor
calls to Interrupt 10h. The Interrupt 10h BIOS routine does not protect
critical sections of code that program the video controller. The TSR must
therefore ensure that it does not interrupt such nonreentrant operations.

The activities of the operating system also affect the system status. With
few exceptions, DOS functions are not reentrant and must not be interrupted.
However, monitoring DOS is somewhat more complicated than monitoring
hardware. Discussion of this subject is deferred until Section 19.4.

The following comments describe the chain of events depicted in Figure 19.1.
Each comment refers to one of the numbered pointers in the figure.


    1.  At time = t, the timer handler activates. It finds the flag
        TsrRequestFlag  clear, indicating that the TSR has not been requested.
        The handler terminates without taking further action. Notice that
        Interrupt 13h is currently processing a disk I/O operation.

    2.  Before the next timer interrupt, the keyboard handler detects the hot
        key, signalling a request for the TSR. The handler sets
        TsrRequestFlag  and returns.

    3.  At time = t + 1/18 second, the timer handler again activates and finds
        TsrRequestFlag  set. The handler checks other active flags to
        determine if the TSR can safely execute. Since Interrupt 13h has not
        yet completed its disk operation, the timer handler finds
        DiskActiveFlag  set. The handler therefore terminates without invoking
        the TSR.

    4.  At time = t + 2/18 second, the timer handler again finds
        TsrRequestFlag set and repeats its scan of the active flags.
        DiskActiveFlag  is now clear, but in the interim, Interrupt 10h has
        activated as indicated by the flag  VideoActiveFlag. The timer handler
        accordingly terminates without invoking the TSR.

    5.  At time = t + 3/18 second, the timer handler repeats the process. This
        time it finds all active flags clear, indicating that the TSR may
        safely execute. The timer handler calls the TSR, which sets its own
        active flag to ensure that it will not interrupt itself if requested
        again.

    6.  The timer and other interrupts continue to function normally while the
        TSR executes.



19.2.3  Determining Whether to Invoke the TSR

Once a handler receives a request signal for the TSR, it checks the various
active flags maintained by the handlers that monitor system status. If any
of the flags are set, the handler ignores the request and exits. If the
flags are clear, the handler invokes the TSR, usually through a near or far
call. Figure 19.1 illustrates how a timer handler detects a request and then
periodically scans various active flags until all the flags are clear.

A TSR that changes stacks must not interrupt itself. Otherwise, the second
execution would overwrite the stack data belonging to the first. A TSR
prevents this by setting its own active flag before executing, as shown in
Figure 19.1. A handler must check this flag along with the other active
flags when determining whether the TSR can safely execute.


19.3  Example of a Simple TSR: ALARM

This section presents a simple alarm clock TSR that demonstrates some of the
material covered so far. The program accepts an argument from the command
line that specifies the alarm setting in military form, such as 1635 for
4:35 P.M. For the sake of simplicity, the argument must consist of four
digits, including leading zeros. To set the alarm at 7:45 A.M., for example,
enter:

    ALARM 0745

The installation section of the program begins with the  Install  procedure.
    Install  computes the number of five-second intervals that must elapse
before the alarm sounds and stores this number in the word  CountDown. The
procedure then obtains the vector for Interrupt 08 (timer) through Interrupt
21h Function 35h and stores it in the far pointer  OldTimer. Interrupt 21h
Function 25h replaces the vector with the far address of the new timer
handler  NewTimer. Once installed, the new timer handler executes at every
timer interrupt. These interrupts occur 18.2 times per second or 91 times
every five seconds.

Each time it executes, NewTimer  subtracts one from a secondary counter
called  Tick91. By counting 91 timer ticks,  Tick91  accurately measures a
period of five seconds. When  Tick91  reaches zero, it's reset to 91 and
CountDown  is decremented by one. When  CountDown  reaches zero, the alarm
sounds.

    ;* ALARM.ASM - A simple memory-resident program that beeps
    the speaker
    ;* at a prearranged time. Can be loaded more than once for multiple
    ;* alarm settings. During installation, ALARM establishes a handler
    ;* for the timer interrupt (interrupt 08). It then terminates through
    ;* the terminate-and-stay-resident function (function 31h). After
    the
    ;* alarm sounds, the resident portion of the program retires by setting
    ;* a flag that prevents further processing in the handler.
    ;*
    ;* NOTE: You must assemble this program as a .COM file, either as
    a PWB
    ;*       build option or with the ML /AT option.

    .MODEL tiny, pascal, os_dos
            .STACK
            .CODE
            ORG     5Dh                     ; Location of time argument
    in PSP,
    CountDown       LABEL   WORD            ;  converted to number of
    5-second
                                            ;  intervals to elapse
            .STARTUP
            jmp     Install                 ; Jump over data and resident
    code

    ; Data must be in code segment so it won't be thrown away with Install
    code.

    OldTimer        DWORD   ?               ; Address of original
    timer routine
    tick_91         BYTE    91              ; Counts 91 clock ticks (5
    seconds)
    TimerActiveFlag BYTE    0               ; Active flag for timer handler

    ;* NewTimer - Handler routine for timer interrupt (interrupt 08).
    ;* Decrements CountDown every 5 seconds. No other action is taken
    ;* until CountDown reaches 0, at which time the speaker sounds.

    NewTimer PROC   FAR
            .IF     cs:TimerActiveFlag != 0 ; If timer busy or retired:
            jmp     cs:OldTimer             ; Jump to original timer routine
            .ENDIF
            inc     cs:TimerActiveFlag      ; Set active flag
            pushf                           ; Simulate interrupt by pushing
    flags,
            call    cs:OldTimer             ;  then far-calling original
    routine
            sti                             ; Enable interrupts
            push    ds                      ; Preserve DS register
            push    cs                      ; Point DS to current segment
    for
            pop     ds                      ;  further memory access
            dec     tick_91                 ; Count down for 91 ticks

    .IF     zero?                   ; If 91 ticks have
    elapsed:
            mov     tick_91, 91             ; Reset secondary counter
    and
            dec     CountDown               ;  subtract one 5-second interval
            .IF     zero?                   ; If CountDown drained:
            call    Sound                   ; Sound speaker
            inc     TimerActiveFlag         ; Alarm has sounded, set flag
            .ENDIF
            .ENDIF

            dec     TimerActiveFlag         ; Decrement active flag
            pop     ds                      ; Recover DS
            iret                            ; Return from interrupt handler
    NewTimer ENDP

    ;* Sound - Sounds speaker with the following tone and duration:

    BEEP_TONE       EQU     440             ; Beep tone in hertz
    BEEP_DURATION   EQU     6               ; Number of clocks during
    beep,
                                            ;  where 18 clocks = approx
    1 second

    Sound   PROC    USES ax bx cx dx es     ; Save registers used in this
    routine
            mov     al, 0B6h                ; Initialize channel 2 of
            out     43h, al                 ;  timer chip
            mov     dx, 12h                 ; Divide 1,193,180 hertz
            mov     ax, 34DCh               ;  (clock frequency) by
            mov     bx, BEEP_TONE           ;  desired frequency
            div     bx                      ; Result is timer clock count
            out     42h, al                 ; Low byte of count to timer
            mov     al, ah
            out     42h, al                 ; High byte of count to timer
            in      al, 61h                 ; Read value from port 61h
            or      al, 3                   ; Set first two bits
            out     61h, al                 ; Turn speaker on

    ; Pause for specified number of clock ticks

            mov     dx, BEEP_DURATION       ; Beep duration in clock ticks
            sub     cx, cx                  ; CX:DX = tick count for pause
            mov     es, cx                  ; Point ES to low memory data
            add     dx, es:[46Ch]           ; Add current tick count to
    CX:DX
            adc     cx, es:[46Eh]           ; Result is target count in
    CX:DX
            .REPEAT
            mov     bx, es:[46Ch]           ; Now repeatedly poll clock
            mov     ax, es:[46Eh]           ;  count until the target
            sub     bx, dx                  ;  time is reached
            sbb     ax, cx
            .UNTIL  !carry?

            in      al, 61h                 ; When time elapses, get port
    value
            xor     al, 3                   ; Kill bits 0-1 to turn
            out     61h, al                 ;  speaker off
            ret
    Sound   ENDP

    ;* Install - Converts ASCII argument to valid binary number,
    replaces
    ;* NewTimer as the interrupt handler for the timer, then makes program
    ;* memory-resident by exiting through function 31h.
    ;*
    ;* This procedure marks the end of the TSR's resident section and
    the
    ;* beginning of the installation section. When ALARM terminates through
    ;* function 31h, the above code and data remain resident in memory.
    The
    ;* memory occupied by the following code is returned to DOS.

    Install PROC

    ; Time argument is in hhmm military format. Converts ASCII digits
    to
    ; number of minutes since midnight, then converts current time to
    number
    ; of minutes since midnight. Difference is number of minutes to elapse
    ; until alarm sounds. Converts to seconds-to-elapse, divides by 5
    seconds,
    ; and stores result in word CountDown.

    DEFAULT_TIME    EQU     3600              ; Default alarm setting
    = 1 hour
                                            ;  (in seconds) from present
    time
            mov     ax, DEFAULT_TIME
            cwd                               ; DX:AX = default time in
    seconds
            .IF     BYTE PTR CountDown != ' ' ; If not blank argument:
            xor     CountDown[0], '00'        ; Convert 4 bytes of ASCII
            xor     CountDown[2], '00'        ;  argument to binary

            mov     al, 10                    ; Multiply 1st hour digit
    by 10
            mul     BYTE PTR CountDown[0]     ;  and add to 2nd hour digit
            add     al, BYTE PTR CountDown[1]
            mov     bh, al                    ; BH = hour for alarm to
    go off
            mov     al, 10                    ; Repeat procedure for minutes
            mul     BYTE PTR CountDown[2]     ; Multiply 1st minute digit
    by 10
            add     al, BYTE PTR CountDown[3] ; and add to 2nd minute
    digit
            mov     bl, al                    ; BL = minute for alarm
    to go off
            mov     ah, 2Ch                   ; Request function 2Ch
            int     21h                       ; Get Time (CX = current
    hour/min)
            mov     dl, dh
            sub     dh, dh
            push    dx                        ; Save DX = current seconds

    mov     al, 60                    ; Multiply current
    hour by 60
            mul     ch                        ;  to convert to minutes
            sub     ch, ch
            add     cx, ax                    ; Add current minutes to
    result
                                            ; CX = minutes since midnight
            mov     al, 60                    ; Multiply alarm hour by
    60
            mul     bh                        ;  to convert to minutes
            sub     bh, bh
            add     ax, bx                    ; AX = number of minutes
    since
                                            ;  midnight for alarm setting
            sub     ax, cx                    ; AX = time in minutes to
    elapse
                                            ;  before alarm sounds

    .IF     carry?                    ; If alarm time is
    tomorrow:
            add     ax, 24 * 60               ; Add minutes in a day
            .ENDIF

            mov     bx, 60
            mul     bx                        ; DX:AX =
minutes-to-elapse-times-60
            pop     bx                        ; Recover current seconds
            sub     ax, bx                    ; DX:AX = seconds to elapse
    before
            sbb     dx, 0                     ;  alarm activates
            .IF     carry?                    ; If negative:
            mov     ax, 5                     ; Assume 5 seconds
            cwd
            .ENDIF
            .ENDIF

    mov     bx, 5                     ; Divide result by
    5 seconds
            div     bx                        ; AX = number of 5-second
    intervals
            mov     CountDown, ax             ;  to elapse before alarm
    sounds

            mov     ax, 3508h                 ; Request function 35h
            int     21h                       ; Get Vector for timer
(interrupt
    08)
            mov     WORD PTR OldTimer[0], bx  ; Store address of original
            mov     WORD PTR OldTimer[2], es  ;  timer interrupt
            mov     ax, 2508h                 ; Request function 25h
            mov     dx, OFFSET NewTimer       ; DS:DX points to new timer
    handler
            int     21h                       ; Set Vector with address
    of NewTimer

            mov     dx, OFFSET Install        ; DX = bytes in resident
    section
            mov     cl, 4
            shr     dx, cl                    ; Convert to number of
paragraphs
            inc     dx                        ;  plus one
            mov     ax, 3100h                 ; Request function 31h,
    error code=0
            int     21h                       ; Terminate-and-stay-resident
    Install ENDP
            END

Note the following points about ALARM:


    ■   The constant  BEEP_TONE  specifies the alarm tone. Practical values
        for the tone range from approximately 100 to 4,000 hertz.

    ■   The  Install  procedure marks the beginning of the installation
        section of the program. Execution begins here when ALARM.COM is
        loaded. A TSR generally places its installation code after the
        resident section. This allows the TSR to include the installation code
        and data and to return memory to DOS when the program terminates.
        Since the installation section executes only once, the TSR can discard
        it after becoming resident.

    ■   You can install ALARM any number of times in quick succession, each
        time with a new alarm setting. The timer handler does not restore the
        original timer vector after the alarm sounds. In effect, the multiple
        installations are daisy-chained in memory. The address in  OldTimer
        for one installation is the address of  NewTimer  in the preceding
        installation.

    ■   Until a system reboot,  NewTimer  remains in place as the Interrupt 08
        handler, even after the alarm sounds. To save unnecessary activity,
        the byte  TimerActiveFlag  remains set after the alarm sounds. This
        forces an immediate jump to the original handler for all subsequent
        executions of  NewTimer.

    ■   NewTimer  and  Sound  alter registers DS, AX, BX, CX, DX, and ES. To
        preserve the original values in these registers, the procedures first
        push them onto the stack and then restore the original values before
        exiting. This ensures that the process interrupted by  NewTimer
        continues with valid registers after  NewTimer  returns.

    ■   ALARM requires little stack space. It assumes that the current stack
        is adequate and makes no attempt to set up a new one. More
        sophisticated TSRs, however, should as a matter of course provide
        their own stacks to ensure adequate stack depth. The example program
        presented in Section 19.8 demonstrates this safety measure.



19.4  Using DOS in Active TSRs

This section explains how to write active TSRs that can safely call DOS
functions. The material explores the problems imposed by DOS's nonreentrance
and explains how a TSR can resolve those problems. The solution consists of
four parts:


    ■   Understanding how DOS uses stacks

    ■   Determining when DOS is active

    ■   Determining whether a TSR can safely interrupt an active DOS function

    ■   Monitoring the Critical Error flag



19.4.1  Understanding DOS Stacks

DOS functions set up their own stacks, which makes them nonreentrant. If a
TSR interrupts a DOS function and then executes another function that sets
up the same stack, the second function will overwrite everything placed on
the stack by the first function. The problem occurs when the second function
returns and the first is left with unusable stack data. A TSR that calls a
DOS function must not interrupt any function that uses the same stack.

With few exceptions, DOS functions use their own stacks when they execute.

DOS versions 2.0 and later use three internal stacks: an I/O stack, a disk
stack, and an auxiliary stack. The current stack depends on the DOS
function. Functions 01 through 0Ch set up the I/O stack. Functions higher
than 0Ch (with few exceptions) use the disk stack, as do Interrupts 25h and
26h. DOS normally uses the auxiliary stack only when it executes Interrupt
24h (Critical Error Handler).


19.4.2  Determining DOS Activity

A TSR's handlers can determine when DOS is active by consulting a one-byte
flag called the InDos flag. Every DOS function sets this flag upon entry and
clears it upon termination. During installation, a TSR locates the flag
through Function 34h (Get Address of InDos Flag), which returns the address
as ES:BX. The installation portion then stores the address so that the
handlers can later find the flag without again calling Function 34h.

Theoretically, a TSR can wait to execute until the InDos flag is clear, thus
sidestepping the entire issue of interrupting DOS. However, several
low-order functions─such as Function 0Ah (Get Buffered Keyboard Input)─wait
idly for an expected keystroke before they terminate. If a TSR were allowed
to execute only after DOS returned, it too would be forced to wait for the
terminating event.

The solution lies in determining when the low-order functions are active.
DOS provides another service for this purpose: Interrupt 28h, the Idle
Interrupt.


19.4.3  Interrupting DOS Functions

DOS continually calls Interrupt 28h from the low-order polling functions as
they wait for keyboard input. This signal says that DOS is idle and that a
TSR may interrupt provided it does not overwrite the I/O stack.

A TSR may interrupt DOS Functions 01 through 0Ch provided it does not call
them.

An active TSR that calls DOS must monitor Interrupt 28h with a handler. When
the handler gains control, it checks the TSR request flag. If the flag
indicates the TSR has been requested and if system hardware is inactive, the
handler executes the TSR. Since control must eventually return to the idle
DOS function which has stored data on the I/O stack, the TSR in this case
must not call any DOS function that also uses the I/O stack. Table 19.1
shows which functions set up the I/O stack for various versions of DOS.

Table 19.1  DOS Internal Stacks

╓┌───────────┌──────────────┌──────┌───────┌─────────────────────────────────╖
            Critical
Function    Error flag
────────────────────────────────────────────────────────────────────────────
01-0Ch      Clear          I/O*   I/O     I/O
            Set            Aux*   Aux     Aux

33h         Clear          Disk*  Disk    Caller*
            Set            Disk   Disk    Caller

50h-51h     Clear          I/O    Caller  Caller
            Set            Aux    Caller  Caller

59h         Clear          n/a*   I/O     Disk
            Set            n/a    Aux     Disk

5D0Ah       Clear          n/a    n/a     Disk
            Set            n/a    n/a     Disk

62h         Clear          n/a    Caller  Caller
            Set            n/a    Caller  Caller
            Critical
Function    Error flag
────────────────────────────────────────────────────────────────────────────
            Set            n/a    Caller  Caller

All others  Clear          Disk   Disk    Disk
            Set            Disk   Disk    Disk

────────────────────────────────────────────────────────────────────────────



* I/O = I/O stack, Aux = auxiliary stack, Disk = disk stack, Caller =
caller's stack,    n/a = function not available.


TSRs that perform tasks of long or indefinite duration should themselves
call Interrupt 28h. For example, a TSR that polls for keyboard input should
include an INT 28h instruction in the polling loop, as shown here:

    poll:      int     28h              ; Signal idle state
                mov     ah, 1
                int     16h              ; Key waiting?
                jnz     poll             ; If not, repeat polling loop
                sub     ah, ah
                int     16h              ; Otherwise, get key

This courtesy gives other TSRs a chance to execute if the InDos flag happens
to be set.


19.4.4  Monitoring the Critical Error Flag

DOS sets the Critical Error flag to a nonzero value when it detects a
critical error. It then invokes Interrupt 24h (Critical Error Handler) and
clears the flag when Interrupt 24h returns. DOS functions higher than 0Ch
are illegal during critical error processing. Therefore, a TSR that calls
DOS must not execute while the Critical Error flag is set.

DOS versions 3.1 and later locate the Critical Error flag in the byte
preceding the InDos flag. A single call to Function 34h (Get Address of
InDos Flag) thus effectively returns the addresses of both flags. For
earlier versions of DOS or for the compatibility version of DOS in OS/2, a
TSR must call Function 34h and then scan the segment returned in the ES
register for one of the two following sequences of instructions:

    ; Sequence of instructions in DOS Versions 2.0 - 3.0
            cmp     ss:[CriticalErrorFlag], 0
            jne     @F
            int     28h

    ; Sequence of instructions in OS/2's compatibility
    ;  version of DOS
            test    [CriticalErrorFlag], 0FFh
            jnz     @F
            push    ss:[ ? ]
            int     28h

The question mark inside brackets in the PUSH statement above indicates that
the operand for the PUSH instruction can be any legal operand.

In either version of DOS, the operand field in the first instruction gives
the flag's offset. The value in ES determines the segment address. The
example program presented in Section 19.8 demonstrates how to locate the
Critical Error flag with this technique.


19.5  Preventing Interference

This section describes how an active TSR can avoid interfering with the
process it interrupts. Interference occurs when a TSR commits an error or
performs an action that affects the interrupted process after the TSR
returns. Examples of interference range from the relatively harmless, such
as moving the cursor, to the serious, such as overrunning a stack.

Although a TSR can potentially interfere with another process in many
different ways, protection against interference involves only three steps:


    1.  Recording a current configuration

    2.  Changing the configuration so it applies to the TSR

    3.  Restoring the original configuration before terminating


The example program in Section 19.8 demonstrates all the noninterference
safeguards described in this section. These safeguards by no means exhaust
the subject of noninterference. More sophisticated TSRs may require more
sophisticated methods. However, noninterference methods generally fall into
one of the following categories:


    ■   Trapping errors

    ■   Preserving an existing condition

    ■   Preserving existing data



19.5.1  Trapping Errors

A TSR committing an error that triggers an interrupt must handle the
interrupt to trap the error. Otherwise, the existing interrupt routine,
which belongs to the underlying process, would attempt to service an error
the underlying process did not commit.

For example, a TSR that accepts keyboard input should include handlers for
Interrupts 23h and 1Bh to trap keyboard break signals. When DOS detects
CTRL+C from the keyboard or input stream, it transfers control to Interrupt
23h (CTRL+C Handler). Similarly, the BIOS keyboard routine calls Interrupt
1Bh (CTRL+BREAK Handler) when it detects a CTRL+BREAK key combination. Both
routines normally terminate the current process.

A TSR that calls DOS should also trap critical errors through Interrupt 24h
(Critical Error Handler). DOS functions call Interrupt 24h when they
encounter certain hardware errors. The TSR must not allow the existing
interrupt routine to service the error, since the routine might allow the
user to abort service and return control to DOS. This would terminate both
the TSR and the underlying process. By handling Interrupt 24h, the TSR
retains control if a critical error occurs.

An error-trapping handler differs in two ways from a TSR's other handlers:


    1.  It is temporary, in service only while the TSR executes. At start-up,
        the TSR copies the handler's address to the interrupt vector table; it
        then restores the original vector before terminating.

    2.  It provides complete service for the interrupt; it does not pass
        control on to the original routine. However, if the error is not a TSR
        error, the handler needs to pass the error to the original routine.


Error-trapping handlers often set a flag to let the TSR know that the error
has occurred. For example, a handler for Interrupt 1Bh might set a flag when
the user

presses CTRL+BREAK. The TSR can check the flag as it polls for keyboard
input, as shown here:

    BrkHandler PROC FAR              ; Handler for Interrupt 1Bh

            mov     BreakFlag, TRUE  ; Raise break flag
            iret                     ; Terminate interrupt

    BrkHandler ENDP
            .
            .
            .
            mov     BreakFlag, FALSE ; Initialize break flag
    poll:   .
            .
            .
            cmp     BreakFlag, TRUE  ; Keyboard break pressed?
            je      exit             ; If so, break polling loop
            mov     ah, 1
            int     16h              ; Key waiting?
            jnz     poll             ; If not, repeat polling loop


19.5.2  Preserving an Existing Condition

A TSR and its interrupt handlers must preserve register values so that all
registers are returned intact to the interrupted process. This is usually
done by pushing the registers onto the stack before changing them, then
popping the original values before returning.

Setting up a new stack is another important safeguard against interference.
A TSR should usually provide its own stack to avoid the possibility of
overrunning the current stack. Exceptions to this rule are simple TSRs such
as the sample program ALARM that make minimal stack demands.

A TSR that alters the video configuration should return the configuration to
its original state upon return. Video configuration includes cursor
position, cursor shape, and video mode. The services provided through
Interrupt 10h enable a TSR to determine the existing configuration and alter
it if necessary.

However, some applications set video parameters by directly programming the
video controller. When this happens, BIOS remains unaware of the new
configuration and consequently returns inaccurate information to the TSR.
Unfortunately, there is no solution to this problem if the controller's data
registers provide write-only access and thus cannot be queried directly. For
more information on video controllers, refer to Richard Wilton, Programmer's
Guide to the PC & PS/2 Video Systems. (See "Books for Further Reading" in
the Introduction.)


19.5.3  Preserving Existing Data

A TSR requires its own disk transfer area (DTA) if it calls DOS functions
that access the DTA. These include file control block functions, as well as
Functions 11h, 12h, 4Eh, and 4Fh. The TSR must switch to a new DTA to avoid
overwriting the one belonging to the interrupted process. On becoming
active, the TSR calls Function 2Fh to obtain the address of the current DTA.
The TSR stores the address and then calls Function 1Ah to establish a new
DTA. Before returning, the TSR again calls Function 1Ah to restore the
address of the original DTA.

DOS versions 3.1 and later allow a TSR to preserve extended error
information. This prevents the TSR from destroying the original information
if it commits a DOS error.

The TSR retrieves the current extended error data by calling DOS Function
59h. It then copies registers AX, BX, CX, DX, SI, DI, DS, and ES to an
11-word data structure in the order given. DOS reserves the last three words
of the structure, which should each be set to zero. Before returning, the
TSR calls Function 5Dh, with AL equalling 0Ah and DS:DX pointing to the data
structure. This call restores the extended error data to their original
state.


19.6  Communicating through the Multiplex Interrupt

The Multiplex interrupt (Interrupt 2Fh) provides the Microsoft-approved way
for a program to verify the presence of an installed TSR and to exchange
information with it. DOS version 2.x uses Interrupt 2Fh only as an interface
for the resident print spooler utility PRINT.COM. Later DOS versions
standardize calling conventions so that multiple TSRs can share the
interrupt.

A TSR chains to the Multiplex interrupt by setting up a handler. The TSR's
installation code records the Interrupt 2Fh vector and then replaces it with
the address of the new multiplex handler.


19.6.1  The Multiplex Handler

A program communicates with a multiplex handler by calling Interrupt 2Fh
with an identity number in the AH register. As each handler in the chain
gains control, it compares the value in AH with its own identity number. If
the handler finds that it is not the intended recipient of the call, it
passes control to the previous handler. The process continues until control
reaches the target handler. When the target handler finishes its tasks, it
returns via an IRET instruction to terminate the interrupt.

The target handler determines its tasks from the function number in AL.
Convention reserves Function 0 as a request for installation status. A
multiplex handler must respond to Function 0 by setting AL to 0FFh, to
inform the caller of the handler's presence in memory. The handler should
also return other information to provide a completely reliable
identification. For example, it might return in ES:BX a far pointer to the
TSR's copyright notice. This assures the caller it has located the intended
TSR and not another TSR that has already claimed the identity number in AH.


Identity numbers range from 192 to 255, since DOS reserves lesser values for
its own use. During installation, a TSR must verify the uniqueness of its
number. It must not set up a multiplex handler identified by a number
already in use. A TSR usually obtains its identity number through one of the
following methods:


    ■   The programmer assigns the number in the program.

    ■   The user chooses the number by entering it as an argument in the
        command line, placing it into an environment variable, or by altering
        the contents of an initialization file.

    ■   The TSR selects its own number through a process of trial and error.


The last method offers the most flexibility. It finds an identity number not
currently in use among the installed multiplex handlers and does not require
intervention from the user.

To use this method, a TSR calls Interrupt 2Fh during installation, with AH =
192 and AL = 0. If the call returns AL = 0FFh, the program tests other
registers to determine if it has found a prior installation of itself. If
the test fails, the program resets AL to zero, increments AH to 193, and
again calls Interrupt 2Fh. The process repeats with incrementing values in
AH until the TSR locates a prior installation of itself─in which case it
should abort with an appropriate message to the user─or until AL returns as
zero. The TSR can then use the value in AH as its identity number and
proceed with installation.

The SNAP.ASM program in Section 19.8 demonstrates how a TSR can use this
trial-and-error method to select a unique identity number. During
installation, the program calls Interrupt 2Fh to verify that SNAP is not
already installed. When deinstalling, the program again calls Interrupt 2Fh
to locate the resident TSR in memory. SNAP's multiplex handler services the
call and returns the address of the resident code's program-segment prefix.
The calling program can then locate the resident code and deinstall it, as
explained in Section 19.7.


19.6.2  Using the Multiplex Interrupt Under DOS Version 2.x

A TSR can use the Multiplex interrupt under DOS version 2.x with certain
limitations. Under version 2.x, only DOS's print spooler PRINT, itself a TSR
program, provides an Interrupt 2Fh service. The Interrupt 2Fh vector remains
null until PRINT or another TSR is installed that sets up a multiplex
handler.

Therefore, a TSR running under version 2.x must first check the existing
Interrupt 2Fh vector before installing a multiplex handler. The TSR locates
the current Interrupt 2Fh handler through Function 35h (Get Interrupt
Vector). If the function returns a null vector, the TSR's handler will be
last in the chain of Interrupt 2Fh handlers. The handler must terminate with
an IRET instruction rather than pass control to a nonexistent routine.

PRINT in DOS version 2.x does not pass control on to the previous handler.
If the user intends to run PRINT under version 2.x, the program must be
installed before other TSRs that also handle Interrupt 2Fh. This places
PRINT's multiplex handler last in the chain of handlers.


19.7  Deinstalling TSRs

A TSR should provide a means for the user to remove or "deinstall" it from
memory. Deinstallation returns occupied memory to the system, offering these
benefits:


    ■   The freed memory becomes available to subsequent programs which may
        require additional memory space.

    ■   Deinstallation restores the system to a normal state. This allows
        sensitive programs that may be incompatible with TSRs a chance to
        execute without the presence of installed routines.


A deinstallation program must first locate the TSR in memory, usually by
requesting an address from the TSR's multiplex handler. When it has located
the TSR, the deinstallation program should then compare addresses in the
vector table with the addresses of the TSR's handlers. A mismatch indicates
that another TSR has chained a handler to the interrupt routine. In this
case, the deinstallation program should deny the request to deinstall. If
the addresses of the TSR's handlers match those in the vector table,
deinstallation can safely continue.

Deinstall the TSR in three steps:


    1.  Restore to the vector table the original interrupt vectors replaced by
        the handler addresses.

    2.  Read the segment address stored at offset 2Ch of the resident TSR's
        program segment prefix (PSP). This address points to the TSR's
        "environment block," a list of environment variables that DOS copies
        into memory when it loads a program. Place the block's address in the
        ES register and call DOS Function 49h (Release Memory Block) to return
        the block's memory to the operating system.

    3.  Place the resident PSP segment address in ES and again call Function
        49h. This call releases the block of memory occupied by the TSR's code
        and data.


The example program in the next section demonstrates how to locate a
resident TSR through its multiplex handler and deinstall it from memory.


19.8  Example of an Advanced TSR: SNAP

This section presents SNAP, a memory-resident program that demonstrates most
of the techniques discussed in the chapter. SNAP takes a snapshot of the
current screen and copies the text to a specified file. SNAP accommodates
screens with various column and line counts, such as CGA's 40-column mode or
VGA's 50-line mode. The program ignores graphics screens.

Once installed, SNAP occupies approximately 7.5K (kilobytes) of memory. When
it detects the ALT+LEFT SHIFT+S key combination, SNAP displays a prompt for
a file specification. The user can type a new file name, accept the previous
file name by pressing ENTER, or press ESC to cancel the request.

SNAP reads text directly from the video buffer and copies it to the
specified file. The program sets the file pointer to the end of the file so
that text is appended without overwriting previous data. SNAP copies each
line only to the last character, ignoring trailing spaces. The program adds
a carriage return-linefeed sequence (0D0Ah) to the end of each line. This
makes the file accessible to any text editor that can read ASCII files.

To demonstrate how a program accesses resident data through the Multiplex
interrupt, SNAP can reset the display attribute of its prompt box. After
installing SNAP, run the main program with the /C option to change box
colors:

    SNAP /Cxx

The argument xx specifies the desired attribute as a two-digit hexadecimal
number─for example, 7C for red on white, or 0F for monochrome high
intensity. For a list of color and monochrome display attributes, refer to a
description of Basic's COLOR command or to the "Tables" section of the Macro
Assembler Reference.

SNAP can deinstall itself, provided another TSR has not been loaded after
it. Deinstall SNAP by executing the main program with the /D option:

    SNAP /D

If SNAP successfully deinstalls, it displays the following message:

    TSR deinstalled


19.8.1  Building SNAP.EXE

SNAP combines four modules: SNAP.ASM, COMMON.ASM, HANDLERS.ASM, and
INSTALL.ASM. Source files are located on one of your distribution disks.
Each module stores temporary code and data in the segments INSTALLCODE and
INSTALLDATA. These segments apply only to SNAP's installation phase; DOS
recovers the memory they occupy when the program exits through the
terminate-and-stay-resident function. The following briefly describes each
module:


    ■   SNAP.ASM contains the TSR's main code and data.

    ■   COMMON.ASM contains procedures used by other example programs.

    ■   HANDLERS.ASM contains interrupt handler routines for Interrupts 08,
        09, 10h, 13h, 15h, 28h, and 2Fh. It also provides simple
        error-trapping handlers for Interrupts 1Bh, 23h, and 24h. Additional
        routines set up and deinstall the handlers.

    ■   INSTALL.ASM contains an exit routine that calls the
        terminate-and-stayresident function and a deinstallation routine that
        removes the program from memory. The module includes error-checking
        services and a command-line parser.


This building-block approach allows you to create other TSRs by replacing
SNAP.ASM and linking with the HANDLERS and INSTALL object modules. The
library of routines accommodates both keyboard-activated and timeactivated
TSRs. A time-activated TSR is a program that activates at a predetermined
time of day, similar to the example program ALARM introduced in Section
19.3. The header comments for the  Install  procedure in HANDLERS.ASM
explain how to install a time-activated TSR.

You can write new TSRs in assembly language or any high-level language that
conforms to the Microsoft conventions for ordering segments. Regardless of
the language, the new code must not invoke a DOS function that sets up the
I/O stack (see Section 19.4.3). Code in Microsoft C, for example, must not
call getche or kbhit, since these functions in turn call DOS Functions 01
and 0Bh.

Code written in a high-level language must not check for stack overflows.
Compiler-generated stack probes do not recognize the new stack setup when
the TSR executes, and therefore must be disabled. The example program
BELL.C, included on disk with the TSR library routines, demonstrates how to
disable stack checking in Microsoft C using the check_stack pragma.


19.8.2  Outline of SNAP

The following sections outline in detail how SNAP works. Each part of the
outline covers a specific portion of SNAP's code. Headings refer to earlier
sections of this chapter, providing cross-references to SNAP's key
procedures. For example, the part of the outline that describes how SNAP
searches for its start-up signal refers to Section 19.2.1, "Auditing
Hardware Events for TSR Requests."

Figures 19.2 through 19.4 are flow charts of the SNAP program. Each chart
illustrates a separate phase of SNAP's operation, from installation through
memory-residency to deinstallation.

(This figure may be found in the printed book.)

(This figure may be found in the printed book.)

(This figure may be found in the printed book.)

As you read through the following outline, you may wish to refer to the flow
charts. They will help you maintain a larger perspective while exploring the
details of SNAP's operation. Discussions in the outline cross-reference the
charts.

Note that information in both the outline and the flow charts is generic.
Except for references to the SNAP procedure, all descriptions in the outline
and the flow charts apply to any TSR created with the HANDLERS and INSTALL
modules.


Auditing Hardware Events for TSR Requests

To search for its start-up signal, SNAP audits the keyboard with an
interrupt handler for either Interrupt 09 (keyboard) or Interrupt 15h
(Miscellaneous System Services). See Section 19.2.1 for information on this
topic. The  Install  procedure determines which of the two interrupts to
handle based on the following code:

    .IF     HotScan == 0    ; If valid scan code given:
            mov     ah, HotShift    ; AH = hour to activate
            mov     al, HotMask     ; AL = minute to activate
            call    GetTimeToElapse ; Get number of 5-second intervals
            mov     CountDown, ax   ;  to elapse before activation

            .ELSE                   ; Force use of KeybrdMonitor as
                                    ;  keyboard handler
            cmp     Version, 031Eh  ; DOS Version 3.3 or higher?
            jb      setup           ; No?  Skip next step

    ; Test for IBM PS/2 series. If not PS/2, use Keybrd and
    ; SkipMiscServ as handlers for Interrupts 09 and 15h
    ; respectively. If PS/2 system, set up KeybrdMonitor as the
    ; Interrupt 09 handler. Audit keystrokes with MiscServ
    ; handler, which searches for the hot key by handling calls
    ; to Interrupt 15h (Miscellaneous System Services). Refer to
    ; Section 19.2.1 for more information about keyboard handlers.

            mov     ax, 0C00h       ; Function 0Ch (Get System
            int     15h             ;  Configuration Parameters)
            sti                     ; Compaq ROM may leave disabled

            jc      setup           ; If carry set,
            or      ah, ah          ;  or if AH not 0,
            jnz     setup           ;  services are not supported

    ; Test bit 4 to see if Intercept is implemented
            test    BYTE PTR es:[bx+5], 00010000y
            jz      setup

    ; If so, set up MiscServ as Interrupt 15h handler
            mov     ax, OFFSET MiscServ
            mov     WORD PTR intMisc.NewHand, ax
            .ENDIF

    ; Set up KeybrdMonitor as Interrupt 09 handler
            mov     ax, OFFSET KeybrdMonitor
            mov     WORD PTR intKeybrd.NewHand, ax

This is the code's logic:


    ■   If the program is running under DOS version 3.3 or higher and if
        Interrupt 15h supports Function 4Fh, set up handler  MiscServ  to
        search for the hot key. Handle Interrupt 09 with  KeybrdMonitor  only
        to maintain the keyboard active flag.

    ■   Otherwise, set up a handler for Interrupt 09 to search for the hot
        key. Handle calls to Interrupt 15h with the routine  SkipMiscServ,
        which contains this single instruction:

        jmp     cs:intMisc.OldHand

        The jump immediately passes control to the original Interrupt 15h
        routine; thus, SkipMiscServ  has no effect. It serves only to simplify
        coding in other parts of the program.


At each keystroke, the keyboard interrupt handler (either  Keybrd  or
MiscServ) calls the procedure  CheckHotKey  with the scan code of the
current key.  CheckHotKey  compares the scan code and shift status with the
bytes  HotScan  and  HotShift. If the current key matches, CheckHotKey
returns the carry flag clear to indicate that the user has pressed the hot
key.

If the keyboard handler finds the carry flag clear, it sets the flag
TsrRequestFlag  and exits. Otherwise, the handler transfers control to the
original interrupt routine to service the interrupt.

The timer handler  Clock  reads the request flag at every occurrence of the
timer interrupt.  Clock  takes no action if it finds a zero value in
TsrRequestFlag. Figures 19.1 and 19.3 depict the relationship between the
keyboard and timer handlers.


Monitoring System Status

Because SNAP produces output to both video and disk, it avoids interrupting
either video or disk operations. The program uses interrupt handlers  Video
and DiskIO  to monitor Interrupts 10h (video) and 13h (disk). SNAP also
avoids interrupting keyboard use. The instructions at the far label
KeybrdMonitor  serve as the monitor handler for Interrupt 09 (keyboard). See
Section 19.2.2 for information on this topic.

The three handlers perform similar functions. Each sets an active flag and
then calls the original routine to service the interrupt. When the service
routine returns, the handler clears the active flag to indicate that the
device is no longer in use.

The BIOS Interrupt 13h routine clears or sets the carry flag to indicate the
operation's success or failure.  DiskIO  therefore preserves the flags
register when returning, as shown here:

    DiskIO  PROC    FAR
            mov     cs:intDiskIO.Flag, TRUE ; Set active flag
    ; Simulate interrupt by pushing flags and far-calling old
    ;  Int 13h routine
            pushf
            call    cs:intDiskIO.OldHand
    ; Clear active flag without disturbing flags register
            mov     cs:intDiskIO.Flag, FALSE
            sti                             ; Enable interrupts
    ; Simulate IRET without popping flags (since services use
    ;  carry flag)
            ret     2
    DiskIO  ENDP

The terminating RET 2 instruction discards the original flags from the stack
when the handler returns.


Determining Whether to Invoke the TSR

The procedure  CheckRequest  determines if the TSR


    ■   Has been requested

    ■   Can safely interrupt the system


Each time it executes, the timer handler  Clock  calls  CheckRequest  to
read the flag  TsrRequestFlag. If  CheckRequest  finds the flag set, it
scans other flags maintained by the TSR's interrupt handlers and by DOS.
These flags indicate the current system status. As the flow chart in Figure
19.3 shows,  CheckRequest  calls  CheckDos  (described below) to determine
the status of the operating system.  CheckRequest  then calls  CheckHardware
    to check hardware status. See Section 19.2.2 for information on this topic.


CheckHardware  queries the interrupt controller to determine if any device
is currently being serviced. It also reads the active flags maintained by
the  KeybrdMonitor,  Video, and  DiskIO  handlers. If the controller,
keyboard, video, and disk are all inactive,  CheckHardware  clears the carry
flag and returns.

CheckRequest  indicates system status with the carry flag. If the procedure
returns the carry flag set, the caller exits without invoking the TSR. A
clear carry signals that the caller can safely execute the TSR.


Determining DOS Activity

As Figure 19.2 shows, the procedure  GetDosFlags  locates the InDos flag
during SNAP's installation phase.  GetDosFlags  calls Function 34h (Get
Address of InDos Flag) and then stores the flag's address in the far pointer
InDosAddr. See Section 19.4.2 for information on this topic.

When called from the  CheckRequest  procedure,  CheckDos  reads InDos to
determine if the operating system is active. Note that  CheckDos  reads the
flag directly from the address in  InDosAddr. It does not call Function 34h
to locate the flag, since it has not yet established whether DOS is active.
This follows from the general rule that interrupt handlers must not call any
DOS function.

The next two sections describe the procedure  CheckDos  more fully.


Interrupting DOS Functions

Figure 19.3 shows that the call to  CheckDos  can initiate either from
Clock  (timer handler) or  Idle  (Interrupt 28h handler). If  CheckDos
finds the InDos flag set, it reacts in different ways depending on the
caller:


    ■   If called from  Clock,  CheckDos  cannot know which DOS function is
        active. In this case, it returns the carry flag set, indicating that
        Clock  must deny the request for the TSR.

    ■   If called from  Idle,  CheckDos  assumes that one of the low-order
        polling functions is active. It therefore clears the carry flag to let
        the caller know the TSR can safely interrupt the function.


See Section 19.4.3 for information on this topic.


Monitoring the Critical Error Flag

The procedure  GetDosFlags  (Figure 19.2) determines the address of the
Critical Error flag. The procedure stores the flag's address in the far
pointer  CritErrAddr. See Section 19.4.4 for information on this topic.

When called from either the  Clock  or  Idle  handlers, CheckDos  reads the
Critical Error flag. A nonzero value in the flag indicates that the Critical
Error Handler (Interrupt 24h) is processing a critical error and the TSR
must not interrupt. In this case,  CheckDos  sets the carry flag and
returns, causing the caller to exit without executing the TSR.


Trapping Errors

As Figure 19.3 shows,  Clock  and  Idle  invoke the TSR by calling the
procedure  Activate. See Section 19.5.1 for information on this topic.
Before calling the main body of the TSR,  Activate  sets up the following
handlers:

Handler Name  For Interrupt                 Receives Control When
────────────────────────────────────────────────────────────────────────────
CtrlBreak     1Bh (CTRL+BREAK Handler)      CTRL+BREAK sequence entered at
                                            keyboard

CtrlC         23h (CTRL+C                   DOS detects a CTRL+C sequence
                Handler)                      from the keyboard or input
                                            stream

CritError     24h (Critical Error Handler)  DOS encounters a critical
                                            error


These handlers trap keyboard break signals and critical errors that would
otherwise trigger the original handler routines. The  CtrlBreak  and  CtrlC
handlers contain a single IRET instruction, thus rendering a keyboard break
ineffective. The  CritError  handler contains the following instructions:

    CritError PROC  FAR
            sti
            sub     al, al          ; Assume DOS 2.x
                                    ; Set AL = 0 for ignore error
            .IF     cs:major != 2   ; If DOS 3.x, set AL = 3
            mov     al, 3           ; DOS call fails
            .ENDIF
            iret
    CritError ENDP

The return code in AL forces DOS to take no further action when it
encounters a critical error.

As an added precaution,  Activate  also calls Function 33h (Get or Set
CTRL+BREAK Flag) to determine the current setting of the checking flag.
Activate  stores the setting, then calls Function 33h again to turn off
break checking.

When the TSR's main procedure finishes its work, it returns to  Activate,
which then restores the original setting for the checking flag. It also
replaces the original vectors for Interrupts 1Bh, 23h, and 24h.

SNAP's error-trapping safeguards enable the TSR to retain control in the
event of an error. Pressing CTRL+BREAK or CTRL+C at SNAP's prompt has no
effect. If the user specifies a nonexistent drive─a critical error─SNAP
merely beeps the speaker and returns normally.


Preserving an Existing Condition

Activate  records the stack pointer SS:SP in the doubleword  OldStackAddr.
The procedure then resets the pointer to the address of a new stack before
calling the TSR. Switching stacks ensures that SNAP has adequate stack depth
while it executes. See Section 19.5.2 for information on this topic.

The label  NewStack  points to the top of the new stack buffer, located in
the code segment of the HANDLERS.ASM module. The equate constant  STACK_SIZ
determines the size of the stack. The include file TSR.INC contains the
declaration for  STACK_SIZ.

Activate  preserves the values in all registers by pushing them onto the new
stack. It does not push DS, since that register is already preserved in the
Clock  or  Idle  handler.

SNAP does not alter the application's video configuration other than by
moving the cursor. Figure 19.3 shows that  Activate  calls the procedure
Snap, which executes Interrupt 10h to determine the current cursor position.
    Snap  stores the row and column in the word  OldPos. The procedure restores
the cursor to its original location before returning to  Activate.


Preserving Existing Data

Because SNAP does not call a DOS function that writes to the DTA, it does
not need to preserve the DTA belonging to the interrupted process. However,
the code for switching and restoring the DTA is included within IFDEF blocks
in the procedure  Activate. The equate constant  DTA_SIZ, declared in the
TSR.INC file, governs the assembly of the blocks as well as the size of the
new DTA. See Section 19.5.3 for information on this topic.

SNAP can potentially overwrite existing extended error information by
committing a file error. The program does not attempt to preserve the
original information by calling Functions 59h and 5Dh. In certain rare
instances, this may confuse the interrupted process after SNAP returns.


Communicating through the Multiplex Interrupt

The program uses the Multiplex interrupt (Interrupt 2Fh) to


    ■   Verify that SNAP is installed

    ■   Select a unique multiplex identity number

    ■   Locate resident data


See Section 19.6 for information on this topic.

SNAP accesses Interrupt 2Fh through the procedure  CallMultiplex, as shown
in Figures 19.2 and 19.4. By searching for a prior installation,
CallMultiplex  ensures that SNAP is not installed more than once. During
deinstallation,  CallMultiplex  locates data required to deinstall the
resident TSR.

The procedure  Multiplex  serves as SNAP's multiplex handler. When it
recognizes its identity number in AH,  Multiplex  determines its tasks from
the function number in the AL register. The handler responds to Function 0
by returning AL equalling 0FFh and ES:DI pointing to an identifier string
unique to SNAP.

CallMultiplex  searches for the handler by invoking Interrupt 2Fh in a loop,
beginning with a trial identity number of 192 in AH. At the start of each
iteration of the loop, the procedure sets AL to zero to request presence
verification from the multiplex handler. If the handler returns 0FFh in AL,
CallMultiplex  compares its copy of SNAP's identifier string with the text
at memory location ES:DI. A failed match indicates that the multiplex
handler servicing the call is not SNAP's handler. In this case,
CallMultiplex  increments AH and cycles back to the beginning of the loop.

The process repeats until the call to Interrupt 2Fh returns a matching
identifier string at ES:DI or until AL returns as zero. A matching string
verifies that SNAP is installed, since its multiplex handler has serviced
the call. A return value of zero indicates that SNAP is not installed and
that no multiplex handler claims the trial identity number in AH. In this
case, SNAP assigns the number to its own handler.


Deinstalling TSRs

During deinstallation,  CallMultiplex  locates SNAP's multiplex handler as
described above. The handler  Multiplex  receives the verification request
and returns in ES the code segment of the resident program. See Section 19.7
for information on this topic.

Deinstall  reads the addresses of the following interrupt handlers from the
data structure in the resident code segment:

Handler Name                      Description
────────────────────────────────────────────────────────────────────────────
Clock                             Timer handler

Keybrd                            Keyboard handler (non-PS/2)

KeybrdMonitor                     Keyboard monitor handler (PS/2)

Video                             Video monitor handler

DiskIO                            Disk monitor handler

SkipMiscServ                      Miscellaneous Systems Services handler
                                    (non-PS/2)

MiscServ                          Miscellaneous Systems Services handler
                                    (PS/2)

Idle                              DOS Idle handler

Multiplex                         Multiplex handler

Deinstall  calls DOS Function 35h (Get Interrupt Vector) to retrieve the
current vectors for each of the listed interrupts. By comparing each handler
address with the corresponding vector,  Deinstall  ensures that SNAP can be
safely deinstalled. Failure in any of the comparisons indicates that another
TSR has been installed after SNAP and has set up a handler for the same
interrupt. In this case,  Deinstall  returns an error code, causing the
program to abort with the following message:

    Can't deinstall TSR

If all addresses match,  Deinstall  calls Interrupt 2Fh with SNAP's identity
number in AH and AL set to 1. The handler  Multiplex  responds by returning
in ES the address of the resident code's PSP.  Deinstall  then calls DOS
Function 25h (Set Interrupt Vector) to restore the vectors for the original
service routines. This is called "unhooking" or "unchaining" the interrupt
handlers.

After unhooking all of SNAP's interrupt handlers,  Deinstall  returns with
AX pointing to the resident code's PSP. The procedure  FreeTsr  then calls
DOS Function 49h (Release Memory) to return SNAP's memory to the operating
system. The program terminates with the message

    TSR deinstalled

to indicate a successful deinstallation.

Deinstalling SNAP does not guarantee more available memory space for the
next program. If another TSR loads after SNAP but handles interrupts other
than 08, 09, 10h, 13h, 15h, 28h, or 2Fh, SNAP still deinstalls properly. The
result is a harmless gap of deallocated memory formerly occupied by SNAP.
DOS can use the free memory to store the next program's environment block.
However, DOS loads the program itself above the still-resident TSR.


19.9  Related Topics in Online Help

In addition to information covered in this chapter, information on the
following topics can be found in online help.

Topic                             Access
────────────────────────────────────────────────────────────────────────────
DOS and BIOS function calls       From the "MASM 6.0 Contents" screen,
                                    choose "DOS Calls" or "BIOS Calls" from
                                    the list of "System Resources"

Processor Flags                   From the "MASM 6.0 Contents" screen,
                                    choose "Language Overview" and then
                                    choose "Processor Flag Summary"

IN, OUT                           From the "MASM 6.0 Contents" screen,
                                    choose "Processor Instructions" and then
                                    choose "System and I/O Access"







Chapter 20  Mixed-Language Programming
────────────────────────────────────────────────────────────────────────────

Mixed-language programming allows you to combine the unique strengths of
Microsoft Basic, C, FORTRAN, and Pascal with your assembly-language
routines. Any one of these languages can call MASM routines, and you can
call any of these languages from within MASM routines. This makes virtually
all of the routines from extensive high-level-language libraries available
to a mixedlanguage program.

MASM 6.0 has a number of new features that make the interface in
assemblylanguage programs similar to the interface in high-level-language
programs. For example, you can now use the INVOKE directive to call
high-level-language procedures, and the assembler handles the
argument-passing details for you. You can also use H2INC to translate C
header files to MASM include files (see Chapter 16).

The new mixed-language features do not make the older methods of defining
mixed-language interfaces obsolete. In most cases mixed-language programs
written with previous versions of MASM will assemble and link correctly
under MASM 6.0. (See Appendix A for more information.)

This chapter explains how to write assembly routines that can be called from
high-level-language modules and how to call high-level language routines
from MASM. It assumes that you have a basic understanding of the languages
you wish to combine and that you already know how to write, compile, and
link multiple-module programs with these languages.

This chapter is restricted to MASM's interface with C, Basic, FORTRAN, and
Pascal; it does not cover mixed-language programming between high-level
languages. The focus in this chapter is the Microsoft versions of C, Basic,
FORTRAN, Pascal, and QuickPascal, but the same principles apply to other
languages and compilers. The material in Section 7.3 on writing procedures
in MASM and in Chapter 8 on multiple-module programming explains many of the
techniques used in this chapter.

Section 20.1 looks at naming and calling conventions, and Section 20.2
provides a template for writing the MASM procedure. Specific implementations
of this convention in C, Basic, FORTRAN, and Pascal are described in Section
20.3. These language-specific sections also provide details on how the
language manages various data structures so that your MASM programs are
compatible with the data from the high-level language. This chapter also
contains examples of MASM procedures called from C, FORTRAN, Basic, Pascal,
and QuickPascal.


20.1  Naming and Calling Conventions

The naming convention specifies the way the compiler or assembler alters the
name of the routine or identifier before placing it into an object file.
Each language alters the name of the identifiers. You must be sure that the
naming conventions for mixed-language programming are compatible.

A calling convention specifies the way a language implements a call to a
procedure. MASM implements mixed-language calls according to the particular
calling convention specified in the procedure declaration or prototype.

MASM supports three different calling conventions. The assembler uses the C
calling convention when the langtype is C or SYSCALL; it uses the Pascal
calling convention when the langtype is PASCAL, BASIC, or FORTRAN; and it
uses the STDCALL calling convention when the langtype is STDCALL. To MASM,
BASIC, PASCAL, and FORTRAN are synonymous when specifying the Pascal calling
convention for a procedure.

There are several ways to set the calling convention. Using .MODEL with a
langtype sets the default for the module. You can also use the OPTION
directive to do the same. This is equivalent to the /Gc or /Gd option from
the command line. Procedure prototypes and declarations can specify a
langtype to override the default.

You can change the default calling convention.

When you write mixed-language routines, the easiest way to ensure calling
convention compatibility is to adopt the calling conventions of the language
of the called procedure. However, Microsoft languages (except QuickPascal)
can change their calling conventions, so at times you may want to change the
calling convention to use a particular argument-passing method instead of
the defaults for a particular language. Section 20.4 explains how to change
the calling convention. The fastcall calling convention is not directly
supported by the assembler. This section provides more detail on the
information summarized in Table 20.1:

Table 20.1  Naming and Calling Conventions

╓┌─────────────────────────┌─────┌────────┌────────┌────────┌────────┌───────╖
Convention                dddC  SYSCALL  STDCALL  B BASIC  FORTRAN  PASCAL
Convention                dddC  SYSCALL  STDCALL  B BASIC  FORTRAN  PASCAL
────────────────────────────────────────────────────────────────────────────
Leading                   dddX           ddddX
underscore

Capitalize all                                    BA BX    FORX     PA X

Arguments pushed left to                          BS    X  FORX     PA X
right

Arguments pushed right    dddX  SYSX     ddddX
to left

Caller stack cleanup      dddX           dddd*

:VARARG allowed           dddX  SYSX     ddddX

────────────────────────────────────────────────────────────────────────────



* The STDCALL language type uses caller stack cleanup if the :VARARG
parameter is used. Otherwise, the called routine must clean up the stack.



20.1.1  Naming Conventions

The naming convention determines the way the compiler or assembler stores
identifiers. If you set the LINK command-line option /NOI, then the names of
public variables or called routines are stored differently in the object
modules being linked. As a result, LINK will not be able to find a match. It
will instead report unresolved external references. Therefore, you must use
valid identifiers for each language and be sure the naming convention for
the linked modules is the same.

The C naming convention is used when the langtype is C or STDCALL, the
SYSCALL naming convention is used when the langtype is SYSCALL, and the
Pascal naming convention is used when the langtype is PASCAL, BASIC, or
FORTRAN. The list below describes each convention. For example, assume you

have a variable named  Big Time  in your source code. The list below shows
the result of each convention applied to this variable.

Langtype Specified                Characteristics
────────────────────────────────────────────────────────────────────────────
C, STDCALL                        The assembler and the compiler add
                                    leading underscores to the names seen by
                                    the linker. They do not translate case.
                                    The linker sees the variable as  _Big
                                    Time.

SYSCALL                           Leaves the name unmodified. The linker
                                    sees the variable as  Big Time.

PASCAL, FORTRAN, BASIC            Converts all names to uppercase. The
                                    linker sees the variable as  BIG TIME.


20.1.2  The C Calling Convention

C and SYSCALL are identical as calling conventions.

You must specify the C calling convention for MASM routines that link with C
modules using the default calling convention. You can change the default
calling convention for FORTRAN, Basic, and Pascal routines to the C calling
convention, if you prefer. The characteristics of the C calling convention
are summarized below.

Because the C calling convention allows for a variable number of arguments
to be passed to the procedure, you may want to use this convention when you
need this flexibility.

When you specify SYSCALL for the langtype, the C calling convention is used,
but a leading underscore is not added to the name of the global routine (see
the next section). SYSCALL is provided for compatibility with system calls
in OS/2 version 2.0.

Argument Passing  - With the C calling convention, the caller pushes
arguments from right to left. The assembler places arguments on the stack in
the reverse of the order that they appear in the source code. The first
argument is lowest in memory (because it is the last argument to be placed
on the stack, and the stack grows downward). The code to remove arguments
from the stack follows the procedure call, so the caller pops arguments off
the stack.

Register Preservation - The called routine should save BP, SI, DI, DS, and
SS if they are modified.

C and SYSCALL allow a variable number of arguments.

Varying Number of Arguments - Because the first argument is always the last
one pushed, it is always on the top of the stack. Thus, it has the same
address relative to the frame pointer, regardless of how many arguments were
actually passed. Therefore, calling procedures with a variable number of
arguments are possible. If the high-level-language procedure uses the C
calling convention and expects a variable number of arguments, the prototype
for the function must end with :VARARG. See Section 7.3.3, "Declaring
Parameters with the PROC Directive," for information on using PROC and
INVOKE with VARARG.


20.1.3  The Pascal Calling Convention

By default, the FORTRAN, BASIC, and PASCAL langtype select the Pascal
calling convention. This convention pushes arguments left to right so that
the last argument is lowest on the stack, and it requires that the called
routine remove arguments from the stack. Section 20.3.4 explains the Pascal
naming convention.

Argument Passing  - Arguments are placed on the stack in the same order in
which they appear in the source code. The first argument is highest in
memory (because it is also the first argument to be placed on the stack),
and the stack grows downward.

Register Preservation - Routines using the Pascal calling convention must
preserve SI, DI, BP, and DS and not modify SS. (This does not apply to
procedures called by QuickPascal. See Section 20.3.5.) For 32-bit code, the
EBX, ES, FS, and GS registers must be preserved as well as EBP, ESI, and
EDI. The direction flag is also cleared upon entry and must be preserved.

Varying Number of Arguments - Passing a variable number of arguments is not
possible with the Pascal calling convention.


20.1.4  The Standard Calling Convention

The STDCALL calling convention is the same as the C calling convention, with
the exception that the responsibility for removing arguments from the stack
belongs to the called routine. The C calling convention is followed exactly
if the STDCALL procedure also specifies VARARG, allowing a variable number
of parameters. STDCALL is provided for compatibility with 32-bit versions of
Microsoft compilers which have STDCALL as their default.

Argument Passing - Argument passing order is the same as the C calling
convention. The caller pushes the arguments from right to left. Unlike the C
calling convention, however, the called routine must remove arguments from
the stack unless the routine uses VARARG to specify a variable number of
arguments, in which case the caller removes the parameters from the stack.

Register Preservation - Routines using the STDCALL convention must preserve
the same registers required by the C calling convention: BP, SI, DI, DS, and
SS. The direction flag is also cleared on entry and must be preserved.

Varying Number of Arguments - If the routine uses VARARG to specify that a
variable number of arguments can be passed, the calling routine must remove
arguments from the stack.


20.2  Writing the Assembly-Language Procedure

MASM 6.0 simplifies the coding required for linking MASM routines to
high-level-language routines. You can use the new PROTO directive to write
procedure prototypes, and the new INVOKE directive to call external
routines. This list summarizes the ways MASM simplifies procedure-related
tasks.


    ■   The PROTO directive improves error checking on argument types.

    ■   INVOKE pushes arguments onto the stack and converts argument types to
        types expected when possible. These arguments can be referenced by
        their parameter label, rather than as offsets of the stack pointer.

    ■   The LOCAL directive following the PROC statement saves places on the
        stack for local variables. These variables can also be referenced by
        name, rather than as offsets of the stack pointer.

    ■   PROC sets up the appropriate stack frame according to the processor
        mode.

    ■   The USES keyword preserves registers given as arguments.

    ■   The C calling conventions specified in the PROC syntax allow for a
        variable number of arguments to be passed to the procedure.

    ■   The RET keyword adjusts the stack upward by the number of bytes in the
        argument list, removes local variables from the stack, and pops saved
        registers.

    ■   The PROC statement lists parameter names and types. The parameters can
        be referenced by name inside the procedure.


The complete syntax and parameter descriptions for these procedure
directives are explained in Section 7.3, "Procedures." This section
summarizes information from Section 7.3 by giving a template you can use for
writing a MASM routine to be called from a high-level language.

The template looks like this:

Label PROC «distance langtype visibility <prologueargs> USES reglist
parmlist»  LOCAL varlist     RET Label ENDP

Replace the italicized words with appropriate keywords, registers, or
variables as defined by the syntax in Section 7.3.3, "Declaring Parameters
with the PROC Directive."

The distance (NEAR or FAR) and visibility (PUBLIC, PRIVATE, or EXPORT) that
you give in the procedure declaration override the current defaults. In some
languages, the model can also be specified with command-line options.

The langtype determines the calling convention for accessing arguments and
restoring the stack. See Section 20.1 for information on calling
conventions.

The types for the parameters listed in the parmlist must be given. Also, if
any of the parameters are pointers, the assembler does not generate code to
get the value of the pointer references. You must write this code yourself.
An example of how to do this is in Section 7.3.3.

If you need to code your own stack-frame setup manually, or if you do not
want the assembler to generate the standard stack setup and cleanup, see
Section 7.3.2, "Passing Arguments on the Stack," and, in Section 7.3.8.2,
"User-Defined Prologue and Epilogue Code."


20.3  The MASM/High-Level-Language Interface

Since high-level-language routines require certain program initialization
code, the main program for a mixed-language program must be written in the
high-level language, or you must add  EXTERN A__ACRTUSED  to your program to
force the start-up code from the high-level-language run times to be loaded.
Once the high-level-language code calls an assembly routine, the assembly
routine can then call high-level-language routines as needed.

Use INVOKE to call high-level-language procedures.

For procedures with prototypes, INVOKE makes calls from MASM to
high-level-language programs, much like procedure or function calls in the
high-level language. INVOKE calls procedures and generates the code to push
arguments in the order specified by the procedure's calling convention and
to remove arguments from the stack at the end of the procedure.

INVOKE can also do some type checking and data conversion for the argument
types so that the procedure receives compatible data. Section 7.3.6,
"Declaring Procedure Prototypes," explains how to write procedure prototypes
and gives several examples of procedure declarations and the corresponding
prototypes.

Use H2INC to translate C prototypes to MASM.

For programs that mix assembly language and C, the H2INC utility makes it
easy to write prototypes and data declarations for the C procedures you want
to call from MASM. H2INC translates the C prototypes and declarations into
the corresponding MASM prototypes and declarations, which INVOKE can use to
call the procedure. Chapter 16 explains how to use H2INC. See Section 20.3.1
for examples of using H2INC to write prototypes.

Mixed-language programming also allows the main program or a routine to use
external data─data defined in the other module. External data is the data
that is stored in a set place in memory (unlike dynamic and local data,
which is allocated on the stack and heap) and is visible to other modules.

External data is shared by all routines. One of the modules must define the
static data, which causes the compiler to allocate storage for the data. The
other modules that access the data must declare the data as external.

This section describes argument-passing options and the standards for
preserving registers and pushing addresses that are common to all high-level
languages. It also explains the two methods that compilers use to store
arrays─row-major and column-major order.


Argument Passing

Each language has its own convention for how an argument is actually passed.
If the argument-passing conventions of your routines do not agree, then a
called routine receives bad data. Microsoft languages support three
different methods for passing an argument:


    ■   Near reference. Passes a variable's near (offset) address. This
        address is expressed as an offset from the default data segment.

        This method gives the called routine direct access to the variable
        itself. Any change the routine makes to the parameter is reflected in
        the calling routine.

    ■   Far reference. Passes a variable's far (segmented) address.

        This method is similar to passing by near reference, except that an
        address made up of a segment and an offset is passed, and it is
        slower. But it is necessary when you pass data that is outside of the
        default data segment. (This is not an issue in Basic or Pascal unless
        you have specifically requested far memory.)

    ■   Value. Passes only the variable's value, not its address.

        With this method, the called routine gets the copy of the value of the
        argument but has no access to the original variable. Changes to a
        value argument have no effect on the value of the argument in the
        calling routine once the routine terminates.


You can also change the default argument-passing method.

When you pass arguments between MASM and another language, you need to make
sure that the called routine and the calling routine use the same method. In
most cases, you should check the argument-passing defaults used by each
language and make any necessary adjustments. Most languages have features
that allow you to change argument-passing methods.


Register Preservation

A procedure called from any high-level language should preserve the
direction flag and the values of BP, SI, DI, SS, and DS. Routines called
from MASM must not alter SI, DI, SS, DS, or BP.


Pushing Addresses

Microsoft high-level languages push segment addresses before pushing
offsets. This facilitates use of the LES and LDS instructions. Furthermore,
when pushing arguments longer than two bytes, high-order words are always
pushed before low-order words, and arguments longer than two bytes are
stored on the stack from most significant to least significant.


Array Storage

Most high-level-language compilers store arrays in row-major order. This
means that all elements of a row are stored consecutively. The first five
elements of an array with four rows and three columns are stored in
row-major order as

    A[1, 1], A[1, 2], A[1, 3], A[2, 1], A[2, 2]

In column-major order, the column elements are stored consecutively. For
example, the same array defined above would be stored in column-major order
as

    A[1, 1], A[2, 1], A[3, 1], A[4, 1], A[1, 2], A[2, 2]


20.3.1  The C/MASM Interface

This section summarizes the details unique to the C and MASM interface. The
information is accurate for Microsoft C 6.0 and QuickC version 2.5.

With the default naming and calling convention, the assembler (or compiler)
pushes arguments right to left and adds a leading underscore to routine
names.

Compatible Data Types - This list shows the C data types that are equivalent
to the MASM 6.0 data types.

C Type                            Equivalent MASM Type
────────────────────────────────────────────────────────────────────────────
unsigned char                     BYTE

char                              SBYTE

unsigned short, unsigned int      WORD

int, short                        SWORD

unsigned long                     DWORD

float                             REAL4

C Type                            Equivalent MASM Type
────────────────────────────────────────────────────────────────────────────
long                              SDWORD

double                            REAL8

long double                       REAL10

Naming Restrictions - C is case sensitive and does not convert names to
uppercase. Since C normally links with the /NOI command-line option,
assemble MASM modules with the /Cx or /Cp option to prevent the assembler
from converting names to uppercase.

Argument-Passing Defaults - When the C module is compiled in small or medium
model and when a distance is not specified, the C compiler passes arrays by
near reference. In compact, large, or huge model, C arrays are passed by far
reference (if a distance is not explicitly specified). All other types
defined in the C module are passed by value. You can pass by reference if
you specifically pass pointers or addresses.

Changing the Calling Convention - Put _pascal or _fortran in the C function
declaration to specify the Pascal calling convention.

Equivalent Arrays - Array declarations give the number of elements. A1[a][b]
    declares a two-dimensional array in C with  a  rows and  b  columns. By
default, the array's lower bound is zero. Arrays are stored by the compiler
in row-major order. By default, passing arrays from C passes a pointer to
the first element of the array.

String Format - C stores strings as arrays of bytes and uses a null
character as the end-of-string delimiter. For example, consider the string
declared as follows:

    char msg[] = "string of text"

The string occupies 15 bytes of memory as:

(This figure may be found in the printed book.)

Since  msg  is an array of characters, it is passed by reference. To pass by
value, declare the string to be a member of a structure and pass the
structure.

External data can be accessed directly by other modules.

External Data - In C, the extern keyword tells the compiler that the data or
function is external. You can define a static data object in a C module by
defining a data object outside all functions and subroutines. Do not use the
static keyword in C with a data object that you wish to be public.

C structures are word-aligned by default.

Structure Alignment - By default, C uses word alignment (unpacked storage)
for all data objects longer than one byte. This storage method specifies
that occasional bytes may be added as padding, so that word and doubleword
objects start on an even boundary. In addition, all nested structures and
records start on a word boundary. MASM is byte-aligned by default.

When transferring .H files with H2INC, you can use the /Zp command-line
option to specify structure alignment. If the /Zp option is not specified,
H2INC uses word-alignment. Without H2INC, set the alignment to 2 when
declaring the MASM structure, or compile the C module with /Zp1 or the MASM
module with /Zp2.

Compiling and Linking - Use the same memory model for both C and MASM.

Returning Values - The assembler returns simple data types in registers.
Table 20.2 shows the register conventions for returning simple data types to
a C program.

Table   20.2 Register Conventions for Simple Return Values

Data Type                         Registers
────────────────────────────────────────────────────────────────────────────
char                              AL

int, short, near                  AX

long, far                         High-order portion (or segment address)
                                    in DX;
                                    low-order portion (or offset address) in
                                    AX

────────────────────────────────────────────────────────────────────────────


Procedures using the C calling convention and returning type float or type
double store their return values into static variables. In multi-threaded
programs, this could mean that the return value may be overwritten. You can
avoid this by using the Pascal calling convention for multi-threaded
programs so float or double values are passed on the stack.

Your procedures can also return structures.

Structures less than four bytes long are returned in DX:AX. To return a
longer structure from a procedure that uses the C calling convention, you
must copy the structure to a global variable and then return a pointer to
that variable in the AX register (DX:AX, if you compiled in compact, large,
or huge model or if the variable is declared as a far pointer).

Structures, Records, and User-Defined Data Types - You can pass structures,
records, and user-defined types as arguments by value or by reference.

Writing Procedure Prototypes - The H2INC utility simplifies the task of
writing prototypes for the C functions you want to call from MASM. The C
prototype converted by H2INC into a MASM prototype allows INVOKE to
correctly call the C function. Here are some examples of C functions and the
MASM prototypes created with H2INC.

    /* Function Prototype Declarations to Convert with H2INC */

    long checktypes (
            char *name,
    unsigned char a,
    int b,
    float d,
    unsigned int *num );

    my_func (float fNum, unsigned int x);

    extern my_func1 (char *argv[]);

    struct videoconfig _far * _far pascal my_func2 (int, scri );

For the C prototypes above, H2INC generates this code:

    TYPEDEF         PROTO C :PTR SBYTE, :BYTE,
                                            :SWORD, :REAL4, :PTR WORD
    checktypes      PROTO           @proto_0

    @proto_1        TYPEDEF         PROTO C :REAL4, :WORD
    my_func         PROTO           @proto_1

    @proto_2        TYPEDEF         PROTO C :PTR PTR SBYTE
    my_func1        PROTO           @proto_2

    @proto_3        TYPEDEF         PROTO FAR PASCAL :SWORD, :scri
    my_func2        PROTO           @proto_3

Example - As shown in the short example below, the main module (written in
C) calls an assembly routine,  Power2.

    #include <stdio.h>

    extern int Power2( int factor, int power );

    void main()
    {
        printf( "3 times 2 to the power of 5 is %dn", Power2( 3, 5 )
    );
    }

Figure 20.2 shows how functions that observe the C calling convention use
the stack frame.

(This figure may be found in the printed book.)

The MASM module that contains the  Power2  routine looks like this:

    .MODEL  small, c

    Power2  PROTO C factor:SWORD, power:SWORD
            .CODE

    Power2  PROC  C factor:SWORD, power:SWORD
            mov     ax, factor    ; Load Arg1 into AX
            mov     cx, power     ; Load Arg2 into CX
            shl     ax, cl        ; AX = AX * (2 to power of CX)
                                ; Leave return value in AX
            ret
    Power2  ENDP
    END

The MASM procedure declaration for the  Power2  routine specifies the C
langtype and the parameters expected by the procedure. The langtype
specifies the calling and naming conventions for the interface between MASM
and C. The routine is public by default. When the C module calls  Power2, it
passes two arguments,  3  and  5 by value.

The C module first defines a prototype for the MASM routine. MASM 6.0 also
supports prototyping of procedures and functions. See Section 7.3.6,
"Declaring Procedure Prototypes," and the examples in this section.


20.3.2  The FORTRAN/MASM Interface

This section summarizes the specific details important to calling FORTRAN
procedures or receiving arguments from FORTRAN routines that call MASM
routines. It includes a sample MASM and FORTRAN module. A FORTRAN procedure
follows the Pascal calling convention by default. This convention passes
arguments in the order listed, and the calling procedure removes the
arguments from the stack. The naming convention determines that exported
names are uppercase.

Compatible Data Types - This list shows the FORTRAN data types that are
equivalent to the MASM 6.0 data types.

FORTRAN Type                      Equivalent MASM Type
────────────────────────────────────────────────────────────────────────────
CHARACTER*1                       BYTE

INTEGER*1                         SBYTE

INTEGER*2                         SWORD

REAL*4                            REAL4

INTEGER*4                         SDWORD

REAL*8, DOUBLE PRECISION          REAL4

Naming Restrictions - FORTRAN allows 31 characters for identifier names. A
digit or an underscore cannot be the first character in an identifier name.

Argument-Passing Defaults - By default, FORTRAN passes arguments by
reference as far addresses if the FORTRAN module is compiled in large or
huge memory model. It passes them as near addresses if the FORTRAN module is
compiled in medium model. Versions of FORTRAN prior to Version 4.0 always
requires large model.

The FORTRAN compiler passes an argument by value when declared with the
VALUE attribute. This declaration can occur either in a FORTRAN INTERFACE
block (which determines how to pass an argument) or in a function or
subroutine declaration (which determines how to receive an argument).

In FORTRAN you can apply the NEAR (or FAR) attribute to reference
param-eters. These keywords override the default. They have no effect when
they specify the same method as the default.

Changing the Calling Convention - A call to a FORTRAN function or subroutine
declared with the PASCAL or C attribute passes all arguments by value in the
parameter list (except for parameters declared with the REFERENCE
attribute). This change in default passing method applies to function and
subroutine definitions as well as to the functions and subroutines described
by INTERFACE blocks.

Equivalent Arrays - When you declare FORTRAN arrays, you can specify any
integer for the lower bound (the default is 1). The FORTRAN compiler

stores all arrays in column-major order─that is, the leftmost subscript
increments most rapidly. For example, the first seven elements of an array
defined as  A[3,4]  are stored as

    A[1,1], A[2,1], A[3,1], A[1,2], A[2,2], A[3,2], A[1,3]

FORTRAN strings do not have an end-of-string delimiter.

String Format  - FORTRAN stores strings as a series of bytes at a fixed
location in memory, with no delimiter at the end of the string. When passing
a variable-length FORTRAN string to another language, you need to devise a
method by which the target routine can find the end of the string.

Consider the string declared as

    CHARACTER*14 MSG

    MSG = 'String of text'

The string is stored in 14 bytes of memory like this:

(This figure may be found in the printed book.)

Strings are passed by reference. Although FORTRAN has a method for passing
length, the variable-length FORTRAN strings cannot be used in a
mixedlanguage interface because other languages cannot access the temporary
variable that FORTRAN uses to communicate string length. However,
fixed-length strings can be passed if the FORTRAN INTERFACE statement
declares the length of the string in advance.

External Data - FORTRAN routines can directly access external data. In
FORTRAN you can declare data to be external by adding the EXTERN attribute
to the data declaration. You can also access a FORTRAN variable from MASM if
it is declared in a COMMON block.

A FORTRAN program can call an external assembly procedure with the use of
the INTERFACE statement. However, the INTERFACE statement is not strictly
necessary unless you intend to change one of the FORTRAN defaults.

Structure Alignment - By default, FORTRAN uses word alignment (packed
storage) for all data objects larger than one byte. This storage method
specifies that occasional bytes may be added as padding, so that word and
doubleword objects start on an even boundary. In addition, all nested
structures and records start

on a word boundary. MASM's default is byte-alignment, so specify an
alignment of 2 for MASM structures or use the /Zp1 option when compiling in
FORTRAN.

Compiling and Linking - Use the same memory model for the MASM and FORTRAN
modules.

Returning Values - You must use a special convention to return
floating-point values, records, user-defined types, arrays, and values
larger than four bytes to a FORTRAN module from an assembly procedure. The
FORTRAN module creates space in the stack segment to hold the actual return
value. When the call to the assembly procedure is made, an extra parameter
is passed. This parameter is the last one pushed. The segment address of the
return value is contained in SS.

In the assembly procedure, put the data for the return value at the location
pointed to by the return value offset. Then copy the return-value offset
(located at BP + 6) to AX, and copy SS to DX. This is necessary because the
calling module expects DX:AX to point to the return value.

Structures, Records, and User-Defined Data Types - The FORTRAN structure
variable, defined with the STRUCTURE keyword and declared with the RECORD
statement, is equivalent to the Pascal RECORD and the C struct. You can pass
structures as arguments by value or by reference (the default).

MASM structures can be compatible with FORTRAN COMPLEX types.

The FORTRAN types COMPLEX*8 and COMPLEX*16 are not directly implemented in
MASM. However, you can write structures that are equivalent. The type
COMPLEX*8 has two fields, both of which are four-byte floating-point
numbers; the first contains the real component, and the second contains the
imaginary component. The type COMPLEX is equivalent to the type COMPLEX*8.

The type COMPLEX*16 is similar to COMPLEX*8. The only difference is that
each field of the former contains an eight-byte floating-point number.

A FORTRAN LOGICAL*2 is stored as a one-byte indicator value (1=true,
0=false) followed by an unused byte. A FORTRAN LOGICAL*4 is stored as a
one-byte indicator value followed by three unused bytes. The type LOGICAL is
equivalent to LOGICAL*4, unless $STORAGE:2 is in effect.

To pass or receive a FORTRAN LOGICAL type, declare a MASM structure with the
appropriate fields.

Varying Number of Arguments  - In FORTRAN, you can call routines with a
variable number of arguments by including the VARYING attribute in your
interface to the routine, along with the C attribute. You must use the C
attribute because a variable number of arguments is possible only with the C
calling convention. The VARYING attribute prevents FORTRAN from enforcing a
matching number of parameters.

LOCNEAR and LOCFAR determine addresses.

Pointers and Addresses - FORTRAN programs can determine near and far
addresses with the LOCNEAR and LOCFAR functions. Store the result as
INTEGER*2 (with the LOCNEAR function) or as INTEGER*4 (with the  LOCFAR
function). If you pass the result of LOCNEAR or LOCFAR to another language,
be sure to pass by value.

Example - In the following example, the FORTRAN module calls an assembly
procedure that calculates  A*2^B, where  A  and  B  are the first and second
parameters, respectively. This is done by shifting the bits in  A  to the
left  B  times.

    INTERFACE TO INTEGER*2 FUNCTION POWER2(A, B)
        INTEGER*2 A, B
        END

        PROGRAM MAIN
        INTEGER*2 POWER2
        INTEGER*2 A, B
        A = 3
        B = 5
        WRITE (*, *) '3 TIMES 2 TO THE B OR 5 IS ',POWER2(A, B)
        END

To understand how to write the assembly procedure, consider how the
param-eters are placed on the stack, as illustrated in Figure 20.4.

(This figure may be found in the printed book.)

Figure 20.4 assumes that the FORTRAN module is compiled in large model. If
you compile the FORTRAN module in medium model, then each argument is passed
as a two-byte, not four-byte, address. The return address is four bytes long
because procedures called from FORTRAN must always be FAR.

The assembler code looks like this:

    .MODEL LARGE, FORTRAN

    Power2  PROTO  FORTRAN, factor:FAR PTR SWORD, power:FAR PTR SWORD

            .CODE

    Power2  PROC   FORTRAN, factor:FAR PTR SWORD, power:FAR PTR SWORD

            les     bx, factor
            mov     ax, ES:[bx]
            les     bx, power
            mov     cx, ES:[bx]
            shl     ax, cl
            ret
    Power2  ENDP        END


20.3.3  The Basic/MASM Interface

This section explains how to call MASM procedures or functions from Basic
and how to receive Basic arguments for the MASM procedure. Pascal is the
default naming and calling convention, so all lowercase letters are
converted to uppercase. Routines defined with the FUNCTION keyword return
values, but routines defined with SUB do not. Basic DEF FN functions and
GOSUB routines cannot be called from another language.

The information provided pertains to Microsoft's Basic and QuickBasic
compilers. Differences between the two compilers are noted when necessary.

Compatible Data Types - The list shows the Basic data types that are
equivalent to the MASM 6.0 data types.

Basic Type                        Equivalent MASM Type
────────────────────────────────────────────────────────────────────────────
STRING*1                          WORD

INTEGER   (X%)                    SWORD

SINGLE   (X!)                     REAL4

LONG   (X&),                      SDWORD
CURRENCY

DOUBLE   (X#)                     REAL8

Naming Conventions - Basic recognizes up to 40 characters of a name. In the
object code, Basic also drops any of its reserved characters: %, &, !, #, @,
&.

Argument-Passing Defaults - Basic can pass data in several ways and can
receive it by value or by near reference.

By default, Basic arguments are passed by near reference as two-byte
addresses. To pass a near address, pass only the offset; if you need to pass
a far address, pass the segment and offset separately as integer arguments.
Pass the segment address first, unless you have specified C compatibility
with the CDECL keyword.

Basic passes each argument in a call by far reference when CALLS is used to
invoke a routine. You can also use SEG to modify a parameter in a preceding
DECLARE statement so that Basic passes that argument by far reference.

To pass a Basic argument by value, apply the BYVAL keyword to the argument
in the DECLARE statement. Arrays and user-defined types cannot be passed by
value.

    DECLARE SUB Test(BYVAL a%, b%, SEG c%)

    CALL Test(x%, y%, z%)

    CALLS Test(x%, y%, z%)

The CALL statement above passes the first argument (a%) by value, the second
argument (b%) by near reference, and the third argument (c%) by far
reference. The statement  CALLS Test2(x%, y%, z%)  passes each argument by
far reference.

Changing the Calling Convention - Including the CDECL keyword in the Basic
DECLARE statement enables the C calling and naming convention. This also
allows a call to a MASM procedure with a varying number of arguments.

Equivalent Arrays - The DIM statement sets the number of dimensions for a
Basic array and also sets the array's maximum subscript value. In the array
declaration  DIM x(a,b), the upper bounds (the maximum number of values
possible) of the array are  a  and  b. The default lower bound is 0. The
default upper bound for an array subscript is 10.

Basic stores arrays in column-major order.

The default for column storage in Basic is column-major order, as in
FORTRAN. For an array defined as  DIM Arr%(3,3), reference the last element
as  Arr%(3,3). The first five elements of  Arr (3,3)  are

    Arr(0,0), Arr(1,0), Arr(2,0), Arr(0,1), Arr(1,1)

When you pass an array from Basic to a language that expects arrays to be
stored in row-major order, use the command-line option /R when compiling the
Basic module.

Most Microsoft languages permit you to reference arrays directly. Basic uses
an array descriptor, however, which is similar in some respects to a Basic
string

descriptor. The array descriptor is necessary because Basic may shift the
location of array data in memory; Basic handles memory allocation for arrays
dynamically.

To pass arrays to MASM, you need to follow several rules.

A reference to an array in Basic is really a near reference to an array
descriptor. Array descriptors are always in DGROUP, even though the data may
be in far memory. Array descriptors contain information about type,
dimensions, and memory locations of data. You can safely pass arrays to MASM
routines only if you follow three rules:


    ■   Pass the array's address by applying the VARPTR function to the first
        element of the Basic array and passing the result by value. To pass
        the far address of the array, apply both the VARPTR and VARSEG
        functions and pass each result by value. The receiving language gets
        the address of the first element and considers it to be the address of
        the entire array. It can then access the array with its normal
        array-indexing syntax.

    ■   If the MASM routine that receives the array makes a call back to
        Basic, then the location of the array data may change, and the address
        that was passed to the routine will be meaningless.

    ■   Basic can pass any member of an array by value. When passing
        individual array elements, the above restrictions do not apply.


You can apply LBOUND and UBOUND to a Basic array to determine lower and
upper bounds, and then pass the results to another routine. This way, the
size of the array does not need to be determined in advance.

String Format - Strings are stored in Basic as four-byte string descriptors,
as shown below. The first field of the string descriptor contains a two-byte
integer indicating the length of the actual string text. The second field
contains the address of this text.

(This figure may be found in the printed book.)

Basic's string descriptors are not compatible with the string formats of
other languages.

This address is an offset into the default data area and is assigned by
Basic's string-space management routines. These management routines need to
be available to reassign this address whenever the length of the string
changes, yet these management routines are available only to Basic.
Therefore, your MASM procedure should not alter the length of a Basic
string.

Prior to version 7.0 of the Microsoft Basic Compiler, there are two ways to
pass strings:


    1.  Pass the address of the Basic string data to the other language

    2.  Mimic the form of the Basic string descriptor in the other language,
        then use that to access the string as Basic would access one of its
        own strings


────────────────────────────────────────────────────────────────────────────
NOTE

Version 7.0 of the Microsoft Basic Compiler provides new functions that
access the string descriptors and allow simplified string passing between
Basic and other languages. Follow the instructions in the Basic
documentation.
────────────────────────────────────────────────────────────────────────────

The routine that receives the string must not call any Basic routine. If it
does, Basic's string-space management routines may change the location of
the string data without warning.

The SADD function returns the address of a specified string variable. Basic
should pass the result of the SADD function by value. Bear in mind that the
string's address, not the string itself, is passed by value. This amounts to
passing the string itself by reference. The Basic module passes the string
address, and the other module receives the string address. The address
returned by SADD is declared as type INTEGER but is actually equivalent to a
C near pointer or Pascal ADR variable.

To return the far address of a string variable, version 7.0 (or later) of
Basic provides the SSEGADD function. See your Basic documentation.

MASM can access data declared with a COMMON statement.

External Data - Variables can be global to modules in a Basic program by
declaring them with the COMMON statement. Global variables do not require
any additional declarations to be used by MASM procedures.

Structure Alignment - Basic packs user-defined types. For MASM structures to
be compatible, select byte-alignment.

Use medium memory model with Basic.

Compiling and Linking - Always assemble the MASM module with medium model
when you are linking to Basic. If you are listing other libraries on the
LINK command line, specify Basic libraries first. (There are differences
between the QBX and command-line compilation. See your Basic documentation.)

Returning Values - Basic follows the usual convention of returning values in
AX or DX:AX. If the value is not floating point, an array, or a structured
type, or if it is less than 4 bytes long, then the two-byte integers should
be returned from the MASM procedure in AX and four-byte integers should be
returned in DX:AX.  For all other types, return the near offset in AX.

User-Defined Data Types - The Basic TYPE statement defines structures
composed of individual fields. These types are equivalent to the C struct,
FORTRAN record (declared with the STRUCTURE keyword), and Pascal Record
types.

You can use any of the Basic data types except variable-length strings or
dynamic arrays in a user-defined type. Once defined, Basic types can be
passed only by reference.

Varying Number of Arguments - You can vary the number of arguments in a
Basic routine only when you use CDECL to change the calling convention. To
call a function with a varying number of arguments, you also need to
suppress the type-checking that normally forces a call to be made with a
fixed number of arguments. In Basic, you can remove this type checking by
omitting a parameter list from the DECLARE statement.

Pointers and Addresses - VARSEG accesses a variable's segment address, and
VARPTR accesses a variable's offset address. The values returned by these
intrinsic Basic functions should then be passed or stored as ordinary
integer variables. Pass segment addresses first unless your procedure
specifies the cdecl calling convention. If you pass them to MASM procedures,
pass by value. Otherwise you are attempting to pass the address of the
address, rather than the address itself.

Example - This example calls the  Power2  procedure in the MASM 6.0 module.

    DEFINT A-Z

    DECLARE FUNCTION Power2 (A AS INTEGER, B AS INTEGER)
    PRINT "3 times 2 to the power of 5 is ";
    PRINT Power2(3, 5)

    END

The first argument,  A, is higher in memory than  B  because Basic pushes
arguments in the same order in which they appear.

Figure 20. 6 shows how the arguments are placed on the stack:

(This figure may be found in the printed book.)

The assembly procedure can be written as follows:

    .MODEL  medium

    Power2  PROTO   PASCAL, Factor:PTR WORD, Power:PTR WORD
            .CODE
    Power2  PROC    PASCAL, Factor:PTR WORD, Power:PTR WORD

            mov     bx, WORD PTR Factor ; Load Factor into
            mov     ax, [bx]            ;  AX
            mov     bx, WORD PTR Power  ; Load Power into
            mov     cx, [bx]            ;  CX
            shl     ax, cl              ; AX = AX * (2 to power
                                        ;  of CX)
            ret
    Power2  ENDP
            END

Note that each parameter must be loaded in a two-step process because the
address of each is passed rather than the value. The return address is four
bytes long because procedures called from Basic must be FAR.


20.3.4  The Pascal/MASM Interface

This section summarizes details important to calling Microsoft Professional
Pascal, Version 4.0, routines from MASM and MASM routines from Pascal. It
includes information on parameters and data types specific to Pascal source
modules. The information in this section does not apply to QuickPascal (see
Section 20.3.5 for that).

The Pascal calling convention─the default─places arguments on the stack in
the same order in which they appear in the Pascal source code. The first
argument is highest in memory because it is also the first argument to be
placed on the stack, and the stack grows downward. The default naming
convention exports names in uppercase.

Compatible Data Types - This list shows the Pascal types that are equivalent
to the MASM 6.0 data types.

Pascal Type                       Equivalent MASM Type
────────────────────────────────────────────────────────────────────────────
BYTE, CHAR, BOOLEAN               BYTE

WORD                              WORD

INTEGER2                          SWORD

REAL, REAL4                       REAL4

INTEGER4                          SDWORD

REAL8                             REAL8

Naming Restrictions  - Microsoft Pascal Version 4.0 recognizes only the
first 8 characters of any name, while the assembler recognizes the first
256. Names used publicly with Pascal should not be longer than 8 characters.

The default for Pascal is passing by value.

Argument-Passing Defaults - By default, Pascal arguments are passed by
value, but they can be passed by near reference when declared as VAR or
CONST and as far reference when declared as VARS or CONSTS. A VARS or CONSTS
argument includes both a two-byte segment address and a two-byte offset with
the segment pushed first.

Pascal arguments are also passed by near (or far) reference when the ADR (or
ADS) of a variable, or a pointer to a variable, is passed by value. In other
words, the address of the variable is first determined. Then this address is
passed by value.

Pascal routines can use the C calling convention.

Changing the Calling Convention - To use the C calling convention from
Pascal, type  [C]  at the end of the declarations before the semicolon, as
shown:

    Procedure MyProc ( x : integer ) [C]; EXTERN;

Equivalent Arrays - The lower bound for Pascal arrays can be any integer.
Subscripts vary in row-major order.

String Format - Pascal has two types of strings, each of which uses a
different format: a fixed-length type STRING and the variable-length type
LSTRING.

The format used for STRING is identical to that of the FORTRAN string.The
format of an LSTRING stores the length in the first byte. For example,
consider an LSTRING declared as

    VAR Msg:LSTRING(14);
    Msg := 'String of text'

Pascal strings store the string length in the first byte.

The string is stored in 15 bytes of memory. The first byte indicates the
length of the string text. The remaining bytes contain the string text
itself:

(This figure may be found in the printed book.)

The Pascal data type LSTRING is not compatible with the formats used by the
other languages. You can pass an LSTRING indirectly, however, by first
assigning it to a STRING variable. Pascal supports such assignments by
performing a conversion of the data.

Pascal passes an additional two-byte argument that indicates string length
whenever you pass an argument of type STRING or LSTRING. To suppress the
passing of this additional argument, declare a fixed-length type.

External Data - Pascal routines can directly access external data. You can
declare data as external by adding the EXTERN attribute to the data
declaration.

Structure Alignment - Pascal uses word alignment (unpacked storage) for all
data objects larger than one byte. In addition, all nested structures and
records start on a word boundary. You can turn on packing for Pascal
modules, or you can define structures in MASM to have 2 for their alignment
value.

Compiling and Linking - Always use large model for the MASM module when
linking with Pascal.

Returning Values - Functions that return REAL, REAL4, or REAL8 values use
the long return method; that is, the caller passes an additional, hidden
offset of a temporary stack variable that will receive the result.

INVOKE cannot handle long return values directly, but you can add an
additional parameter to the prototype for the Pascal procedure. For example,
a prototype for a Pascal procedure that expects an SWORD argument looks like
this:

    PascalProc PROTO Pascal arg1:SWORD, PtrRetVal:NEAR PTR

Before calling the Pascal procedure with INVOKE, allocate space on the stack
with

    add     sp, space
            mov     cx, sp
            INVOKE  PascalProc, ax, cx
            .
            .
            .
            sub     sp, space

These statements place the address of the allocated space in CX.

Since calls to Pascal procedures must be made from within a MASM procedure
previously called from the Pascal module, an alternative way to handle a
long return value is to create a local variable to receive the return value.
This example illustrates this technique:

    Proc1   PROC    arg1:SWORD
            LOCAL   RetVal:REAL8
            INVOKE  PascalProc, ax, ADDR RetVal

To return structures from MASM using the Pascal calling convention, the
calling program allocates space for the return value on the stack and passes
a pointer (as a hidden argument) to the location where the return value is
to be placed. Copy the MASM structure into the location pointed to by the
hidden argument and return the pointer to that location in the AX register
(or DX:AX for far data models).

Use the C and VARYING attributes for routines that will receive a variable
number of arguments.

Varying Number of Arguments - In Pascal, you can call routines with a
variable number of arguments by including the VARYING attribute in your
interface to the routine, along with the C attribute. You must use the C
attribute for the Pascal routine, because a variable number of arguments is
possible only with the C calling convention.

Each time you call the routine, you will not be required to pass the same
number of arguments as are declared in the interface to the routine.
However, each actual argument that you pass will be type-checked against
whatever formal parameters you may have declared.

Structures, Records, and User-Defined Types - You can pass Pascal
structures, records, and user-defined types as arguments by value or by
reference depending on the size of the data.

Pointers and Addresses - The Pascal ADR and ADS types are equivalent to the
C near and far pointers. You can pass ADR and ADS variables as ADRMEM or
ADSMEM.

Example - This example shows the  Power2  procedure as it is called by
Pascal.

    Program Asmtest( input, output );
    function Power2( a:integer; b:integer ): integer; extern;
    begin
        writeln( '3 times 2 to the power of 5 is ', Power2( 3, 5 ) );
    end.

To understand how to write the assembly procedure, consider how the
arguments are placed on the stack, as illustrated in Figure 20.8.

(This figure may be found in the printed book.)

The first argument,  3, is higher in memory than  5  because Pascal pushes
arguments in the same order they appear. Both arguments are passed by value.


The MASM 6.0 module can be written as follows:

    .MODEL  medium, PASCAL
            .386
    Power2  PROTO PASCAL  factor:WORD, power:WORD
            .CODE

    Power2  PROC    factor:WORD, power:WORD

            mov     ax, factor    ; Load Factor into AX
            mov     cx, power     ; Load Power into CX
            shl     ax, cl        ; AX = AX * (2 to power of CX)
            ret                   ; Leave return value in AX

    Power2  ENDP
            END

The AX and CX registers can be loaded directly because the arguments are
passed by value.


20.3.5  The QuickPascal/MASM Interface

The QuickPascal implementation of Pascal uses several data types and
defaults that are different from version 4.0 of the Microsoft Pascal
compiler. This section summarizes the techniques for calling MASM procedures
from QuickPascal and for accessing QuickPascal data and routines from MASM.
The following information also applies to other compilers that are
compatible with QuickPascal.

The Pascal calling convention pushes arguments in the order listed and
exports identifiers in uppercase.

Compatible Data Types - This list gives the QuickPascal data types that are
equivalent to the MASM 6.0 data types.

QuickPascal Type                  Equivalent MASM Type
────────────────────────────────────────────────────────────────────────────
Char, Boolean                     BYTE

Byte, ShortInt                    SBYTE

Word                              WORD

Integer                           SWORD

Single                            REAL4

LongInt                           SDWORD

Real                              FWORD

Comp, Double                      REAL8

Extended                          REAL10

Naming Restrictions - The first 63 characters of QuickPascal identifiers are
significant. Identifiers are not case sensitive and the first character must
be a letter or an underscore character (_). Digits can be used in the
indentifier's name.

By default, Pascal passes arguments by value.

Register Preservation - Procedures called by QuickPascal must preserve the
values of the BP, SP, SS, and DS registers. BP and SP are preserved by
standard entry and exit code. If you need to alter DS or SS, you must
preserve the current values.

Argument-Passing Defaults - When an argument is passed by value, QuickPascal
takes different actions depending on the data type and size. This

convention for value parameters is not shared by other Microsoft high-level
languages, which always push arguments passed by value directly onto the
stack.


    ■   Enumerated type arguments are passed as unsigned bytes if the
        enumeration has 256 or fewer values; otherwise they are passed as an
        unsigned word.

    ■   Types Single (4 bytes), Real (6 bytes), Double (8 bytes), Comp (8
        bytes), and Extended (10 bytes) are passed on the stack.

    ■   Pointer types are passed as doublewords. The segment is pushed before
        the offset so the offset is lowest in memory.

    ■   If the value parameter is Char, Boolean, any pointer, any Integer, or
        any floating-point type, QuickPascal pushes the argument onto the
        stack.

    ■   If the argument is a string or set type, QuickPascal passes a pointer
        to the data. This action is really the same as passing by reference.
        If you want to avoid any possibility of altering the data, make a
        temporary copy of the data and then work with the temporary data.

    ■   If the argument is an array or record type and if it is not more than
        four bytes long, QuickPascal pushes the variable directly onto the
        stack. Otherwise, it pushes a pointer to the data.


When an argument is passed by reference, QuickPascal pushes a four-byte
pointer to the data. The offset portion of the pointer is always pushed
first and is therefore higher in memory.

Changing the Calling Convention - QuickPascal supports only the Pascal
calling convention.

Equivalent Arrays - Arrays are stored in row-major order. Arrays (and
records with one, two, or four bytes) are passed directly on the stack.

String Format - In the STRING format, the first byte of the string stores
the string length. In the CSTRING format, there is no length indicator and
there is a terminating null byte.

External Data - You cannot declare public data in a data segment of the MASM
module for the QuickPascal module to reference. QuickPascal can use private,
static data in MASM modules; however, the data declared in the MASM module
must be initialized with ?. MASM can reference data in a QuickPascal unit.

Structure Alignment - QuickPascal records are byte-aligned.

Compiling and Linking - For QuickPascal to access an assembled MASM module
(named MASMMOD.OBJ), include this line at the beginning of your QuickPascal
program:

    {$L QPEX.OBJ}

You do not need to use LINK or any other utility to produce executable
files.

QuickPascal sets up the link to the MASM module by copying the MASM object
file into the program and changing the file into its own internal
object-code format. The disk-based object file is left unchanged.

Returning Values - To return a value to a QuickPascal module, follow these
conventions:


    ■   For a String, CSTRING, Comp, or floating-point type other than Real,
        QuickPascal passes an additional argument. This argument is pushed
        first and is a pointer to a temporary storage location. The function
        must place the result of the function in this location and not remove
        this pointer.

    ■   For ordinal types, (including Char, Boolean, and any integer), place
        the result in AL if one byte, in AX if two bytes, and in DX:AX if a
        doubleword (in which DX holds the most-significant byte).

    ■   QuickPascal does not support functions that return array or record
        types. However, you can set the value of an array or record if
        QuickPascal passes it as a VAR parameter.


Example   - This example includes a Pascal program to call the assembly
module Power2.

    {$L QPEX.OBJ}

    program  Asmtest( input, output );
    function POWER2( factor:integer; power:integer ): integer; external;
    begin
        writeln( '3 times 2 to the power of 5 is ', POWER2( 3, 5 ) );

    end.

This is the assembly module to be called from the Pascal program.

    Power2  PROTO PASCAL  factor:WORD, power:WORD

    CODE SEGMENT WORD PUBLIC
    ASSUME  CS:CODE

    Power2  PROC PASCAL   factor:WORD, power:WORD

    mov     ax, factor    ; Load factor into AX
    mov     cx, power     ; Load power into CX
    shl     ax, cl        ; AX = AX * (2 to power of CX)
                                ; Leave return value in AX
            ret
    Power2  ENDP

    CODE    ENDS
            END

You cannot use the /Zi command-line option when assembling a module to be
called from QuickPascal.


20.4  Related Topics in Online Help

Other information available online which relates to topics in this chapter
is listed below:

Topic                             Access
────────────────────────────────────────────────────────────────────────────
/NOI Linker option                From the list of Utilities on the
                                    "Microsoft Advisor Contents" screen,
                                    choose "LINK"; then choose "LINK Options"

PROC, LOCAL,                      From the "MASM 6.0 Contents" screen,
INVOKE, LABEL                     choose "Directives"; then choose
                                    "Procedures and Code Labels"

H2INC                             From the "ML Contents" screen, choose
                                    "H2INC Utility"

STRUCT                            From the "MASM 6.0 Contents" screen,
                                    choose "Directives"; then choose
                                    "Complex Data Types"

EXTERN,                           From the "MASM 6.0 Contents" screen,
EXTERNDEF, PUBLIC                 choose "Directives"; then choose "Scope
                                    and Visibility"

USES, RET, VARARG                 From the MASM Index, select PROC





Appendix A  Differences between MASM 6.0 and 5.1
────────────────────────────────────────────────────────────────────────────

Version 6.0 of the Microsoft Macro Assembler contains significant changes
over previous versions. Some of these changes include:


    ■   An environment called Programmer's WorkBench (PWB) from which you can
        write, edit, debug, and execute code

    ■   Expanded functionality for structures, unions, and type definitions

    ■   New directives for generating loops and decision statements, and for
        declaring and calling procedures

    ■   Simplified methods for applying public attributes to variables and
        routines in multiple-module programs

    ■   Enhancements for writing and using macros

    ■   Flat-model support for OS/2 version 2.0 and new instructions for the
        80486 processor


Section A.1 describes the new features of MASM 6.0. The appendix does not go
into great detail about the new features, but it does provide references to
the information presented elsewhere in the MASM 6.0 documentation. For full
explanations and coding examples, see the documentation listed in the
cross-references.

Section A.2 discusses compatibility with MASM 5.1. To get your MASM 5.1 code
running under MASM 6.0 using OPTION M510 (or the /Zm command-line option),
see Section A.2.1, "Rewriting Code for Compatibility." To remove OPTION M510
(or /Zm) from your code, see Section A.2.2, "Using the OPTION Directive."


A.1  New Features of Version 6.0

MASM 6.0 contains many new features. This section briefly describes each
one. Some new features, such as the new behavior of structures, also allow
you to select compatibility options. These features are also discussed in
Section A.2, "Compatibility between MASM 5.1 and 6.0."


A.1.1  The Assembler, Environment, and Utilities

Most of the executable files provided with MASM 6.0 are new or revised. For
a complete list of these files, read the PACKING.LST file on the
distribution disk. The book Installing and Using the Professional
Development System also provides more information about setting up the
environment, assembler, and online help system.

The Assembler - The macro assembler, now named ML.EXE, is capable of
assembling and linking in one step. The command-line options are completely
new. For example, the new /EP option produces a listing file during the
assembler's first pass. Command-line options now are case-sensitive and must
be separated by spaces.

For backward compatibility with version 5.1 makefiles, a MASM.EXE utility is
included. When you run MASM.EXE, it translates version 5.1 command-line
options to the new version 6.0 command-line options and calls ML.EXE. See
the Microsoft Macro Assembler Reference for details.

H2INC - H2INC converts C include files to MASM include files. It translates
data structures and declarations but does not translate executable code. For
more information, see Chapter 16, "Converting C Header Files to MASM Include
Files."

NMAKE - NMAKE is the new version of the MAKE utility. NMAKE provides new
functionality in evaluating target files and more flexibility with macros
and command-line options. For more information, see Chapter 10, "Managing
Projects with NMAKE."

Integrated Environment - PWB is an integrated environment for writing,
developing, and debugging programs. See Installing and Using for information
on using PWB, and the Reference for information on command-line options. See
also Chapter 14, "Customizing the Microsoft Programmer's WorkBench," and
Chapter 15, "Debugging Assembly-Language Programs with CodeView."

Online Help - The Microsoft Advisor online help system has been added to
MASM 6.0. It provides a vast database of online help about all aspects of
MASM, including the syntax and timings for processor and coprocessor
instructions, MASM directives, command-line options, and support programs
such as LINK and PWB.

See Installing and Using, Chapter 4, for information on how to set up the
help system. You can invoke the help system from within PWB or from the
QuickHelp program (QH).

HELPMAKE - You can use the HELPMAKE utility to create additional help files
from ASCII text files, allowing you to customize the online help system. For
more information, see Chapter 11, "Creating Help Files with HELPMAKE."

Other Programs - MASM 6.0 contains the most recent versions of LINK, LIB,
BIND, CodeView, and the mouse driver. The CREF program is not included in
MASM 6.0. The Source Browser provides the information that CREF provided
under MASM 5.1. For more information on the source browser, see Chapter 3 of
Installing and Using the Professional Development System or online help.


A.1.2  Segment Management

This section lists the changes and additions to memory-model and
operatingsystem support as well as to directives that relate to these
topics.

New Predefined Symbols - The following new predefined symbols (also called
predefined equates) provide information about simplified segments:

Predefined Symbol                 Value
────────────────────────────────────────────────────────────────────────────
@stack                            DGROUP for near stacks, STACK for far
                                    stacks

@Interface                        Information about language parameters

@Model                            Information about the current memory
                                    model

@Line                             The source line in the current file

@Date                             The current date

@FileCur                          The current file

@Time                             The current time

@Environ                          The current environment variables

For more information, see Section 1.2.3, "Predefined Symbols," or online
help.

Enhancements to the ASSUME Directive - MASM automatically generates ASSUME
values for the code segment register (CS) when a segment is opened. It is no
longer necessary to include lines such as

    ASSUME CS:MyCodeSegment

in your programs. In addition, the ASSUME directive can now include ERROR,
FLAT, or register:type. Generating ASSUME values for the code segment
register CS to be other than the current segment or group is no longer
valid.

For more information, see Sections 2.3.3, "Setting the ASSUME Directive for
Segment Registers," and 3.3.2, "Defining Register Types with ASSUME."

Relocatable Offsets - For compatibility with Windows programs, the new
LROFFSET operator can calculate a relocatable offset, which is resolved by
the loader at run time. See online help for details.

Flat Model - In the flat memory model (available only in version 2.0 of
OS/2), segments may be as large as four gigabytes because offsets contain 32
bits instead of 16. Segments are limited to 64K in all other memory models
supported by DOS and earlier versions of OS/2. Version 2.0 of OS/2 runs only
on 80386/486 processors. For more information about memory models, see
Section 2.2.1, "Defining Basic Attributes with .MODEL."

Operating Systems Support - Specifying the new OS_OS2 or OS_DOS keywords in
the .MODEL statement allows the new .STARTUP directive to generate start-up
code appropriate for the language and operating system. The new .EXIT
directive generates the appropriate exit code.

Section 2.2.1, "Defining Basic Attributes with .MODEL," provides more
information on specifying an operating system. Also see Section 2.2.6,
"Starting and Ending Code with .STARTUP and .EXIT."


A.1.3  Data Types

MASM 6.0 introduces an entirely new concept of data typing for assembly
language. This section summarizes new and changed features relating to data
declarations in MASM 6.0.

Defining Typed Variables - You can now use the type names as directives to
define variables. Initializers are unsigned by default. The following are
equivalent:

    var1    DB      25
    var1    BYTE    25

Signed Types - You can use the new SBYTE, SWORD, and SDWORD directives to
declare signed data. See Section 4.1.1, "Allocating Memory for Integer
Variables."

Floating-Point Types - MASM 6.0 also introduces new directives for declaring
floating-point variables, REAL4, REAL8, and REAL10. See Section 6.1.1,
"Declaring Floating-Point Variables and Constants," for information on these
new type directives.

Qualified Types - MASM 6.0 allows type definitions to include distance and
language type attributes. Procedures, procedure prototypes, and external
declarations allow the type to be specified as a qualified type. Section
1.2.6, "Data Types," gives a complete description of qualified types.

Structures - Structures have changed in several ways:


    ■   Structures can be nested.

    ■   The names of structure fields need not be unique. As a result,
        references to field names must be qualified.

    ■   Initialization of structure variables can continue over multiple lines
        as long as the final noncomment character in the line is a comma.

    ■   Curly braces and angle brackets are equivalent.


For example, this code works in MASM 6.0:

    SCORE           STRUCT
    team1         BYTE    10 DUP (?)
    score1        BYTE    ?
    team2         BYTE    10 DUP (?)
    score2        BYTE    ?
    SCORE          ENDS

    first   SCORE  {"BEARS", 20,        ; This comment is allowed.
                    "CUBS",  10 }

            mov     al, [bx].score.team1 ; Field name must be qualified
                                        ;  with structure name.

You can use OPTION OLDSTRUCTS or OPTION M510 to enable MASM 5.1 behavior for
structures. See Section A.2, "Compatibility between MASM 5.1 and 6.0." For
more information on structures and unions, see Section 5.2.

Unions - MASM 6.0 allows the definition of unions. Unions differ from
structures in that all field initializers occupy the same data space. The
new UNION directive defines these variables. For more information, see
Section 5.2, "Structures and Unions."

Types Defined with TYPEDEF - The new TYPEDEF directive defines a type for
use later in the program. It is most useful for defining pointer types. For
more information, see Sections 1.2.6, "Data Types," and 3.3.1, "Defining
Pointer Types with TYPEDEF."

Names of Identifiers - The names of identifiers in MASM 6.0 can be up to 247
characters long, and all the characters are significant. In previous
versions of MASM (or if OPTION M510 is enabled), names are significant to 31
characters only. For more information on identifiers, see Section 1.2.2,
"Identifiers." For more information on the OPTION directive, see Section
1.3.2, "Using the OPTION Directive."

Multiple-Line Initializers - In MASM 6.0, a comma at the end of a line
implies that the line continues. For example, the following code is legal in
MASM 6.0:

    longstring      BYTE    "This string ",
                            "continues over two lines."
    bitmasks        BYTE    80h, 40h, 20h, 10h,
                            08h, 04h, 02h, 01h

For more information, see Section 1.2.8, "Statements."

Comments in Extended Lines - Earlier versions of MASM allow a backslash ( 
) as the line-continuation character if it is the last nonspace character in
the line. MASM 6.0 permits a comment to follow the backslash.

Determining Size and Length of Data Labels - The new LENGTHOF operator
returns the number of data items allocated for a data label. MASM 6.0 also
has a new SIZEOF operator. When applied to a type, the SIZEOF operator
returns the size attribute of the type expression. When applied to a data
label, SIZEOF returns the number of bytes used by the initializer in the
label's definition. In this case, SIZEOF for a variable equals the number of
bytes in the type multiplied by LENGTHOF for the variable.

The LENGTH and SIZE operators have been retained for backward compatibility.
See "Length and Size of Labels with OPTION M510" in Section A.2.2 for the
behavior of SIZE under OPTION M510, and see "LENGTH Operator Applied to
Record Types" in Section A.2.1.2 for obsolete behavior with the LENGTH
operator.

For information on LENGTHOF and SIZEOF, see Section 5.1.1, "Declaring and
Referencing Arrays," Section 5.1.2, "Declaring and Initializing Strings,"
Section 5.2.1, "Declaring Structure and Union Variables," and Section 5.3.2,
"Defining Record Variables."

HIGHWORD and LOWWORD Operators - These new operators return the high and low
words for the 32-bit operand given. They are similar to the HIGH and LOW
operators of MASM 5.1 except that HIGHWORD and LOWWORD can take only
constants as operands, not relocatables (labels).

PTR and CodeView  - In MASM 5.1, the PTR operator, when applied to a data
initializer, specifies what information should be generated by CodeView.

Semantically using PTR in this manner is still valid, but this does not
affect CodeView typing. Defining pointers with the TYPEDEF directive allows
CodeView to generate correct information. See Section 3.3.1, "Defining
Pointer Types with TYPEDEF."


A.1.4  Procedures, Loops, and Jumps

Significant changes have been made for procedure and jump handling in MASM
6.0. The new functionality closely resembles high-level-language
implementations of the procedure calls. MASM now generates the code to
correctly handle argument passing, to check type compatibility between
parameters and arguments, and to process a variable number of arguments.
MASM 6.0 can also handle jumps intelligently and optimize the coding
according to the distance from the target.

Function Prototypes and Calls - The PROTO directive prototypes a function,
which enables type-checking and type conversion of arguments if the function
is called with INVOKE. For more information, see Section 7.3.6, "Declaring
Procedure Prototypes."

The new INVOKE directive calls a procedure and correctly passes the
arguments according to the prototype. For more information, see Section
7.3.7, "Calling Procedures with INVOKE."

You can also use the new VARARG keyword to pass a variable number of
arguments to a procedure with INVOKE. See Section 7.3.3, "Declaring
Parameters with the PROC Directive."

The ADDR keyword is also new. When used with INVOKE, it changes an
expression to an address expression (for passing by reference instead of by
value). See Section 7.3.7, "Calling Procedures with INVOKE."

High-Level Flow-Control Constructions - MASM 6.0 contains several new
directives that generate code for loops and decisions depending on the
status of a conditional statement. The conditions are tested at run time
rather than at assembly time.

The new directives are .IF, .ELSE, .ELSEIF, .REPEAT, .UNTIL, .UNTILCXZ,
.WHILE, and .ENDW. MASM 6.0 also implements the associated .BREAK and
.CONTINUE directives to use in loops and if statements and the binary
operators used in the C language to form binary expressions.

For more information, see Section 7.2, "Loops," and Section 7.1.2.6,
"Decision Directives."

Automatic Optimization for Unconditional Jumps  - MASM 6.0 automatically
determines the smallest encoding for direct unconditional jumps. See Section
7.1.1, "Unconditional Jumps."

Automatic Lengthening for Conditional Jumps  - If a conditional jump
requires a distance other than SHORT, MASM automatically generates the
necessary comparison and unconditional jump to the destination. See Section
7.1.2, "Conditional Jumps."

User-Defined Stack Frame Setup and Cleanup - The code generated following a
PROC statement─a prologue─sets up the stack for parameters and local
variables. The epilogue code handles stack cleanup. MASM 6.0 allows the
implementation of user-defined prologues and epilogues with macros and the
OPTION directive. See Section 7.3.8, "Generating Prologue and Epilogue
Code."


A.1.5  Simplifying Multiple-Module Projects

Previous versions of MASM require that you declare data and routines used in
more than one module both public and external by using the PUBLIC and EXTRN
directives in the appropriate modules. With MASM 6.0, you can now use a
single directive to accomplish the same task. This makes include files much
more convenient for collecting all the common data and procedure
declarations for your projects.

EXTERNDEF in Include Files - The EXTERNDEF directive allows you to put
global data declarations within an include file. The data is then visible to
all source files that include the file. For more information, see Section
8.2.2.1, "Using EXTERNDEF."

Search Order for Include Files - MASM 6.0 searches for include files in the
directory of the main source file rather than in the current directory.
Similarly, it searches for nested include files in the directory of the
include file. You can specify additional paths to search with the /I
command-line option. For more information, see Section 8.2.1, "Organizing
Modules."

Enforcing Case Sensitivity - In MASM 6.0, langtype takes precedence over the
command-line options that specify case sensitivity. In MASM 5.1, only the
command-line options influence case, not langtype.

Alternate Names for Externals - The syntax for EXTERN allows you to specify
an alternate symbol name, which the linker can use to resolve an external if
the symbol is not otherwise referenced. See Section 8.4.2, "Using EXTERN
with Library Routines."


A.1.6  Expanded State Control

Several new directives enable or disable various aspects of the assembler
control, such as the new 80486 coprocessor instructions and use of
compatibility options.

The OPTION Directive - The new OPTION directive allows you to selectively
define the assembler's behavior, including the enabling of compatibility
with MASM 5.1. See Sections 1.3.2, "Using the OPTION Directive," and A.2,
"Compatibility between MASM 5.1 and 6.0."

The .NO87 Directive - The new .NO87 directive disables all coprocessor
instructions. See online help for more information.

The .486 and .486P Directives - To enable the 80486 instructions, use the
new .486 directive. The .486P directive enables 80486 instructions at the
highest privilege level (recommended for systems-level programs only). See
online help for more information.

The PUSHCONTEXT and POPCONTEXT Directives - The directive PUSHCONTEXT saves
the assembly environment, and POPCONTEXT restores it. The environment
includes the segment register assumes, the radix, the listing and CREF
flags, and the current processor and coprocessor. Note that .NOCREF (the
MASM equivalent to .XCREF) still determines whether information for a given
symbol will be added to Browser information and to the symbol table in the
listing file. See Appendix C or online help for more information on listing
files.


A.1.7  New Processor Instructions

MASM 6.0 supports these new instructions for the 80486 processor:

80486 Instruction                 Description
────────────────────────────────────────────────────────────────────────────
BSWAP                             Byte swap

CMPXCHG                           Compare and exchange

INVD                              Invalidate data cache

INVLPG                            Invalidate Translation Lookaside Buffer
                                    entry

WBINVD                            Write back and invalidate data cache

XADD                              Exchange and add

See the Reference or online help for full descriptions of these new
instructions.


A.1.8  Renamed Directives

To make the language more consistent, the following directives have been
renamed. The new, preferred, name is in the left column. MASM 6.0 still
supports the old, obsolete names in the right column.

╓┌──────────────────────────────┌────────────────────────────────────────────╖
MASM 6.0                       MASM 5.1
MASM 6.0                       MASM 5.1
────────────────────────────────────────────────────────────────────────────
.DOSSEG                        DOSSEG
.LISTIF                        .LFCOND
.LISTMACRO                     .XALL
.LISTMACROALL                  .LALL
.NOCREF                        .XCREF
.NOLIST                        .XLIST
.NOLISTIF                      .SFCOND
.NOLISTMACRO                   .SALL
ECHO                           %OUT
EXTERN                         EXTRN
FOR                            IRP
FORC                           IRPC
REPEAT                         REPT
STRUCT                         STRUC
SUBTITLE                       SUBTTL


Specifying 16-Bit and 32-Bit Instructions - MASM 6.0 supports all
instructions that work with the extended (32-bit) registers of the
80386/486. On certain instructions, you can override the default operand
size with the W (word) and the D (doubleword) suffixes. See online help or
the Reference for details.


A.1.9  Macro Enhancements

The changes to macro functionality in MASM 6.0 are also significant. New
directives provide for a variable number of arguments, loop constructions,
definitions of text equates, and macro functions.

Variable Arguments - In MASM 5.1, extra arguments passed to macros are
ignored. In MASM 6.0, you can pass a variable number of arguments to a macro
by appending the VARARG keyword to the last macro parameter in the macro
definition. Additional arguments passed to this macro can then be referenced
relative to the last declared parameter. Section 9.6, "Returning Values with
Macro Functions," explains how to do this.

Required and Default Macro Arguments - With MASM 6.0, you can use REQ or the
:= operator to specify required or default arguments. See Section 9.2.3.

New Directives for Macro Loops - Within a macro definition, WHILE repeats
assembly as long as a condition remains true. Other macro loop directives,
IRP, IRPC, and REPT, have been renamed FOR, FORC, and REPEAT. For more
information, see Section 9.4, "Defining Repeat Blocks with Loop Directives."

Text Macros - You should use the EQU directive to define numeric constants,
but MASM 6.0 also has a new TEXTEQU directive for defining text macros.
TEXTEQU allows greater functionality than EQU. For example, it can assign
the value calculated by a macro function to a label. For more information,
see Section 9.1, "Text Macros."

The GOTO Directive for Macros - Within a macro definition, GOTO transfers
assembly to a labeled line. Lines in macros can be labeled using a leading
colon(:). The GOTO directive can then be used to change the flow of control
within that macro. See online help.

Macro Functions - At assembly time, macro functions can determine and return
a text value using EXITM. Predefined macro string functions concatenate
strings, return the size of a string, find a substring in a string, and
return the position of a substring within a string. For information on
writing your own macro functions, see Section 9.6, "Returning Values with
Macro Functions."

Predefined Macro Functions - The following predefined text macro functions
are new:

Symbol           Value Returned
────────────────────────────────────────────────────────────────────────────
@CatStr          A concatenated string
@InStr           The position of one string within another
@SizeStr         The size of a string
@SubStr          A substring

For more information, see Section 9.5, "String Directives and Predefined
Functions."


A.1.10  MASM 6.0 Programming Practices

As you can see, MASM 6.0 provides many new features that can make MASM 6.0
code simpler to write. If you are familiar with MASM 5.1 programming, you
may find it helpful to adopt this list of new programming practices for
programming with the new assembler. This list summarizes many of the changes
discussed in the next section, "Compatibility between MASM 5.1 and 6.0."


    ■   Select identifier names that do not begin with the dot operator (.).

    ■   Use the dot operator (.) only to reference structure fields, and the
        plus operator (+) when not referencing structures.

    ■   Different structures can have the same field names if you like, but
        the names of structure fields must always be qualified with the
        structure's type.

    ■   Separate macro arguments with commas, not spaces.

    ■   Avoid adding extra ampersands in macros. (Section A.2.2.3, "OPTION
        OLDMACROS," and Section 9.3.3, "Substitution Operator," give the new
        rules for using ampersands in macros.)

    ■   By default, code labels defined with a colon are local. Place two
        colons after code labels if you want to reference the label outside of
        the procedure.



A.2  Compatibility between MASM 5.1 and 6.0

This section discusses the differences between MASM 5.1 and MASM 6.0.
Section A.2.1 provides information in addition to that found on the MASM 6.0
Quick Start card. The information in this section explains what changes you
may need to make in order to get your MASM 5.1 code to run under MASM 6.0 in
compatibility mode.

────────────────────────────────────────────────────────────────────────────
Note

If you have not already done so, please read the Quick Start for MASM 5.0
and 5.1 Users card provided in your MASM 6.0 package.
────────────────────────────────────────────────────────────────────────────

Once your code runs in compatibility mode using OPTION M510 or the /Zm
command-line option, you may want to modify your code so it runs under MASM
6.0 without the compatibility options. To learn how to do this, see Section
A.2.2, "Using the OPTION Directive."

You may notice that the .OBJ and .EXE files differ between MASM 5.1 and MASM
6.0. These differences do not necessarily indicate compatibility problems,
since MASM 6.0 generates optimal encoding.


A.2.1  Rewriting Code for Compatibility

In some cases, MASM 6.0 with OPTION M510 does not support MASM 5.1 behavior.
Several of these changes result from correcting bugs reported against MASM
5.1. To update your code to MASM 6.0, use the instructions in this section.
This usually requires only minor changes.

Many of the items listed in this section will not exist in your code. The
items most likely to occur are listed first, followed by those that are less
likely to occur.

In addition, you may have conflicts between identifier names and new
reserved words. You can use OPTION NOKEYWORD to resolve errors generated due
to use of reserved words as identifiers. See Section A.2.2.9 for more
information.


A.2.1.1  Bug Fixes from MASM 5.1

This section lists the differences between MASM 5.1 and MASM 6.0 due to bug
corrections from MASM 5.1.

Invalid Use of LOCK, REPNE, and REPNZ  - MASM 6.0 flags illegal uses of the
instruction prefixes LOCK, REPNE, and REPNZ. The error generated for invalid
uses of the LOCK, REPNE, and REPNZ prefixes is error A2068:

    instruction prefix not allowed

Table A.1 summarizes the correct use of the instruction prefixes. It lists
each string instruction with the type of repeat prefix it uses and indicates
whether the instruction works on a source, a destination, or both.


Table A.1  Requirements for String Instructions

╓┌─────────────┌───────────────┌───────────────────┌─────────────────────────╖
Instruction   Repeat Prefix   Source/Destination  Register Pair
────────────────────────────────────────────────────────────────────────────
MOVS          REP             Both                DS:SI, ES:DI
SCAS          REPE/REPNE      Destination         ES:DI
CMPS          REPE/REPNE      Both                DS:SI, ES:DI
LODS          None            Source              DS:SI
STOS          REP             Destination         ES:DI
INS           REP             Destination         ES:DI
OUTS          REP             Source              DS:SI
────────────────────────────────────────────────────────────────────────────


No Closing Quotation Marks in Macro Arguments - In MASM 5.1, both single and
double quotation marks (' and ") can be used to begin strings in macro
arguments, and the assembler does not generate an error or warning if the

string does not end with quotation marks on a macro call. Instead, the
assembler considers the remainder of the line to be part of the macro
argument containing the opening quote (as if there were a closing quotation
mark at the end of the line).

By default, MASM 6.0 now generates error A2046:

    missing single or double quotation mark in string

so all single and double quotation marks in macro arguments must be matched.
(Angle brackets not enclosed by brackets must also be matched.)

To correct errors the assembler finds, either end the string with a closing
quotation mark as shown in this example, or use the macro escape character
(!) to treat the quotation mark literally.

    ; MASM 5.1 code
    MyMacro     "all this in one argument

    ; Default MASM 6.0 code
    MyMacro     "all this in one argument"

Making a Scoped Label Public  - MASM 5.1 considers code labels defined with
a single colon inside a procedure to be local to that procedure if the
module contains a .MODEL directive with a language type. Although the label
is local, MASM 5.1 does not generate an error if it is also declared PUBLIC.
MASM 6.0 generates error A2203:

    cannot declare scoped code label as PUBLIC."

If you want to make the label PUBLIC, it must not be local. You can use the
double colon operator to define a non-scoped label, as shown in this
example:

    PUBLIC  publicLabel
    publicLabel::                  ; Non-scoped label MASM 6.0

Byte Form of BT, BTS, BTC, and BTR Instructions - MASM 5.1 allows a byte
argument for the 80386 bit-test instructions, but encodes it as a word
argument. The byte form is not supported by the processor.

MASM 6.0 does not support this behavior and generates error A2024:

    invalid operand size for instruction

Rewrite your code to use a word-sized argument.

Default Values for Record Fields - In MASM 5.1, default values for record
fields can range down to -2n (where n is the number of bits in the field),
resulting in the loss of the sign bit.

The allowed range for default values in MASM 6.0 is -2n-1 to 2n-1. Illegal
initializers generate error A2071:

    initializer too large for specified size


A.2.1.2  Design Change Issues

MASM 6.0 makes some changes in MASM 5.1 behavior to make the language more
consistent. These design changes are not affected by the OPTION  directive.
Therefore, they require revisions in your code. In most cases, the necessary
revisions are minor and the circumstances requiring changes are rare.

Conflicting Structure Definitions - MASM 5.1 allows two structures to be
defined with the same name. The second definition replaces the first
definition. However, the fields from the first are still defined. MASM 6.0
does not allow conflicting definitions of a structure. Errors A2160 through
A2165 are generated when the assembler finds a conflicting definition. Each
error notes a specific conflict, such as conflicting number of fields,
conflicting names of fields, or conflicting initializers.

Forward References to Text Macros Outside of Expressions - MASM 5.1 allows
forward references to text macros in specialized cases. MASM 6.0 with OPTION
M510 also permits forward references, but only when the text macro is
referenced in an expression. To revise your code, place all macro
definitions at the beginning of the file.

HIGH and LOW Applied to Relocatable Operands - In MASM 5.1, applying HIGH
and LOW to relocatable memory expressions is acceptable in some cases. For
example, MASM 5.1 allows this code sequence:

    ; MASM 5.1 code
    EXTRN   var1:WORD
    var2    DW      0
            mov     al, LOW var1  ; These two instructions yield the
            mov     ah, HIGH var1 ;  same as mov ax, OFFSET var1

However,  mov ax, LOW var2  is not legal. MASM 6.0 generates error A2105:

    HIGH and LOW require immediate operands

The OFFSET operator is required on these operands in MASM 6.0, as shown
below. Rewrite your code if necessary.

    ; MASM 6.0 code
            mov     al, LOW OFFSET var1
            mov     ah, HIGH OFFSET var2

OFFSET Applied to Group Names and Indirect Memory Operands -  In MASM 6.0,
you cannot apply OFFSET to a group name, indirect argument, or procedure
argument. Doing so generates error A2098:

    invalid operand for OFFSET

LENGTH Operator Applied to Record Types - In MASM 5.1, the LENGTH operator,
when applied to a record type, returns the total number of bits in a record
definition.

In MASM 6.0, the statement  LENGTH recordName  returns error A2143:

    expected data label

Rewrite your code if necessary. The new SIZEOF operator returns information
about records in MASM 6.0. See Section 5.3.2, "Defining Record Variables,"
for more information.

Signed Comparison of Hexadecimal Values Using GT, GE, LE, or LT -  The rules
for two's-complement comparisons have changed. In MASM 5.1, the statement

    0FFFFh GT -1

is false because the two's-complement values are equal. However, because
hexadecimal numbers are now treated as unsigned, the expression is true in
MASM 6.0. To update, rewrite the affected code.

RET Used with a Constant in Procedures with Epilogues - By default in MASM
6.0, the RET instruction followed by a constant suppresses automatic
generation of epilogue (stack cleanup) code. MASM 5.1 ignores the operand
and generates the epilogue. Remove the argument if necessary. See Section
7.3.8, "Generating Prologue and Epilogue Code."

Code Labels at Top of Procedures with Prologues - By default in MASM 5.1, a
code label defined on the same line as the first procedure instruction
refers to the first byte of the prologue (the stack frame setup).

In MASM 6.0, a code label defined at the beginning of a procedure refers to
the first byte of the procedure after the prologue. If a label is needed
before the prologue, then the label must be placed before the PROC
statement. See Section 7.3.8, "Generating Prologue and Epilogue Code," for
more information.

Use of % as an Identifier Character - MASM 5.1 allows % as an identifier
character. This undocumented behavior leads to ambiguities when % is used as
the expansion operator in macros. Since % is not allowed as a character in
MASM 6.0 identifiers, you must change the names of any identifiers
containing the % character. See Section 1.2.2 for a list of legal identifier
characters.

ASSUME CS Set to Wrong Value - MASM 6.0 does not require the use of the
ASSUME statement for the CS register. Instead, MASM 6.0 generates an
automatic ASSUME statement for the code segment register to the current
segment or group (see Section 2.3.3). Additionally, MASM 6.0 does not allow
explicit ASSUME statements for CS that contradict the automatically set
ASSUME statement.

MASM 5.1 allows CS to be assumed to the current segment, even if that
segment is a member of a group. With MASM 6.0, this results in warning
A4004:

    cannot ASSUME CS

To avoid this warning with MASM 6.0, delete the ASSUME statement for CS.


A.2.1.3  Code Requiring Two-Pass Assembly

MASM 6.0 does not perform the standard two source passes that previous
versions do. Therefore pass-dependent constructs are no longer meaningful.

Obsolete Two-Pass Directives - Because MASM 6.0 assembles in one pass, the
directives referring to two passes are no longer supported. These include
.ERR1, .ERR2, IF1, IF2, ELSEIF1, and ELSEIF2. If you use IF2 or .ERR2, the
assembler generates error A2061:

    [ELSE]IF2/.ERR2 not allowed : single-pass assembler

The .ERR1 directive is treated as though it were .ERR, and the IF1 directive
is treated as though it were IF.

MASM 5.1 directives that refer to the first pass are always true. Directives
that refer to the second pass are flagged as errors. This change requires
you to rewrite the affected code, since OPTION M510 does not enable this
behavior.

You typically use pass-sensitive directive when doing the following: (Each
example shows a MASM 6.0 rewrite.)


    ■   Declaring  var  external only if it is not defined in this module:

        ; PREVIOUS VERSIONS OF MASM:
                IF2
                    IFNDEF  var
                        EXTRN var:far
                    ENDIF
                ENDIF

            ; MASM 6.0:
                EXTERNDEF   var:far


    ■   Including a file of definitions only once to speed assembly:

        ; PREVIOUS VERSIONS OF MASM:
                IF1
                    INCLUDE file1.inc
                ENDIF

            ; MASM 6.0:
                INCLUDE FILE1.INC


    ■   Generating a  %OUT  or  .ERR  message only once:

        ; PREVIOUS VERSIONS OF MASM:
                IF2
                    %OUT This is my message
                ENDIF

                IF2
                    .ERRNZ A NE B
                ENDIF

            ; MASM 6.0:
                ECHO This is my message

                .ERRNZ A NE B    <ASSERTION FAILURE: A NE B>


    ■   Generating an error if a symbol is not defined but may be forward
        referenced:

        ; PREVIOUS VERSIONS OF MASM:
                IF2
                    .ERRNDEF    var
                ENDIF

            ; MASM 6.0:
                    .ERRNDEF    var



See Section 1.3.3 for information on conditional directives.

────────────────────────────────────────────────────────────────────────────
Note
In the following three cases, MASM 6.0 generates warnings if OPTION M510 is
used.
────────────────────────────────────────────────────────────────────────────

IFDEF and IFNDEF with Forward-Referenced Identifiers - If you use a symbol
name that has not yet been defined in an IFDEF or IFNDEF expression, MASM
6.0 returns FALSE for the IFDEF expression and TRUE for the IFNDEF
expression. The assembler generates warning A5005:

    IF condition may be pass-dependent

when OPTION M510 is enabled. To resolve the error, move the symbol
definition to the beginning of the file.

Address Spans as Constants - The value of offsets calculated on the first
assembly pass may not be the same as those calculated on later passes.
Therefore, comparisons with a constant, such as the following, should be
avoided:

    IF OFFSET var1 - OFFSET var2 EQ 10

Note that expressions containing span distances can be used with the .ERR
directives, since these directives are evaluated after all offsets are
determined:

    .ERRE OFFSET var1 - OFFSET var2 - 10, <span incorrect>

.TYPE with Forward References - In MASM 5.1, .TYPE is evaluated on both
assembly passes. This means it yields zero on the first pass and non-zero on
the second pass if applied to an expression that forward references a
symbol.

In MASM 6.0, .TYPE is evaluated on the first assembly pass. As a result, if
the operand references a symbol that has not yet been defined, .TYPE will
yield 0. This means that .TYPE, if used in a conditional-assembly
construction, may yield different results with MASM 6.0 than with MASM 5.1.



A.2.1.4  Obsolete Features No Longer Supported

This section lists features no longer supported by MASM 6.0. Because both of
these items are obscure features provided by early versions of the
assembler, they probably do not affect your MASM 5.1 code.

The ESC Instruction - The ESC instruction, typically used to send hand-coded
commands to the coprocessor, is no longer supported. Because MASM 6.0
recognizes and assembles the full set of coprocessor mnemonics, the ESC
instruction is not necessary . Using the ESC instruction generates error
A2205:

    ESC instruction is obsolete: ignored

To update MASM 5.1 code, use the coprocessor instructions instead of ESC.

The MSFLOAT Binary Format - MASM 6.0 does not support the .MSFLOAT
directive, which provided the Microsoft Binary Format (MSB) for
floating-point numbers in variable initializers. Using the .MSFLOAT
directive generates error A2204:

    .MSFLOAT directive is obsolete: ignored

Use IEEE format or, if MSB format is necessary, initialize variables with
hexadecimal values. See Section 6.1.2, "Storing Numbers in Floating-Point
Format."



A.2.2  Using the OPTION Directive

The OPTION directive can be used with various arguments to control
compatibility with MASM 5.1 code. This section explains the differences in
MASM 5.1 and MASM 6.0 behavior that can be influenced with the OPTION
directive.

Section A.2.2.1 discusses the M510 argument to the OPTION directive, which
selects the MASM 5.1 compatibility mode. In this mode, MASM 6.0 implements
MASM 5.1 behavior relating to macros, offsets, scope of code labels,
structures, identifier names, identifier case, and other behaviors.

────────────────────────────────────────────────────────────────────────────
Note

Wherever this appendix suggests using OPTION M510 in your code, you can set
the /Zm command-line option instead.
────────────────────────────────────────────────────────────────────────────

If you prefer to choose specific MASM 5.1 behaviors, rather than all those
implemented by the OPTION M510 directive, use the OPTION arguments discussed
in Sections A.2.2.2 through A.2.2.9. Each section also explains how to
revise your code if you want to remove OPTION  directives from your MASM 5.1
code.

If you have used any processor or coprocessor instruction names as label
names in your code, you can use the OPTION NOKEYWORD directive to remove
them from the reserved word list. See Section A.2.2.9.


A.2.2.1  OPTION M510

Using OPTION M510 is equivalent to adding /Zm to the command line. The
OPTION M510 directive automatically sets the following:

    OPTION OLDSTRUCTS       ; MASM 5.1 structures
                            ;  See Section A.2.2.2
    OPTION OLDMACROS        ; MASM 5.1 macros
                            ;  See Section A.2.2.3
    OPTION DOTNAME          ; Identifiers may begin with a dot (.)
                            ;  See Section A.2.2.4

If you do not have a .386, 386P .486, or 486P directive in your module, then
OPTION M510 adds:

    OPTION EXPR16           ; 16-bit expression precision
                            ;  See Section A.2.2.5

If you do not have a .MODEL directive in your module, OPTION M510 adds:

    OPTION OFFSET:SEGMENT   ; OFFSET operator defaults to
                            ;  segment-relative
                            ;  See Section A.2.2.6

If you do not have a .MODEL directive with a language specifier in your
module, OPTION M510 also adds:

    OPTION NOSCOPED         ; Code labels are not local inside
                            ;  procedures
                            ;  See Section A.2.2.7
    OPTION PROC:PRIVATE     ; Labels defined with PROC are not
                            ;  public by default
                            ;  See Section A.2.2.8

If you want to remove OPTION M510 from your code (or /Zm from the command
line), add the OPTION directive arguments to your module according to the
conditions stated above.

There may be compatibility issues affecting your code that are supported
under OPTION M510, but are not covered by the other OPTION directive
arguments. Once your source code has been modified so it no longer requires
behavior supported by OPTION M510, you can replace OPTION M510 with other
OPTION directive arguments. These compatibility issues are discussed in
Sections A.2.2.2 through A.2.2.9.

Once you have replaced OPTION M510 with other forms of the OPTION directive
and your code works correctly, try removing the OPTION directives, one at a
time. Make appropriate source modifications as necessary (see Sections
A.2.2.2 through A.2.2.9), until your code uses only MASM 6.0 defaults.

────────────────────────────────────────────────────────────────────────────
Note

OPTION M510 enables the behaviors discussed below in addition to the
behaviors corrected by the OPTION directive arguments described in Sections
A.2.2.2 through A.2.2.9.
────────────────────────────────────────────────────────────────────────────

Reserved Keywords Dependent on CPU Mode with OPTION M510 -  With OPTION
M510, keywords and instructions that are not available in the current CPU
mode (such as ENTER under .8086) are not treated as keywords. This also
means the USE32, FLAT, FAR32, and NEAR32 segment types and the 80386/486
registers are not keywords with a processor selection less than .386.

If you remove OPTION M510, then any reserved word that you use as an
identifier generates a syntax error. You can either rename the identifiers
or use OPTION NOKEYWORD. See Section A.2.2.9 for more information on OPTION
NOKEYWORD.

Invalid Use of Instruction Prefixes with OPTION M510 - Code without OPTION
M510 generates errors for all invalid uses of the instruction prefixes.
Using OPTION M510 suppresses some of these errors in order to match MASM 5.1
behavior. MASM 5.1 does not check for illegal uses of the instruction
prefixes LOCK, REP, REPE, REPZ, REPNE, and REPNZ.

Illegal uses of these prefixes result in error A2068:

    instruction prefix not allowed

See Section 5.1.3.1, "Overview of String Operations", and Section A.2.1.1,
"Bug Fixes from MASM 5.1" for more information on these instruction
prefixes.

Sizes of Constant Operands with OPTION M510 - In MASM 5.1, a constant whose
value is so large it can fit only in the CPU's default word (four bytes for
.386 and .486, two bytes otherwise) is assigned a size attribute of the
default word size. The value of the constant affects the number of bytes
changed by the instruction. For example,

    ; Legal only with OPTION M510
            mov     [bx], 0100h

is legal in OPTION M510 mode. Since  0100h  cannot fit in a byte, it is
interpreted as a word.

Without OPTION M510, the assembler never assigns a size automatically. You
must state it explicitly. Use OPTION M510 to enable the MASM 5.1 behavior if
you do not want to change your MASM 5.1 code.

For code without OPTION M510, the example above could be rewritten as:

    ; Without OPTION M510
            mov     ax, WORD PTR 0100h

Code Labels in Data Definition with OPTION M510 - MASM 5.1 allows a code
label definition in a data definition statement if that statement does not
also define a data label. This is also allowed by MASM 6.0 if OPTION M510 is
enabled; otherwise it is illegal.

    ; Legal only with OPTION M510
    MyCodeLabel:    DW      0

SEG Operator with OPTION M510 - In MASM 5.1, the SEG operator returns a
label's segment unless the frame is explicitly specified, in which case the
frame is returned. A statement such as  SEG DGROUP:var  always returns
DGROUP, whereas  SEG var  always returns the segment of  var. OPTION M510
provides this behavior.

If you do not use OPTION M510, the behavior of the SEG operator is
determined by the OPTION OFFSET directive. See Section A.2.2.6.

When you use the SEG operator with a variable that is not external, code
without OPTION M510 returns the address of the frame (the segment, group, or
the value assumed to the segment register) if one has been explicitly set.
Otherwise, it returns the group if one has been specified. In the absence of
a defined group, SEG returns the segment where the variable is defined.

Expression Evaluation with OPTION M510 - By default, MASM 6.0 changes the
way that expressions are evaluated. In MASM 5.1,

    var-2[bx]

is parsed as

    (var-2)[bx]

Without OPTION M510, you need to rewrite this statement, since it is parsed
as

    var-(2[bx])

which generates an error. OPTION M510 provides the MASM 5.1 behavior.

Length and Size of Labels with OPTION M510 - With OPTION M510, the LENGTH
and SIZE operators can be applied to any label. For a code label, SIZE
returns  0FFFFh  for NEAR and  0FFFEh  for FAR, and LENGTH always returns 1.
For strings, SIZE and LENGTH return 1.

Without OPTION M510, LENGTH returns 1 except when used with DUP. In this
case, the LENGTH operator returns the outermost DUP count. SIZE returns the
length multiplied by the size of the type. However, the new LENGTHOF and
SIZEOF operators return the number of data items and the number of bytes
used by the initializer.

If you specify OPTION M510 and the current word size is 2, NEAR16 and FAR16
correspond to the constants  0FFFFh  and  0FFFEh, respectively. When the
current word size is 4, NEAR and FAR (mapped to NEAR32 and FAR32,
respectively) correspond to  0FFFFh  and  0FFFEh.

Without OPTION M510, the distance attributes SHORT, NEAR16, NEAR32, FAR16,
and FAR32 correspond to  0FF01h,  0FF02h,  0FF04h,  0FF05h, and 0FF06h,
respectively.

The behavior of the new SIZEOF and LENGTHOF operators for labels and strings
is discussed in Section 5.1.1, "Declaring and Referencing Arrays"; Section
5.1.2, "Declaring and Initializing Strings"; Section 5.2.2, "Defining
Structure and Union Variables"; and Section 5.3.2, "Defining Record
Variables."

Comparing Types Using EQ and NE with OPTION M510 - With OPTION M510, types
are converted to a constant value equal to the size of the data type before
comparisons with EQ and NE. Code types are converted to 0FFFFh  (near) and
0FFFEh  (far). If OPTION M510 is not enabled, types are converted to
constants only when comparing them with constants; two types are equal only
if they are equivalent qualified types.

For existing MASM 5.1 code, these distinctions affect only the use of the
TYPE operator in conjunction with EQ and NE. The following example
illustrates this situation:

    MYSTRUCT        STRUC
    f1              DB            0
    f2              DB            0
    MYSTRUCT        ENDS

    ; With OPTION M510

    val     =       (TYPE MYSTRUCT) EQ WORD    ; True: 2 EQ 2
    val     =       2 EQ WORD                  ; True: 2 EQ 2
    val     =       WORD EQ WORD               ; True: 2 EQ 2
    val     =       SWORD EQ SWORD             ; True: 2 EQ 2

    ; Without OPTION M510

    val     =       (TYPE MYSTRUCT) EQ WORD    ; False: MyStruct NE WORD
    val     =       2 EQ WORD                  ; True:  2 EQ 2
    val     =       WORD EQ WORD               ; True:  WORD EQ WORD
    val     =       SWORD EQ SWORD             ; False: SWORD NE WORD

Use of Constant and PTR as a Type with OPTION M510 - A constant can be used
as the left operand to PTR when OPTION M510 is enabled. Otherwise a type
expression must be used. With OPTION M510, a constant must have a value of 1
(byte), 2 (word), 4 (dword), 6 (fword), 8 (qword) or 10 (tbyte), and it is
treated as if the parenthesized type had been specified instead. Note that
the TYPE operator yields a type expression, but the SIZE operator yields a
constant.

    ; With OPTION M510

    MyData  DW      0

            mov     WORD PTR [bx], 10           ; Legal
            mov     (TYPE MyData) PTR [bx], 10  ; Legal
            mov     (SIZE MyData) PTR [bx], 10  ; Legal
            mov     2 ptr [bx], 10              ; Legal

    ; Without OPTION M510

            mov     WORD PTR [bx], 10           ; Legal
            mov     (TYPE MyData) PTR [bx], 10  ; Legal
    ;       mov     (SIZE MyData) PTR [bx], 10  ; Illegal
    ;       mov     2 PTR [bx], 10              ; Illegal

Structure Type Cast on Expressions with OPTION M510 - As with MASM 5.1, a
constant can be type cast with the PTR operator to a structure type. This is
most often used in data initializers to affect the CodeView information of
the data label being defined. Without OPTION M510, the assembler generates
an error.

    MYSTRC  STRUC
    f1      DB      0
    MYSTRC  ENDS

    MyPtr   DW      MYSTRC PTR 0    ; Illegal without OPTION M510

The type of initializers does not influence CodeView's type information with
MASM 6.0.

Hidden Coercion of OFFSET Expression Size with OPTION M510 -  When
programming for the 80386 or 80486, the size of an OFFSET expression may be
two bytes (for a symbol in a USE16 segment) or 4 bytes (for a symbol in a
USE32 or FLAT segment). However, with OPTION M510, a 32-bit OFFSET
expression may be used in a 16-bit context. Without OPTION M510, the LOWWORD
operator must be used to convert the offset size.

    ; With OPTION M510

            .386

    seg32   SEGMENT USE32
    MyLabel WORD    0
    seg32   ENDS

    seg16   SEGMENT USE16 'code'                 ; With OPTIONS M510:
            mov     ax,  OFFSET MyLabel          ; Legal
            mov     ax,  LOWWORD OFFSET MyLabel  ; Legal
            mov     eax, OFFSET MyLabel          ; Legal
    seg16   ENDS

    ; Without OPTION M510

            .386

    seg32   SEGMENT USE32
    MyLabel WORD    0
    seg32   ENDS

    seg16   SEGMENT USE16 'code'                ; Without OPTION M510:
    ;       mov     ax,  OFFSET MyLabel         ; Illegal
            mov     ax,  LOWWORD offset MyLabel ; Legal
            mov     eax, OFFSET MyLabel         ; Legal
    seg16   ENDS

Specifying Radixes with OPTION M510 - If the current radix in your code
(without OPTION M510) is greater than 10, then the radix specifiers B
(binary) and D (decimal) are not supported. You will need to change B to Y
for binary, and D to T for decimal, since both B and D are legitimate
hexadecimal values, making numbers such as  12D  ambiguous. See Section
1.2.4, "Integer Constants and Constant Expressions," for more information.

If you don't want to change radix specifiers when the current radix is
greater than 10, you need to specify OPTION M510 in your code.

Naming Conventions with OPTION M510 - By default in MASM 5.1, specifying a
language type of PASCAL, FORTRAN, or BASIC does not cause names to be mapped
to uppercase when publicly declared variables are written into the object
file.

Unless you use OPTION M510 in your code, these language types map identifier
names to uppercase by default in MASM 6.0, even if you assemble with the /Cp
or /Cx command-line options. See Section 20.1, "Naming and Calling
Conventions."

When you link with /NOI«GNORECASE», case must be matched in the object files
to resolve externals.

Length Significance of Symbol Names with OPTION M510 - With MASM 5.1, only
the first 31 characters of a symbol name are considered significant, and
only the first 31 characters of a public or external symbol name are placed
in the object file.

Without OPTION M510, the entire name is considered significant. The maximum
number of characters placed in the object file is controlled with the
/Hnumber command-line option, with a default of 247 (the maximum length of
an identifier in MASM 6.0).

String Defaults in Structure Variables with OPTION M510 - With OPTION M510,
a structure field initialized to a string value can be overridden with a
constant. Without OPTION M510, a string can be overridden only with another
string or with a list. To update your code, surround the constant override
value with angle brackets or curly braces to indicate a list with one
element.

    MTSTRUCT        STRUCT
    MyString        BTYE        "This is a string"
    MTSTRUCT        ENDS

    ; With OPTION M510

    MyInst          MTSTRUCT    <0>

    ; Without OPTION M510, either of these statement is correct

    MyInst          MTSTRUCT    <<0>>

    MyInst          MTSTRUCT    {<0>}

Effects of the ? Initializer in Data Definitions with OPTION M510 -  When ?
is used as a data initializer, it is sometimes treated as a zero and
sometimes causes a byte to be left unspecified in the object file. The
conditional behavior for MASM 6.0 without OPTION M510 is explained in
Section 5.1.2. With OPTION M510, however, the ? initializer is always
treated as a zero unless it is used with the DUP operator. This rarely
affects program execution.

Current Address Operator with OPTION M510 - When OPTION M510 is enabled, the
value of the current address operator ($) for a structure instance is the
offset of the first byte of the instance. When OPTION M510 is not enabled,
the value of $ is the offset of the current field in the instance.

Segment Association for FAR Externals with OPTION M510 - With MASM 5.1, a
FAR external symbol defined inside a segment is considered to be inside that
segment unless a .MODEL directive is used. With MASM 6.0, such a symbol is
never considered to be inside that segment unless OPTION M510 is used, in
which case the MASM 5.1 behavior is emulated. Segment association for
externals affects the frame of fixups generated on references to the
symbols.

Defining Aliases Using EQU with OPTION M510 - In MASM 5.1, a  symbol can be
equated to another symbol. These equates are called "aliases" in MASM 5.1.
This behavior is simulated with OPTION M510.

If you don't use OPTION M510, aliases cannot be defined using EQU. The right
operand of an EQU directive must be an immediate expression or text. Change
aliases to use the TEXTEQU directive, which is described in Section 9.1.
This change should have no effect on your code but may cause an expression
to evaluate differently.

These examples illustrate MASM 5.1 code, MASM 6.0 code with OPTION M510, and
MASM 6.0 code without OPTION M510:

    ; MASM 5.1 code
    var1    EQU     3
    var2    EQU     var1 ; var2 taken as an alias
                        ; var2 references var1 anywhere var2 is
                        ;  used as a symbol

    ; MASM 6.0 with OPTION M510
    var1    EQU     3
    var2    EQU     var1 ; var2 taken as a var2 EQU <var1>
                        ; var2 substituted for var1 whenever
                        ;  text macros substituted

    ; MASM 6.0 without OPTION M510
    var1    EQU     3
    var2    EQU     var1 ; Treated as var2 EQU 3

Difference in Text Macro Expansions with OPTION M510 - When the name of a
text macro is supplied as a text item, MASM 5.1 replaces the text macro name
with its text value. However, if that text value contains other text macro
names, no recursive expansion occurs. With MASM 6.0, recursive expansion
occurs unless OPTION M510 is enabled, as shown in the following example:

    ; With OPTION M510

    tm1     EQU     <contains tm2>
    tm2     EQU     <value>

    tm3     CATSTR  tm1         ; == <contains tm2>

    ; Without OPTION M510

    tm3     CATSTR  tm1         ; == <contains value>

Conditional Directives and Missing Operands with OPTION M510 - MASM 5.1
considers a missing argument to be a zero. MASM 6.0 requires an argument
unless OPTION M510 is enabled.


A.2.2.2  OPTION OLDSTRUCTS

Changes made in MASM 6.0 that apply to structures are discussed in this
section. With OPTION OLDSTRUCTS or OPTION M510:


    ■   The plus operator can be used in structure field references in MASM
        6.0. (The dot operator is required with OPTION NOOLDSTRUCTS, the
        default.)

    ■   Labels and structure field names cannot have the same name with OPTION
        OLDSTRUCTS (but they can with OPTION NOOLDSTRUCTS).


Plus Operator Not Allowed with MASM 6.0 Structures - By default, each
reference to structure member names must use the dot (.) operator to
separate the structure variable name from the field name. Note that the dot
(.) operator cannot be used as the plus (+) operator, nor can the plus
operator be used as the dot operator.

To convert your code so that it does not need OPTION OLDSTRUCTS:


    ■   Qualify all structure field references

    ■   Change all uses of the dot operator ( . ) that occur outside of
        structure references to use the plus operator ( + )


If you remove OPTION OLDSTRUCTS from your code, the assembler generates
errors on all lines needing to be changed. Non-structure uses of the dot
operator result in error A2166:

    structure field expected

Unqualified structure references result in error A2006:

    undefined symbol : identifier

This example shows code that doesn't work under the default, OPTION
NOOLDSTRUCTS, and how to change it:

    ; OPTION OLDSTRUCTS (Does not work with OPTION NOOLDSTRUCTS)
    structname      STRUC
    a               BYTE  ?
    b               WORD  ?
    structname      ENDS

    structinstance  structname <>

            mov     ax, [bx].b
            mov     al, structinstance.a
            mov     ax, [bx].4

    ; OPTION NOOLDSTRUCTS (the MASM 6.0 default)
    structname      STRUCT
    a               BYTE  ?
    b               WORD  ?
    structname      ENDS

    structinstance  structname <>

            mov     ax, [bx].structname.b  ; Add qualifying type
            mov     al, structinstance.a   ; No change needed
            mov     ax, [bx]+4             ; Change dot to plus
    ; Alternative methods in MASM 6.0
            ASSUME  bx:PTR structname
            mov     ax, [bx] ; OR:

            mov     ax, (structname PTR[bx]).b

Non-Unique Structure Field Names Allowed in MASM 6.0 - With the default,
OPTION NOOLDSTRUCTS, label and structure field names may have the same name.
With OPTION OLDSTRUCTS (the MASM 5.1 default), labels and structure fields
cannot have the same name. For more information, see Section 5.2,
"Structures and Unions."


A.2.2.3  OPTION OLDMACROS

If you use MASM 6.0 without OPTION OLDMACROS or OPTION M510, the behavior of
macros is changed in several ways. If you want the MASM 5.1 macro behavior,
add OPTION OLDMACROS or OPTION M510 to your MASM 5.1 code.

Depending on the complexity of your MASM 5.1 macros and your programming
style, it may be easy to make the necessary changes to remove OPTION
OLDMACROS. This section describes the differences.

Commas Separating Macro Arguments - MASM 5.1 allows white spaces or commas
to separate arguments to macros. MASM 6.0 with OPTION NOOLDMACROS (the
default), requires commas between arguments. For example, in the macro call

    MyMacro  var1 var2 var3, var4

OPTION OLDMACROS passes four arguments (separated by spaces), but OPTION
NOOLDMACROS passes only two arguments (separated by a comma). To convert
your macro code, replace any space delimiters between macro arguments with
commas.

New Behavior with Ampersands in Macros - Using the MASM 6.0 assembler
default, OPTION NOOLDMACROS, causes ampersands (&) to be interpreted within
a macro differently than in MASM 5.1. The number of ampersands and their
positions in a statement determine the result of the macro expansion in MASM
5.1. Parameters for use in nested MASM 5.1 macros must be prefixed with
several ampersands, since the assembler removes one ampersand for each level
of macro expansion. Using OPTION OLDMACROS enables this behavior.

Without OPTION OLDMACROS, ampersands are removed only once no matter how
deeply nested the macro. To update your MASM 5.1 macros, a simple rule can
be followed: Replace every sequence of ampersands with a single ampersand.
The only exception to this is when macro parameters immediately precede and
follow the ampersand, and both are to be substituted. In this case, two
ampersands are needed. See Section 9.3.3, "Substitution Operator," for a
description of the new rules.

This example shows how to update a MASM 5.1 macro:

    ; OPTION OLDMACROS (the MASM 5.1 behavior)

    createNames     macro   arg
        irp         tail, <Next, Last>
            irp     num,  <1, 2>
            ; Define more names of the form: abcNext1?
    arg&&tail&&&num&&&?   label   BYTE
            ENDM
        ENDM
    ENDM

    ; OPTION NOOLDMACROS (the MASM 6.0 default)

    createNames     macro   arg
        for         tail, <Next, Last>  ; FOR is the MASM 6.0
            for     num,  <1, 2>        ;  synonym for irp
            ; Define more names of the form: abcNext1?
    arg&&tail&&num&?   label   BYTE
            ENDM
        ENDM
    ENDM


A.2.2.4  OPTION DOTNAME

MASM 5.1 allows names of identifiers to begin with a period. The MASM 6.0
default is OPTION NODOTNAME. Adding OPTION DOTNAME to your code provides the
MASM 5.1 behavior.

If you don't want to use this directive in your source code, rename the
identifiers whose names begin with a period.


A.2.2.5  OPTION EXPR16

The OPTION EXPR16 statement sets the expression word size to 16 bits. If you
do not have .386, .386P, .486, or .486P directives in your MASM 5.1 code,
OPTION EXPR16 is the default. For MASM 6.0, OPTION EXPR32 (an expression
word size of 32 bits) is the default.

It may not be easy to determine the effect of changing from 16-bit internal
expression size to 32-bit size. In many cases, the 32-bit word size results
in no change to MASM 5.1. code. However, problems may arise due to
differences in intermediate values during evaluation of expressions. If you
generate a listing file with the /Fl and /Sa command-line options with and
without  OPTION EXPR16, you can compare the files for differences.

It is illegal to change the expression size once it has been set with the
OPTION directive. Changing the CPU type to .386 or .486 also sets OPTION
EXPR32.


A.2.2.6  OPTION OFFSET

In MASM 5.1 code, offsets are computed with respect to the segment when the
.MODEL is not used. This is equivalent to OPTION OFFSET:SEGMENT. OPTION M510
adds OPTION OFFSET:SEGMENT to your code if there is no .MODEL directive.

When the .MODEL directive is used, offsets are computed with respect to the
group. This is equivalent to MASM 6.0's OPTION OFFSET:GROUP (the MASM 6.0
default).

Changing from OPTION OFFSET:SEGMENT to OPTION OFFSET:GROUP usually causes no
problems. However, it is not easy to determine if changes are needed.

The behavior of the OFFSET operator depends on the arguments used with
OPTION OFFSET. If no GROUP directives are used, no changes are needed.
Otherwise, use of the OFFSET operator must be examined to see if the operand
is in a grouped segment with no group override. If so, a segment name
override must be used. The following example shows equivalent statements for
OPTION OFFSET:SEGMENT and OPTION OFFSET:GROUP:

    ; OPTION OFFSET:SEGMENT
    MyGroup GROUP   MySeg

    MySeg   SEGMENT 'data'
    MyLabel LABEL   BYTE
            DW      OFFSET MyLabel
            DW      OFFSET MyGroup:MyLabel
            DW      OFFSET MySeg:MyLabel
    MySeg   ENDS

In this example, the first use of OFFSET must be changed to OFFSET
MySeg:MyLabel. The second and third uses do not need to be changed:

    ; OPTION OFFSET:GROUP
    MyGroup GROUP   MySeg

    MySeg   SEGMENT 'data'
    MyLabel LABEL   BYTE
            DW      OFFSET MySeg:MyLabel
            DW      OFFSET MyGroup:MyLabel
            DW      OFFSET MySeg:MyLabel
    MySeg   ENDS

Without OPTION M510, the OPTION OFFSET directive determines whether SEG is
group- or segment-relative. When you don't use OPTION M510, the SEG operator
behaves the same as the OFFSET operator does relative to OPTION OFFSET. With
OPTION M510, SEG is always segment-relative by default, regardless of the
current value of OPTION OFFSET (including the effect on OPTION OFFSET of a
.MODEL directive).

To remove OPTION M510 from your code, add OPTION OFFSET:SEGMENT if there is
no .MODEL directive in your code.


A.2.2.7  OPTION NOSCOPED

Under MASM 5.1, code labels are scoped (local to the current procedure) if
the .MODEL directive specifies a language type.They are not scoped (not
local to the current procedure) if a language is not specified. Without
OPTION M510 or OPTION NOSCOPED, code labels are always scoped.

If your MASM 5.1 code does not specify a language type and you want to
assemble without OPTION M510, add OPTION NOSCOPED to your code.

To determine which labels need to be changed, remove the OPTION NOSCOPED
directive and assemble the module. The assembler generates error A2006:

    undefined symbol : identifier

for each reference to a non-local symbol.


A.2.2.8  OPTION PROC

By default, MASM 6.0 procedures are public (OPTION PROC:PUBLIC), but you can
explicitly specify the default for procedure visibility with OPTION
PROC:PRIVATE or OPTION PROC:EXPORT.

If your module does not have a language specifier with the MODEL directive,
using OPTION M510 adds OPTION PROC:PRIVATE to the module. If you do not want
to use OPTION PROC:PRIVATE, you can add the PRIVATE keyword to each
procedure you want to make private. The following example shows how to
change MASM 5.1 code to make a procedure private:

    ; MASM 5.1 (OPTION PROC:PRIVATE)
    MyProc PROC NEAR

    ; MASM 6.0 (OPTION PROC:PUBLIC)
    MyProc PROC NEAR PRIVATE

This is necessary only to avoid naming conflicts between public names in
multiple modules or libraries. The symbol table in a listing file shows the
visibility (public, private, or export) of each procedure.


A.2.2.9  OPTION NOKEYWORD

MASM 5.1 allows you to use reserved words for names of identifiers, macro
parameters, and text macros. Several new reserved words have been added to
MASM 6.0. If your existing code uses a reserved word as a symbol name, your
code generates a syntax error on assembly.

Identifiers and text macros can be keywords if you disable individual
keywords with the OPTION NOKEYWORD directive. For example,

    OPTION NOKEYWORD:<INVOKE STRUCT>

removes two keywords, INVOKE and STRUCT from the reserved word list.

As an alternative to using OPTION NOKEYWORD, you can rename the offending
label. For example, a label named  Str  could be renamed  Str1.

The following list names all the new reserved words in MASM 6.0:

.BREAK           CMPXCHG          IRETDF           PUSHW
.CONTINUE        ECHO             IRETF            REAL10
.DOSSEG          EXTERN           LENGTHOF         REAL4
.ELSE            EXTERNDEF        LOOPD            REAL8
.ELSEIF          FAR16            LOOPED           REPEAT
.ENDIF           FAR32            LOOPEW           SBYTE
.ENDW            FLAT             LOOPNED          SDWORD
.EXIT            FLDENVD          LOOPNEW          SIGN?
.IF              FLDENVW          LOOPNZD          SIZEOF
.LISTALL         FNSAVED          LOOPNZW          STDCALL
.LISTIF          FNSAVEW          LOOPW            STRUCT
.LISTMACRO       FNSTENVD         LOOPZW           SUBTITLE
.LISTMACROALL    FNSTENVW         LOWWORD          SWORD
.NO87            FOR              LROFFSET         SYSCALL
.NOCREF          FORC             NEAR16           TEXTEQU
.NOLIST          FRSTORD          NEAR32           TR3
.NOLISTIF        FRSTORW          OPATTR           TR4
.NOLISTMACRO     FSAVED           OPTION           TR5
.REPEAT          FSAVEW           OVERFLOW?        TYPEDEF
.STARTUP         FSTENVD          PARITY?          UNION
.UNTIL           FSTENVW          POPAW            VARARG
.UNTILCXZ        GOTO             POPCONTEXT       WBINVD
.WHILE           HIGHWORD         PROTO            WHILE
ADDR             INVD             PUSHAW           XADD
ALIAS            INVLPG           PUSHCONTEXT      ZERO?
BSWAP            INVOKE           PUSHD
CARRY?

A.2.3  Changes to Instruction Encodings

MASM 6.0 contains changes to the encodings for several instructions. In some
cases, the changes help optimize code size.

Coprocessor Instructions - MASM 5.1 adds an extra NOP instruction before the
no-wait versions of coprocessor instructions. MASM 6.0 does not. In the rare
case that the missing NOP affects the timing, insert NOP.

Also, in .286 mode, MASM 6.0 does not prefix any 8087, 80287, 80387, or
80486 coprocessor instruction with FWAIT (unless the instruction is the WAIT
form of an instruction that has a NOWAIT form). MASM 5.1 prefixes some of
these instructions with FWAIT.

RET Instruction - If the operand to RET, RETN, or RETF is 0, MASM 6.0 uses
the one-byte encoding. MASM 5.1 generates the three-byte encoding in this
case. Thus, it is possible to suppress the epilogue generation but still
specify the default size for the RET (NEAR or FAR), by coding the return as


    RET 0

If the operand for RET, RETN, or RETF is an external absolute, MASM 6.0
generates the three-byte encoding. In this case, MASM 5.1 ignores the
parameter and generates the one-byte encoding.

LEA Instruction with Direct Memory Operands - When the second operand to the
LEA instruction is a direct memory operand (that is, the second operand does
not contain registers), MASM 6.0 encodes the instruction as

    mov     reg, OFFSET directmem

This is smaller and faster than the equivalent LEA encoding that MASM 5.1
generates. This should not affect your MASM 5.1 code.

Arithmetic Instructions - If your program uses the arithmetic instructions
ADC, ADD, AND, CMP, OR, SUB, SBB, and XOR, and the following conditions are
also true:


    ■   Either AX or EAX is the first operand

    ■   A sign-extendable byte constant is the second operand


then the instructions are encoded in MASM 5.1 as ax/eax, imm16/32.

MASM 6.0 uses this encoding instead: rm16/32. imm8.

With the AX register, there is no size or speed difference between the two
encodings. In the EAX case, MASM 6.0's encoding is two bytes smaller. The
OPTION NOSIGNEXTEND directive provides the MASM 5.1 behavior.








Appendix B  BNF Grammar
────────────────────────────────────────────────────────────────────────────

The BNF grammar gives the full description of the MASM language. The MASM
BNF follows the Backus-Naur Form (BNF) for grammar notation.

You can use the BNF to determine the exact syntax for any language
component. The BNF format clearly defines recursive definitions and shows
all the available options for any placeholder.


Definitions

Terminals are endpoints in a BNF definition. No other resolution of their
definition is possible. Terminals include the set of reserved words and
user-defined objects.

Nonterminals are placeholders in the BNF definition. All nonterminals are
defined elsewhere in the BNF.

The BNF references two types of expressions before they are formally
defined: constExpr and immExpr. A constExpr is an expression whose value is
not relocatable and not completely known at assembly time. An immExpr is
similar to a constExpr, except that it may also be relocatable.


Conventions

The conventions use different font attributes for different items in the
BNF. The symbols and formats are as follows:

Attribute                         Description
────────────────────────────────────────────────────────────────────────────
nonterminal                       Italic type indicates nonterminals.

RESERVED                          Terminals in boldface type are literal
                                    reserved words and symbols that must be
                                    entered as shown. Characters in this
                                    context are always case insensitive.

« »                               Objects enclosed in double brackets (« »)
                                    are optional. The brackets do not
                                    actually appear in the source code.

|                                 A vertical bar indicates a choice
                                    between the items on each side of the
                                    bar.

Attribute                         Description
────────────────────────────────────────────────────────────────────────────
.8086                             Underlined items indicate the default
                                    option if one is given.

default typeface                  Characters in the set described or
                                    listed can be used as terminals in MASM
                                    statements.


How to Use

To illustrate the use of the BNF, Figure B.1 explores the definition of the
TYPEDEF directive by starting with the nonterminal typedefDir.

Of course typedefDir is also an option given in the definition for a
nonterminal "higher" than typedefDir. Look at the BNF definition for
generalDir as an example.

The entries under each horizontal brace in Figure B.1 are terminals (such as
NEAR16, NEAR32, FAR16, and FAR32) or nonterminals (such as qualifier,
qualifiedType, distance, and protoSpec) that can be further defined. Each
nonterminal (italicized word) in the typedefDir definition is also an entry
in the BNF. Three vertical dots mean that the BNF description for that
nonternminal is not illustrated in this figure (but is in the BNF).

Definitions can be recursive. As an example, note that qualifiedType is used
in one of the two possible definitions for qualifiedType and is also a
component of the definition for qualifier.

(This figure may be found in the printed book.)

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
;;                                endOfLine
                                    | comment
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | comment

=Dir                              id = immExpr ;;

addOp                             + | -

aExpr                             term
                                    | aExpr && term

alpha                             a thru z
                                    | A thru Z
                                    | ? | @ | _ | $

altId                             id

arbitraryText                     charList

asmInstruction                    mnemonic « exprList »

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

assumeDir                         ASSUME assumeList ;;
                                    | ASSUME NOTHING ;;

assumeList                        assumeRegister
                                    | assumeList , assumeRegister

assumeReg                         register : assumeVal

assumeRegister                    assumeSegReg
                                    | assumeReg

assumeSegReg                      segmentRegister : assumeSegVal

assumeSegVal                      frameExpr
                                    | NOTHING | ERROR

assumeVal                         qualifiedType
                                    | NOTHING | ERROR
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | NOTHING | ERROR

bcdConst                          « sign » decNumber

binaryOp                          == | != | >= | <= | > | < | &

bitDef                            bitFieldId : bitFieldSize « = constExpr
                                    »

bitDefList                        bitDef
                                    | bitDefList , « ;; » bitDef

bitFieldId                        id

bitFieldSize                      constExpr

blockStatements                   directiveList
                                    | .CONTINUE « .IF cExpr »
                                    | .BREAK « .IF cExpr »
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | .BREAK « .IF cExpr »

byteRegister                      AL | AH | BL | BH | CL | CH | DL | DH

cExpr                             aExpr
                                    | cExpr || aExpr

character                         Any character value (ordinal in the
                                    range 0-255)
                                    except linefeed (10)

charList                          character
                                    | charList character

className                         string

commDecl                          « nearfar » « langType » id : commType
                                    « : constExpr »

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

commDir                           COMM commList ;;

comment                           ; text ;;

commentDir                        COMMENT delimiter
                                    text
                                    text delimiter text ;;

commList                          commDecl
                                    | commList , commDecl

commType                          type
                                    | constExpr

constant                          digits « radixOverride »

constExpr                         expr

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

contextDir                        PUSHCONTEXT contextItemList ;;
                                    | POPCONTEXT contextItemList ;;

contextItem                       ASSUMES | RADIX | LISTING | CPU | ALL

contextItemList                   contextItem
                                    | contextItemList , contextItem

controlBlock                      whileBlock
                                    | repeatBlock

controlDir                        controlIf
                                    | controlBlock

controlElseif                     .ELSEIF cExpr ;;
                                    directiveList
                                    « controlElseif »

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

controlIf                         .IF cExpr ;;
                                    directiveList
                                    « controlElseif »
                                    « .ELSE ;;
                                    directiveList »
                                    .ENDIF ;;

coprocessor                       .8087 | .287 | .387 | .NO87

crefDir                           crefOption ;;

crefOption                        .CREF
                                    | .XCREF « idList »
                                    | .NOCREF « idList »

cxzExpr                           expr
                                    | ! expr
                                    | expr == expr
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | expr == expr
                                    | expr != expr

dataDecl                          DB | DW | DD | DF | DQ | DT | dataType |
                                    typeId

dataDir                           « id » dataItem ;;

dataItem                          dataDecl scalarInstList
                                    | structTag structInstList
                                    | typeId structInstList
                                    | unionTag structInstList
                                    | recordTag recordInstList

dataType                          BYTE | SBYTE | WORD | SWORD | DWORD
                                    | SDWORD | FWORD | QWORD | TBYTE
                                    | REAL4 | REAL8 | REAL10

decdigit                          0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
decdigit                          0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

decNumber                         decdigit
                                    | decNumber decdigit

delimiter                         Any character other than
                                    whiteSpaceCharacter

digits                            decdigit
                                    | digits decdigit
                                    | digits hexdigit

directive                         generalDir
                                    | segmentDef

directiveList                     directive
                                    | directiveList directive

distance                          nearfar
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
distance                          nearfar
                                    | NEAR16 | NEAR32 | FAR16 | FAR32

e01                               e01 orOp e02
                                    | e02

e02                               e02 AND e03
                                    | e03

e03                               NOT e04
                                    | e04

e04                               e04 relOp e05
                                    | e05

e05                               e05 addOp e06
                                    | e06

e06                               e06 mulOp e07
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
e06                               e06 mulOp e07
                                    | e06 shiftOp e07
                                    | e07

e07                               e07 addOp e08
                                    | e08

e08                               HIGH e09
                                    | LOW e09
                                    | HIGHWORD e09
                                    | LOWWORD e09
                                    | e09

e09                               OFFSET e10
                                    | LROFFSET e10
                                    | TYPE e10
                                    | THIS e10
                                    | e09 PTR e10
                                    | e09 : e10
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | e09 : e10
                                    | e10

e10                               e10 . e11
                                    | e10 « expr »
                                    | e11

e11                               ( expr )
                                    | « expr »
                                    | WIDTH id
                                    | MASK id
                                    | SIZE sizeArg
                                    | SIZEOF sizeArg
                                    | LENGTH id
                                    | LENGTHOF id
                                    | recordConst
                                    | string
                                    | constant
                                    | type
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | type
                                    | id
                                    | $
                                    | segmentRegister
                                    | register
                                    | ST
                                    | ST ( expr )

echoDir                           ECHO arbitraryText ;;

elseifBlock                       elseifStatement ;;
                                    directiveList
                                    « elseifBlock »

elseifStatement                   ELSEIF constExpr
                                    | ELSEIFE constExpr
                                    | ELSEIFB textItem
                                    | ELSEIFNB textItem
                                    | ELSEIFDEF id
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | ELSEIFDEF id
                                    | ELSEIFNDEF id
                                    | ELSEIFDIF textItem , textItem
                                    | ELSEIFDIFI textItem , textItem
                                    | ELSEIFIDN textItem , textItem
                                    | ELSEIFIDNI textItem , textItem
                                    | ELSEIF1
                                    | ELSEIF2

endDir                            END « immExpr » ;;

endpDir                           procId ENDP ;;

endsDir                           id ENDS ;;

equDir                            textMacroId EQU equType ;;

equType                           immExpr
                                    | textLiteral
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | textLiteral

errorDir                          errorOpt ;;

errorOpt                          .ERR « textItem »
                                    | .ERRE constExpr « optText »
                                    | .ERRNZ constExpr « optText »
                                    | .ERRB textItem « optText »
                                    | .ERRNB textItem « optText »
                                    | .ERRDEF id « optText »
                                    | .ERRNDEF id « optText »
                                    | .ERRDIF textItem , textItem « optText
                                    »
                                    | .ERRDIFI textItem , textItem « optText
                                    »
                                    | .ERRIDN textItem , textItem « optText
                                    »
                                    | .ERRIDNI textItem , textItem « optText
                                    »
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    »
                                    | .ERR1 « textItem »
                                    | .ERR2 « textItem »

exitDir                           .EXIT « expr » ;;

exitmDir:                         EXITM
                                    | EXITM textItem

exponent                          E « sign » decNumber

expr                              SHORT e05
                                    | .TYPE e01
                                    | OPATTR e01
                                    | e01

exprList                          expr
                                    | exprList , expr

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

externDef                         « langType » id « ( altId ) » :
                                    externType

externDir                         externKey externList ;;

externKey                         EXTRN | EXTERN | EXTERNDEF

externList                        externDef
                                    | externList , « ;; » externDef

externType                        ABS
                                    | qualifiedType

fieldAlign                        constExpr

fieldInit                         « initValue »
                                    | structInstance

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

fieldInitList                     fieldInit
                                    | fieldInitList , « ;; » fieldInit

fileChar                          Any character value (ordinal in the
                                    range 0-255) except backspace (8), tab
                                    (9), linefeed (10), vertical tab (11),
                                    form feed (12), carriage return (13), ^Z
                                    (26), or space (32)

fileCharList                      fileChar
                                    | fileCharList fileChar

fileSpec                          fileCharList
                                    | textLiteral

flagName                          ZERO? | CARRY? | OVERFLOW?
                                    | SIGN? | PARITY?

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

floatNumber                       « sign » decNumber . « decNumber » «
                                    exponent »
                                    | digits R
                                    | digits r

forcDir                           FORC | IRPC

forDir                            FOR | IRP

forParm                           id « : forParmType »

forParmType                       REQ
                                    | = textLiteral

frameExpr                         expr

generalDir                        modelDir | segOrderDir | nameDir
                                    | includeLibDir | commentDir
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | includeLibDir | commentDir
                                    | groupDir | assumeDir
                                    | structDir | recordDir | typedefDir
                                    | externDir | publicDir | commDir |
                                    protoTypeDir
                                    | equDir | =Dir | textDir
                                    | contextDir | optionDir | processorDir
                                    | radixDir
                                    | titleDir | pageDir | listDir
                                    | crefDir | echoDir
                                    | ifDir | errorDir | includeDir
                                    | macroDir | macroCall | macroRepeat |
                                    purgeDir
                                    | macroWhile | macroFor | macroForc
                                    | aliasDir

gpRegister                        AX | EAX | BX | EBX | CX | ECX | DX |
                                    EDX
                                    | BP | EBP | SP | ESP | DI | EDI | SI |
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | BP | EBP | SP | ESP | DI | EDI | SI |
                                    ESI

groupDir                          groupId GROUP segIdList

groupId                           id

hexdigit                          a | b | c | d | e | f
                                    | A | B | C | D | E | F

id                                alpha
                                    | id alpha
                                    | id decdigit

idList                            id
                                    | idList , id

ifDir                             ifStatement ;;
                                    directiveList
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    directiveList
                                    « elseifBlock »
                                    « ELSE ;;
                                    directiveList »
                                    ENDIF ;;

ifStatement                       IF constExpr
                                    | IFE constExpr
                                    | IFB textItem
                                    | IFNB textItem
                                    | IFDEF id
                                    | IFNDEF id
                                    | IFDIF textItem , textItem
                                    | IFDIFI textItem , textItem
                                    | IFIDN textItem , textItem
                                    | IFIDNI textItem , textItem
                                    | IF1
                                    | IF2

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

immExpr                           expr

includeDir                        INCLUDE fileSpec ;;

includeLibDir                     INCLUDELIB fileSpec ;;

initValue                         immExpr
                                    | string
                                    | ?
                                    | constExpr DUP ( scalarInstList )
                                    | floatNumber
                                    | bcdConst

inSegDir                          « labelDef » inSegmentDir

inSegDirList                      inSegDir
                                    | inSegDirList inSegDir

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

inSegmentDir                      instruction
                                    | dataDir
                                    | controlDir
                                    | startupDir
                                    | exitDir
                                    | offsetDir
                                    | labelDir
                                    | procDir « localDirList » «
                                    inSegDirList » endpDir
                                    | invokeDir
                                    | generalDir

instrPrefix                       REP | REPE | REPZ | REPNE | REPNZ | LOCK

instruction                       « instrPrefix » asmInstruction

invokeArg                         register :: register
                                    | expr
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | expr
                                    | ADDR expr

invokeDir                         INVOKE expr « , « ;; » invokeList » ;;

invokeList                        invokeArg
                                    | invokeList , « ;; » invokeArg

keyword                           Any reserved word

keywordList                       keyword
                                    | keyword keywordList

labelDef                          id :
                                    | id ::
                                    | @:

labelDir                          id LABEL qualifiedType ;;

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

langType                          C | PASCAL | FORTRAN | BASIC
                                    | SYSCALL | STDCALL

listDir                           listOption ;;

listOption                        .LIST
                                    | .NOLIST | .XLIST
                                    | .LISTALL
                                    | .LISTIF | .LFCOND
                                    | .NOLISTIF | .SFCOND
                                    | .TFCOND
                                    | .LISTMACROALL | .LALL
                                    | .NOLISTMACRO | .SALL
                                    | .LISTMACRO | .XALL

localDef                          LOCAL idList ;;

localDir                          LOCAL parmList ;;
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
localDir                          LOCAL parmList ;;

localDirList                      localDir
                                    | localDirList localDir

localList                         localDef
                                    | localList localDef

macroArg                          % constExpr
                                    | % textMacroId
                                    | % macroFuncId ( macroArgList )
                                    | string
                                    | arbitraryText
                                    | < arbitraryText >

macroArgList                      macroArg
                                    | macroArgList , macroArg

macroBody                         « localList »
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
macroBody                         « localList »
                                    macroStmtList

macroCall                         id macroArgList ;;
                                    | id ( macroArgList )

macroDir                          id MACRO « macroParmList » ;;
                                    macroBody
                                    ENDM ;;

macroFor                          forDir forParm , < macroArgList > ;;
                                    macroBody
                                    ENDM ;;

macroForc                         forcDir id , textLiteral ;;
                                    macroBody
                                    ENDM ;;

macroFuncId                       id
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
macroFuncId                       id

macroId                           macroProcId
                                    | macroFuncId

macroIdList                       macroId
                                    | macroIdList , macroId

macroLabel                        id

macroParm                         id « : parmType »

macroParmList                     macroParm
                                    | macroParmList , « ;; » macroParm

macroProcId                       id

macroRepeat                       repeatDir constExpr ;;
                                    macroBody
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    macroBody
                                    ENDM ;;

macroStmt                         directive
                                    | exitmDir
                                    | : macroLabel
                                    | GOTO macroLabel

macroStmtList                     macroStmt ;;
                                    | macroStmtList macroStmt ;;

macroWhile                        WHILE constExpr ;;
                                    macroBody
                                    ENDM ;;

mapType                           ALL | NONE | NOTPUBLIC

memOption                         TINY | SMALL | MEDIUM | COMPACT
                                    | LARGE | HUGE | FLAT
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | LARGE | HUGE | FLAT

mnemonic                          Instruction name

modelDir                          .MODEL memOption « , modelOptlist » ;;

modelOpt                          langType
                                    | osType
                                    | stackOption

modelOptlist                      modelOpt
                                    | modelOptlist , modelOpt

module                            « directiveList » endDir

mulOp                             * | / | MOD

nameDir                           NAME id ;;

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

nearfar                           NEAR | FAR

nestedStruct                      structHdr « id » ;;
                                    structBody
                                    ENDS ;;

offsetDir                         offsetDirType ;;

offsetDirType                     EVEN
                                    | ORG immExpr
                                    | ALIGN « constExpr »

offsetType                        GROUP | SEGMENT | FLAT

oldRecordFieldList                « constExpr »
                                    | oldRecordFieldList , « constExpr »

optionDir                         OPTION optionList ;;
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
optionDir                         OPTION optionList ;;

optionItem                        CASEMAP : mapType
                                    | DOTNAME | NODOTNAME
                                    | EMULATOR | NOEMULATOR
                                    | EPILOGUE : macroId
                                    | LANGUAGE : langType
                                    | LJMP | NOLJMP
                                    | M510 | NOM510
                                    | NOKEYWORD : < keywordList >
                                    | NOSIGNEXTEND
                                    | OFFSET : offsetType
                                    | OLDMACROS | NOOLDMACROS
                                    | OLDSTRUCTS | NOOLDSTRUCTS
                                    | PROC : oVisibility
                                    | PROLOGUE : macroId
                                    | READONLY | NOREADONLY
                                    | SCOPED | NOSCOPED
                                    | SEGMENT : segSize
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | SEGMENT : segSize

optionList                        optionItem
                                    | optionList , « ;; » optionItem

optText                           , textItem

orOp                              OR | XOR

osType                            OS_DOS | OS_OS2

oVisibility                       PUBLIC | PRIVATE | EXPORT

pageDir                           PAGE « pageExpr » ;;

pageExpr                          +
                                    | « pageLength » « , pageWidth »

pageLength                        constExpr
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
pageLength                        constExpr

pageWidth                         constExpr

parm                              parmId « : qualifiedType »
                                    | parmId [ constExpr ] « : qualifiedType
                                    »

parmId                            id

parmList                          parm
                                    | parmList , « ;; » parm

parmType                          REQ
                                    | = textLiteral
                                    | VARARG

pOptions                          « distance » « langType » « oVisibility
                                    »
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    »

primary                           expr binaryOp expr
                                    | flagName
                                    | expr

procDir                           procId PROC « pOptions » « <
                                    macroArgList  > »
                                    « usesRegs » « procParmList »

processor                         .8086
                                    | .186
                                    | .286 | .286C | .286P
                                    | .386 | .386C | .386P
                                    | .486 | .486P

processorDir                      processor ;;
                                    | coprocessor ;;

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

procId                            id

procParmList                      « « , « ;; » » parmList »
                                    « « , « ;; » » parmId :VARARG»

protoArg                          « id » : qualifiedType

protoArgList                      « « , « ;; » » protoList »
                                    « « , « ;; » » « id » :VARARG »

protoList                         protoArg
                                    | protoList , « ;; » protoArg

protoSpec                         « distance » « langType » « protoArgList
                                    »
                                    | typeId

protoTypeDir                      id PROTO protoSpec
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
protoTypeDir                      id PROTO protoSpec

pubDef                            « langType » id

publicDir                         PUBLIC pubList ;;

pubList                           pubDef
                                    | pubList , « ;; » pubDef

purgeDir                          PURGE macroIdList

qualifiedType                     type
                                    | « distance » PTR « qualifiedType »

qualifier                         qualifiedType
                                    | PROTO protoSpec

quote                             "
                                    | '
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | '

radixDir                          .RADIX constExpr ;;

radixOverride                     h | o | q | t | y
                                    | H | O | Q | T | Y

recordConst                       recordTag { oldRecordFieldList }
                                    | recordTag < oldRecordFieldList >

recordDir                         recordTag RECORD bitDefList ;;

recordFieldList                   « constExpr »
                                    | recordFieldList , « ;; » « constExpr »

recordInstance                    { « ;; »  recordFieldList « ;; » }
                                    |  < oldRecordFieldList >
                                    | constExpr DUP ( recordInstance )

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

recordInstList                    recordInstance
                                    | recordInstList , « ;; » recordInstance

recordTag                         id

register                          specialRegister
                                    | gpRegister
                                    | byteRegister

regList                           register
                                    | regList register

relOp                             EQ | NE | LT | LE | GT | GE

repeatBlock                       .REPEAT ;;
                                    blockStatements ;;
                                    untilDir ;;

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

repeatDir                         REPEAT | REPT

scalarInstList                    initValue
                                    | scalarInstList , « ;; » initValue

segAlign                          BYTE | WORD | DWORD | PARA | PAGE

segAttrib                         PUBLIC
                                    | STACK
                                    | COMMON
                                    | MEMORY
                                    | AT constExpr
                                    | PRIVATE

segDir                            .CODE « segId »
                                    | .DATA
                                    | .DATA?
                                    | .CONST
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | .CONST
                                    | .FARDATA « segId »
                                    | .FARDATA? « segId »
                                    | .STACK « constExpr »

segId                             id

segIdList                         segId
                                    | segIdList , segId

segmentDef                        segmentDir « inSegDirList » endsDir
                                    | simpleSegDir « inSegDirList » «
                                    endsDir »

segmentDir                        segId SEGMENT « segOptionList » ;;

segmentRegister                   CS | DS | ES | FS | GS | SS

segOption                         segAlign
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
segOption                         segAlign
                                    | segRO
                                    | segAttrib
                                    | segSize
                                    | className

segOptionList                     segOption
                                    | segOptionList segOption

segOrderDir                       .ALPHA | .SEQ | .DOSSEG | DOSSEG

segRO                             READONLY

segSize                           USE16 | USE32 | FLAT

shiftOp                           SHR | SHL

sign                              - | +

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

simpleExpr                        ( cExpr )
                                    | primary

simpleSegDir                      segDir ;;

sizeArg                           id
                                    | type
                                    | e10

specialChars                      : | . | « | » | ( | ) | < | > | { | }
                                    | + | - | / | * | & | % | !
                                    | ' |  | = | ; | , | "
                                    | white space (8, 9, 11-13, 26, 32) |
                                    endOfLine

specialRegister                   CR0 | CR2 | CR3
                                    | DR0 | DR1 | DR2 | DR3 | DR6 | DR7
                                    | TR3 | TR4 | TR5 | TR6 | TR7
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | TR3 | TR4 | TR5 | TR6 | TR7

stackOption                       NEARSTACK | FARSTACK

startupDir                        .STARTUP ;;

stext                             stringChar
                                    | stext stringChar

string                            quote « stext » quote

stringChar                        quote quote
                                    | Any character value (ordinal in the
                                    range 0-255)
                                    except linefeed (10) and elements of
                                    quote

structBody                        structItem ;;
                                    | structBody structItem ;;
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | structBody structItem ;;

structDir                         structTag structHdr « fieldAlign »
                                    «, NONUNIQUE » ;;
                                    structBody
                                    structTag ENDS ;;

structHdr                         STRUC | STRUCT | UNION

structInstance                    < « fieldInitList » >
                                    | { « ;; » « fieldInitList » « ;; » }
                                    | constExpr DUP ( structInstList )

structInstList                    structInstance
                                    | structInstList , « ;; » structInstance

structItem                        dataDir
                                    | generalDir
                                    | offsetDir
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | offsetDir
                                    | nestedStruct

structTag                         id

term                              simpleExpr
                                    | ! simpleExpr

text                              textLiteral
                                    | text character
                                    | ! character text
                                    | character
                                    | ! character

textDir                           id textMacroDir ;;

textItem                          textLiteral
                                    | textMacroId
                                    | % constExpr
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
                                    | % constExpr

textLen                           constExpr

textList                          textItem
                                    | textList , « ;; » textItem

textLiteral                       < text >;;

textMacroDir                      CATSTR « textList »
                                    | TEXTEQU « textList »
                                    | SIZESTR textItem
                                    | SUBSTR textItem , textStart « ,
                                    textLen »
                                    | INSTR « textStart , » textItem ,
                                    textItem

textMacroId                       id

Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────

textStart                         constExpr

titleDir                          titleType arbitraryText ;;

titleType                         TITLE | SUBTITLE | SUBTTL

type                              structTag
                                    | unionTag
                                    | recordTag
                                    | distance
                                    | dataType
                                    | typeId

typedefDir                        typeId TYPEDEF qualifier

typeId                            id

unionTag                          id
Nonterminal                       Definition
────────────────────────────────────────────────────────────────────────────
unionTag                          id

untilDir                          .UNTIL cExpr ;;
                                    .UNTILCXZ « cxzExpr » ;;

usesRegs                          USES regList

whileBlock                        .WHILE cExpr ;;
                                    blockStatements ;;
                                    .ENDW

whiteSpaceCharacter               ASCII 8, 9, 11-13, 32








Appendix C  Generating and Reading Assembly Listings
────────────────────────────────────────────────────────────────────────────

MASM creates an assembly listing of your source file whenever you select the
appropriate option in PWB, use one of the related source code directives, or
specify the /Fl option on the MASM command line. The assembly listing
contains both the statements in the source file and the binary code (if any)
generated for each statement. The listing also shows the names and values of
all labels, variables, and symbols in your file.

The assembler creates tables for macros, structures, unions, records,
segments, groups, and other symbols. These tables are placed at the end of
the assembly listing. MASM lists only the types of symbols encountered in
the program. For example, if your program has no macros, the symbol table
does not have a macros section.


C.1  Generating Listing Files

MASM 6.0 provides several ways to generate a listing file. From within PWB,
follow these steps:


    1.  From the "Options" menu, choose MASM Options.

    2.  In the MASM Options dialog box, choose Set Debug or Release Options.


The resulting dialog box for Set Debug or Release Options lists the choices
summarized in Table C.1. This table also shows the equivalent directives you
can use in your source code or the equivalent command-line options.

Table C.1  Options for Generating or Modifying Listing Files

╓┌─────────────────────┌──────────────────┌──────────────────┌───────────────►
To generate this                         In source          From command
information:          In PWB(1),         code, enter:       line, enter:
                        select:
─────────────────────────────────────────────────────────────────────────────
Default               Generate Listing   .LIST (default)    /Fl
listing─includes all  File
To generate this                         In source          From command
information:          In PWB(1),         code, enter:       line, enter:
                        select:
listing─includes all  File
assembled lines

Turn off all source   Generate Listing   .NOLIST            ─
listings (overrides   File (turn off)    (synonym =
all listing                              .SFCOND)
directives)

List all source       Include All        .LISTALL           /Fl /Sa
lines, including      Source Lines
false conditionals
and generated code

Show                  List Generated     ─                  /Fl /Sg
assembler-generated   Instructions
code

Include false         List False         .LISTIF            /Fl /Sx
To generate this                         In source          From command
information:          In PWB(1),         code, enter:       line, enter:
                        select:
Include false         List False         .LISTIF            /Fl /Sx
conditionals(2)       Conditionals       (synonym =
                                            .LFCOND)

Suppress listing of   List False         .NOLISTIF          ─
any subsequent        Conditionals       (synonym =
conditional blocks    (turn off)         .SFCOND)
whose condition is
false

Toggle between        ─                  .TFCOND            ─
.LISTIF and
.NOLISTIF

Suppress symbol       Generate Symbol    ─                  /Fl /Sn
table generation      Table (turn off
                        the default)

To generate this                         In source          From command
information:          In PWB(1),         code, enter:       line, enter:
                        select:

List all processed    ─                  .LISTMACROALL      ─
macro statements                         (synonym = .LALL)

List only             ─                  .LISTMACRO         ─
instructions, data,                      (default)
and segment                              (synonym = .XALL)
directives in macros

Turn off all listing  ─                  .NOLISTMACRO       ─
during macro                             (synonym = .SALL)
expansion

Specify title for     ─                  TITLE name         /St
each page (use only
once per file)

Specify subtitle for  ─                  SUBTITLE name      /Ss
To generate this                         In source          From command
information:          In PWB(1),         code, enter:       line, enter:
                        select:
Specify subtitle for  ─                  SUBTITLE name      /Ss
page

Designate page        ─                  PAGE «length,      /Sp length
length and line                          width»«+»          /Sl width
width, increment
section number, or
generate page breaks

─────────────────────────────────────────────────────────────────────────────



(1)  Select MASM Options from the "Options" menu. Then choose Set Dialog
Options from the MASM Options dialog box.


(2)  See Section 1.3.2.2, "Conditional Directives."



C.1.1  Generating a First Pass Listing

The /EP command-line option may be used to produce a listing during the
assembler's first pass. This listing is printed to standard output and is
suitable for processing by the assembler. A first pass listing can be
helpful for locating problems when there are many errors, or when unmatched
nesting errors occur.


C.1.2  Controlling the Contents of the Listing File

With source code directives you can vary the contents of the listing file
for different sections of the source file, whereas (in the absence of source
code directives) the PWB or command-line options affect the entire listing.


The /Fl command-line option enables a listing. Without /Fl, no listing is
produced. The /S options are legal without /Fl, but they have no effect.

A file generated with /Fl shows all assembled source lines and provides a
header at the beginning of the listing. It also adds a header before the
symbol table and each section of the symbol table but does not add any page
breaks between sections.


C.1.3  Controlling Listing Information on Macros

The only way to control the listing of macro expansions is with the source
directives. The assembler always lists the full macro definition. The
directives affect only expansion of macro calls. Macro comments are never
listed in macro expansions. The default, .LISTMACRO, ignores comments and
equates. The .NOLISTMACRO directive shows the initial macro call but not the
source lines generated by the initial call or by recursive calls.

The assembler lists normal comments in macros only when you specify the
.LISTMACROALL directive. This directive produces all statements processed
during a macro expansion, including normal comments (preceded by a single
semicolon) but not macro comments (preceded by a double semicolon).


C.1.4  Controlling the Page Format

With source code directives or command-line options, you can specify the
line length, page length, title, and subtitle of the pages in a listing
file. In PWB, you can enter listing file options in the "Additional Options"
section of the MASM Options dialog box. Table C.1 gives the command-line
options and source code listings for control of page format.


C.1.5  Precedence of Command-Line Options and Listing Directives

Since command-line options and source code directives can specify opposite
behavior for the same listing file option, the assembler interprets the
commands according to the precedence levels below. Selecting PWB options is
equivalent to specifying /Fl /Sletter on the command line:


    ■   /Sa overrides any source code directives that suppress listing.

    ■   Source code directives override all command-line options except /Sa.

    ■   .NOLIST overrides other listing directives such as .NOLISTIF and
        .LISTMACROALL.

    ■   The /Sx, /Ss, /Sp, and /Sl options set initial values for their
        respective features. Directives in the source file override these
        command-line options.



C.2  Reading the Listing File

The first column of the listing file gives the offset and binary code
generated by the assembler. The next column gives the source statement
exactly as it appears in the source file or as expanded by a macro. Various
symbols and abbreviations in this column provide information about the code,
as explained below.


C.2.1  Code Generated

The assembler lists the code generated from the statements of a source file.
Each line has this syntax:

    offset [[code]]

The offset is the offset from the beginning of the current segment to the
code. If the statement generates code or data, code shows the numeric value
in hexadecimal notation if the value is known at assembly time. If the value
is calculated at run time, the assembler indicates what action is necessary
to compute the value.


C.2.2  Error Messages

If any errors occur during assembly, each error message and error number
appears directly below the statement where the error occurred. An example of
an error line and message is shown below:

    mov     ax, [dx][di] listtst.asm(66):
    error A2031: must be index or base register


C.2.3  Symbols and Abbreviations

The assembler uses the symbols and abbreviations shown in Table C.2 to
indicate addresses that need to be resolved by the linker or values that
were generated in a special way. The example in this section illustrates
many of these symbols. The numbers in column one correspond to the location
of this symbol in the sample listing file.

The listing file was produced using "List-Generated Instructions" from PWB
(or using /Fl /Sg from the command line).

Table   C.2 Symbols and Abbreviations in Listings

╓┌──────┌──────────┌─────────────────────────────────────────────────────────╖
Label  Character  Meaning
────────────────────────────────────────────────────────────────────────────
1      C          Line from include file
2      =          EQU or equal-sign (=) directive
3      nn[xx]     DUP expression: nn copies of the value xx
4      ----       Segment/group address (linker must resolve)
Label  Character  Meaning
────────────────────────────────────────────────────────────────────────────
4      ----       Segment/group address (linker must resolve)
4      R          Relocatable address (linker must resolve)
4      *          Assembler-generated code
5      E          External address (linker must resolve)
6      n          Macro-expansion nesting level (+ if more than 9)
7      |          Operator size override
8      &          Address size override
9      nn:        Segment override in statement
10     nn/        REP or LOCK prefix instruction
────────────────────────────────────────────────────────────────────────────


The sample listing file also shows the size of structures and unions in the
first column.

    Microsoft (R) Macro Assembler Version 6.00 Nov 13 01:27:05 1990
    listtst.asm                                  Page 1 - 1

        1             2

    .MODEL  small, c
                                .386
                                .DOSSEG
                                .STACK  256
                                INCLUDE dos.mac
                    C StrDef  MACRO   name1, text
                    C name1   BYTE    &text
                    C         BYTE    13d, 10d
                    C l&name1 EQU     LENGTHOF name1
                    C         ENDM
                    C
                    C Display MACRO   string
                    C         mov     ah, 09h
                    C         mov     dx, OFFSET string
                    C         int     21h
                    C         ENDM
                    C
    = 0020              num     EQU     20h
                        COLOR   RECORD  b:1, r:3=1, i:1=1, f:3=7
    = 35                value   TEXTEQU %3 + num
    = 32                tnum    TEXTEQU %num
    = 04                strpos  TEXTEQU @InStr( , <person>, son> )

    PutStr  PROTO   pMsg:PTR BYTE

    0004                DATE    STRUCT
    0000  05            month   BYTE    5
    0001  07            day     BYTE    7
    0002  07C3          year    WORD    1987
                        DATE    ENDS

    0002                U1      UNION
    0000  0028          fsize   WORD    40
                        bsize   BYTE    60
                        U1      ENDS

    0000                        .DATA

        3

    0000 00000000       ddData  DWORD   ?
    0004 1F             text    COLOR   <>
    0005 09 16 07C3     today   DATE    <9,22,1987>
    0009 00             flag    BYTE    0
    000A  001E [        buffer  WORD    30 DUP (0)
            0000
        ]

    StrDef   ending, "Finished."
    0046 46 69 6E 69 73 68   1  ending   BYTE    "Finished."
        65 64 2E
    004F  0D 0A              1           BYTE    13d, 10d
    = 0009                   1  lending  EQU     LENGTHOF ending
    0051 54 68 69 73 20 69      Msg      BYTE    "This is a string","0"
        73 20 61 20 73 74
        72 69 6E 67 30

    float    TYPEDEF      REAL4
                        FPBYTE   TYPEDEF FAR  PTR BYTE
    0062 ---- 0051 R   FPMSG    FPBYTE       Msg
                        PBYTE    TYPEDEF      PTR BYTE
                        NPWORD   TYPEDEF NEAR PTR WORD
                        PVOID    TYPEDEF      PTR
                        PPBYTE   TYPEDEF      PTR PBYTE

    4

    0000                        .CODE
                                .STARTUP
    0000  B8 ---- R    *    mov    ax, DGROUP
    0003  8E D8        *    mov    ds, ax
    0005  8C D3        *    mov    bx, ss
    0007  2B D8        *    sub    bx, ax
    0009  C1 E3 04     *    shl    bx, 004h
    000C  8E D0        *    mov    ss, ax
    000E  03 E3        *    add    sp, bx

    5

    EXTERNDEF        work:NEAR
    0010  E8 0000 E             call    work

    6

    Display ending
    0013  B4 09         1       mov     ah, 09h
    0015  BA 0046 R     1       mov     dx, OFFSET ending
    0018  CD 21         1       int     21h

7  8

    001A  66| A1 0000 R         mov     eax, ddData
    001E  67& FE 03             inc     BYTE PTR [ebx]

    INVOKE  PutStr, ADDR msg
    0021  B8 0051 R    *    lea    ax, DGROUP:Msg
    0024  50           *    push   ax
    0025  E8 0042 R    *    call   PutStr
    0028  83 C4 02     *    add    sp, 00002h

    9   10

    002B  B8 ---- R             mov     ax, @data
    002E  8E C0                 mov     es, ax
    0030  B8 0063               mov     ax, 'c'
    0033  26: 8B 0E 0020        mov     cx, es:num
    0038  BF 0052               mov     di, 82
    003B  F2/ AE                repne   scasb
    003D  57                    push    di

    .EXIT
    003E  B4 4C        *    mov    ah, 04Ch
    0040  CD 21        *    int    021h

    0042               PutStr  PROC    pMsg:PTR BYTE
    0042  55           *    push   bp
    0043  8B EC        *    mov    bp, sp
    0045  B4 02                 mov     ah, 02H
    0047  8B 7E 04              mov     di, pMsg
    004A  8A 15                 mov     dl, [di]
                                mov     ax, [dx][di]
    isttst.asm(71): error A2031: must be index or base register
                                .WHILE  (dl)
    004C  EB 10        *    jmp    @C0001
    004E               *@C0002:
    004E  CD 21                 int     21h
    0050  47                    inc     di
    0051  8A 15                 mov     dl, [di]
                                .ENDW
    0053               *@C0001:
    0053  0A D2        *    or     dl, dl
    0055  75 02        *    jne    @C0002
                                ret
    0057  5D           *    pop    bp
    0058  C3           *    ret    00000h
    0059               PutStr   ENDP

    END


C.2.4  Reading Tables in a Listing File

The tables at the end of a listing file list the macros, structures, unions,
records, segments, groups, and symbols that appear in a source file. These
tables are not printed in the sample listing, but this section summarizes
the information.

Macro Table - Lists all macros in the main file or the include files.
Differentiates between macro functions and macro procedures.

Structures and Unions Table - Provides the size in bytes of the structure or
union and the offset of each field. The type of each field is also given.

Record Table - "Width" gives the number of bits of the entire record.
"Shift" provides the offset in bits from the low-order bit of the record to
the low-order bit of the field. "Width" for fields gives the number of bits
in the field. "Mask" gives the maximum value of the field, expressed in
hexadecimal notation. "Initial" gives the initial value supplied for the
field.

Type Table - The "Size" column in this table gives the size of the TYPEDEF
type in bytes, and the "Attr" column gives the base type for the TYPEDEF
definition.

Segment and Group Table - "Size" specifies whether the segment is 16 bit or
32 bit. "Length" gives the size of the segment in bytes. "Align" gives the
segment alignment (WORD, PARA, and so on). "Combine" gives the combine type
(Public, Stack, etc.). "Class" gives the segment's class (DATA, STACK, CODE,
etc.).

Procedures, Parameters, and Locals - Gives the types and offsets from BP of
all parameters and locals defined in each procedure, as well as the size and
memory location of each procedure.

Symbol Table - All symbols (except names for macros, structures, unions,
records, and segments) are listed in a symbol table at the end of the
listing. The "Name" column lists the names in alphabetical order. The "Type"
column lists each symbol's type.

The length of a multiple-element variable, such as an array or string, is
the length of a single element, not the length of the entire variable.

If the symbol represents an absolute value defined with an EQU or equal-sign
(=) directive, the "Value" column shows the symbol's value. The value may be
another symbol, a string, or a constant numeric value (in hexadecimal),
depending on the type. If the symbol represents a variable or label, the
"Value" column shows the symbol's hexadecimal offset from the beginning of
the segment in which it is defined.

The "Attr" column shows the attributes of the symbol. The attributes include
the name of the segment (if any) in which the symbol is defined, the scope
of the symbol, and the code length. A symbol's scope is given only if the
symbol is defined using the EXTERN and PUBLIC directives. The scope can be
external, global, or communal. The "Attr" column is blank if the symbol has
no attribute.






Appendix D  MASM Reserved Words
────────────────────────────────────────────────────────────────────────────

This appendix lists the reserved words recognized by MASM. They are divided
primarily by their use in the language. The primary categories are


    ■   Operands and symbols

    ■   Registers

    ■   Operators and directives

    ■   Processor instructions

    ■   Coprocessor instructions


Reserved words in MASM 6.0 are reserved under all CPU modes. Words enabled
in .8086 mode, the default, can be used in all higher CPU modes. To use
words from subcategories such as "Special Operands for the 80386" (Section
D.1.1) requires .386 mode or higher.

You can disable the recognition of any reserved word specified in this
appendix by setting the NOKEYWORD option for the OPTION directive. Once
disabled, the word can be used in any way as a user-defined symbol (provided
the word is a valid identifier). If you want to remove the STR instruction,
the MASK operator, and the NAME directive, for instance, from the set of
words MASM recognizes as reserved, add this statement to your program:

    OPTION NOKEYWORD:<STR MASK NAME>

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.


D.1  Operands and Symbols

The words on the two lists in this section are the operands to certain
directives. They have special meaning to the assembler. The words on the
first list are not reserved words. They can be used in every way as normal
identifiers, without affecting their use as operands to directives. The
assembler interprets their use from context.

Even though the words on the first list are not reserved, they should not be
defined to be text macros or text macro functions. If they are, they will
not be recognized in their special contexts. The assembler does not give a
warning if such a redefinition occurs.

(This figure may be found in the printed book.)

These operands are reserved words. Reserved words are never case sensitive.


(This figure may be found in the printed book.)

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.


D.1.1  Special Operands for the 80386/486

(This figure may be found in the printed book.)


D.1.2  Predefined Symbols

Unlike most MASM reserved words, the predefined symbols are case sensitive.


(This figure may be found in the printed book.)


D.2  Registers

(This figure may be found in the printed book.)

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.


D.3  Operators and Directives

(This figure may be found in the printed book.)

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.

(This figure may be found in the printed book.)


D.4  Processor Instructions

MASM processor instructions are not case sensitive.


D.4.1  8086/8088 Processor Instructions

(This figure may be found in the printed book.)

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.

(This figure may be found in the printed book.)


D.4.2  80186 Processor Instructions

(This figure may be found in the printed book.)

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.


D.4.3  80286 Processor Instructions

(This figure may be found in the printed book.)


D.4.4  80286 and 80386 Privileged-Mode Instructions

(This figure may be found in the printed book.)


D.4.5  80386 Processor Instructions

(This figure may be found in the printed book.)

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.


D.4.6  80486 Processor Instructions

(This figure may be found in the printed book.)


D.4.7  Instruction Prefixes

(This figure may be found in the printed book.)


D.5  Coprocessor Instructions

MASM coprocessor instructions are not case sensitive.


D.5.1  8087 Coprocessor Instructions

(This figure may be found in the printed book.)

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.

(This figure may be found in the printed book.)


D.5.2  80287 Privileged-Mode Instruction

(This figure may be found in the printed book.)


D.5.3  80387 Instructions

(This figure may be found in the printed book.)

* Words in this appendix identified with an asterisk (*) are new to MASM
6.0.








Appendix E  Default Segment Names
────────────────────────────────────────────────────────────────────────────

If you use simplified segment directives by themselves, you do not need to
know the names assigned for each segment. However, it is possible to mix
full segment definitions with simplified segment directives, in which case
you need to know the segment names.

Table E.1 shows the default segment names created by each directive.

If you use .MODEL, a _TEXT segment is always defined, even if all .CODE
directives specify a name. The default segment name used as part of far-code
segment names is the filename of the module. The default name associated
with the .CODE directive can be overridden, as can the default names for
.FARDATA and .FARDATA?.

The segment and group table at the end of listings always shows the actual
segment names. However, the GROUP and ASSUME statements generated by the
.MODEL directive are not shown in listing files. For a program that uses all
possible segments, group statements equivalent to the following would be
generated:

    DGROUP      GROUP    _DATA, CONST, _BSS, STACK

For the tiny model, these ASSUME statements would be generated:

    ASSUME   cs:DGROUP, ds:DGROUP, ss:DGROUP

For small and compact models with NEARSTACK, these ASSUME statements would
be generated:

    ASSUME   cs: _TEXT, ds:DGROUP, ss:DGROUP

For medium, large, and huge models with NEARSTACK, these ASSUME statements
would be generated:

    ASSUME   cs:name_TEXT, ds:DGROUP, ss:DGROUP

Table E.1  Default Segments and Types for Standard Memory Models

╓┌───────────┌───────────┌───────────┌──────┌────────┌───────────┌───────────╖
Model       Directive   Name        Align  Combine  Class       Group
Model       Directive   Name        Align  Combine  Class       Group
────────────────────────────────────────────────────────────────────────────
Tiny        .CODE       _TEXT       WORD   PUBLIC   'CODE'      DGROUP

            .FARDATA    FAR_DATA    PARA   PRIVATE  'FAR_DATA'

            .FARDATA?   FAR_BSS     PARA   PRIVATE  'FAR_BSS'

            .DATA       _DATA       WORD   PUBLIC   'DATA'      DGROUP

            .CONST      CONST       WORD   PUBLIC   'CONST'     DGROUP

            .DATA?      _BSS        WORD   PUBLIC   'BSS'       DGROUP

────────────────────────────────────────────────────────────────────────────

Small       .CODE       _TEXT       WORD   PUBLIC   'CODE'

            .FARDATA    FAR_DATA    PARA   PRIVATE  'FAR_DATA'

            .FARDATA?   FAR_BSS     PARA   PRIVATE  'FAR_BSS'
Model       Directive   Name        Align  Combine  Class       Group
────────────────────────────────────────────────────────────────────────────
            .FARDATA?   FAR_BSS     PARA   PRIVATE  'FAR_BSS'

            .DATA       _DATA       WORD   PUBLIC   'DATA'      DGROUP

            .CONST      CONST       WORD   PUBLIC   'CONST'     DGROUP

            .DATA?      _BSS        WORD   PUBLIC   'BSS'       DGROUP

            .STACK      STACK       PARA   STACK    'STACK'     DGROUP*

────────────────────────────────────────────────────────────────────────────

Medium      .CODE       name_TEXT   WORD   PUBLIC   'CODE'

            .FARDATA    FAR_DATA    PARA   PRIVATE  'FAR_DATA'

            .FARDATA?   FAR_BSS     PARA   PRIVATE  'FAR_BSS'

            .DATA       _DATA       WORD   PUBLIC   'DATA'      DGROUP
Model       Directive   Name        Align  Combine  Class       Group
────────────────────────────────────────────────────────────────────────────
            .DATA       _DATA       WORD   PUBLIC   'DATA'      DGROUP

            .CONST      CONST       WORD   PUBLIC   'CONST'     DGROUP

            .DATA?      _BSS        WORD   PUBLIC   'BSS'       DGROUP

            .STACK      STACK       PARA   STACK    'STACK'     DGROUP*

────────────────────────────────────────────────────────────────────────────

Compact     .CODE       _TEXT       WORD   PUBLIC   'CODE'

            .FARDATA    FAR_DATA    PARA   PRIVATE  'FAR_DATA'

            .FARDATA?   FAR_BSS     PARA   PRIVATE  'FAR_BSS'

            .DATA       _DATA       WORD   PUBLIC   'DATA'      DGROUP

            .CONST      CONST       WORD   PUBLIC   'CONST'     DGROUP
Model       Directive   Name        Align  Combine  Class       Group
────────────────────────────────────────────────────────────────────────────
            .CONST      CONST       WORD   PUBLIC   'CONST'     DGROUP

            .DATA?      _BSS        WORD   PUBLIC   'BSS'       DGROUP

            .STACK      STACK       PARA   STACK    'STACK'     DGROUP*




Large or    .CODE       name_TEXT   WORD   PUBLIC   'CODE'
huge

            .FARDATA    FAR_DATA    PARA   PRIVATE  'FAR_DATA'

            .FARDATA?   FAR_BSS     PARA   PRIVATE  'FAR_BSS'

            .DATA       _DATA       WORD   PUBLIC   'DATA'      DGROUP

            .CONST      CONST       WORD   PUBLIC   'CONST'     DGROUP
Model       Directive   Name        Align  Combine  Class       Group
────────────────────────────────────────────────────────────────────────────
            .CONST      CONST       WORD   PUBLIC   'CONST'     DGROUP

            .DATA?      _BSS        WORD   PUBLIC   'BSS'       DGROUP

            .STACK      STACK       PARA   STACK    'STACK'     DGROUP*

────────────────────────────────────────────────────────────────────────────

Flat        .CODE       _TEXT       DWORD  PUBLIC   'CODE'

            .FARDATA    _DATA       DWORD  PUBLIC   'DATA'

            .FARDATA?   _BSS        DWORD  PUBLIC   'BSS'

            .DATA       _DATA       DWORD  PUBLIC   'DATA'

            .CONST      CONST       DWORD  PUBLIC   'CONST'

            .DATA?      _BSS        DWORD  PUBLIC   'BSS'
Model       Directive   Name        Align  Combine  Class       Group
────────────────────────────────────────────────────────────────────────────
            .DATA?      _BSS        DWORD  PUBLIC   'BSS'

            .STACK      STACK       DWORD  PUBLIC   'STACK'

────────────────────────────────────────────────────────────────────────────



* unless the stack type is FARSTACK







Appendix F  Error Messages
────────────────────────────────────────────────────────────────────────────

This appendix lists MASM 6.0 error and warning messages. Each message
includes an explanation of what went wrong and what action to take to
correct the problem.

Error numbers consist of a one- or two-letter prefix and four digits. The
first digit indicates a severity level:


    ■   Fatal errors stop execution and are numbered  1xxx.

    ■   Errors numbered  2xxx  are usually nonfatal; execution continues if
        possible.

    ■   Warnings do not stop execution but indicate a possible problem; they
        are numbered  4xxx.


Error messages may also display the input file and line number where the
error occurred.


F.1  BIND Error Messages

This section lists error messages generated by the Microsoft Bind Utility
(BIND). BIND errors (U12xx) are always fatal.

Number                            BIND Error Message
────────────────────────────────────────────────────────────────────────────
U1250                             invalid executable file

                                    The executable file cannot be bound.
                                    Either the header is invalid, or the
                                    executable file has an invalid magic
                                    number.

                                    Repeat with a backup version of the
                                    executable file, or rebuild the file and
                                    repeat.

U1251                             cannot create file : filename

                                    BIND was unable to create a temporary
                                    file or the map file, probably because
                                    the disk was full.

U1252                             unrecoverable I/O error

                                    The system returned an I/O error when
                                    reading the executable file.

U1253                             cannot open file : filename

                                    The given file could not be opened.

                                    The following are possible causes of
                                    this error:

                                    ■ The file does not exist.

                                    ■ The file is in use by another process.

                                    ■ The disk is full.

U1254                             structure error in .EXE file

                                    The executable file has an invalid
                                    structure.

                                    Rebuild the file.

U1255                             structure error in .LIB file : filename

                                    The given library file has an invalid
                                    structure. Library files must conform to
                                    Microsoft object module format.

                                    Repeat with a backup version of the
                                    library file, or rebuild the library and
                                    repeat.

U1256                             out of memory

                                    There was insufficient memory for BIND
                                    to run.

U1257                             too many libraries specified, number
                                    allowed

                                    The BIND command line contained more
                                    than the given number of libraries.

                                    Combine some libraries.

U1258                             resource tables not supported

                                    Protected-mode executable files that use
                                    resource tables cannot be bound because
                                    when the bound executable file runs in
                                    DOS mode the resources would be unknown.

U1259                             internal error ─ Lname not found : lname

                                    BIND encountered an internal error.

                                    Repeat the attempt with a new copy of
                                    BIND. If the problem persists, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions on the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

U1260                             import by ordinal not defined : dllname.
                                    ordinal

                                    The given DLL does not contain a
                                    function with the given ordinal value.
                                    As a result, fixups from function calls
                                    to this function cannot be made.

U1261                             system call syscall return error

                                    BIND encountered an internal error.

                                    Repeat the attempt with a new copy of
                                    BIND. If the problem persists, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions in the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

U1262                             cannot find LINK.EXE in path

                                    BIND could not find LINK.EXE in any
                                    directory specified by the PATH
                                    environment variable.

                                    BIND needs the linker to complete the
                                    binding operation.

U1263                             error during link of file, link error
                                    status : status

                                    A linking error occurred during the LINK
                                    session invoked by BIND.

                                    The following are possible causes of
                                    this error:

                                    ■ Unresolved references exist in the
                                    files. BIND could not resolve references
                                    with API.LIB or other support libraries.

                                    ■ APILMR.OBJ was used when the
                                    executable file was created, and LINK
                                    gave error L2044,  symbol multiply
                                    defined, use /NOE. Relink using the LINK
                                    option /NOE, then rebind.

                                    ■ There was not enough memory.

                                    ■ A disk I/O error occurred.

U1264                             unrecognized option : option

                                    The BIND command line contained the
                                    given unrecognized option.

U1265                             unrecognized argument : string

                                    The given string is not a valid argument
                                    for the option it was specified with.

U1266                             no infile specified

                                    No executable file to be bound was named
                                    on the BIND command line.

U1267                             no outfile specified

                                    The option for naming an outfile, /o,
                                    was given on the command line, but no
                                    file was named.

U1268                             duplicate infile name given : filename

                                    The given file was named in more than
                                    one place on the BIND command line.

U1269                             duplicate global name : name

                                    The given global name was defined in
                                    more than one place in the specified
                                    libraries, making a unique fixup
                                    impossible.

                                    This error can be caused by specifying
                                    both OS2.LIB and DOSCALLS.LIB. To
                                    correct the error, specify only OS2.LIB.

U1270                             terminated by user

                                    BIND was halted by CTRL+C or CTRL+BREAK.

U1271                             insufficient disk space

                                    There was not enough room on the disk.
                                    BIND creates temporary files that take
                                    up disk space.

                                    Make some room on the disk and repeat.

U1272                             cannot bind a PROTMODE executable

                                    The module-definition file used to
                                    create the executable file contained a
                                    PROTMODE statement. This statement
                                    creates an executable file that cannot
                                    be run under DOS and prevents the file
                                    from being bound.


F.2  CodeView Error Messages

CodeView displays an error message whenever it detects a command it cannot
execute. Most errors terminate the CodeView command in error, but do not
terminate the debugger. Start-up errors terminate CodeView.

Depending on the context of the error, CodeView may display only the text of
the message without the error number. This section is organized in
alphabetical order by message text.

In some cases, CodeView may display the error number by itself. To obtain
the error message and an explanation of the error in thoses cases, use
online help. Click the right mouse button on the error number or use the
Help (H) Command-window command. For example,

    H CV1020

displays help for the error  Divide by zero.

Error Message
────────────────────────────────────────────────────────────────────────────
Access denied (CV0013)

                                        A specified file's permission setting
                                    does not allow the required access.

                                    One of the following may have occurred:

                                    ■ An attempt was made to write to a
                                    read-only file.

                                    ■ A locking or sharing violation
                                    occurred.

                                    ■ An attempt was made to open a
                                    directory instead of a file.

Address of register variable cannot be watched (CV1049)

                                        An attempt was made to evaluate the
                                    address of a register variable. A
                                    register variable can be watched but not
                                    the address of a register variable.

                                    One of the following occurred:

                                    ■ The variable was declared as a
                                    register variable. Recompile the program
                                    with the register declaration removed.

                                    ■ The optimizer converted an ordinary
                                    variable into a register variable to
                                    speed up execution. Recompile the
                                    program using the /Od option to turn
                                    optimization off.

                                    ■ The function was defined with
                                    _fastcall, causing parameters to be
                                    passed in registers. Remove the
                                    _fastcall designation and recompile.

All threads blocked (CV3502)

                                        The block may be due to a request for a
                                    system service semaphore. When the
                                    semaphore is cleared, the block will
                                    clear.

                                    The block may also be due to a deadlock
                                    situation that will not clear until one
                                    or more of the threads are terminated.

Arg list too long (CV0007)

                                        CodeView is not able to restart the
                                    program being debugged because the
                                    number of arguments to the executable
                                    program exceeds the limit of 128.

Argument to IMAG/DIMAG must be simple type (CV1121)

                                        An invalid argument was specified to
                                    IMAG or DIMAG, such as an array with no
                                    subscripts.

Array must have subscript (CV1101)

                                        An array was specified without any
                                    subscripts, such as  IARRAY+2. A correct
                                    example would be  IARRAY(1)+2.

Bad integer or real constant (CV1105)

                                        An illegal numeric constant was
                                    specified in an expression.

Bad intrinsic function (CV1106)

                                        An illegal intrinsic function name was
                                    specified in an expression.

Bad subscript (CV1100)

                                        An illegal subscript expression was
                                    specified for an array.

                                    For example,  IARRAY(3.3)  and
                                    IARRAY((3,3))  are illegal. The correct
                                    expression is  IARRAY(3,3).

Badly formed type (CV1009)

                                        CodeView detected corrupt information i
                                    the symbol table of the file being
                                    debugged.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

Breakpoint number or '*' expected (CV1006)

                                        A breakpoint was specified without a
                                    number or asterisk.

                                    A Breakpoint Clear (BC), Breakpoint
                                    Disable (BD), or Breakpoint Enable (BE)
                                    command requires one or more numbers to
                                    specify the breakpoints, or an asterisk
                                    to specify all breakpoints.

                                    For example, the following command
                                    causes this error:

                                    bc a

Cannot cast complex constant component into REAL (CV1112)

                                        Both the real and imaginary components
                                    of a COMPLEX constant must be compatible
                                    with the type REAL.

Cannot cast IMAG/DIMAG argument to COMPLEX (CV1122)

                                        Arguments to IMAG and DIMAG must be
                                    simple numeric types.

Cannot create CURRENT.STS (CV1063)

                                        CodeView could not find an existing
                                    state file (CURRENT.STS), and it tried
                                    to create one but failed.

                                    One of the following may have occurred:

                                    ■ There was not enough space either on
                                    the disk containing the program to be
                                    debugged or on the disk pointed to by
                                    the INIT environment variable.

                                    ■ There were not enough free file
                                    handles. In DOS, increase the number of
                                    file handles by changing the FILES
                                    setting in CONFIG.SYS to allow a larger
                                    number of open files. FILES=20 is the
                                    recommended setting. In OS/2, if
                                    multiple processes are running, removing
                                    one or more of them may release enough
                                    file handles.

                                    ■ The environment variable INIT pointed
                                    to a directory that does not exist. If
                                    the variable points to more than one
                                    directory, the first directory listed
                                    does not exist.

Cannot create QUEUESCVP (CV3601)

                                        One or more of the required queues coul
                                    not be created.

                                    When debugging multiprocess programs,
                                    CodeView creates multiple copies of
                                    itself that intercommunicate through
                                    queues.

                                    The failure to create queues may be due
                                    to lack of memory, or to having too many
                                    OS/2 processes running at one time.

Cannot create SEMCVP (CV3605)

                                        The required semaphore could not be
                                    assigned.

                                    When debugging multiprocess programs,
                                    CodeView allocates areas of shared
                                    memory for interprocess communication.

                                    The failure to assign a semaphore may be
                                    due to lack of memory or to having too
                                    many OS/2 processes running at one time.

Cannot create SHAREMEMCVP (CV3604)

                                        The required shared memory could not be
                                    assigned.

                                    When debugging multiprocess programs,
                                    CodeView allocates areas of shared
                                    memory for interprocess communication.

                                    The failure to assign shared memory may
                                    be due to lack of memory or to having
                                    too many OS/2 processes running at one
                                    time.

Cannot open CV.EXE (CV1310)

                                        An error occurred while CV.EXE was bein
                                    opened.

                                    One of the following may have occurred:

                                    ■ The file could be corrupt. Copy CV.EXE
                                    from the original disks and retry.

                                    ■ The operating system could not find
                                    CV.EXE due to a disk error.

                                    ■ There were not enough free file
                                    handles. In DOS, increase the number of
                                    file handles by changing the FILES
                                    setting in CONFIG.SYS to allow a larger
                                    number of open files. FILES=20 is the
                                    recommended setting. In OS/2, if
                                    multiple processes are running, removing
                                    one or more of them may release enough
                                    file handles.

                                    If the error recurs, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions in the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

Cannot open QUEUESCVP (CV3602)

                                        One or more of the required queues coul
                                    not be opened.

                                    When debugging multiprocess programs,
                                    CodeView creates multiple copies of
                                    itself that intercommunicate through
                                    queues.

                                    The failure to open queues may be due to
                                    lack of memory or to having too many
                                    OS/2 processes running at one time.

Cannot open SHAREMEMCVP (CV3606)

                                        The required shared memory could not be
                                    opened.

                                    When debugging multiprocess programs,
                                    CodeView tries to access areas of shared
                                    memory for interprocess communication.

                                    The failure to open shared memory may be
                                    due to lack of memory or to having too
                                    many OS/2 processes running at one time.

Cannot open SEMCVP (CV3607)

                                        The required semaphore could not be
                                    opened.

                                    When debugging multiprocess programs,
                                    CodeView tries to access areas of shared
                                    memory for interprocess communication.

                                    The failure to open a semaphore may be
                                    due to lack of memory or to having too
                                    many OS/2 processes running at one time.

Cannot read CV.EXE (CV1311)

                                        An error occurred while CV.EXE was bein
                                    read. Possibly the operating system
                                    could not find CV.EXE due to a disk
                                    error.

                                    If the error recurs, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions in the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

Cannot read file (CV5004)

                                        A file was selected from a dialog box,
                                    and CodeView then opened the file. The
                                    read process failed while the file was
                                    being read.

                                    Read the file again. If the second read
                                    fails, exit and restart CodeView. If the
                                    read process still fails, the file may
                                    be corrupt.

Cannot read this version of CURRENT.STS (CV1054)

                                        The state file (CURRENT.STS) has a
                                    version number that is not recognized by
                                    this version of CodeView.

                                    Check the directories for older copies
                                    and delete them.

Cannot restart program, out of system resources (CV3611)

                                        The operating system reached its limit
                                    of one of the following resources:

                                    ■ Memory

                                    ■ Screen groups

                                    ■ Threads

Cannot select (CV5001)

                                        The cursor was not on the same line as
                                    an automatically selectable symbol.

Cannot understand entry in TOOLS.INI or CURRENT.STS (CV1056)

                                        At least one line in the given file
                                    (either the state file or the TOOLS.INI
                                    file) could not be interpreted.

                                    On start-up, CodeView reads the state
                                    file (CURRENT.STS) and the TOOLS.INI
                                    file (if the latter is available).

                                    Examine the given file to find the
                                    problem.

Cannot use second monitor from VIO window (CV3610)

                                        The operating system cannot support a
                                    second monitor from a virtual I/O window
                                    (Presentation-Manager text window).

Cannot use struct or union as scalar (CV1025)

                                        A structure or union was used in an
                                    expression, but no element was specified.

                                    When requesting display of a structure
                                    or union variable, the name of the
                                    variable may appear by itself, without a
                                    field qualifier. If a structure or union
                                    is used in an expression, it must be
                                    qualified with the specific element
                                    desired.

                                    Specify the element whose value is to be
                                    used in the expression.

Character constant too long (CV1109)

                                        A character constant was specified that
                                    is too long for the FORTRAN expression
                                    evaluator (the limit is 126 bytes).

                                    Use the Radix (N) command to change the
                                    radix.

Character too big for current radix (CV1120)

                                        A radix was specified in a constant tha
                                    is larger than the current radix.

Command incompatible with history (CV2202)

                                        The command entered is illegal while
                                    recording because it changes the state
                                    of CodeView and/or the program being
                                    debugged.

                                    For example, the Restart (L) command
                                    cannot be used during recording.

                                    Turn off history to use the command.

Constant too big (CV1028)

                                        CodeView cannot accept an unsigned
                                    integer constant larger than
                                    4,294,967,295 (0xFFFFFFFF hex), or a
                                    floating-point constant whose magnitude
                                    is larger than approximately 1.8E+308.

Corrupt debug OMF detected in file, discarding source line information
(CV2206)

                                        The linker used was not the current
                                    version of the Microsoft linker.

                                    Conditions that require the most current
                                    linker include use of the alloc_text
                                    pragma in a C program and use of
                                    multiple segments in an
                                    assembly-language module.

Corrupted CV.EXE (CV1318)

                                        The CV.EXE file has been corrupted. Cop
                                    CV.EXE from the original disks and retry.

                                    If the error recurs, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions on the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

CURRENT.STS not found─creating default (CV1057)

                                        The state file (CURRENT.STS) could not
                                    be located at start-up, so CodeView
                                    created a state file.

Divide by zero (CV1020)

                                        The expression contains a divisor of
                                    zero, which is illegal. This divisor
                                    might be the literal number zero, or it
                                    might be an expression that evaluates to
                                    zero.

/E: EMM driver not loaded (CV1304)

                                        The EMM driver must be installed in
                                    order to use expanded memory.

/E: EMM internal error (CV1309)

                                        An unexpected error from the EMM driver
                                    occurred. The driver may be corrupted or
                                    may have malfunctioned.

                                    If replacing the EMM driver does not
                                    correct the problem, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions in the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

/E: EMM not LIM 4.0 or later (CV1305)

                                        The EMM driver must be LIM EMS version
                                    4.0 or later in order to contain the
                                    calls needed for CodeView to use
                                    expanded memory.

/E: no EMM handle available (CV1306)

                                        No handle is available for the CodeView
                                    overlay code.

                                    One of the following may be a solution:

                                    ■ If possible, increase the number of
                                    EMM handles that are allocated when the
                                    EMM driver is loaded.

                                    ■ If multiple applications are running,
                                    remove one or more of the applications
                                    that use expanded memory. This should
                                    free enough handles to permit CodeView
                                    to run properly.

                                    ■ Some memory may have become
                                    inaccessible due to program error.
                                    Reboot in order to free the memory.

/E: not enough free expanded memory (CV1308)

                                        There is currently not enough room in
                                    expanded memory to load overlays.

                                    One of the following may be a solution:

                                    ■ Decrease the size of memory allocated
                                    to SMARTDRV.SYS or RAMDRIVE.SYS to free
                                    expanded memory.

                                    ■ Reconfigure the EMM driver or hardware
                                    to allocate more expanded memory.

/E: not enough total expanded memory (CV1307)

                                        There is not enough room in all of
                                    expanded memory to load overlays.
                                    Freeing expanded memory will not help.

                                    If possible, reconfigure the EMM driver
                                    or hardware to allocate more expanded
                                    memory.

EMM error (CV3010)

                                        An unknown expanded memory error has
                                    occurred.

                                    One of the following may have occurred:

                                    ■ The EMM driver may be corrupted or may
                                    have malfunctioned. Reload the driver
                                    and retry.

                                    ■ There was a disk error.

                                    If the error recurs, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions on the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

EMM hardware error (CV3001)

                                        An error has occurred in expanded memor

                                    Exit CodeView and reboot the computer.
                                    If this does not correct the problem,
                                    the expanded memory board may need
                                    service.

EMM memory not found (CV3011)

                                        CodeView cannot find expanded memory.

                                    The EMM driver or expanded memory board
                                    is not installed, or the board has a
                                    malfunction.

EMM software error (CV3000)

                                        An error has occurred in the EMM driver

                                    Exit CodeView and reboot the computer.
                                    If the problem recurs, replace the EMM
                                    driver file with a fresh copy from the
                                    EMM driver's distribution disk. If this
                                    does not correct the problem, the
                                    expanded memory board may need service.

Executable file format error (CV0008)

                                        The system is not able to load the
                                    program to be debugged. The file is not
                                    an executable file, or it has an invalid
                                    format for this operating system.

                                    Try to run the program outside of
                                    CodeView.

Expression not a memory address (CV1050)

                                        The expression entered does not evaluat
                                    to an address. An address must be a
                                    numeric value.

                                    An lvalue (so called because it appears
                                    on the left side of an assignment
                                    statement) is an expression that refers
                                    to a memory location.

                                    For example,  buffer[count]  is a valid
                                    lvalue because it points to a specific
                                    memory location. The logical comparison
                                    zed != 0  is not a valid lvalue because
                                    it evaluates to TRUE or FALSE, not a
                                    memory address.

Expression too complex (CV1019)

                                        The expression entered was too complex
                                    for the amount of storage space
                                    available to the expression evaluator.

                                    Overflow usually occurs because of too
                                    many pending calculations. Rearrange the
                                    expression so that each component of the
                                    expression can be evaluated immediately,
                                    rather than having to wait for other
                                    parts of the expression to be calculated.

Extra input ignored (CV1003)

                                        The first part of the command line was
                                    interpreted correctly.

                                    The remainder of the line could not be
                                    interpreted or was unnecessary.

File error (CV1041)

                                        CodeView could not write to the disk.

                                    One of the following may have occurred:

                                    ■ There was not enough space on the disk.

                                    ■ The file was locked by another process.

Flip/Swap option off─application output lost (CV1043)

                                        The program being debugged wrote to the
                                    display when Flip/Swap was off. The
                                    program output was lost.

                                    When flipping is on, video page 1 is
                                    normally reserved for CodeView, while
                                    programs by default write to video page
                                    0. Programs that write to video page 1
                                    must be debugged with swapping on.

                                    Turn Flip/Swap on to be able to view
                                    program output.

Floating-point support not loaded (CV1048)

                                        An attempt was made to access the math
                                    processor registers in a program that
                                    does not use floating-point arithmetic.

                                    Several situations can cause this error:

                                    ■ The math processor registers can only
                                    be accessed through the floating-point
                                    library code. This code is not loaded if
                                    the program does not perform
                                    floating-point calculations.

                                    ■ If the program does not use
                                    floating-point instructions, this error
                                    may occur when attempting to access the
                                    math processor before any floating-point
                                    instructions have been performed. The C
                                    run-time library includes a
                                    floating-point instruction near the
                                    beginning so that the math processor
                                    registers are always accessible.

                                    ■ If a floating-point instruction occurs
                                    in an assembly-language routine before
                                    such an instruction occurs in the C code
                                    that calls the routine, this error
                                    occurs.

Function argument may not be byte register (CV4058)

                                        The register specified in the function
                                    does not accept a byte value. The
                                    register must be assigned a word or
                                    doubleword value.

Function call before stack frame initialization (CV1026)

                                        A function call cannot be executed unti
                                    after the BP (stack frame) register has
                                    been initialized.

                                    Run the program to a statement that
                                    follows initialization of the BP
                                    register. This is usually set up as the
                                    first statement in the first function of
                                    the program.

Function returning struct/union not supported (CV1060)

                                        CodeView cannot evaluate a function tha
                                    returns a structure or union variable.

I/O error (CV0005)

                                        An attempt was made to access an addres
                                    that is not accessible to the program
                                    being debugged.

                                    Check the previous command for numeric
                                    constants used as addresses and for
                                    pointers used for indirection.

Illegal instruction (CV4001)

                                        An assembler instruction was not
                                    recognized.

                                    The instruction may have been mistyped.

Illegal operand (CV4003)

                                        The specified operand is not permitted
                                    with this instruction.

                                    The operand name may have been mistyped.

Illegal size for item (CV4036)

                                        The wrong size was specified for the
                                    data item.

Illegal usage of CS register (CV4059)

                                        The CS (code segment) register cannot b
                                    addressed in the function specified.

Index out of bound (CV1102)

                                        A subscript value was specified that is
                                    outside the bounds declared for the
                                    array.

Insufficient EMM memory (CV3007)

                                        CodeView tried to allocate expanded
                                    memory, but there was not enough space.

                                    Possible solutions include the
                                    following:

                                    ■ Run CVPACK on the executable file to
                                    reduce the demand on memory for symbolic
                                    information.

                                    ■ Recompile without symbolic information
                                    in some of the modules. CodeView
                                    requires memory to hold information
                                    about the program being debugged.
                                    Compile some modules with the /Zd option
                                    instead of /Zi, or don't use either
                                    option.

                                    ■ If multiple applications are running,
                                    remove one or more of the applications
                                    that use expanded memory. This may free
                                    enough memory to permit CodeView to run
                                    properly.

                                    ■ Allocate more expanded memory in the
                                    system configuration.

Internal debugger error: n (CV0100)

                                        CodeView has encountered an internal
                                    error. Quit and restart.

                                    If the error recurs, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions on the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

Internal error─unrecoverable fault (CV1319)

                                        The DOS extender encountered a general
                                    protection fault.

                                    The CodeView file may be corrupt. Reboot
                                    and copy CV.EXE from the original disks
                                    and retry.

                                    If the error recurs, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions on the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

Invalid address (CV0014)

                                        The View (V) command was followed by an
                                    argument that could not be interpreted
                                    as a valid address.

                                    A name or constant may have been
                                    specified without the period (.) that
                                    indicates a filename or line number.

Invalid argument (CV0022)

                                        An invalid value was given as an
                                    argument in the most recent command.

                                    One of the following may have occurred:

                                    ■ An invalid argument was passed to the
                                    Go (G) command.

                                    ■ An invalid argument was passed to the
                                    Delete Watch Expression (Y)
                                    command.

Invalid breakpoint command (CV1001)

                                        CodeView could not interpret the
                                    breakpoint command.

                                    The command probably used an invalid
                                    symbol or the incorrect command format.

Invalid executable file─please relink (CV1046)

                                        The executable file did not have a vali
                                    format.

                                    One of the following may have occurred:

                                    ■ The executable file was not created
                                    with the linker released with this
                                    version of CodeView. Relink the object
                                    code using the current version of
                                    LINK.EXE.

                                    ■ The .EXE file may have been corrupted.
                                    Recompile and relink the program.

Invalid flag (CV1022)

                                        An attempt was made to examine or chang
                                    a flag, but the flag name was not valid.

                                    Any flags preceding the invalid name
                                    were changed to the values specified.
                                    Any flags after the invalid name were
                                    not changed.

                                    Use the flag mnemonics displayed after
                                    entering the R FL command.

Invalid format in CV.EXE (CV1313)

                                        The CV.EXE file has been corrupted. Cop
                                    CV.EXE from the original disks and retry.

                                    If the error recurs, note the
                                    circumstances of the error and notify
                                    Microsoft Corporation by following the
                                    instructions on the Microsoft Product
                                    Assistance Request form at the back of
                                    one of your manuals.

Invalid format specifier (use one of ABDILSTUW) (CV1021)

                                        A Dump (D), Enter (E), or View Memory (
                                    VM) command included a format specifier
                                    that is not recognized by CodeView.

                                    The valid format specifiers are

╓┌─────────────────────────────────┌─────────────────────────────────────────╖
Specifier                         Display Format
────────────────────────────────────────────────────────────────────────────
A                                 ASCII

B                                 Byte

I                                 Integer

U                                 Unsigned integer

W                                 Word

D                                 Doubleword

S                                 Short real

L                                 Long real
Specifier                         Display Format
────────────────────────────────────────────────────────────────────────────
L                                 Long real

T                                 10-byte real



Invalid format string (CV1038)

    An invalid format specifier followed an expression.

Invalid operation (CV1062)

    An attempt was made to set the IP register to a line or address in a
    different segment.

Invalid process ID (CV3603)

    An attempt was made to run a process using an ID that does not exist.

The ID may have been mistyped.

Invalid radix (use 8, 10, or 16) (CV1027)

    The Radix (N) command takes three radixes: 8 (octal), 10 (decimal), and
    16 (hexadecimal). Other radixes are not permitted. The new radix is
    always entered as a decimal number, regardless of the current radix.

Invalid register (CV1004)

    The Register (R) command named a register that does not exist or cannot
    be displayed. CodeView can display the following registers:

    AX     SP     DS     IP
    BX     BP     ES     FL
    CX     SI     SS
    DX     DI     CS

When running under DOS or Windows on an 80386/486 machine, the 386 option
can be selected to display the following registers:

    EAX     ESP     DS     GS
    EBX     EBP     ES     SS
    ECX     ESI     FS     EIP
    EDX     EDI     CS     EFL

Invalid tab setting─assumed 8 (CV2210)

    The value for tabs cannot be less than 0 or greater than 19. If you
    supply a value that is not in this range, CodeView defaults to a tab
    value of 8.

Invalid thread ID (CV3500)

    An attempt was made to run a thread using an ID that does not exist.

The ID may have been mistyped.

Invalid type cast (CV1008)

    An attempt was made to cast a variable to an undefined or user-defined
    type.

A cast can be made only to fundamental C types.

Library module not loaded (CV1042)

    The program being debugged uses load-on-demand DLLs. At least one of
    these libraries is needed but does not currently exist on the path
    specified by the LIBPATH environment variable.

LIM 4.0 function not supported (CV3013)

    CodeView required a function that is not supported in the EMM driver
    present on the system.

Either of the following must be done:


    ■   Run CodeView without using expanded memory.

    ■   Obtain an EMM driver that fully supports LIM EMS version 4.0 or later.


LIM 4.0 subfunction not supported (CV3014)

    CodeView required a subfunction that is not supported in the EMM driver
    present on the system.

Either of the following must be done:


    ■   Run CodeView without using expanded memory.

    ■   Obtain an EMM driver that fully supports LIM EMS version 4.0 or later.


Loaded symbols for module module (CV2207)

    CodeView automatically loaded the symbols for the given DLL. The DLL can
    now be debugged.

Losing History (CV5010)

    When you restarted the program, CodeView was not able to maintain debug
    history.

Match not found (CV1016)

    No string was found that matched the search pattern.

Missing ')' (CV1000)

    The command contained a left parenthesis ( ( ) that lacked a matching
    right parenthesis ( ) ).

Missing ']' (CV1014)

    The command contained a left bracket ( [ ) that lacked a matching right
    bracket ( ] ).

Missing '(' (CV1034)

    The command contained a right parenthesis ( ( ) that lacked a matching
    left parenthesis ( ) ).

Missing '(' in complex constant (CV1110)

    CodeView expected an opening parenthesis of a complex constant in an
    expression, but it was missing.

Missing ')' in complex constant (CV1111)

    CodeView expected a closing parenthesis of a complex constant, but it
    was missing.

Missing '(' to intrinsic (CV1113)

    CodeView expected an opening parenthesis for an intrinsic function, but
    it was missing.

Missing ')' to intrinsic (CV1114)

    CodeView expected a closing parenthesis for an intrinsic function, but
    it was missing.

Missing ')' in substring (CV1119)

    CodeView expected a closing parenthesis for a substring expression, but
    it was missing.

Missing or corrupt emulator info (CV1051)

    Status information about the floating-point emulator is missing or
    corrupt.

The program probably wrote to this area of memory. Check all pointers to
confirm that they refer to their intended objects.

No closing double quotation mark (CV1029)

    The double quotation mark (") expected at the end of the string was
    missing.

No closing single quotation mark (CV1030)

    The single quotation mark (') expected at the end of the character
    constant was missing.

No code at this line number (CV1023)

    An attempt was made to set a breakpoint at a line that does not
    correspond to machine code. Such a line could be a blank line, a comment
    line, a line with program declarations, or a line moved or removed by
    compiler optimization.

To set a breakpoint at a line deleted by the optimizer, recompile the
program with the /Od option to turn optimization off.

Note that in a multiline statement the code is associated only with one line
of the statement.

No CodeView source information (CV1059)

    There is no CodeView symbol listing for the source file or module being
    debugged.

Be sure the file was compiled with the /Zi option or the /Zd option. If
linking in a separate step, be sure to use the /CO option.

No debugging information (CV5003)

    The program file did not contain the debugging information needed.

Recompile the program using the /Zi option to include CodeView symbolic
information. If linking in a separate step, use the LINK /CO option.

No file selected (CV5005)

    A module must be selected before OK is chosen.

To exit the dialog box without selecting a module, choose Cancel.

No free EMM memory handles (CV3005)

    No expanded memory handle is available for the symbolic information.

One of the following may be a solution:


    ■   If multiple applications are running, remove one or more of the
        applications that use expanded memory. This should free enough handles
        to permit CodeView to run properly.

    ■   Reconfigure the EMM driver to allow more handles.


No immediate mode (CV4056)

    The instruction does not take an immediate-mode operand.

No match found (CV5008)

    There was no match for the specified string in the file.

No previous regular expression (CV1011)

    The Repeat Last Find command was executed, but no previous regular
    expression (search string) has been specified.

No process status, /O not specified (CV5002)

    CodeView must be started with the /O option in order to debug
    multiprocess programs.

Exit and restart CodeView with the /O option.

No second monitor connected to system (CV1061)

    CodeView was invoked with the /2 option, but there was no second monitor
    for CodeView to use.

No source lines at this address (CV1031)

    An attempt was made to view an address which has no source code.

No Source window open (CV1058)

    A command was entered to manipulate the contents of the Source window,
    but no Source window is open.

No space left on device (CV0028)

    No more space for writing is available on the disk.

One of the following may have occurred:


    ■   CodeView could not find room for writing a temporary file.

    ■   An attempt was made to write to a disk that was full.


No such file or directory (CV0002)

    The specified file does not exist or a pathname does not specify an
    existing directory.

Check the file or directory name in the most recent command.

One of the following may have occurred:


    ■   The View (V) command or the Open Source command from the File menu was
        used to view a nonexistent file.

    ■   An attempt was made to print to a nonexistent file or directory.


No symbolic information for filename (CV0101)

    The executable file (or DLL if in OS/2) did not contain the symbols
    needed by CodeView.

Be sure to compile the program or DLL using the /Zi option. If linking in a
separate step, be sure to use the /CO option. Use the most current version
of LINK.

No watch variables to delete (CV5009)

    An attempt was made to delete one or more watch variables (watch
    expressions), but no watch expressions are currently selected.

Not a text file (CV1039)

    An attempt was made to load a file that is not a text file, possibly a
    binary-data file or an executable program file. This error can also
    occur if the first line of a file includes characters that are not in
    the range of ASCII 9 to 13 or ASCII 32 to 126.

The Source window only works with text files.

Not DOS 3.0 or later (CV1315)

    CodeView requires DOS version 3.0 or later. CodeView does not support
    DOS versions 1.x and 2.x.

Not enough memory to load CV.EXE (CV1314)

    There was not enough conventional memory to load CodeView.

Possible solutions include the following:


    ■   Free memory by removing terminate-and-stay-resident software.

    ■   Reduce the settings in CONFIG.SYS for FILES, BUFFERS, and LASTDRIVE.


Operand expected (CV4027)

    The operation or instruction requires an operand, but none was
    specified.

Operand must be register (CV4018)

    The operand for this instruction must be a register, not a label or
    variable.

Operand must have size (CV4035)

    No variable size was specified for the operand.

Specify the size of the variable being accessed by using the BY, WO, or DW
operator.

Operand types incorrect for this operation (CV1010)

    The operand types specified are not legal for the operation.

For example, a pointer cannot be multiplied by any value.

Operand types must match (CV4031)

    The command or instruction takes two or more operands, all of the same
    type.

Operator must have a struct/union type (CV1033)

    Components of structure variables or unions must be fully qualified.
    Components cannot be entered without full specification.

Operator needs lvalue (CV1032)

    An expression that does not evaluate to an lvalue was specified for an
    operation that requires an lvalue.

An lvalue (so called because it appears on the left side of an assignment
statement) is an expression that refers to a memory location.

For example,  buffer[count]  is a valid lvalue because it points to a
specific memory location. The logical comparison  zed != 0  is not a valid
lvalue because it evaluates to TRUE or FALSE, not a memory address.

Outdated EMM software (LIM 4.0 required) (CV3012)

    The EMM driver must be LIM EMS version 4.0 or later in order to contain
    the calls needed for CodeView to use expanded memory.

Out of memory (CV0012)

    CodeView was unable to allocate or reallocate the memory that it
    required because not enough memory was available.

Possible solutions include the following:


    ■   Run CVPACK on the executable file to reduce the demand on memory for
        symbolic information.

    ■   Recompile without symbolic information in some of the modules.
        CodeView requires memory to hold information about the program being
        debugged. Compile some modules with the /Zd option instead of /Zi, or
        don't use either option.

    ■   Remove other programs or drivers running in the system that could be
        consuming significant amounts of memory.

    ■   Decrease the settings in CONFIG.SYS for FILES and BUFFERS.


Out of memory (CV3608)

    CodeView needed additional conventional memory, but insufficient memory
    was available.

Possible solutions include the following:


    ■   Run CVPACK on the executable file to reduce the demand on memory for
        symbolic information.

    ■   Recompile without symbolic information in some of the modules.
        CodeView requires memory to hold information about the program being
        debugged. Compile some modules with the /Zd option instead of /Zi, or
        don't use either option.

    ■   Remove other programs or drivers running in the system that could be
        consuming significant amounts of memory.

    ■   Free some memory by removing terminate-and-stay-resident software.

    ■   Remove unneeded watches or breakpoints.

    ■   Compile some modules with optimizations enabled to reduce the demand
        on memory made by the program being debugged.


Overlay Manager stack overflow (CV1317)

    The CodeView file may be corrupt. Copy CV.EXE from the original disks
    and retry.

If the error recurs, note the circumstances of the error and notify
Microsoft Corporation by following the instructions on the Microsoft Product
Assistance Request form at the back of one of your manuals.

Overlay not resident (CV1047)

    An attempt was made to disassemble machine code from an overlay section
    of code that is not currently resident in memory.

Execute the program until the overlay is loaded.

Packed file (CV5012)

    (DOS only)

CodeView cannot debug files in DOS that are linked with the /EXEPACK option.
Relink without this option to debug the file and then switch back to linking
with /EXEPACK for the release version of your program.

Path of execution different from history (CV5006)

    The code executed during dynamic replay differed from the recorded
    history.

This may be normal if the program being debugged responds to asynchronous
events.

Radix must be between 2 and 36 inclusive (CV1107)

    A radix outside the allowable range was specified.

Register must be AX or AL (CV4060)

    The destination register for the instruction must be AX or AL.

Register variable out of scope (CV1024)

    An attempt was made to display a register variable outside the scope of
    the function containing it.

One of the following occurred:


    ■   The variable was declared as a register variable. Recompile the
        program with the register declaration removed.

    ■   The optimizer converted an ordinary variable into a register variable
        to speed up execution. Recompile the program using the /Od option to
        turn optimization off.

    ■   The function was defined with _fastcall, causing parameters to be
        passed in registers. Remove the _fastcall designation and recompile.


Regular expression too long (CV1012)

    The regular expression entered was too long or complex for CodeView to
    handle.

Use a simpler regular expression.

Relative jump out of range (CV4053)

    An address jump was specified that is greater than permitted.

A jump may be forward no more than 127 bytes and backward no more than 128
bytes relative to the next instruction.

Restart illegal in child CodeView (CV3612)

    A request was made to restart the program within a child copy of
    CodeView.

The Restart command cannot be used on a child process in a child CodeView.
It is necessary to restart the parent program to begin the child process
again.

Restart program to edit options (CV2204)

    The program must be restarted before the recording or playback options
    can be modified.

Restart program to record (CV5007)

    Recording cannot begin while the program is executing.

Restart the program before recording.

Resynchronizing the user tape (CV2205)

    The command history and user input tapes are out of synchronization.
    CodeView automatically adjusted the user tape to be synchronized with
    the command tape.

Screen session ended─application output lost (CV1044)

    Under OS/2, each screen display is handled by a different session. When
    CodeView tried to switch from one display to the other, the other
    display's session had ended and the output was gone.

Exit CodeView and restart it.

Simple variable can not have arguments (CV1115)

    In an expression, an argument was specified to a simple variable.

For example, given the declaration  INTEGER NUM, the expression  NUM(I)  is
not allowed.

Specified number of lines not supported, using default (CV1052)

    A display mode was selected that is not supported by either the
    monitor's hardware or the driver routines.

Exit CodeView, then restart it with an appropriate command-line option for
the display mode, either /25, /43, or /50.

Substring range out of bound (CV1118)

    A character expression exceeded the length specified in the CHARACTER
    statement.

Symbol not defined (CV4009)

    The symbol specified has not been previously defined.

The symbol name may have been mistyped.

Syntax error (CV1017)

    The command contained a syntax error.

The most likely cause is an invalid command or expression.

The program has terminated, restart to continue (CV0003)

    CodeView has detected a termination request by the program being
    debugged.

The program cannot be executed because it has terminated and has not been
restarted. Program memory remains allocated and may still be examined at
this point.

To run the program again, reload it using the Restart command.

Thread blocked (CV3501)

    The requested thread will not run because it is blocked by another
    thread.

If this is not expected behavior for the program being debugged, it may be
necessary to terminate the threads that are blocking the requested thread.

Too few array bounds given (CV1103)

    The bounds specified in an array subscript do not match the array
    declaration.

For example, given the array declaration  INTEGER IARRAY(3,4), the
expression  IARRAY(I)  would produce this message.

Too many array bounds given (CV1104)

    Too many subscripts were specified for the array.

For example, given the array declaration  INTEGER IARRAY(3,4), the
expression  IARRAY(I,3,J)  would produce this error message.

Too many open files (CV0024)

    CodeView could not open a file it needed because no more file handles
    are available.

In DOS, increase the number of file handles by changing the FILES setting in
CONFIG.SYS to allow a larger number of open files. FILES=20 is the
recommended setting. In OS/2, if multiple processes are running, removing
one or more of them may release enough file handles.

The program being debugged may have so many files open that all available
handles are exhausted. Check that the program has not left files open
unnecessarily. The first four handles are reserved by the operating system.


Too many watch objects (CV1036)

    More watch objects were specified than CodeView can handle.

The number of watch expressions that can be specified varies with the
demands made upon CodeView's internal memory resources.

Remove one or more of the watch expressions, or remove some breakpoints.

TOOLS.INI not found (CV1053)

    The directory listed in the INIT environment variable did not contain a
    TOOLS.INI file.

Check the INIT variable to be sure it points to the correct directory.

Type clash in function argument (CV1117)

    The type of an actual parameter did not match the corresponding formal
    parameter.

This message also appears when a routine that uses alternate returns is
called and the values of the return labels in the actual parameter list are
not 0.

Type conversion too complex (CV1037)

    Too many levels of type casting were specified.

Type casting is limited to two levels, as in

    (char) ((int) (floatvar))

Unable to create tape (CV2200)

    CodeView could not open a disk file (tape) to record commands and data
    for later replay.

Choosing the History On option from the Run menu causes CodeView to open
disk files program.CVH and program.CVI to record all commands and data for a
debugging session.

One of the following situations may have caused the error:


    ■   There was not enough space on the disk containing the program to be
        debugged.

    ■   There were not enough free file handles. In DOS, increase the number
        of file handles by changing the FILES setting in CONFIG.SYS to allow a
        larger number of open files. FILES=20 is the recommended setting. In
        OS/2, if multiple processes are running, removing one or more of them
        may release enough file handles to permit creating the tape.


Unable to open file (CV1007)

    The file specified cannot be opened.

One of the following may have occurred:


    ■   The file may not exist in the specified directory.

    ■   The filename was misspelled.

    ■   The file's attributes are set so that it cannot be opened.

    ■   A locking or sharing violation occurred.


Unable to open tape (CV2201)

    CodeView could not open the history file (tape) for replay.

Choosing the History On option from the Run menu causes CodeView to open
disk files program.CVH and program.CVI to record all commands and data for a
debugging session.

There probably were not enough free file handles. In DOS, increase the
number of file handles by changing the FILES setting in CONFIG.SYS to allow
a larger number of open files. FILES=20 is the recommended setting. In OS/2,
if multiple processes are running, removing one or more of them may release
enough file handles to permit opening the tape.

Unexpected EMM error (CV1316)

    An unexpected error occurred when reading overlays into expanded memory.


One of the following has probably occurred:


    ■   The EMM driver may be corrupted or may have malfunctioned. Reload the
        driver and retry.

    ■   Expanded memory has been corrupted.


If the error recurs, note the circumstances of the error and notify
Microsoft Corporation by following the instructions on the Microsoft Product
Assistance Request form at the back of one of your manuals.

Unexpected end-of-file in CV.EXE (CV1312)

    An unexpected end-of-file occurred while CV.EXE was being read.

The CodeView file may be corrupt. Copy CV.EXE from the original disks and
retry.

If the error recurs, note the circumstances of the error and notify
Microsoft Corporation by following the instructions on the Microsoft Product
Assistance Request form at the back of one of your manuals.

Unknown queue request─ignored (CV3609)

    One of the CodeView processes sent a command or data to another CodeView
    process that the latter process did not recognize. This is not a fatal
    error.

If this is a recurring error, please note the circumstances of the error and
notify Microsoft Corporation by following the instructions on the Microsoft
Product Assistance Request form at the back of one of your manuals.

Unknown symbol (CV1018)

    The symbolic name specified could not be found.

One of the following may have occurred:


    ■   The specified name was misspelled.

    ■   The wrong case was used when case sensitivity was on. Case sensitivity
        is toggled by the Case Sensitivity command from the Options menu, or
        set by the Option (O) Command-window command.

    ■   The module containing the specified symbol may not have been compiled
        with the /Zi option to include symbolic information.


User Tape Disabled (CV2208)

    The current CodeView session was invoked with the /K option to disable
    the keyboard. CodeView issues this warning as a reminder that the
    recording ability is limited when /K is used. You can record CodeView
    commands made during a debugging session, but not user keystrokes.

User tape may be truncated (CV2203)

    A request was made to start recording again without completely rerunning
    the original history tape. Any unexecuted commands will be discarded.

Value out of range (CV4050)

    The value specified was out of range for the data item.

Video mode changed without /S option (CV1040)

    The program being debugged changed screen modes, and CodeView was not
    set for swapping. The program output is now damaged or unrecoverable.

To be able to view program output, exit CodeView and restart it with the
Swap (/S) option.

Wrong number of function arguments (CV1116)

    An incorrect number of arguments was specified in a function call.

Wrong type of register (CV4019)

    The register specified is not permitted for this operation or
    instruction.

The mnemonic for the register may have been mistyped.

/X: CPU in protected or virtual mode (CV1301)

    The DOS extender was unable to switch to protected mode.

One of the following may have occurred:


    ■   OS/2 is running.

    ■   An EMM driver is running in protected mode.

    ■   A protected-mode application is running.


/X: CPU not 80286 or later (CV1300)

    The DOS extender runs in protected mode, which is supported only on the
    80286 and later processors.

/X: HIMEM.SYS not loaded (CV1302)

    HIMEM.SYS is used by the DOS extender to allocate extended memory and
    must be installed.

/X: not enough extended memory (CV1303)

    There was not enough space in extended memory to load the DOS extender.


One of the following may be a solution:


    ■   Remove programs that are using extended memory.

    ■   Run CodeView without the /X option.


/X: Unexpected initialization error (CV1320)

    The DOS extender encountered a general protection fault.

The CodeView file may be corrupt. Copy CV.EXE from the original disks and
retry.

If the error recurs, note the circumstances of the error and notify
Microsoft Corporation by following the instructions on the Microsoft Product
Assistance Request form at the back of one of your manuals.


F.3  EXEHDR Error Messages

This section lists error messages generated by the Microsoft EXE File Header
Utility (EXEHDR). EXEHDR errors (U11xx) are always fatal.

Number                            EXEHDR Error Message
────────────────────────────────────────────────────────────────────────────
U1100                             invalid magic number number

                                    EXEHDR discovered an unknown signature
                                    in the header for the file.

                                    The signature in the header for a file
                                    gives the operating system under which
                                    the executable file will run. EXEHDR
                                    recognizes signatures for DOS and OS/2
                                    only.

U1101                             automatic data segment greater than 64K;
                                    correcting heap size

                                    There was not enough space in the
                                    automatic, or default, data segment
                                    (DGROUP) to accommodate the requested
                                    new heap size. EXEHDR adjusted the heap
                                    size to the maximum available space.

                                    This error applies only to OS/2 programs.

U1102                             automatic data segment greater than 64K;
                                    correcting stack size

                                    There was not enough space in the
                                    automatic, or default, data segment
                                    (DGROUP) to accommodate the requested
                                    new stack size. EXEHDR adjusted the
                                    stack size to the maximum available
                                    space.

                                    This error applies only to OS/2 programs.

U1103                             invalid .EXE file : actual length less
                                    than reported

                                    The second and third fields in the
                                    input-file header indicate a file size
                                    greater than the actual size.

U1104                             cannot change load-high program

                                    When the minimum allocation value and
                                    the maximum allocation value are both 0,
                                    the file cannot be modified.

U1105                             minimum allocation less than stack;
                                    correcting minimum

                                    If the minimum allocation is not enough
                                    to accommodate the stack (either the
                                    original stack request or the modified
                                    request), the minimum allocation value
                                    is adjusted.

                                    This error applies only to DOS programs.

U1106                             minimum allocation greater than maximum;
                                    correcting maximum

                                    If the minimum allocation is greater
                                    than the maximum allocation, the maximum
                                    allocation value is adjusted.

                                    If a display of DOS header values is
                                    requested, the values shown will be the
                                    values after the packed file is expanded.

                                    This error applies only to DOS programs.

U1107                             unexpected end of resident/nonresident
                                    name table

                                    While decoding run-time relocation
                                    records, EXEHDR found the end of either
                                    the resident names table or the
                                    nonresident names table. The executable
                                    file is probably corrupted.

                                    This error applies only to OS/2 and
                                    Windows programs.

U1108                             cannot display compressed relocation
                                    records

                                    EXEHDR cannot decode the information in
                                    the file header because the header is
                                    not in a standard format.

U1109                             illegal value argument

                                    The given argument was invalid for the
                                    EXEHDR option it was specified with.

U1110                             malformed number number

                                    A command-line option for EXEHDR
                                    required a value, but the specified
                                    number was mistyped.

U1111                             option requires value

                                    A command-line option for EXEHDR
                                    required a value, but no value was
                                    specified, or the specified value was in
                                    an illegal format for the given option.

U1112                             value out of legal range lower-upper

                                    A command-line option for EXEHDR
                                    required a value, but the specified
                                    number did not fall in the required
                                    decimal range.

U1113                             value out of legal range lower-upper

                                    A command-line option for EXEHDR
                                    required a value, but the specified
                                    number did not fall in the required
                                    hexadecimal range.

U1114                             missing option value; option option
                                    ignored

                                    A command-line option for EXEHDR
                                    required a value, but nothing was
                                    specified. EXEHDR ignored the option.

U1115                             option option ignored

                                    A command-line option for EXEHDR was
                                    ignored. This error usually occurs with
                                    error U1116,  unrecognized option.

U1116                             unrecognized option: option

                                    A command-line option for EXEHDR was not
                                    recognized. This error usually occurs
                                    with either U1115,  option ignored, or
                                    U1111,  option requires value.

U1120                             input file missing

                                    No input file was specified on the
                                    EXEHDR command line.

U1121                             command line too long: commandline

                                    The given EXEHDR command line exceeded
                                    the limit of 512 characters.

U1130                             cannot read filename

                                    EXEHDR could not read the input file.
                                    Either the file is missing or the file
                                    attribute is set to prevent reading.

U1131                             invalid .EXE file

                                    The input file specified on the EXEHDR
                                    command line was not a valid executable
                                    file.

U1132                             unexpected end-of-file

                                    EXEHDR found an unexpected end-of-file
                                    condition while reading the executable
                                    file. The file is probably corrupt.

U1140                             out of memory

                                    There was not enough memory for EXEHDR
                                    to decode the header of the executable
                                    file.


F.4  HELPMAKE Error Messages

This section lists error messages generated by the Microsoft Help File
Maintenance Utility (HELPMAKE):


    ■   Fatal errors (H1xxx) cause HELPMAKE to stop execution. No output file
        is produced.

    ■   Errors (H2xxx) do not prevent an output file from being produced, but
        parts of the conversion are not completed.

    ■   Warnings (H4xxx) do not prevent an output file from being produced,
        but problems may exist in the output.



F.4.1  HELPMAKE Fatal Errors

Number                            HELPMAKE Error Message
────────────────────────────────────────────────────────────────────────────
H1000                             /A requires character

                                    The /A option requires an
                                    application-specific control character.

                                    The correct form is

                                    /Ac

                                    where c is the control character.

H1001                             /E compression level must be numeric

                                    The /E option requires either no
                                    argument or a numeric value in the range
                                    0-15. The correct form is

                                    /En

                                    where n specifies the amount of
                                    compression requested.

H1002                             multiple /O parameters specified

                                    Only one output file can be specified
                                    with the /O option.

H1003                             invalid /S file-type identifier

                                    The /S option was given an argument
                                    other than 1, 2, or 3.

                                    The /S option requires specification of
                                    the type of input file. An invalid
                                    file-type identifier was specified. The
                                    correct form is

                                    /Sn

                                    where n specifies the format of the
                                    input help text file. The only valid
                                    values are 1 (RTF), 2 (QuickHelp format),
                                    and 3 (minimally formatted ASCII).

H1004                             /S requires file-type identifier

                                    The /S option requires specification of
                                    the type of input file. There was no
                                    file-type identifier specified.

                                    The correct form is

                                    /Sn

                                    where n specifies the format of the
                                    input help text file. The only valid
                                    values are 1 (RTF), 2 (QuickHelp format),
                                    and 3 (minimally formatted ASCII).

H1005                             /W fixed width invalid

                                    An invalid width was specified with the
                                    /W option. The valid range is 11-255.

H1006                             multiple /K parameters specified

                                    The option for specifying a keyword
                                    separator file, /K, was used more than
                                    once on the HELPMAKE command line.

                                    Only one file containing separator
                                    characters may be specified.

H1050                             option invalid with /DS

                                    The /C, /L, and /O options for encoding
                                    are invalid with the /DS option for
                                    decoding.

H1051                             improper arguments for /D

                                    The /D option permits either no argument
                                    or an S or U argument. In addition, /D
                                    is invalid with the /C or /L option.

H1052                             encode requires /O option

                                    Database encoding was requested without
                                    a specified output-file name for the
                                    operation.

H1053                             compression level exceeds 15

                                    A value greater than 15 was specified
                                    with the /E option.

                                    The /E option requires either no
                                    argument or a numeric value in the range
                                    0-15. The correct form is

                                    /En

                                    where n specifies the amount of
                                    compression requested.

H1097                             no operation specified

                                    The HELPMAKE command line did not
                                    contain an option for encoding, decoding,
                                    or help.

                                    HELPMAKE requires the /E, /D, /H, or /?
                                    option.

H1098                             unrecognized option

                                    An unrecognized name followed the option
                                    indicator.

                                    An option is specified by a forward
                                    slash (/) or a dash (-) and an option
                                    name.

H1099                             syntax error on command line

                                    HELPMAKE cannot interpret the command
                                    line.

H1100                             cannot open file

                                    One of the files specified on the
                                    HELPMAKE command line could not be found
                                    or created.

H1101                             error writing file

                                    The output file could not be written,
                                    probably because the disk is full.

H1102                             no input file specified

                                    In an encoding operation, no input help
                                    text file was specified.

H1103                             no context strings found

                                    No context strings were found in the
                                    input stream while encoding.

                                    Either the file is empty, or the
                                    specified /S value does not correspond
                                    to the help text formatting.

H1104                             no topic text found

                                    No topic text was found in the help text
                                    file.

                                    Either the file is empty, or the
                                    specified /S value does not correspond
                                    to the help text formatting.

H1107                             cannot overwrite input file

                                    The /DS option for splitting a
                                    concatenated help file was specified,
                                    but the help file contained a database
                                    with the same name as the help file.

                                    Rename the help file to a filename other
                                    than one of the database names.

H1200                             insufficient memory to allocate context
                                    buffer

                                    There was insufficient memory to run
                                    HELPMAKE.

                                    HELPMAKE requires 256K free memory.

H1201                             insufficient memory to allocate utility
                                    buffer

                                    There was insufficient memory to run
                                    HELPMAKE.

                                    HELPMAKE requires 256K free memory.

H1250                             not a valid compressed help file

                                    The input file specified for a
                                    decompression operation is not a valid
                                    help database file.

H1251                             cannot decompress locked help file

                                    An attempt was made to decompress a help
                                    database file that is locked.

                                    A file is locked if the /L option is
                                    specified when the help file is created.

H1300                             word too long in RTF processing

                                    A single word was longer than the
                                    specified format width (set by the /W
                                    option) or was found to be longer than
                                    128 characters when HELPMAKE was
                                    reformatting a paragraph.

H1302                             attribute stack overflow processing RTF

                                    RTF attribute groups are nested too
                                    deeply. HELPMAKE supports a maximum of
                                    50 levels of attribute-group nesting in
                                    RTF format.

H1303                             unknown RTF attribute

                                    An unknown RTF formatting command was
                                    found.

                                    One of the following may have occurred:

                                    ■ A new RTF attribute was used. HELPMAKE
                                    recognizes a set of attributes that were
                                    current at the time this version of
                                    HELPMAKE was created. It interprets some
                                    of the attributes and knows to ignore
                                    the others. Any RTF attribute defined
                                    after HELPMAKE was created is not known
                                    by HELPMAKE and will cause this error.

                                    ■ The RTF file is corrupted.

H1304                             topic too large

                                    A topic exceeded the limit for the size
                                    of topics.

                                    A single topic cannot exceed 64K.

H1305                             topic text without context string

                                    The source file contained topic text
                                    that was not preceded by a .context
                                    definition.

H1900                             internal virtual memory error

                                    This message indicates an internal
                                    HELPMAKE error.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

H1901                             out of local memory

                                    This message indicates an internal
                                    HELPMAKE error.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

H1902                             out of disk space for swap file

                                    The current drive or directory is full.

                                    HELPMAKE uses a temporary swap file,
                                    written to the current drive and
                                    directory. The temporary file can grow
                                    to 1.5 times the size of the input files
                                    (for large help files) and is not
                                    removed until the final help file is
                                    completed.

H1903                             cannot open swap file

                                    HELPMAKE was unable to create its
                                    temporary swap file on the current drive
                                    and directory for one of the following
                                    reasons:

                                    ■ The current drive or directory is full.

                                    ■ The device cannot be written to.

H1990                             internal compression error

                                    This message indicates an internal
                                    HELPMAKE error.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions in the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.


F.4.2  HELPMAKE Errors

Number                            HELPMAKE Error Message
────────────────────────────────────────────────────────────────────────────
H2000                             line too long, truncated

                                    A line exceeded the fixed width
                                    specified by the /W option or the
                                    default of 76 characters. HELPMAKE
                                    truncated the extra characters.

H2001                             duplicate context string

                                    A context string preceded more than one
                                    topic in a help database. A context
                                    string can be associated with only one
                                    block of topic text.

H2002                             zero length hot spot

                                    A cross-reference was specified, but the
                                    word or anchored text associated with it
                                    was of zero length.

                                    With no visible text to associate with
                                    the cross-reference, the hot spot will
                                    be inoperative. This error is issued as
                                    a warning and does not prevent the
                                    building of a help file. However, some
                                    applications may not be able to use the
                                    resulting help file correctly.

                                    The following example will cause this
                                    error:

                                    avcross_referencev

H2003                             unrecognized dot command

                                    A line in the source file contained a
                                    dot (.) in column 1, but it was not
                                    followed by a command recognized by
                                    HELPMAKE.


F.4.3  HELPMAKE Warnings

Number                            HELPMAKE Warning
────────────────────────────────────────────────────────────────────────────
H4000                             keyword compression analysis table size
                                    exceeded no further new words will be
                                    analyzed

                                    The maximum number (16,000) of unique
                                    keywords has been encountered during
                                    keyword compression. This happens only
                                    in very large help files. No further
                                    keywords will be included in the
                                    analysis. HELPMAKE continues to analyze
                                    how frequently words occur that it has
                                    already encountered.

H4002                             reference to undefined local context

                                    A string specifying a local context was
                                    used in a cross-reference but was not
                                    defined in a .context statement.

                                    A local context begins with an at sign
                                    (@). Each local context that is used
                                    must be defined in a .context statement
                                    in one of the input files to HELPMAKE.

H4003                             negative left indent

                                    Topic text in an RTF file was formatted
                                    with a left indent to a position to the
                                    left of column 1. HELPMAKE deleted all
                                    text preceding column 1.


F.5  H2INC Error Messages

This section lists error messages generated by the C to MASM Include File
Translator (H2INC). The error messages produced by the compiler fall into
three categories:


    ■   Fatal error messages

    ■   Compilation error messages

    ■   Warning messages


The messages for each category are listed below in numerical order, with a
brief explanation of each error. To look up an error message, first
determine the message category, then find the error number. All messages
give the filename and line number where the error occurs.


Fatal Error Messages

Fatal error messages indicate a severe problem, one that prevents the
compiler from processing your program any further. These messages have the
following format:

filename (line) : fatal error HI1xxx: messagetext

After the compiler displays a fatal-error message, it terminates without
producing an include file or checking for further errors.


Compilation Error Messages

Compilation error messages identify actual header errors. There messages
appear in the following format:

filename (line) : error HI2xxx: messagetext

The compiler does not produce an include file for a header file that has
compilation errors. When the compiler encounters such errors, it attempts to
recover from the error. If possible, it continues to process the header file
and produce error messages. If errors are too numerous or too severe, the
compiler stops processing.


Warning Messages

Warning messages are informational only; they do not prevent compilation.
These messages appear in the following format:

filename (line) : warning HI4xxx: messagetext


F.5.1  H2INC Fatal Errors

Number                            Message
────────────────────────────────────────────────────────────────────────────
HI1003                            error count exceeds n; stopping
                                    compilation

                                    Errors in the program were too numerous
                                    or too severe to allow recovery, and the
                                    compiler must terminate.

HI1004                            unexpected end-of-file found

                                    The default disk drive did not contain
                                    sufficient space for the compiler to
                                    create temporary files. The space
                                    required is approximately two times the
                                    size of the source file.

                                    This message also appears when the #if
                                    directive occurs without a corresponding
                                    closing #endif directive while the #if
                                    test directs the compiler to skip the
                                    section.

HI1007                            unrecognized flag string in option

                                    The string in the command-line option
                                    was not a valid option.

HI1008                            no input file specified

                                    The compiler was not given a file to
                                    compile.

HI1009                            compiler limit : macros nested too
                                    deeply

                                    Too many macros were being expanded at
                                    the same time.

                                    This error occurs when a macro
                                    definition contains macros to be
                                    expanded and those macros contain other
                                    macros.

                                    Try to split the nested macros into
                                    simpler macros.

HI1011                            compiler limit : identifier : macro
                                    definition too big

                                    The macro definition was longer than
                                    allowed.

                                    Split the definition into shorter
                                    definitions.

HI1012                            unmatched parenthesis nesting - missing
                                    character

                                    The parentheses in a preprocessor
                                    directive were not matched. The missing
                                    character is either a left, (, or right,
                                    ), parenthesis.

HI1016                            #if[n]def expected an identifier

                                    An identifier must be specified with the
                                    #ifdef and #ifndef directives.

HI1017                            invalid integer constant expression

                                    The expression in an #if directive
                                    either did not exist or did not evaluate
                                    to a constant.

HI1018                            unexpected '#elif'

                                    The #elif directive is legal only when
                                    it appears within an #if, #ifdef, or
                                    #ifndef construct.

HI1019                            unexpected '#else'

                                    The #else directive is legal only when
                                    it appears within an #if, #ifdef, or
                                    #ifndef construct.

HI1020                            unexpected '#endif'

                                    An #endif directive appeared without a
                                    matching #if, #ifdef, or #ifndef
                                    directive.

HI1021                            invalid preprocessor command string

                                    The characters following the number sign
                                    (#) did not form a valid preprocessor
                                    directive.

HI1022                            expected '#endif'

                                    An #if, #ifdef, or #ifndef directive was
                                    not terminated with an #endif directive.

HI1023                            cannot open source file filename

                                    The given file either did not exist,
                                    could not be opened, or was not found.

                                    Make sure the environment settings are
                                    valid and that the correct path name for
                                    the file is specified.

                                    If this error appears without an error
                                    message, the compiler has run out of
                                    file handles. If in DOS, increase the
                                    number of file handles by changing the
                                    FILES setting CONFIG.SYS to allow a
                                    larger number of open files. FILES=20 is
                                    the recommended setting.

HI1024                            cannot open include file filename

                                    The specified file in an #include
                                    preprocessor directive could not be
                                    found.

                                    Make sure settings for the INCLUDE and
                                    TMP environment variables are valid and
                                    that the correct path name for the file
                                    is specified.

                                    If this error appears without an error
                                    message, the compiler has run out of
                                    file handles. If in DOS, increase the
                                    number of file handles by changing the
                                    FILES setting in CONFIG.SYS to allow a
                                    larger number of open files. FILES=20 is
                                    the recommended setting.

HI1026                            parser stack overflow, please simplify
                                    your program

                                    The program cannot be processed because
                                    the space required to parse the program
                                    causes a stack overflow in the compiler.

                                    Simplify the program by decreasing the
                                    complexity of expressions. Decrease the
                                    level of nesting in for and switch
                                    statements by putting some of the more
                                    deeply nested statements in separate
                                    functions. Break up very long
                                    expressions involving ',' operators or
                                    function calls.

HI1033                            cannot open assembly language output
                                    file filename

                                    There are several possible causes for
                                    this error:

                                    ■ The given name is not valid.

                                    ■ The file cannot be opened for lack of
                                    space.

                                    ■ A read-only file with the given name
                                    already exists.

HI1036                            cannot open source listing file filename

                                    There are several possible causes for
                                    this error:

                                    ■ The given name is not valid.

                                    ■ The file cannot be opened for lack of
                                    space.

                                    ■ A read-only file with the given name
                                    already exists.

HI1039                            unrecoverable heap overflow in Pass 3

                                    The post-optimizer compiler pass
                                    overflowed the heap and could not
                                    continue.

                                    One of the following may be a solution:

                                    ■ Break up the function containing the
                                    line that caused the error.

                                    ■ Recompile with the /Od option,
                                    removing optimization.

                                    ■ In OS/2, recompile using the /B3 C3L
                                    option to invoke the large-model version
                                    of the third pass of the compiler.

                                    ■ In DOS, remove other programs or
                                    drivers running in the system which
                                    could be consuming significant amounts
                                    of memory.

                                    ■ In DOS, if using NMAKE, compile
                                    without using NMAKE.

HI1040                            unexpected end-of-file in source file
                                    filename

                                    The compiler detected an unexpected
                                    end-of-file condition while creating a
                                    source listing or mingled source/object
                                    listing.

                                    This occurs under OS/2 if the source
                                    file is deleted or overwritten while it
                                    is being read.

HI1047                            limit of option exceeded at string

                                    The given option was specified too many
                                    times. The given string is the argument
                                    to the option that caused the error.

                                    If the CL or H2INC environment variables
                                    have been set, options in these
                                    variables are read before options
                                    specified on the command line. The CL
                                    environment variable is read before the
                                    H2INC environment variable.

HI1048                            unknown option character in option

                                    The given character was not a valid
                                    letter for the option.

                                    For example, the following line

                                    #pragma optimize("q", on)

                                    causes the following error

                                    unknown option 'q' in '#pragma optimize'

HI1049                            invalid numerical argument string

                                    A numerical argument was expected
                                    instead of the given string.

HI1050                            segment : code segment too large

                                    A code segment grew to within 36 bytes
                                    of 64K during compilation.

                                    A 36-byte pad is used because of a bug
                                    in some 80286 chips that can cause
                                    programs to exhibit strange behavior
                                    when, among other conditions, the size
                                    of a code segment is within 36 bytes of
                                    64K.

HI1052                            compiler limit : #if/#ifdef nested too
                                    deeply

                                    The program exceeded the maximum of 32
                                    nesting levels for #if and #ifdef
                                    directives.

HI1053                            compiler limit : struct/union nested too
                                    deeply

                                    A structure or union definition was
                                    nested to more than 15 levels.

                                    Break the structure or union into two
                                    parts by defining one or more of the
                                    nested structures using typedef.

HI1090                            segment data allocation exceeds 64K

                                    The size of the named segment exceeds
                                    64K.

                                    This error occurs with _based allocation.

HI1800                            option : unrecognized option

                                    A command-line option was specified that
                                    was not understood by H2INC.


F.5.2  H2INC Compilation Errors

Number                            Message
────────────────────────────────────────────────────────────────────────────
HI2000                            UNKNOWN ERROR Contact Microsoft Product
                                    Support Services

                                    The compiler detected an unknown error
                                    condition.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

HI2001                            newline in constant

                                    A string constant was continued onto a
                                    second line without either a backslash
                                    or closing and opening quotes.

                                    To break a string constant onto two
                                    lines in the source file, do one of the
                                    following:

                                    ■ End the first line with the
                                    line-continuation character, a backslash,
                                     .

                                    ■ Close the string on the first line
                                    with a double quotation mark, and open
                                    the string on the next line with another
                                    quotation mark.

                                    It is not sufficient to end the first
                                    line with n, the escape sequence for
                                    embedding a newline character in a
                                    string constant.

                                    The following two examples demonstrate
                                    causes of this error:

                                    printf("Hello,
                                    world");

                                    or

                                    printf("Hello,n
                                    world");

                                    The following two examples show ways to
                                    correct this error:

                                    printf("Hello,
                                    world");

                                    or

                                    printf("Hello,"
                                    " world");

                                    Note that any spaces at the beginning of
                                    the next line after a line-continuation
                                    character are included in the string
                                    constant. Note, also, that neither
                                    solution actually places a newline
                                    character into the string constant. To
                                    embed this character:

                                    printf("Hello,n
                                    world");

                                    or

                                    printf("Hello,
                                    nworld");

                                    or

                                    printf("Hello,n"
                                    "world");

                                    or

                                    printf("Hello,"
                                    "nworld");

HI2003                            expected defined id

                                    An identifier was expected after the
                                    preprocessing keyword defined.

HI2004                            expected defined(id)

                                    An identifier was expected after the
                                    left parenthesis, (, following the
                                    preprocessing keyword defined.

HI2005                            #line expected a line number, found
                                    token

                                    A #line directive lacked the required
                                    line-number specification.

HI2006                            #include expected a file name, found
                                    token

                                    An #include directive lacked the
                                    required filename specification.

HI2007                            #define syntax

                                    An identifier was expected following
                                    #define in a preprocessing directive.

HI2008                            character : unexpected in macro
                                    definition

                                    The given character was found
                                    immediately following the name of the
                                    macro.

HI2009                            reuse of macro formal identifier

                                    The given identifier was used more than
                                    once in the formal-parameter list of a
                                    macro definition.

HI2010                            character : unexpected in macro
                                    formal-parameter list

                                    The given character was used incorrectly
                                    in the formal-parameter list of a macro
                                    definition.

HI2012                            missing name following '<'

                                    An #include directive lacked the
                                    required filename specification.

HI2013                            missing '>'

                                    The closing angle bracket (>) was
                                    missing from an #include directive.

HI2014                            preprocessor command must start as first
                                    non-white-space

                                    Non-white-space characters appeared
                                    before the number sign (#) of a
                                    preprocessor directive on the same line.

HI2015                            too many characters in constant

                                    A character constant contained more than
                                    one character.

                                    Note that an escape sequence (for
                                    example, t for tab) is converted to a
                                    single character.

HI2016                            no closing single quotation mark

                                    A newline character was found before the
                                    closing single quotation mark of a
                                    character constant.

HI2017                            illegal escape sequence

                                    An escape sequence appeared where one
                                    was not expected.

                                    An escape sequence (a backslash,  ,
                                    followed by a number or letter) may
                                    occur only in a character or string
                                    constant.

HI2018                            unknown character hexnumber

                                    The ASCII character corresponding to the
                                    given hexadecimal number appeared in the
                                    source file but is an illegal character.

                                    One possible cause of this error is
                                    corruption of the source file. Edit the
                                    file and look at the line on which the
                                    error occurred.

HI2019                            expected preprocessor directive, found
                                    character

                                    The given character followed a number
                                    sign (#), but it was not the first
                                    letter of a preprocessor directive.

HI2021                            expected exponent value, not character

                                    The given character was used as the
                                    exponent of a floating-point constant
                                    but was not a valid number.

HI2022                            number : too big for character

                                    The octal number following a backslash
                                    () in a character or string constant
                                    was too large to be represented as a
                                    character.

HI2025                            identifier : enum/struct/union type
                                    redefinition

                                    The given identifier had already been
                                    used for an enumeration, structure, or
                                    union tag.

HI2026                            identifier : member of enum redefinition

                                    The given identifier has already been
                                    used for an enumeration constant, either
                                    within the same enumeration type or
                                    within another visible enumeration type.

HI2027                            use of undefined enum/struct/union
                                    identifier

                                    The given identifier referred to a
                                    structure or union type that was not
                                    defined.

HI2028                            struct/union member needs to be inside a
                                    struct/union

                                    Structure and union members must be
                                    declared within the structure or union.

                                    This error may be caused by an
                                    enumeration declaration containing a
                                    declaration of a structure member, as in
                                    the following example:

                                    enum a {
                                    january,
                                    february,
                                    int march;    /* Illegal structure
                                    declaration */
                                    };

HI2030                            identifier : struct/union member
                                    redefinition

                                    The identifier was used for more than
                                    one member of the same structure or
                                    union.

HI2031                            identifier : function cannot be
                                    struct/union member

                                    The given function was declared to be a
                                    member of a structure or union.

                                    To correct this error, use a pointer to
                                    the function instead.

HI2033                            identifier : bit field cannot have
                                    indirection

                                    The given bit field was declared as a
                                    pointer (*), which is not allowed.

HI2034                            identifier : type of bit field too small
                                    for number of bits

                                    The number of bits specified in the
                                    bit-field declaration exceeded the
                                    number of bits in the given base type.

HI2035                            struct/union identifier : unknown size

                                    The given structure or union had an
                                    undefined size.

                                    Usually this occurs when referencing a
                                    declared but not defined structure or
                                    union tag.

                                    For example, the following causes this
                                    error:

                                    struct s_tag *ps;
                                    ps = &my_var;
                                    *ps = 17;    /* This line causes the
                                    error */

HI2037                            left of operator specifies undefined
                                    struct/union identifier

                                    The expression before the
                                    member-selection operator ( -> or .)
                                    identified a structure or union type
                                    that was not defined.

HI2038                            identifier : not struct/union member

                                    The given identifier was used in a
                                    context that required a structure or
                                    union member.

HI2041                            illegal digit character for base number

                                    The given character was not a legal
                                    digit for the base used.

HI2042                            signed/unsigned keywords mutually
                                    exclusive

                                    The keywords signed and unsigned were
                                    both used in a single declaration, as in
                                    the following example:

                                    unsigned signed int i;

HI2056                            illegal expression

                                    An expression was illegal because of a
                                    previous error, which may not have
                                    produced an error message.

HI2057                            expected constant expression

                                    The context requires a constant
                                    expression.

HI2058                            constant expression is not integral

                                    The context requires an integral
                                    constant expression.

HI2059                            syntax error : token

                                    The token caused a syntax error.

HI2060                            syntax error : end-of-file found

                                    The compiler expected at least one more
                                    token.

                                    Some causes of this error include:

                                    Omitting a semicolon (;), as in

                                    int *p

                                    Omitting a closing brace (}) from the
                                    last function, as in

                                    main()
                                    {

HI2061                            syntax error : identifier identifier

                                    The identifier caused a syntax error.

HI2062                            type type unexpected

                                    The compiler did not expect the given
                                    type to appear here, possibly because it
                                    already had a required type.

HI2063                            identifier : not a function

                                    The given identifier was not declared as
                                    a function, but an attempt was made to
                                    use it as a function.

HI2064                            term does not evaluate to a function

                                    An attempt was made to call a function
                                    through an expression that did not
                                    evaluate to a function pointer.

HI2065                            identifier : undefined

                                    An attempt was made to use an identifier
                                    that was not defined.

HI2066                            cast to function type is illegal

                                    An object was cast to a function type,
                                    which is illegal.

                                    However, it is legal to cast an object
                                    to a function pointer.

HI2067                            cast to array type is illegal

                                    An object was cast to an array type.

HI2068                            illegal cast

                                    A type used in a cast operation was not
                                    legal for this expression.

HI2069                            cast of void term to nonvoid

                                    The void type was cast to a different
                                    type.

HI2070                            illegal sizeof operand

                                    The operand of a sizeof expression was
                                    not an identifier or a type name.

HI2071                            identifier : illegal storage class

                                    The given storage class cannot be used
                                    in this context.

HI2072                            identifier : initialization of a
                                    function

                                    An attempt was made to initialize a
                                    function.

HI2043                            illegal break

                                    A break statement is legal only within a
                                    do, for, while, or switch statement.

HI2044                            illegal continue

                                    A continue statement is legal only
                                    within a do, for, or while statement.

HI2045                            identifier : label redefined

                                    The label appeared before more than one
                                    statement in the same function.

HI2046                            illegal case

                                    The keyword case may appear only within
                                    a switch statement.

HI2047                            illegal default

                                    The keyword default may appear only
                                    within a switch statement.

HI2048                            more than one default

                                    A switch statement contained more than
                                    one default label.

HI2049                            case value value already used

                                    The case value was already used in this
                                    switch statement.

HI2050                            nonintegral switch expression

                                    A switch expression did not evaluate to
                                    an integral value.

HI2051                            case expression not constant

                                    Case expressions must be integral
                                    constants.

HI2052                            case expression not integral

                                    Case expressions must be integral
                                    constants.

HI2054                            expected '(' to follow identifier

                                    The context requires parentheses after
                                    the function identifier.

                                    One cause of this error is forgetting an
                                    equal sign (=) on a complex
                                    initialization, as in

                                    int array1[]    /* Missing = */
                                    {
                                    1,2,3
                                    };

HI2055                            expected formal-parameter list, not a
                                    type list

                                    An argument-type list appeared in a
                                    function definition instead of a formal-
                                    parameter list.

HI2075                            identifier : array initialization needs
                                    curly braces

                                    There were no curly braces, {}, around
                                    the given array initializer.

HI2076                            identifier : struct/union initialization
                                    needs curly braces

                                    There were no curly braces, {}, around
                                    the given structure or union initializer.

HI2077                            nonscalar field initializer identifier

                                    An attempt was made to initialize a
                                    bit-field member of a structure with a
                                    nonscalar value.

HI2078                            too many initializers

                                    The number of initializers exceeded the
                                    number of objects to be initialized.

HI2079                            identifier uses undefined struct/union
                                    name

                                    The identifier was declared as structure
                                    or union type name, but the name had not
                                    been defined. This error may also occur
                                    if an attempt is made to initialize an
                                    anonymous union.

HI2080                            illegal far _fastcall function

                                    A far _fastcall function may not be
                                    compiled with the /Gw option, nor with
                                    the /Gq option if stack checking is
                                    enabled.

HI2082                            redefinition of formal parameter
                                    identifier

                                    A formal parameter to a function was
                                    redeclared within the function body.

HI2084                            function function already has a body

                                    The function has already been defined.

HI2086                            identifier : redefinition

                                    The given identifier was defined more
                                    than once, or a subsequent declaration
                                    differed from a previous one.

                                    The following are ways to cause this
                                    error:

                                    int a;
                                    char a;
                                    main()
                                    {
                                    }
                                    main()
                                    {
                                    int a;
                                    int a;
                                    }

                                    However, the following does not cause
                                    this error:

                                    int a;
                                    int a;
                                    main()
                                    {
                                    }

HI2087                            identifier : missing subscript

                                    The definition of an array with multiple
                                    subscripts was missing a subscript value
                                    for a dimension other than the first
                                    dimension.

                                    The following is an example of an
                                    illegal definition:

                                    int func(a)
                                    char a[10][];
                                    { }

                                    The following is an example of a legal
                                    definition:

                                    int func(a)
                                    char a[][5];
                                    { }

HI2090                            function returns array

                                    A function cannot return an array. It
                                    can return a pointer to an array.

HI2091                            function returns function

                                    A function cannot return a function. It
                                    can return a pointer to a function.

HI2092                            array element type cannot be function

                                    Arrays of functions are not allowed.
                                    Arrays of pointers to functions are
                                    allowed.

HI2095                            function : actual has type void :
                                    parameter number

                                    An attempt was made to pass a void
                                    argument to a function. The given number
                                    indicates which argument was in error.

                                    Formal parameters and arguments to
                                    functions cannot have type void. They
                                    can, however, have type void * (pointer
                                    to void).

HI2100                            illegal indirection

                                    The indirection operator (*) was applied
                                    to a nonpointer value.

HI2101                            '&' on constant

                                    The address-of operator (&) did not have
                                    an lvalue as its operand.

HI2102                            '&' requires lvalue

                                    The address-of operator (&) must be
                                    applied to an lvalue expression.

HI2103                            '&' on register variable

                                    An attempt was made to take the address
                                    of a register variable.

HI2104                            '&' on bit field ignored

                                    An attempt was made to take the address
                                    of a bit field.

HI2105                            operator needs lvalue

                                    The given operator did not have an
                                    lvalue operand.

HI2106                            operator : left operand must be lvalue

                                    The left operand of the given operator
                                    was not an lvalue.

HI2107                            illegal index, indirection not allowed

                                    A subscript was applied to an expression
                                    that did not evaluate to a pointer.

HI2108                            nonintegral index

                                    A nonintegral expression was used in an
                                    array subscript.

HI2109                            subscript on nonarray

                                    A subscript was used on a variable that
                                    was not an array.

HI2110                            pointer + pointer

                                    An attempt was made to add one pointer
                                    to another using the plus (+) operator.

HI2111                            pointer + nonintegral value

                                    An attempt was made to add a nonintegral
                                    value to a pointer.

HI2112                            illegal pointer subtraction

                                    An attempt was made to subtract pointers
                                    that did not point to the same type.

HI2113                            pointer subtracted from nonpointer

                                    The right operand in a subtraction
                                    operation using the minus (-) operator
                                    was a pointer, but the left operand was
                                    not.

HI2114                            operator : pointer on left; needs
                                    integral right

                                    The left operand of the given operator
                                    was a pointer, so the right operand must
                                    be an integral value.

HI2115                            identifier : incompatible types

                                    An expression contained incompatible
                                    types.

HI2117                            operator : illegal for struct/union

                                    Structure and union type values are not
                                    allowed with the given operator.

HI2118                            negative subscript

                                    A value defining an array size was
                                    negative.

HI2120                            void illegal with all types

                                    The void type was used in a declaration
                                    with another type.

HI2121                            operator : bad left/right operand

                                    The left or right operand of the given
                                    operator was illegal for that operator.

HI2124                            divide or mod by zero

                                    A constant expression was evaluated and
                                    found to have a zero denominator.

HI2128                            identifier : huge array cannot be
                                    aligned to segment boundary

                                    The given huge array was large enough to
                                    cross two segment boundaries, but could
                                    not be aligned to both boundaries to
                                    prevent an individual array element from
                                    crossing a boundary.

                                    If the size of a huge array causes it to
                                    cross two boundaries, the size of each
                                    array element must be a power of two, so
                                    that a whole number of elements will fit
                                    between two segment boundaries.

HI2129                            static function function not found

                                    A forward reference was made to a static
                                    function that was never defined.

HI2130                            #line expected a string containing the
                                    file name, found token

                                    The optional token following the line
                                    number on a #line directive was not a
                                    string.

HI2131                            more than one memory attribute

                                    More than one of the keywords _near,
                                    _far, _huge, or _based were applied to
                                    an item, as in the following example:

                                    typedef int _near nint;
                                    nint _far a;    /* Illegal */

HI2132                            syntax error : unexpected identifier

                                    An identifier appeared in a
                                    syntactically illegal context.

HI2133                            identifier : unknown size

                                    An attempt was made to declare an
                                    unsized array as a local variable.

HI2134                            identifier : struct/union too large

                                    The size of a structure or union
                                    exceeded the 64K compiler limit.

HI2136                            function : prototype must have parameter
                                    types

                                    A function prototype declarator had
                                    formal-parameter names, but no types
                                    were provided for the parameters.

                                    A formal parameter in a function
                                    prototype must either have a type or be
                                    represented by an ellipsis (...) to
                                    indicate a variable number of arguments
                                    and no type checking.

                                    One cause of this error is a misspelling
                                    of a type name in a prototype that does
                                    not provide the names of formal
                                    parameters.

HI2137                            empty character constant

                                    The illegal empty-character constant (`')
                                    was used.

HI2139                            type following identifier is illegal

                                    Two types were used in the same
                                    declaration.

                                    For example:

                                    int double a;

HI2141                            value out of range for enum constant

                                    An enumeration constant had a value
                                    outside the range of values allowed for
                                    type int.

HI2143                            syntax error : missing token1 before
                                    token2

                                    The compiler expected token1 to appear
                                    before token2.

                                    This message may appear if a required
                                    closing brace (}), right parenthesis ()),
                                    or semicolon (;) is missing.

HI2144                            syntax error : missing token before type
                                    type

                                    The compiler expected the given token to
                                    appear before the given type name.

                                    This message may appear if a required
                                    closing brace (}), right parenthesis ()),
                                    or semicolon (;) is missing.

HI2145                            syntax error : missing token before
                                    identifier

                                    The compiler expected the given token to
                                    appear before an identifier.

                                    This message may appear if a semicolon
                                    (;) does not appear after the last
                                    declaration of a block.

HI2146                            syntax error : missing token before
                                    identifier identifier

                                    The compiler expected the given token to
                                    appear before the given identifier.

HI2147                            unknown size

                                    An attempt was made to increment an
                                    index or pointer to an array whose base
                                    type has not yet been declared.

HI2148                            array too large

                                    An array exceeded the maximum legal size
                                    of 64K.

                                    Either reduce the size of the array, or
                                    declare it with _huge.

HI2149                            identifier : named bit field cannot have
                                    0 width

                                    The given named bit field had zero width.
                                    Only unnamed bit fields are allowed to
                                    have zero width.

HI2150                            identifier : bit field must have type
                                    int, signed int, or unsigned int

                                    The ANSI C standard requires bit fields
                                    to have types of int, signed int, or
                                    unsigned int. This message appears only
                                    when compiling with the /Za option.

HI2151                            more than one language attribute

                                    More than one keyword specifying a
                                    calling convention for a function was
                                    given.

HI2152                            identifier : pointers to functions with
                                    different attributes

                                    An attempt was made to assign a pointer
                                    to a function declared with one calling
                                    convention (_cdecl, _fortran, _pascal,
                                    or _fastcall) to a pointer to a function
                                    declared with a different calling
                                    convention.

HI2153                            hex constants must have at least 1 hex
                                    digit

                                    The hexadecimal constants 0x, 0X, and x
                                    are illegal. At least one hexadecimal
                                    digit must follow the x or X.

HI2154                            segment : does not refer to a segment
                                    name

                                    A _based-allocated variable must be
                                    allocated in a segment unless it is
                                    extern and uninitialized.

HI2156                            pragma must be outside function

                                    A pragma that must be specified at a
                                    global level, outside a function body,
                                    occurred within a function.

                                    For example, the following causes this
                                    error:

                                    main()
                                    {
                                    #pragma optimize("l", on)
                                    }

HI2157                            function : must be declared before use
                                    in pragma list

                                    The function name in the list of
                                    functions for an alloc_text pragma has
                                    not been declared prior to being
                                    referenced in the list.

HI2158                            identifier : is a function

                                    The given identifier was specified in
                                    the list of variables in a same_seg
                                    pragma but was previously declared as a
                                    function.

HI2159                            more than one storage class specified

                                    A declaration contained more than one
                                    storage class, as in

                                    extern static int i;

HI2160                            ## cannot occur at the beginning of a
                                    macro definition

                                    A macro definition began with a
                                    token-pasting operator (##), as in

                                    #define mac(a,b) ##a

HI2161                            ## cannot occur at the end of a macro
                                    definition

                                    A macro definition ended with a
                                    token-pasting operator (##), as in

                                    #define mac(a,b) a##

HI2162                            expected macro formal parameter

                                    The token following a stringizing
                                    operator (#) was not a formal-parameter
                                    name.

                                    For example:

                                    #define print(a) printf(#b)

HI2165                            keyword : cannot modify pointers to data

                                    The _fortran, _pascal, _cdecl, or
                                    _fastcall keyword was used illegally to
                                    modify a pointer to data, as in the
                                    following example:

                                    char _pascal *p;

HI2166                            lvalue specifies const object

                                    An attempt was made to modify an item
                                    declared with const type.

HI2167                            function : too many actual parameters
                                    for intrinsic function

                                    A reference to the intrinsic function
                                    name contained too many actual
                                    parameters.

HI2168                            function : too few actual parameters for
                                    intrinsic function

                                    A reference to the intrinsic function
                                    name contained too few actual parameters.

HI2171                            operator : illegal operand

                                    The given unary operator was used with
                                    an illegal operand type, as in the
                                    following example:

                                    int (*fp)();
                                    double d,d1;
                                    fp++;
                                    d = ~d1;

HI2172                            function : actual is not a pointer :
                                    parameter number

                                    An attempt was made to pass an argument
                                    that was not a pointer to a function
                                    that expected a pointer. The given
                                    number indicates which argument was in
                                    error.

HI2173                            function : actual is not a pointer :
                                    parameter number1, parameter list
                                    number2

                                    An attempt was made to pass a nonpointer
                                    argument to a function that expected a
                                    pointer.

                                    This error occurs in calls that return a
                                    pointer to a function. The first number
                                    indicates which argument was in error;
                                    the second number indicates which
                                    argument list contained the invalid
                                    argument.

HI2174                            function : actual has type void :
                                    parameter number1, parameter list
                                    number2

                                    An attempt was made to pass a void
                                    argument to a function. Formal
                                    parameters and arguments to functions
                                    cannot have type void. They can, however,
                                    have type void * (pointer to void).

                                    This error occurs in calls that return a
                                    pointer to a function. The first number
                                    indicates which argument was in error;
                                    the second number indicates which
                                    argument list contained the invalid
                                    argument.

HI2177                            constant too big

                                    Information was lost because a constant
                                    value was too large to be represented in
                                    the type to which it was assigned.

HI2178                            identifier : storage class for same_seg
                                    variables must be extern

                                    The given variable was specified in a
                                    same_seg pragma, but it was not declared
                                    with extern storage class.

HI2179                            identifier : was used in same_seg, but
                                    storage class is no longer extern

                                    The given variable was specified in a
                                    same_seg pragma, but it was redeclared
                                    with a storage class other than extern.

HI2185                            identifier : illegal _based allocation

                                    A _based-allocated variable that
                                    explicitly has extern storage class and
                                    is uninitialized may not have a base of
                                    any of the following:

                                    (_segment) & var
                                    _segname("_STACK")
                                    (_segment)_self
                                    void

                                    If the variable does not explicitly have
                                    extern storage class or it is
                                    uninitialized, then its base must use
                                    _segname("string") where string is any
                                    segment name or reserved segment name
                                    except "_STACK".

HI2187                            cast of near function pointer to far
                                    function pointer

                                    An attempt was made to cast a near
                                    function pointer as a far function
                                    pointer.

HI2189                            #error : string

                                    An #error directive was encountered. The
                                    string is the descriptive text supplied
                                    in the directive.

HI2193                            identifier : already in a segment

                                    A variable in the same_seg pragma has
                                    already been allocated in a segment,
                                    using _based.

HI2194                            segment : is a text segment

                                    The given text segment was used where a
                                    data, const, or bss segment was expected.

HI2195                            segment : is a data segment

                                    The given data segment was used where a
                                    text segment was expected.

HI2200                            function : function has already been
                                    defined

                                    A function name passed as an argument in
                                    an alloc_text pragma has already been
                                    defined.

HI2201                            function : storage class must be extern

                                    A function declaration appears within a
                                    block, but the function is not declared
                                    extern. This causes an error if the /Za
                                    option is in effect.

                                    For example, the following causes this
                                    error, when compiled with

                                    /Za:
                                    main()
                                    {
                                    static int func1();
                                    }

HI2205                            identifier : cannot initialize extern
                                    block-scoped variables

                                    A variable with extern storage class may
                                    not be initialized in a function.

HI2208                            no members defined using this type

                                    An enum, struct, or union was defined
                                    without any members. This is an error
                                    only when compiling with /Za; otherwise,
                                    it is a warning.

HI2209                            type cast in _based construct must be
                                    (_segment)

                                    The only type allowed within a cast in a
                                    _based declarator is (_segment).

HI2210                            identifier : must be near/far data
                                    pointer

                                    The base in a _based declarator may not
                                    be an array, a function, or a _based
                                    pointer.

HI2211                            (_segment) applied to function
                                    identifier function

                                    The item cast in a _based declarator
                                    must not be a function.

HI2212                            identifier : _based not available for
                                    functions/pointers to functions

                                    Functions cannot be _based-allocated.
                                    Use the alloc_text pragma.

HI2213                            identifier : illegal argument to _based

                                    A symbol used as a base must have type
                                    _segment or be a near or far pointer.

HI2214                            pointers based on void require the use
                                    of :>

                                    A _based pointer based on void cannot be
                                    dereferenced. Use the :> operator to
                                    create an address that can be
                                    dereferenced.

HI2215                            :> operator only for objects based on
                                    void

                                    The right operand of the :> operator
                                    must be a pointer based on void, as in

                                    char _based(void) *cbvpi

HI2216                            attribute1 may not be used with
                                    attribute2

                                    The given function attributes are
                                    incompatible.

                                    Some combinations of attributes that
                                    cause this error are

                                    ■ _saveregs and _interrupt

                                    ■ _fastcall and _saveregs

                                    ■ _fastcall and _interrupt

                                    ■ _fastcall and _export

HI2217                            attribute1 must be used with attribute2

                                    The first function attribute requires
                                    the second attribute to be used.

                                    Some causes for this error include

                                    ■ An interrupt function explicitly
                                    declared as near. Interrupt functions
                                    must be far.

                                    ■ An interrupt function or a function
                                    with a variable number of arguments,
                                    when that function is declared with the
                                    _fortran, _pascal, or _fastcall
                                    attribute. Functions declared with the
                                    _interrupt attribute or with a variable
                                    number of arguments must use the C
                                    calling conventions. Remove the _fortran,
                                    _pascal, or _fastcall attribute from the
                                    function declaration.

HI2218                            type in _based construct must be void

                                    The only type allowed within a _based
                                    construct is void.

HI2219                            syntax error : type qualifier must be
                                    after '*'

                                    Either const or volatile appeared where
                                    a type or qualifier is not allowed, as
                                    in

                                    int (const *p);

HI2220                            warning treated as error - no object
                                    file generated

                                    When the compiler option /WX is used,
                                    the first warning generated by the
                                    compiler causes this error message to be
                                    displayed.

                                    Either correct the condition that caused
                                    the warning, or compile at a lower
                                    warning level or without /WX.

HI2221                            '.' : left operand points to
                                    struct/union, use ->

                                    The left operand of the '.' operator
                                    must be a struct/union type. It cannot
                                    be a pointer to a struct/union type.

                                    This error usually means that a ->
                                    operator must be used.

HI2222                            -> : left operand has struct/union type,
                                    use '.'

                                    The left operand of the -> operator must
                                    be a pointer to a struct/union type. It
                                    cannot be a struct/union type.

                                    This error usually means that a '.'
                                    operator must be used.

HI2223                            left of ->member must point to
                                    struct/union

                                    The left operand of the -> operator is
                                    not a pointer to a struct/union type.

                                    This error can occur when the left
                                    operand is an undefined variable.
                                    Undefined variables have type int.

HI2224                            left of .member must have struct/union
                                    type

                                    The left operand of the '.' operator is
                                    not a struct/union type.

                                    This error can occur when the left
                                    operand is an undefined variable.
                                    Undefined variables have type int.

HI2225                            tagname : first member of struct is
                                    unnamed

                                    The struct with the given tag started
                                    with an unnamed member (an alignment
                                    member). Struct definitions must start
                                    with a named member.


F.5.3  H2INC Warnings

Number                            Message
────────────────────────────────────────────────────────────────────────────
HI4000                            UNKNOWN WARNING Contact Microsoft
                                    Product Support Services

                                    The compiler detected an unknown error
                                    condition.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

HI4001                            nonstandard extension used - extension

                                    The given nonstandard language extension
                                    was used when the /Ze option was
                                    specified.

                                    This is a level 4 warning, except in the
                                    case of a function pointer cast to data
                                    when the Quick Compile option, /qc, is
                                    in use, which produces a level 1 warning.

                                    If the /Za option has been specified,
                                    this condition generates a syntax error.

HI4002                            too many actual parameters for macro
                                    identifier

                                    The number of actual arguments specified
                                    with the given identifier was greater
                                    than the number of formal parameters
                                    given in the macro definition of the
                                    identifier.

                                    The additional actual parameters are
                                    collected but ignored during expansion
                                    of the macro.

HI4003                            not enough actual parameters for macro
                                    identifier

                                    The number of actual arguments specified
                                    with the given identifier was fewer than
                                    the number of formal parameters given in
                                    the macro definition of the identifier.

                                    When a formal parameter is referenced in
                                    the definition and the corresponding
                                    actual parameter has not been provided,
                                    empty text is substituted in the macro
                                    expansion.

HI4004                            missing ')' after defined

                                    The closing parenthesis was missing from
                                    an #if defined phrase.

                                    The compiler assumes a right parenthesis,
                                    ), after the first identifier it finds.
                                    It then attempts to compile the
                                    remainder of the line, which may result
                                    in another warning or error.

                                    The following example causes this
                                    warning and a fatal error:

                                    #if defined( ID1 ) || ( ID2 )

                                    The compiler assumed a right parenthesis
                                    after ID1, then found a mismatched
                                    parenthesis in the remainder of the line.
                                    The following avoids this problem:

                                    #if defined( ID1 ) || defined( ID2 )

HI4005                            identifier : macro redefinition

                                    The given identifier was defined twice.
                                    The compiler assumed the new macro
                                    definition.

                                    To eliminate the warning, either remove
                                    one of the definitions or use an #undef
                                    directive before the second definition.

                                    This warning is caused in situations
                                    where a macro is defined both on the
                                    command line and in the code with a
                                    #define directive.

HI4006                            #undef expected an identifier

                                    The name of the identifier whose
                                    definition was to be removed was not
                                    given with the #undef directive. The
                                    #undef was ignored.

HI4007                            identifier : must be attribute

                                    The attribute of the given function was
                                    not explicitly stated. The compiler
                                    forced the attribute.

                                    For example, the function main must have
                                    the _cdecl attribute.

HI4008                            identifier : _fastcall attribute on data
                                    ignored

                                    The _fastcall attribute on the given
                                    data identifier was ignored.

HI4009                            string too big, trailing characters
                                    truncated

                                    A string exceeded the compiler limit of
                                    2047 on string size. The excess
                                    characters at the end of the string were
                                    truncated.

                                    To correct this problem, break the
                                    string into two or more strings.

HI4011                            identifier truncated to identifier

                                    Only the first 31 characters of an
                                    identifier are significant. The
                                    characters after the limit were
                                    truncated.

                                    This may mean that two identifiers that
                                    are different before truncation may have
                                    the same identifier name after
                                    truncation.

HI4015                            identifier : bit-field type must be
                                    integral

                                    The given bit field was not declared as
                                    an integral type. The compiler assumed
                                    the base type of the bit field to be
                                    unsigned.

                                    Bit fields must be declared as unsigned
                                    integral types.

HI4016                            function : no function return type,
                                    using int as default

                                    The given function had not yet been
                                    declared or defined, so the return type
                                    was unknown. A default return type of
                                    int was assumed.

HI4017                            cast of int expression to far pointer

                                    A far pointer represents a full
                                    segmented address. On an 8086/8088
                                    processor, casting an int value to a far
                                    pointer may produce an address with a
                                    meaningless segment value.

                                    The compiler extended the int expression
                                    to a four-byte value.

HI4020                            function : too many actual parameters

                                    The number of arguments specified in a
                                    function call was greater than the
                                    number of parameters specified in the
                                    function prototype or function
                                    definition.

                                    The extra parameters were passed
                                    according to the calling convention used
                                    on the function.

HI4021                            function : too few actual parameters

                                    The number of arguments specified in a
                                    function call was less than the number
                                    of parameters specified in the function
                                    prototype or function definition.

                                    Only the provided actual parameters are
                                    passed. If the called function
                                    references a variable that was not
                                    passed, the results are undefined and
                                    may be unexpected.

HI4022                            function : pointer mismatch : parameter
                                    number

                                    The pointer type of the given parameter
                                    was different from the pointer type
                                    specified in the argument-type list or
                                    function definition.

                                    The parameter will be passed without
                                    change. Its value will be interpreted as
                                    a pointer within the called function.

HI4023                            function : _based pointer passed to
                                    unprototyped function : parameter number


                                    When in a near data model, only the
                                    offset portion of a _based pointer is
                                    passed to an unprototyped function. If
                                    the function expects a far pointer, the
                                    resulting code will be wrong. In any
                                    data model, if the function is defined
                                    to take a _based pointer with a
                                    different base, the resulting code may
                                    be unpredictable.

                                    If a prototype is used before the call,
                                    the call will be generated correctly.

HI4024                            function : different types : parameter
                                    number

                                    The type of the given parameter in a
                                    function call did not agree with the
                                    type given in the argument-type list or
                                    function definition.

                                    The parameter will be passed without
                                    change. The function will interpret the
                                    parameter's type as the type expected by
                                    the function.

HI4028                            parameter number declaration different

                                    The type of the given parameter did not
                                    agree with the corresponding type in the
                                    argument-type list or with the
                                    corresponding formal parameter.

                                    The original declaration was used.

HI4030                            first parameter list longer than the
                                    second

                                    A function was declared more than once
                                    with different parameter lists.

                                    The first declaration was used.

HI4031                            second parameter list is longer than the
                                    first

                                    A function was declared more than once
                                    with different parameter lists.

                                    The first declaration was used.

HI4034                            sizeof returns 0

                                    The sizeof operator was applied to an
                                    operand that yielded a size of zero.

                                    This warning is informational.

HI4040                            memory attribute on identifier ignored

                                    The _near, _far, _huge, or _based
                                    keyword has no effect in the declaration
                                    of the given identifier and is ignored.

                                    One cause of this warning is a huge
                                    array that is not declared globally.
                                    Declare huge arrays outside of main.

HI4042                            identifier : has bad storage class

                                    The storage class specified for
                                    identifier cannot be used in this
                                    context.

                                    The default storage class for this
                                    context was used in place of the illegal
                                    class:

                                    ■ If identifier was a function, the
                                    compiler assumed extern class.

                                    ■ If identifier was a formal parameter
                                    or local variable, the compiler assumed
                                    auto class.

                                    ■ If identifier was a global variable,
                                    the compiler assumed that the variable
                                    was declared with no storage class.

HI4044                            _huge on identifier ignored, must be an
                                    array

                                    The compiler ignored the _huge memory
                                    attribute on the given identifier. Only
                                    arrays may be declared with the _huge
                                    memory attribute. On pointers, _huge
                                    must be used as a modifier, not as a
                                    memory attribute.

HI4047                            operator : different levels of
                                    indirection

                                    An expression involving the specified
                                    operator had inconsistent levels of
                                    indirection.

                                    If both operands are of arithmetic type,
                                    or if both are not (such as two arrays
                                    or pointers), then they are used without
                                    change, though the compiler may DS-
                                    extend one of the operands if one is far
                                    and one is near. If one is arithmetic
                                    and one is not, the arithmetic operator
                                    is converted to the type of the other
                                    operator.

                                    For example, the following code causes
                                    this warning but is compiled without
                                    change:

                                    char **p;
                                    char *q;
                                    p = q;   /* Warning */

HI4048                            array's declared subscripts different

                                    An expression involved pointers to
                                    arrays of different size.

                                    The pointers were used without
                                    conversion.

HI4049                            operator : indirection to different
                                    types

                                    The pointer expressions used with the
                                    given operator had different base types.

                                    The expressions were used without
                                    conversion.

                                    For example, the following code causes
                                    this warning:

                                    struct ts1 *s1;
                                    struct ts2 *s2;
                                    s2 = s1;   /* Warning */

HI4050                            operator : different code attributes

                                    The function-pointer expressions used
                                    with operator had different code
                                    attributes. The attribute involved is
                                    either _export or _loadds.

                                    This is a warning and not an error,
                                    because _export and _loadds affect only
                                    entry sequences and not calling
                                    conventions.

HI4051                            type conversion, possible loss of data

                                    Two data items in an expression had
                                    different base types, causing the type
                                    of one item to be converted. During the
                                    conversion, a data item was truncated.

HI4053                            at least one void operand

                                    An expression with type void was used as
                                    an operand.

                                    The expression was evaluated using an
                                    undefined value for the void operand.

HI4063                            function : function too large for
                                    post-optimizer

                                    Not enough space was available to
                                    optimize the given function.

                                    One of the following may be a solution:

                                    ■ Recompile with fewer optimizations.

                                    ■ Divide the function into two or more
                                    smaller functions.

                                    ■ In OS/2, recompile using the /B3 C3L
                                    option to invoke the large-model version
                                    of the third pass of the compiler.

HI4066                            local symbol-table overflow - some local
                                    symbols may be missing in listings

                                    The listing generator ran out of heap
                                    space for local variables, so the source
                                    listing may not contain symbol-table
                                    information for all local variables.

HI4067                            unexpected characters following
                                    directive directive - newline expected

                                    Extra characters followed a preprocessor
                                    directive and were ignored. This warning
                                    appears only when compiling with the /Za
                                    option.

                                    For example, the following code causes
                                    this warning:

                                    #endif    NO_EXT_KEYS

                                    To remove the warning, compile with /Ze
                                    or use comment delimiters:

                                    #endif    /* NO_EXT_KEYS */

HI4071                            function : no function prototype given

                                    The given function was called before the
                                    compiler found the corresponding
                                    function prototype.

                                    The function will be called using the
                                    default rules for calling a function
                                    without a prototype.

HI4072                            function : no function prototype on
                                    _fastcall function

                                    A _fastcall function was called without
                                    first being prototyped.

                                    Functions that are _fastcall should be
                                    prototyped to guarantee that the
                                    registers assigned at each point of call
                                    are the same as the registers assumed
                                    when the function is defined. A function
                                    defined in the new ANSI style is a
                                    prototype.

                                    A prototype must be added when this
                                    warning appears, unless the function
                                    takes no arguments or takes only
                                    arguments that cannot be passed in the
                                    general- purpose registers.

HI4073                            scoping too deep, deepest scoping merged
                                    when debugging

                                    Declarations appeared at a static
                                    nesting level greater than 13. As a
                                    result, all declarations beyond this
                                    level will seem to appear at the same
                                    level.

HI4076                            type : may be used on integral types
                                    only

                                    The signed or unsigned type modifier was
                                    used with a nonintegral type.

                                    The given qualifier was ignored.

                                    The following example causes this
                                    warning:

                                    unsigned double x;

HI4079                            unexpected token token

                                    An unexpected separator token was found
                                    in the argument list of a pragma.

                                    The remainder of the pragma was ignored.

HI4082                            expected an identifier, found token

                                    An identifier was missing from the
                                    argument list.

                                    The remainder of the pragma was ignored.

HI4083                            expected '(', found token

                                    A left parenthesis, (, was missing from
                                    a pragma's argument list.

                                    The pragma was ignored.

                                    The following example causes this
                                    warning:

                                    #pragma check_pointer on)

HI4084                            expected a pragma keyword, found token

                                    The token following #pragma was not
                                    recognized as a directive.

                                    The pragma was ignored.

                                    The following example causes this
                                    warning:

                                    #pragma (on)

HI4085                            expected [on | off]

                                    The pragma expected an on or off
                                    parameter, but the specified parameter
                                    was unrecognized or missing.

                                    The pragma was ignored.

HI4086                            expected [1 | 2 | 4]

                                    The pragma expected a parameter of
                                    either 1, 2, or 4, but the specified
                                    parameter was unrecognized or missing.

HI4087                            function : declared with void parameter
                                    list

                                    The given function was declared as
                                    taking no parameters, but a call to the
                                    function specified actual parameters.

                                    The extra parameters were passed
                                    according to the calling convention used
                                    on the function.

                                    The following example causes this
                                    warning:

                                    int f1(void);
                                    f1(10);

HI4088                            function : pointer mismatch : parameter
                                    number, parameter list number

                                    The argument passed to the given
                                    function had a different level of
                                    indirection from the given parameter in
                                    the function definition.

                                    The parameter will be passed without
                                    change. Its value will be interpreted as
                                    a pointer within the called function.

HI4089                            function : different types : parameter
                                    number, parameter list number

                                    The argument passed to the given
                                    function did not have the same type as
                                    the given parameter in the function
                                    definition.

                                    The parameter will be passed without
                                    change. The function will interpret the
                                    parameter's type as the type expected by
                                    the function.

HI4090                            different const/volatile qualifiers

                                    A pointer to an item declared as const
                                    was assigned to a pointer that was not
                                    declared as const. As a result, the
                                    const item pointed to could be modified
                                    without being detected.

                                    The expression was compiled without
                                    modification.

                                    The following example causes this
                                    warning:

                                    const char *p = "abcde";
                                    int str(char *s);
                                    str(p);

HI4091                            no symbols were declared

                                    The compiler detected an empty
                                    declaration, as in the following
                                    example:

                                    int ;

                                    The declaration was ignored.

HI4092                            untagged enum/struct/union declared no
                                    symbols

                                    The compiler detected an empty
                                    declaration using an untagged structure,
                                    union, or enumerated variable. The
                                    declaration was ignored.

                                    For example, the following code causes
                                    this warning:

                                    struct { . . . };

HI4093                            unescaped newline in character constant
                                    in inactive code

                                    The constant expression of an #if, #elif,
                                    #ifdef, or #ifndef preprocessor
                                    directive evaluated to 0, making the
                                    code that follows inactive. Within that
                                    inactive code, a newline character
                                    appeared within a set of single or
                                    double quotation marks.

                                    All text until the next double quotation
                                    mark was considered to be within a
                                    character constant.

HI4095                            expected ')', found token

                                    More than one argument was given for a
                                    pragma that can take only one argument.

                                    The compiler assumed the expected
                                    parenthesis and ignored the remainder of
                                    the line.

HI4096                            attribute1 must be used with attribute2

                                    The use of attribute2 requires the use
                                    of attribute1.

                                    For example, using a variable number of
                                    arguments (...) requires that _cdecl be
                                    used. Also, _interrupt functions must be
                                    _far and _cdecl.

                                    The compiler assumed attribute1 for the
                                    function.

HI4098                            void function returning a value

                                    A function declared with a void return
                                    type also returned a value.

                                    A function was declared with a void
                                    return type but was defined as a value.

                                    The compiler assumed the function
                                    returns a value of type int.

HI4104                            identifier : near data in same_seg
                                    pragma, ignored

                                    The given near variable was specified in
                                    a same_seg pragma.

                                    The identifier was ignored.

HI4105                            identifier : code modifiers only on
                                    function or pointer to function

                                    The given identifier was declared with a
                                    code modifier that can be used only with
                                    a function or function pointer.

                                    The code modifier was ignored.

HI4109                            unexpected identifier identifier

                                    The pragma contained an unexpected token.

                                    The pragma was ignored.

HI4110                            unexpected token int constant

                                    The pragma contained an unexpected
                                    integer constant.

                                    The pragma was ignored.

HI4111                            unexpected token string

                                    The pragma contained an unexpected
                                    string.

                                    The pragma was ignored.

HI4112                            macro name name is reserved, command
                                    ignored

                                    The given command attempted to define or
                                    undefine the predefined macro name or
                                    the preprocessor operator defined. The
                                    given command is displayed as either
                                    #define or #undef, even if the attempt
                                    was made using command-line options.

                                    The command was ignored.

HI4113                            function parameter lists differed

                                    A function pointer was assigned to a
                                    function pointer, but the parameter
                                    lists of the functions do not agree.

                                    The expression was compiled without
                                    modification.

HI4114                            same type qualifier used more than once

                                    A type qualifier (const, volatile,
                                    signed, or unsigned) was used more than
                                    once in the same type.

                                    The second occurrence of the qualifier
                                    was ignored.

HI4115                            tag : type definition in formal
                                    parameter list

                                    The given tag was used to define a
                                    struct, union, or enum in the formal
                                    parameter list of a function.

                                    The compiler assumed the definition was
                                    at the global level.

HI4116                            (no tag) : type definition in formal
                                    parameter list

                                    A struct, union, or enum type with no
                                    tag was defined in the formal parameter
                                    list of a function.

                                    The compiler assumed the definition was
                                    at the global level.

HI4119                            different bases name1 and name2
                                    specified

                                    The _based pointers in the expression
                                    have different symbolic bases. There may
                                    be truncation or loss in the code
                                    generated.

HI4120                            _based/unbased mismatch

                                    The expression contains a conversion
                                    between a _based pointer and another
                                    pointer that is unbased. Some
                                    information may have been truncated.

                                    This warning commonly occurs when a
                                    _based pointer is passed to a function
                                    that accepts a near or far pointer.

HI4123                            different base expressions specified

                                    The expression contains a conversion
                                    between _based pointers, but the base
                                    expressions of the _based pointers are
                                    different. Some of the _based
                                    conversions may be unexpected.

HI4125                            decimal digit terminates octal escape
                                    sequence

                                    An octal escape sequence in a character
                                    or string constant was terminated with a
                                    decimal digit.

                                    The compiler evaluated the octal number
                                    without the decimal digit and assumed
                                    the decimal digit was a character.

                                    The following example causes this
                                    warning:

                                    char array1[] = "709";

                                    If the digit 9 was intended as a
                                    character and was not a typing error,
                                    correct the example as follows:

                                    char array[] = "709";  /* String
                                    containing "89" */

HI4126                            flag : unknown memory model flag

                                    The flag used with the /A option was not
                                    recognized and was ignored.

HI4128                            storage-class specifier after type

                                    A storage-class specifier (auto, extern,
                                    register, static) appears after a type
                                    in a declaration. The compiler assumed
                                    that the storage class specifier
                                    occurred before the type.

                                    New-style code places the storage-class
                                    specifier first.

HI4129                            character : unrecognized character
                                    escape sequence

                                    The character following a backslash in a
                                    character or string constant was not
                                    recognized as a valid escape sequence.

                                    As a result, the backslash is ignored
                                    and not printed, and the character
                                    following the backslash is printed.

                                    To print a single backslash (), specify
                                    a double backslash (\).

HI4130                            operator  : logical operation on address
                                    of string constant

                                    The operator was used with the address
                                    of a string literal. Unexpected code was
                                    generated.

                                    For example, the following code causes
                                    this warning:

                                    char *pc;
                                    pc = "Hello";
                                    if (pc == "Hello") ...

                                    The if statement compares the value
                                    stored in the pointer pc to the address
                                    of the string "Hello", which is
                                    separately allocated each time it occurs
                                    in the code. It does not compare the
                                    string pointed to by pc with the string
                                    "Hello".

                                    To compare strings, use the strcmp
                                    function.

HI4131                            function : uses old-style declarator

                                    The function declaration or definition
                                    is not a prototype.

                                    New-style function declarations are in
                                    prototype form.

                                    ■ old style

                                    int addrec( name, id )
                                    char *name;
                                    int id;
                                    { }

                                    ■ new style

                                    int addrec( char *name, int id )
                                    { }

HI4132                            object : const object should be
                                    initialized

                                    The value of a const object cannot be
                                    changed, so the only way to give the
                                    const object a value is to initialize it.

                                    It will not be possible to assign a
                                    value to object.

HI4135                            conversion between different integral
                                    types

                                    Information was lost between two
                                    integral types.

                                    For example, the following code causes
                                    this warning:

                                    int intvar;
                                    long longvar;
                                    intvar = longvar;

                                    If the information is merely interpreted
                                    differently, this warning is not given,
                                    as in the following example:

                                    unsigned uintvar = intvar;

HI4136                            conversion between different floating
                                    types

                                    Information was lost or truncated
                                    between two floating types.

                                    For example, the following code causes
                                    this warning:

                                    double doublevar;
                                    float floatvar;
                                    floatvar = doublevar;

                                    Note that unsuffixed floating-point
                                    constants have type double, so the
                                    following code causes this warning:

                                    floatvar = 1.0;

                                    If the floating-point constant should be
                                    treated as float type, use the F (or f)
                                    suffix on the constant to prevent the
                                    following warning:

                                    floatvar = 1.0F;

HI4138                            */ found outside of comment

                                    The compiler found a closing comment
                                    delimiter (*/) without a preceding
                                    opening delimiter. It assumed a space
                                    between the asterisk (*) and the forward
                                    slash (/).

                                    The following example causes this
                                    warning:

                                    int */*comment*/ptr;

                                    In this example, the compiler assumed a
                                    space before the first comment delimiter
                                    (/*) and issued the warning but compiled
                                    the line normally. To remove the warning,
                                    insert the assumed space.

                                    Usually, the cause of this warning is an
                                    attempt to nest comments.

                                    To comment out sections of code that may
                                    contain comments, enclose the code in an
                                    #if/#endif block and set the controlling
                                    expression to zero, as in:

                                    #if 0
                                    int my_variable;   /* Declaration
                                    currently not needed */
                                    #endif

HI4139                            hexnumber : hex escape sequence is out
                                    of range

                                    A hex escape sequence appearing in a
                                    character or string constant was too
                                    large to be converted to a character.

                                    If in a string constant, the compiler
                                    cast the low byte of the hexadecimal
                                    number to a char. If in a char constant,
                                    the compiler made the cast and then sign
                                    extended the result. If in a char
                                    constant and compiled with /J, the
                                    compiler cast the value to an unsigned
                                    char.

                                    For example, x1ff is out of range for a
                                    character. Note that the following code
                                    causes this warning:

                                    printf("x7Belln");

                                    The number 7be is a legal hex number but
                                    is too large for a character. To correct
                                    this example, use three hex digits:

                                    printf("x007Belln");

HI4186                            string too long - truncated to 40
                                    characters

                                    The string argument for a title or
                                    subtitle pragma exceeded the maximum
                                    allowable length and was truncated.

HI4200                            local variable identifier used without
                                    having been initialized

                                    A reference was made to a local variable
                                    that had not been assigned a value. As a
                                    result, the value of the variable is
                                    unpredictable.

                                    This warning is given only when
                                    compiling with global register
                                    allocation on (/Oe).

HI4201                            local variable identifier may be used
                                    without having been initialized

                                    A reference was made to a local variable
                                    that might not have been assigned a
                                    value. As a result, the value of the
                                    variable may be unpredictable.

                                    This warning is given only when
                                    compiling with the global register
                                    allocation on (/Oe).

HI4202                            unreachable code

                                    The flow of control can never reach the
                                    indicated line.

                                    This warning is given only when
                                    compiling with one of the global
                                    optimizations (/Oe, /Og, or /Ol).

HI4203                            function : function too large for global
                                    optimizations

                                    The named function was too large to fit
                                    in memory and be compiled with the
                                    selected optimization. The compiler did
                                    not perform any global optimizations
                                    (/Oe, /Og, or /Ol). Other /O
                                    optimizations, such as /Oa and /Oi, are
                                    still performed.

                                    One of the following may remove this
                                    warning:

                                    ■ Recompile with fewer optimizations.

                                    ■ Divide the function into two or more
                                    smaller functions.

                                    ■ In OS/2, recompile using the /B2 C2L
                                    option to invoke the large-model version
                                    of the second pass of the compiler.

HI4204                            function : in-line assembler precludes
                                    global optimizations

                                    The use of in-line assembler in the
                                    named function prevented the specified
                                    global optimizations (/Oe, /Og, or /Ol)
                                    from being performed.

HI4205                            statement has no effect

                                    The indicated statement will have no
                                    effect on the program execution.

                                    Some examples of statements with no
                                    effect:

                                    1;
                                    a + 1;
                                    b == c;

HI4209                            comma operator within array index
                                    expression

                                    The value used as an index into an array
                                    was the last one of multiple expressions
                                    separated by the comma operator.

                                    An array index legally may be the value
                                    of the last expression in a series of
                                    expressions separated by the comma
                                    operator. However, the intent may have
                                    been to use the expressions to specify
                                    multiple indexes into a multidimensional
                                    array.

                                    For example, the following line, which
                                    causes this warning, is legal in C, and
                                    specifies the index c into array a:

                                    a[b,c]

                                    However, the following line uses both b
                                    and c as indexes into a two-dimensional
                                    array:

                                    a[b][c]

HI4300                            insufficient memory to process debugging
                                    information

                                    The program was compiled with the /Zi
                                    option, but not enough memory was
                                    available to create the required
                                    debugging information.

                                    One of the following may be a solution:

                                    ■ Split the current file into two or
                                    more files and compile them separately.

                                    ■ Remove other programs or drivers
                                    running in the system which could be
                                    consuming significant amounts of memory.

                                    ■ In OS/2, recompile using the /B3 C3L
                                    option to invoke the large-model version
                                    of the third pass of the compiler.

HI4301                            loss of debugging information caused by
                                    optimization

                                    Some optimizations, such as code motion,
                                    cause references to nested variables to
                                    be moved. The information about the
                                    level at which the variables are
                                    declared may be lost. As a result, all
                                    declarations will seem to be at nesting
                                    level 1.

HI4323                            potential divide by 0

                                    The second operand in a divide operation
                                    evaluated to zero at compile time,
                                    giving undefined results.

                                    The 0 operand may have been generated by
                                    the compiler, as in the following
                                    example:

                                    func1() { int i,j,k; i /= j && k; }

HI4324                            potential mod by 0

                                    The second operand in a remainder
                                    operation evaluated to zero at compile
                                    time, giving undefined results.

HI4800                            more than one memory model specified

                                    There was more than one memory model
                                    given at the command line. The /AT, /AS,
                                    /AM, /AC, /AL, and /AH options specify
                                    the memory model.

                                    This error is caused by conflicting
                                    options specified at the command line
                                    and in the CL and H2INC environment
                                    variables.

HI4801                            more than one target processor specified

                                    There was more than one processor type
                                    given at the command line. The /G0, /G1,
                                    and /G2 options specify the processor
                                    type.

                                    This error is caused by conflicting
                                    options specified at the command line
                                    and in the CL and H2INC environment
                                    variables.

HI4802                            ignoring invalid /Zp value value

                                    The alignment value specified to the /Zp
                                    option was not 1, 2, or 4. The default
                                    of 1 was assumed.

HI4810                            untranslatable basic type size

                                    H2INC could not translate the item to a
                                    MASM type.

                                    The C void type cannot be translated to
                                    a similar MASM type.

HI4811                            static function prototype not translated

                                    H2INC does not translate static items,
                                    as they are not visible outside the C
                                    source file.

HI4812                            static variable declaration not accepted
                                    with /Mn switch

                                    H2INC does not translate static items,
                                    as they are not visible outside the C
                                    source file.

HI4815                            string : EQU string truncated to 254
                                    characters

                                    A #define statement exceeded 254
                                    characters, the maximum length of a MASM
                                    EQU statement. The string was truncated.

HI4816                            ignoring _fastcall function definition

                                    H2INC does not translate function
                                    declarations or prototypes with the
                                    _fastcall attribute. The _fastcall
                                    calling convention cannot be used
                                    directly with MASM. See the
                                    documentation with your C compiler for
                                    details on _fastcall.

HI4820                            ignoring function definition : function()

                                    H2INC does not translate function bodies.

                                    H2INC translates header information
                                    only; it cannot convert program code.


F.6  IMPLIB Error Messages

This section lists error messages generated by the Microsoft Import Library
Manager (IMPLIB):


    ■   Fatal errors (IM16xx) cause IMPLIB to stop execution.

    ■   Errors (IM26xx) prevent IMPLIB from creating an import library.



F.6.1  IMPLIB Fatal Errors

Number                            IMPLIB Error Message
────────────────────────────────────────────────────────────────────────────
IM1600                            out of space on output file

                                    The drive or directory where the import
                                    library is being created is full.

IM1601                            out of heap space

                                    There was not enough room in memory for
                                    the heap needed by IMPLIB.

                                    Increase the available memory.

IM1602                            syntax error in the module definitions
                                    file

                                    IMPLIB could not understand the contents
                                    of the module-definition file.

IM1603                            filename : cannot create file

                                    IMPLIB could not create the given file.

                                    One of the following may be a cause:

                                    ■ The file already exists with a
                                    read-only attribute.

                                    ■ There is insufficient disk space to
                                    create the file.

                                    ■ The drive cannot be written to.

IM1604                            filename : cannot open file

                                    IMPLIB could not find the specified
                                    module-definition file or DLL.


F.6.2  IMPLIB Errors

Number                            IMPLIB Error Message
────────────────────────────────────────────────────────────────────────────
IM2600                            string too long in line number;
                                    truncated to 512 characters

                                    The given line in the module-definition
                                    file exceeded the limit on line length.
                                    IMPLIB ignored text after the first 512
                                    characters.

IM2601                            symbol multiply defined

                                    The given symbol was defined more than
                                    once in the input files.

IM2602                            unexpected end of name table in DLL

                                    A DLL input file was corrupted.

IM2603                            filename : invalid .DLL file

                                    The given DLL input file was corrupted.


F.7  LIB Error Messages

This section lists error messages generated by the Microsoft Library Manager
(LIB):


    ■   Fatal errors (U11xx) cause LIB to stop execution.

    ■   Errors (U21xx) do not stop execution but prevent LIB from creating a
        library.

    ■   Warnings (U41xx) indicate possible problems in the library being
        created.



F.7.1  LIB Fatal Errors

Number                            LIB Error Message
────────────────────────────────────────────────────────────────────────────
U1150                             page size too small

                                    The page size of an input library was
                                    too small, indicating an invalid input
                                    .LIB file.

U1151                             syntax error : illegal file
                                    specification

                                    A command operator was not followed by a
                                    module name or filename.

                                    One possible cause of this error is an
                                    option specified with a dash (-) instead
                                    of a forward slash (/).

U1152                             syntax error : option name missing

                                    A forward slash (/) appeared on the
                                    command line without an option name
                                    after it.

U1153                             syntax error : option value missing

                                    The /PAGE option was given without a
                                    value following it.

U1154                             unrecognized option

                                    An unrecognized name followed the option
                                    indicator.

                                    An option is specified by a forward
                                    slash (/) and a name. The name can be
                                    specified by a legal abbreviation of the
                                    full name.

U1155                             syntax error : illegal input

                                    A specified command did not follow
                                    correct LIB syntax.

U1156                             syntax error

                                    A specified command did not follow
                                    correct LIB syntax.

U1157                             comma or newline missing

                                    A comma or carriage return was expected
                                    in the command line but did not appear.

                                    This may indicate an incorrectly placed
                                    comma, as in the following command line:

                                    LIB math.lib, -mod1 +mod2;

                                    The line must be entered as follows:

                                    LIB math.lib -mod1 +mod2;

U1158                             terminator missing

                                    The last line of the response file used
                                    to start LIB did not end with a carriage
                                    return.

U1159                             option argument missing

                                    An expected argument to an option or
                                    command was missing from the command
                                    line.

U1160                             invalid page size

                                    The argument specified with the /PAGE
                                    option was not valid for that option.
                                    The value must be an integer power of 2
                                    between 16 and 32,768.

U1161                             cannot rename old library

                                    LIB could not rename the old library
                                    with a .BAK extension because the .BAK
                                    version already existed with read-only
                                    protection.

                                    Change the protection on the old .BAK
                                    version.

U1162                             cannot reopen library

                                    The old library could not be reopened
                                    after it was renamed with a .BAK
                                    extension.

                                    One of the following may have occurred:

                                    ■ Another process deleted the file or
                                    changed it to read-only.

                                    ■ The floppy disk containing the file
                                    was removed.

                                    ■ A hard-disk error occurred.

U1163                             error writing to cross-reference file

                                    The disk or root directory was full.

                                    Delete or move files to make space.

U1164                             name length exceeds 255 characters

                                    A filename specified on the command line
                                    exceeded the LIB limit of 255 characters.
                                    Reduce the number of characters in the
                                    name.

U1170                             too many symbols

                                    The number of symbols in all object
                                    files and libraries exceeded the
                                    capacity of the dictionary created by
                                    LIB.

                                    Create two or more smaller libraries.

U1171                             insufficient memory

                                    LIB did not have enough memory to run.

                                    Remove any shells or resident programs
                                    and try again, or add more memory.

U1172                             no more virtual memory

                                    The LIB session required more memory
                                    than the one-megabyte limit imposed by
                                    LIB.

                                    Try using the /NOE option or reducing
                                    the number of object modules.

U1173                             internal failure

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1174                             mark : not allocated

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1175                             free : not allocated

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1180                             write to extract file failed

                                    The disk or root directory was full.

                                    Delete or move files to make space.

U1181                             write to library file failed

                                    The disk or root directory was full.

                                    Delete or move files to make space.

U1182                             filename : cannot create extract file

                                    The disk or root directory was full, or
                                    the given extract file already existed
                                    with read-only protection.

                                    Make space on the disk or change the
                                    protection of the extract file.

U1183                             cannot open response file

                                    The response file was not found.

U1184                             unexpected end-of-file on command input

                                    An end-of-file character was received
                                    prematurely in response to a prompt.

U1185                             cannot create new library

                                    The disk or root directory was full, or
                                    the library file already existed with
                                    read-only protection.

                                    Make space on the disk or change the
                                    protection of the library file.

U1186                             error writing to new library

                                    The disk or root directory was full.

                                    Delete or move files to make space.

U1187                             cannot open temporary file VM.TMP

                                    The disk or root directory was full.

                                    Delete or move files to make space.

U1188                             insufficient disk space for temporary
                                    file

                                    The library manager cannot write to the
                                    virtual memory.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1189                             cannot read from temporary file

                                    The library manager cannot read the
                                    virtual memory.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1190                             interrupted by user

                                    LIB was interrupted during its operation,
                                    with either CTRL+C or CTRL+BREAK.

U1200                             filename : invalid library header

                                    The input library file had an invalid
                                    format.

                                    Either it was not a library file, or it
                                    had been corrupted.

U1203                             filename : invalid object file near
                                    location

                                    The given file was not a valid object
                                    file or was corrupted at the given
                                    location.


F.7.2  LIB Errors

Number                            LIB Error Message
────────────────────────────────────────────────────────────────────────────
U2152                             filename : cannot create listing

                                    One of the following may have occurred:

                                    ■ The directory or disk was full.

                                    ■ The cross-reference-listing file
                                    already existed with read-only
                                    protection.

U2155                             module : module not in library; ignored

                                    The specified module was not found in
                                    the input library.

                                    One cause of this error is a filename or
                                    directory name containing a hyphen, also
                                    called a dash (-). LIB interprets the
                                    dash as the operator for the delete
                                    command. This error occurs if you
                                    install a Microsoft language product in
                                    a directory that has a dash in its
                                    pathname, such as C:MS-C. The SETUP
                                    program calls LIB to create the
                                    Microsoft combined libraries, but the
                                    dash in the command line passed to LIB
                                    causes the library-building session to
                                    fail.

                                    Another possible cause of this error is
                                    an option specified with a dash (-)
                                    instead of a forward slash (/).

U2157                             filename : cannot access file

                                    LIB was unable to open the specified
                                    file, probably because the file did not
                                    exist.

                                    Check the path specification and
                                    filename.

U2158                             library : invalid library header; file
                                    ignored

                                    The given library had an incorrect
                                    format and was not combined.

U2159                             filename : invalid format (number); file
                                    ignored

                                    The given file was not recognized as a
                                    XENIX archive and was not combined.


F.7.3  LIB Warnings

Number                            LIB Warning
────────────────────────────────────────────────────────────────────────────
U4150                             module : module redefinition ignored

                                    A module was specified with the +
                                    operator to be added to a library, but a
                                    module having that name was already in
                                    the library.

                                    One cause of this error is an incorrect
                                    specification of the replace operator, -
                                    +.

U4151                             symbol : symbol defined in module module
                                    ; redefinition ignored

                                    The given symbol was defined in more
                                    than one module.

U4153                             option : value : page size invalid;
                                    ignored

                                    The argument specified with the /PAGE
                                    option was not valid for that option.
                                    The value must be an integer power of 2
                                    between 16 and 32,768. LIB assumed an
                                    existing page size from a library being
                                    combined.

U4155                             modulename : module not in library

                                    The given module specified with a
                                    command operator does not exist in the
                                    library.

                                    If the replacement command (-+) was
                                    specified, LIB addded the file anyway.
                                    If the delete (-), copy (*), or move (-*)
                                    command was specified, LIB ignored the
                                    command.

U4156                             library : output-library specification
                                    ignored

                                    A new library was created because the
                                    filename specified in the oldlibrary
                                    field did not exist, but a filename was
                                    also specified in the newlibrary field.
                                    LIB ignored the newlibrary specification.

                                    For example, both of the following
                                    command lines cause this error if
                                    project.lib does not already exist:

                                    LIB project.lib +one.obj, new.lst,
                                    project.lib

                                    LIB project.lib +one.obj, new.lst,
                                    new.lib

U4157                             insufficient memory, extended dictionary
                                    not created

                                    Insufficient memory prevented LIB from
                                    creating an extended dictionary.

                                    The library is still valid, but the
                                    linker cannot take advantage of the
                                    extended dictionary to speed linking.

U4158                             internal error, extended dictionary not
                                    created

                                    An internal error prevented LIB from
                                    creating an extended dictionary.

                                    The library is still valid, but the
                                    linker cannot take advantage of the
                                    extended dictionary to speed linking.


F.8  LINK Error Messages

This section lists error messages generated by the Microsoft
Segmented-Executable Linker (LINK):


    ■   Fatal errors (L1xxx) cause LINK to stop execution.

    ■   Errors (L2xxx) do not stop execution but prevent LINK from creating an
        output file.

    ■   Warnings (L4xxx) indicate possible problems in the output file being
        created.



F.8.1  LINK Fatal Errors

Number                            LINK Error Message
────────────────────────────────────────────────────────────────────────────
L1001                             option : option name ambiguous

                                    A unique option name did not appear
                                    after the option indicator.

                                    An option is specified by a
                                    forward-slash indicator (/) and a name.
                                    The name can be specified by an
                                    abbreviation of the full name, but the
                                    abbreviation must be unambiguous.

                                    For example, many options begin with the
                                    letter N, so the following command
                                    causes this error:

                                    LINK /N main;

L1003                             /Q and /EXEPACK incompatible

                                    LINK cannot be given both the /Q option
                                    and the /EXEPACK option.

L1004                             value : invalid numeric value

                                    An incorrect value appeared for a LINK
                                    option. For example, this error occurs
                                    when a character string is specified
                                    with an option that requires a numeric
                                    value.

L1005                             option : packing limit exceeds 64K

                                    The value specified with the /PACKC or
                                    /PACKD option exceeded the limit of
                                    65,536 bytes.

L1006                             number : stack size exceeds 64K-1

                                    The value given as a parameter to the
                                    /STACK option exceeded the allowed
                                    maximum of 65,535 bytes.

L1007                             /OVERLAYINTERRUPT : interrupt number
                                    exceeds 255

                                    An overlay interrupt number greater than
                                    255 was specified with the /OV option
                                    value.

                                    Check the DOS Technical Reference or
                                    other DOS technical manual for
                                    information about interrupts.

L1008                             /SEGMENTS : segment limit set too high

                                    The /SEG option was specified with a
                                    limit on the number of definitions of
                                    logical segments that was impossible to
                                    satisfy.

L1009                             value : /CPARM : illegal value

                                    The value specified with the /CPARM
                                    option was not in the range 1-65,535.

L1020                             no object modules specified

                                    No object-file names were specified to
                                    the linker.

L1021                             cannot nest response files

                                    A response file occurred within a
                                    response file.

L1022                             response line too long

                                    A line in a response file was longer
                                    than 255 characters.

L1023                             terminated by user

                                    CTRL+C was entered.

L1024                             nested right parentheses

                                    The contents of an overlay were typed
                                    incorrectly on the command line.

L1025                             nested left parentheses

                                    The contents of an overlay were typed
                                    incorrectly on the command line.

L1026                             unmatched right parenthesis

                                    A right parenthesis was missing from the
                                    contents specification of an overlay on
                                    the command line.

L1027                             unmatched left parenthesis

                                    A left parenthesis was missing from the
                                    contents specification of an overlay on
                                    the command line.

L1030                             missing internal name

                                    An IMPORTS statement specified an
                                    ordinal in the module-definition file
                                    without including the internal name of
                                    the routine.

                                    The name must be given if the import is
                                    by ordinal.

L1031                             module description redefined

                                    A DESCRIPTION statement in the
                                    module-definition file was specified
                                    more than once.

L1032                             module name redefined

                                    The module name was specified more than
                                    once (in a NAME or LIBRARY statement).

L1040                             too many exported entries

                                    The program exceeded the limit of 65,535
                                    exported names.

L1041                             resident names table overflow

                                    The size of the resident names table
                                    exceeded 65,535 bytes.

                                    An entry in the resident names table is
                                    made for each exported routine
                                    designated RESIDENTNAME and consists of
                                    the name plus three bytes of information.
                                    The first entry is the module name.

                                    Reduce the number of exported routines
                                    or change some to nonresident status.

L1042                             nonresident names table overflow

                                    The size of the nonresident names table
                                    exceeded 65,535 bytes.

                                    An entry in the nonresident names table
                                    is made for each exported routine not
                                    designated RESIDENTNAME and consists of
                                    the name plus three bytes of information.
                                    The first entry is the DESCRIPTION
                                    statement.

                                    Reduce the number of exported routines
                                    or change some to resident status.

L1043                             relocation table overflow

                                    More than 32,768 long calls, long jumps,
                                    or other long pointers appeared in the
                                    program.

                                    Try replacing long references with short
                                    references where possible.

L1044                             imported names table overflow

                                    The size of the imported names table
                                    exceeds 65,535 bytes.

                                    An entry in the imported names table is
                                    made for each new name given in the
                                    IMPORTS section, including the module
                                    names, and consists of the name plus one
                                    byte.

                                    Reduce the number of imports.

L1045                             too many TYPDEF records

                                    An object module contained more than 255
                                    TYPDEF records. These records describe
                                    communal variables.

                                    This error can appear only with programs
                                    produced by the Microsoft FORTRAN
                                    Compiler or other compilers that support
                                    communal variables. (TYPDEF is a DOS
                                    term. It is explained in the Microsoft
                                    MS-DOS Programmer's Reference and in
                                    other reference books on DOS.)

L1046                             too many external symbols in one module

                                    An object module specified more than the
                                    limit of 1,023 external symbols.

                                    Break the module into smaller parts.

L1047                             too many group, segment, and class names
                                    in one module

                                    The program contained too many group,
                                    segment, and class names.

                                    Reduce the number of groups, segments,
                                    or classes. Re-create the object file.

L1048                             too many segments in one module

                                    An object module had more than 255
                                    segments.

                                    Split the module or combine segments.

L1049                             too many segments

                                    The program had more than the maximum
                                    number of segments.

                                    Use the /SEG option when linking to
                                    specify the maximum legal number of
                                    segments. The range of valid settings is
                                    0-3,072. The default is 128.

L1050                             too many groups in one module

                                    LINK encountered more than 21 group
                                    definitions (GRPDEF) in a single module.

                                    Reduce the number of group definitions
                                    or split the module. (Group definitions
                                    are explained in the Microsoft MS-DOS
                                    Programmer's Reference and in other
                                    reference books on DOS.)

L1051                             too many groups

                                    The program defined more than 20 groups,
                                    not counting DGROUP.

                                    Reduce the number of groups.

L1052                             too many libraries

                                    An attempt was made to link with more
                                    than 32 libraries.

                                    Combine libraries, or use modules that
                                    require fewer libraries.

L1053                             out of memory for symbol table

                                    The program had more symbolic
                                    information (such as public, external,
                                    segment, group, class, and file names)
                                    than could fit in available memory.

                                    Try freeing memory by linking from the
                                    DOS command level instead of from a MAKE
                                    file or an editor. Otherwise, combine
                                    modules or segments and try to eliminate
                                    as many public symbols as possible.

L1054                             requested segment limit too high

                                    LINK did not have enough memory to
                                    allocate tables describing the number of
                                    segments requested. The number of
                                    segments is the default of 128 or the
                                    value specified with the /SEG option.

                                    Try linking again by using the /SEG
                                    option to select a smaller number of
                                    segments (for example, use 64 if the
                                    default was used previously), or free
                                    some memory by eliminating resident
                                    programs or shells.

L1056                             too many overlays

                                    The program defined more than 63
                                    overlays.

L1057                             data record too large

                                    An LEDATA record (in an object module)
                                    contained more than 1,024 bytes of data.
                                    This is a translator error. (LEDATA is a
                                    DOS term explained in the Microsoft
                                    MS-DOS Programmer's Reference and in
                                    other DOS reference books.)

                                    Note which translator (compiler or
                                    assembler) produced the incorrect object
                                    module. Please report the circumstances
                                    of the error to Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

L1061                             out of memory for /INCR

                                    LINK ran out of memory when trying to
                                    process the additional information
                                    required for ILINK support.

                                    Disable incremental linking.

L1062                             too many symbols for /INCR

                                    The program had more symbols than can be
                                    stored in the .SYM file.

                                    Reduce the number of symbols or disable
                                    incremental linking.

L1063                             out of memory for CodeView information

                                    LINK was given too many object files
                                    with debug information, and it ran out
                                    of space to store them.

                                    Reduce the number of object files that
                                    have full debug information by compiling
                                    some files with either /Zd instead of
                                    /Zi or no CodeView option at all.

L1064                             out of memory─near/far heap exhausted

                                    LINK was not able to allocate enough
                                    memory for the given heap.

                                    One of the following may be a solution:

                                    ■ Under OS/2, increase the swap space.

                                    ■ Reduce the size of code, data, and
                                    symbols in the program.

                                    ■ Under OS/2, split the program into
                                    dynamic-link libraries.

L1070                             segment : segment size exceeds 64K

                                    A single segment contained more than 64K
                                    of code or data.

                                    Try changing the memory model to use far
                                    code or data as appropriate. If the
                                    program is in C, use CL's /NT option or
                                    the #pragma alloc_text to build smaller
                                    segments.

L1071                             segment _TEXT exceeds 64K - 16

                                    This error is likely to occur only in
                                    small-model C programs, but it can occur
                                    when any program with a segment named
                                    _TEXT is linked using the /DOSSEG option
                                    of the LINK command.

                                    Small-model C programs must reserve code
                                    addresses 0 and 1; this range is
                                    increased to 16 for alignment purposes.

                                    Try compiling and linking using the
                                    medium or large model. If the program is
                                    in C, use CL's /NT option or the #pragma
                                    alloc_text to build smaller segments.

L1072                             common area exceeds 64K

                                    The program had more than 65,536 bytes
                                    of communal variables. This error occurs
                                    only with programs produced by the
                                    Microsoft FORTRAN Compiler or other
                                    compilers that support communal
                                    variables.

L1073                             file-segment limit exceeded

                                    The number of physical or file segments
                                    exceeded the limit of 255 imposed by
                                    OS/2 protected mode and by Windows for
                                    each application or dynamic-link library.

                                    A file segment is created for each group
                                    definition, nonpacked logical segment,
                                    and set of packed segments.

                                    Reduce the number of segments, or put
                                    more information into each segment. Use
                                    the /PACKC option or the /PACKD option
                                    or both.

L1074                             group : group exceeds 64K

                                    The given group exceeds the limit of
                                    65,536 bytes.

                                    Reduce the size of the group, or remove
                                    any unneeded segments from the group.
                                    Refer to the map file for a listing of
                                    segments.

L1075                             entry table exceeds 64K - 1

                                    The entry table exceeded the limit of
                                    65,535 bytes.

                                    There is an entry in this table for each
                                    exported routine. The table also
                                    includes an entry for each address that
                                    is the target of a far relocation, when
                                    one of the following conditions is true:

                                    ■ The target segment is designated IOPL
                                    (specific to OS/2).

                                    ■ PROTMODE is not enabled and the target
                                    segment is designated MOVABLE (specific
                                    to Windows).

                                    Declare PROTMODE if applicable, or
                                    reduce the number of exported routines,
                                    or make some segments FIXED or NOIOPL if
                                    possible.

L1078                             file-segment alignment too small

                                    The segment-alignment size specified
                                    with the /ALIGN option was too small.

L1080                             cannot open list file

                                    The disk or the root directory was full.

                                    Delete or move files to make space.

L1081                             out of space for run file

                                    The disk on which the executable file
                                    was being written became full. Free more
                                    space on the disk and restart LINK.

L1082                             filename : stub file not found

                                    LINK could not open the file given in
                                    the STUB statement in the module-
                                    definition file.

                                    The file must be in the current
                                    directory or in a directory specified by
                                    the PATH environment variable.

L1083                             cannot open run file

                                    One of the following may have occurred:

                                    ■ The disk or the root directory was
                                    full.

                                    ■ Another process opened or deleted the
                                    file.

                                    ■ A read-only file existed with the same
                                    name.

                                    ■ The floppy disk containing the file
                                    was removed.

                                    ■ A hard-disk error occurred.

L1084                             cannot create temporary file

                                    One of the following may have occurred:

                                    ■ The disk or the root directory was
                                    full.

                                    ■ The directory specified in the TMP
                                    environment variable did not exist.

L1085                             cannot open temporary file

                                    One of the following may have occurred:

                                    ■ The disk or the root directory was
                                    full.

                                    ■ The directory specified in the TMP
                                    environment variable did not exist.

L1086                             scratch file missing

                                    An internal error has occurred.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

L1087                             unexpected end-of-file on scratch file

                                    The disk with the temporary
                                    linker-output file was removed.

L1088                             out of space for list file

                                    The disk where the listing file was
                                    being written is full.

                                    Free more space on the disk and restart
                                    LINK.

L1089                             filename : cannot open response file

                                    LINK could not find the specified
                                    response file.

                                    Check that the name of the response file
                                    is spelled correctly.

L1090                             cannot reopen list file

                                    The original floppy disk was not
                                    replaced at the prompt.

                                    Restart the link session.

L1091                             unexpected end-of-file on library

                                    The floppy disk containing the library
                                    was probably removed.

                                    Replace the disk containing the library
                                    and run LINK again.

L1092                             cannot open module-definition file

                                    LINK could not open the
                                    module-definition file specified on the
                                    command line or in the response file.

L1093                             filename : object not found

                                    LINK could not find the given object
                                    file.

                                    Check the specification of the object
                                    file.

L1094                             filename : cannot open file for writing

                                    LINK was unable to open the file with
                                    write permission.

                                    Check file permissions.

L1095                             filename : out of space on file

                                    LINK ran out of disk space for the
                                    specified output file.

                                    Delete or move files to make space.

L1100                             stub .EXE file invalid

                                    The file specified in the STUB statement
                                    is not a valid real-mode executable file.

L1101                             invalid object module

                                    One of the object modules was invalid.

                                    Check that the correct version of LINK
                                    is being used.

                                    If the error persists after recompiling,
                                    note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

L1102                             unexpected end-of-file

                                    An invalid format for a library was
                                    encountered.

L1103                             attempt to access data outside segment
                                    bounds

                                    A data record in an object module
                                    specified data extending beyond the end
                                    of a segment. This is a translator error.

                                    Note which translator (compiler or
                                    assembler) produced the incorrect object
                                    module and the circumstances in which it
                                    was produced. Please report this error
                                    to Microsoft Corporation by following
                                    the instructions on the Microsoft
                                    Product Assistance Request form at the
                                    back of one of your manuals.

L1104                             filename : invalid library

                                    The specified file was not a valid
                                    library file.

L1105                             invalid object due to aborted
                                    incremental compile

                                    Delete the object file, recompile the
                                    program, and relink.

L1113                             unresolved COMDEF; internal error

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

L1115                             option : option incompatible with
                                    overlays

                                    The given option is not compatible with
                                    overlays.

                                    Remove the option, or do not use
                                    overlaid modules.

L1116                             /EXEPACK valid only for OS/2 and
                                    real-mode DOS

                                    The /EXEPACK option is incompatible with
                                    Windows programs.

L1123                             segment : segment defined both 16-bit
                                    and 32-bit

                                    Define the segment as either 16-bit or
                                    32-bit.

L1126                             conflicting pwords value

                                    An exported name was specified in the
                                    module-definition file with an IOPL-
                                    parameter-words (pwords) value, and the
                                    same name was specified as an export by
                                    the Microsoft C export pragma with a
                                    different pwords value.

L1127                             far segment references not allowed with
                                    /TINY

                                    The /TINY option for producing a .COM
                                    file was used in a program that has a
                                    far segment reference.

                                    Far segment references are not
                                    compatible with the .COM-file format.
                                    High-level-language programs cause this
                                    error unless the language supports the
                                    tiny memory model. An assembly-language
                                    program that references a segment
                                    address also causes this error.

                                    For example:

                                    mov     ax, seg mydata


F.8.2  LINK Errors

Number                            LINK Error Message
────────────────────────────────────────────────────────────────────────────
L2000                             imported starting address

                                    The program starting address as
                                    specified in the END statement in an
                                    assembly-language file is an imported
                                    routine. This is not supported by OS/2
                                    or Windows.

L2002                             fixup overflow at number in segment
                                    segment

                                    This error message will be followed by
                                    either

                                        target external symbol

                                    or

                                        frm seg name1, tgt seg name2, tgt
                                    offset number

                                    A fixup overflow is an attempted
                                    reference to code or data that is
                                    impossible because the source location
                                    (where the reference is made "from") and
                                    the target address (where the reference
                                    is made "to") are too far apart. Usually
                                    the problem is corrected by examining
                                    the source location.

                                    For information about frame and target
                                    segments, see the Microsoft MS-DOS
                                    Programmer's Reference.

L2003                             near reference to far target at offset
                                    in segment segment pos: offset target
                                    external name

                                    The program issued a near call or jump
                                    to a label in a different segment.

                                    This error occurs most often when
                                    specifically declaring an external
                                    procedure to be near that should be
                                    declared as far.

                                    This error can be caused by compiling a
                                    small-model C program with CL's /NT
                                    option.

L2005                             fixup type unsupported at number in
                                    segment segment

                                    A fixup type occurred that is not
                                    supported by LINK. This is probably a
                                    compiler error.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

L2010                             too many fixups in LIDATA record

                                    The number of far relocations (pointer-
                                    or base-type) in an LIDATA record
                                    exceeds the limit imposed by LINK.

                                    The cause is usually a DUP statement in
                                    an assembly-language program. The limit
                                    is dynamic: a 1,024-byte buffer is
                                    shared by relocations and the contents
                                    of the LIDATA record; there are eight
                                    bytes per relocation.

                                    Reduce the number of far relocations in
                                    the DUP statement.

L2011                             identifier : NEAR/HUGE conflict

                                    Conflicting NEAR and HUGE attributes
                                    were given for a communal variable. This
                                    error can occur only with programs
                                    produced by the Microsoft FORTRAN
                                    Compiler or other compilers that support
                                    communal variables.

L2012                             arrayname : array-element size mismatch

                                    A far communal array was declared with
                                    two or more different array-element
                                    sizes (for instance, an array was
                                    declared once as an array of characters
                                    and once as an array of real numbers).
                                    This error occurs only with the
                                    Microsoft FORTRAN Compiler and any other
                                    compiler that supports far communal
                                    arrays.

L2013                             LIDATA record too large

                                    An LIDATA record contained more than 512
                                    bytes. This is probably a compiler error.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

L2022                             entry (alias internalname) : export
                                    undefined

                                    The internal name of the given exported
                                    function or data item is undefined.

L2023                             entry (alias internalname) : export
                                    imported

                                    The internal name of the given exported
                                    function or data item conflicts with the
                                    internal name of a previously imported
                                    function or data item.

L2024                             symbol : special symbol already defined

                                    The program defined a symbol name
                                    already used by LINK for one of its own
                                    low-level symbols. For example, LINK
                                    generates special symbols used in
                                    overlay support and other operations.

                                    Choose another name for the symbol to
                                    avoid conflict.

L2025                             symbol : symbol defined more than once

                                    The same symbol has been found in two
                                    different object files.

L2026                             entry ordinal number, name name :
                                    multiple definitions for same ordinal

                                    The given exported name with the given
                                    ordinal number conflicted with a
                                    different exported name previously
                                    assigned to the same ordinal. Only one
                                    name can be associated with a particular
                                    ordinal.

L2027                             name : ordinal too large for export

                                    The given exported name was assigned an
                                    ordinal that exceeded the limit of
                                    65,535 (64K-1).

L2028                             automatic data segment plus heap exceed
                                    64K

                                    The total size of data declared in
                                    DGROUP, plus the value given in HEAPSIZE
                                    in the module-definition file, plus the
                                    stack size given by the /STACK option or
                                    STACKSIZE module-definition file
                                    statement, exceeds 64K.

                                    Reduce near-data allocation, HEAPSIZE,
                                    or stack.

L2029                             symbol : unresolved external

                                    A symbol was declared to be external in
                                    one or more modules, but it was not
                                    publicly defined in any module or
                                    library.

                                    The name of the unresolved external
                                    symbol is given, then a list of object
                                    modules that contain references to this
                                    symbol. This message and the list are
                                    written to the map file, if one exists.

                                    One cause of this error is using the
                                    /NOI option for files that use case
                                    inconsistently.

L2030                             starting address not code (use class
                                    CODE)

                                    The program starting address, as
                                    specified in the END statement of an
                                    .ASM file, should be in a code segment.
                                    Code segments are recognized if their
                                    class name ends in CODE. This is an
                                    error in OS/2 protected mode.

                                    The error message may be disabled by
                                    including the REALMODE statement in the
                                    module-definition file.

L2041                             stack plus data exceed 64K

                                    If the total of near data and requested
                                    stack size exceeds 64K, the program will
                                    not run correctly. LINK checks for this
                                    condition only when /DOSSEG is enabled,
                                    which is the case in the library
                                    start-up module for Microsoft language
                                    libraries.

                                    For object modules compiled with the
                                    Microsoft C or FORTRAN optimizing
                                    compilers, recompile with the /Gt
                                    command-line option to set the data-size
                                    threshold to a smaller number.

                                    This is a fatal LINK error.

L2043                             Quick library support module missing

                                    The required module QUICKLIB.OBJ was
                                    missing.

                                    The module QUICKLIB.OBJ must be linked
                                    in when creating a Quick library.

L2044                             symbol : symbol multiply defined, use
                                    /NOE

                                    LINK found what it interprets as a
                                    public-symbol redefinition, probably
                                    because a symbol defined in a library
                                    was redefined.

                                    Relink with the /NOE option. If error
                                    L2025 results for the same symbol, then
                                    this is a genuine symbol-redefinition
                                    error.

L2045                             segment : segment with > 1 class name
                                    not allowed with /INCR

                                    The program defined a segment more than
                                    once, giving the segment different class
                                    names. This is incompatible with the
                                    /INCR option. This error appears only
                                    with assembly-language programs.

                                    For example, the following two
                                    statements define two distinct segments
                                    with the same name but different
                                    classes:

                                    _BSS segment 'BSS'

                                    _BSS segment 'DATA'

L2047                             IOPL attribute conflict - segment
                                    segment in group group

                                    The specified segment is a member of the
                                    specified group but has an IOPL
                                    attribute that is different from other
                                    segments in the group.

L2048                             Microsoft Overlay Manager module not
                                    found

                                    Overlays were designated, but the
                                    Microsoft Overlay Manager module was not
                                    found. This module is defined in the
                                    default library.

L2049                             no segments defined

                                    No code or initialized data was defined
                                    in the program. The resulting executable
                                    file is not likely to be valid.

L2050                             USE16/USE32 attribute conflict - segment
                                    segment in group group

                                    16-bit segments cannot be grouped with
                                    32-bit segments.

L2051                             start address not equal to 0x100 for
                                    /TINY

                                    The program starting address, as
                                    specified in the .COM file, must have a
                                    starting value equal to 100 hexadecimal
                                    (0x100 or 0x0). Any other value is
                                    illegal.

                                    Put the following line of assembly
                                    source code in front of the code
                                    segment:

                                    ORG 100h

L2052                             symbol : unresolved external; possible
                                    calling convention mismatch

                                    A symbol was declared to be external in
                                    one or more modules, but LINK could not
                                    find it publicly defined in any module
                                    or library.

                                    The name of the unresolved external
                                    symbol is given, then a list of object
                                    modules that contain references to this
                                    symbol. The error message and the list
                                    are written to the map file, if one
                                    exists.

                                    This error occurs in a C-language
                                    program when a prototype for an
                                    externally defined function is omitted
                                    and the program is compiled with CL's
                                    /Gr option. The calling convention for
                                    _fastcall does not match the assumptions
                                    that are made when a prototype is not
                                    included for an external function.

                                    Either include a prototype for the
                                    function, or compile without the /Gr
                                    option.


F.8.3  LINK Warnings

Number                            LINK Warning
────────────────────────────────────────────────────────────────────────────
L4000                             segment displacement included near
                                    offset in segment segment

                                    This is the warning generated by the /W
                                    option.

L4001                             frame-relative fixup, frame ignored near
                                    offset in segment segment

                                    A reference was made relative to a
                                    segment or group that is different from
                                    the target segment of the reference.

                                    For example, if  _id1  is defined in
                                    segment  _TEXT, the instruction call
                                    DGROUP:_id1  produces this warning. The
                                    frame  DGROUP  is ignored, so LINK
                                    treats the call as if it were call
                                    _TEXT:_id1.

L4002                             frame-relative absolute fixup near
                                    offset in segment segment

                                    A reference was made relative to a
                                    segment or group that was different from
                                    the target segment of the reference, and
                                    both segments are absolute (defined with
                                    AT).

                                    LINK assumed that the executable file
                                    will be run only under DOS.

L4004                             possible fixup overflow at offset in
                                    segment segment

                                    A near call or jump was made to another
                                    segment which was not a member of the
                                    same group as the segment from which the
                                    call or jump was made.

                                    This can cause an incorrect real-mode
                                    address calculation when the distance
                                    between the paragraph address (frame
                                    number) of the segment group and the
                                    target segment is greater than 64K, even
                                    though the distance between the segment
                                    where the call or jump was actually made
                                    and the target segment is less than 64K.

L4010                             invalid alignment specification

                                    The number specified in the /ALIGN
                                    option must be a power of 2 in the range
                                    2-32,768.

L4011                             /PACKC value exceeding 64K-36 unreliable

                                    The packing limit specified with the
                                    /PACKC option was in the range
                                    65,501-65,536 bytes. Code segments with
                                    a size in this range are unreliable on
                                    some versions of the 80286 processor.

L4012                             /HIGH disables /EXEPACK

                                    The /HIGH and /EXEPACK options cannot be
                                    used at the same time.

L4013                             option : option ignored for segmented
                                    executable file

                                    The given option is not allowed with
                                    OS/2 or Windows programs.

L4014                             option : option ignored for DOS
                                    executable file

                                    The given option is not allowed with DOS
                                    programs.

L4015                             /CO disables /DSALLOC

                                    The /CO and /DSALLOC options cannot be
                                    used at the same time.

L4016                             /CO disables /EXEPACK

                                    The /CO and /EXEPACK options cannot be
                                    used at the same time.

L4017                             option : unrecognized option name;
                                    option ignored

                                    An unrecognized name followed the option
                                    indicator. LINK ignored the option
                                    specification.

                                    An option is specified by a forward
                                    slash (/) and a name. The name can be
                                    specified by a legal abbreviation of the
                                    full name.

                                    For example, the following command
                                    causes this warning:

                                    LINK /NODEFAULTLIBSEARCH main

                                    This error can also occur if the wrong
                                    version of LINK is used. Check the
                                    directories in the PATH environment
                                    variable for other versions of LINK.EXE.

L4018                             missing or unrecognized application
                                    type; option option ignored

                                    The /PM option accepts only the keywords
                                    PM, VIO, and NOVIO.

L4019                             /TINY disables /INCR

                                    The /TINY and /INCR options are
                                    incompatible. A .COM file always
                                    requires a full link and cannot be
                                    incrementally linked. LINK ignored /INCR.

L4020                             segment : code-segment size exceeds
                                    64K-36

                                    Code segments in the range 65,501-65,536
                                    bytes in length may be unreliable on
                                    some versions of the 80286 processor.

L4021                             no stack segment

                                    The program did not contain a stack
                                    segment defined with the STACK combine
                                    type.

                                    Normally, every program should have a
                                    stack segment with the combine type
                                    specified as STACK. This message may be
                                    ignored if there is a specific reason
                                    for not defining a stack or for defining
                                    one without the STACK combine type.
                                    Linking with versions of LINK earlier
                                    than version 2.40 might cause this
                                    message, since these linkers search
                                    libraries only once.

L4022                             group1, group2 : groups overlap

                                    The given groups overlap. Since a group
                                    is assigned to a physical segment,
                                    groups cannot overlap in OS/2 or Windows
                                    executable files.

                                    Reorganize segments and group
                                    definitions so the groups do not overlap.
                                    Refer to the map file.

L4023                             entry (internalname) : export internal
                                    name conflict

                                    The internal name of the given exported
                                    function or data item conflicted with
                                    the internal name of a previous import
                                    definition or export definition.

L4024                             name : multiple definitions for export
                                    name

                                    The given name was exported more than
                                    once, an action that is not allowed.

L4025                             modulename.entry(internalname) : import
                                    internal name conflict

                                    The internal name of the given imported
                                    function or data item conflicted with
                                    the internal name of a previous export
                                    or import. (The given entry is either a
                                    name or an ordinal number.)

L4026                             modulename.entry(internalname) :
                                    self-imported

                                    The given function or data item was
                                    imported from the module being linked.
                                    This is not supported on some systems.

L4027                             name : multiple definitions for import
                                    internal name

                                    The given internal name was imported
                                    more than once. Previous import
                                    definitions are ignored.

L4028                             segment : segment already defined

                                    The given segment was defined more than
                                    once in the SEGMENTS statement of the
                                    module-definition file.

L4029                             segment : DGROUP segment converted to
                                    type DATA

                                    The given logical segment in the group
                                    DGROUP was defined as a code segment.

                                    DGROUP cannot contain code segments
                                    because LINK always considers DGROUP to
                                    be a data segment. The name DGROUP is
                                    predefined as the automatic (or default)
                                    data segment.

                                    LINK converted the named segment to type
                                    DATA.

L4030                             segment : segment attributes changed to
                                    conform with automatic data segment

                                    The given logical segment in the group
                                    DGROUP was given sharing attributes (
                                    SHARED/NONSHARED) that differed from the
                                    automatic data attributes as declared by
                                    the DATA instance specification (
                                    SINGLE/MULTIPLE). The attributes are
                                    converted to conform to those of DGROUP.

                                    The name DGROUP is predefined as the
                                    automatic (or default) data segment.
                                    DGROUP cannot contain code segments
                                    because LINK always considers DGROUP to
                                    be a data segment.

L4031                             segment : segment declared in more than
                                    one group

                                    A segment was declared to be a member of
                                    two different groups.

L4032                             segment : code-group size exceeds 64K-36

                                    The given code group has a size in the
                                    range 65,501-65,536 bytes, a size that
                                    is unreliable on some versions of the
                                    80286 processor.

L4033                             first segment in mixed group group is a
                                    USE32 segment

                                    A 16-bit segment must be first in a
                                    group created with both USE16 and USE32
                                    segments.

                                    LINK continued to build the executable
                                    file, but the resulting file may not run
                                    correctly.

L4034                             more than 239 overlay segments; extra
                                    put in root

                                    The link command line or response file
                                    designated too many segments to go into
                                    overlays.

                                    The limit on the number of segments that
                                    can go into overlays is 239. Segments
                                    starting with the 240th segment are
                                    assigned to the permanently resident
                                    portion of the program (the root).

L4036                             no automatic data segment

                                    The application did not define a group
                                    named DGROUP.

                                    DGROUP has special meaning to LINK,
                                    which uses it to identify the automatic
                                    (or default) data segment used by the
                                    operating system. Most OS/2 and Windows
                                    applications require DGROUP.

                                    This warning will not be issued if DATA
                                    NONE is declared or if the executable
                                    file is a dynamic-link library.

L4038                             program has no starting address

                                    The OS/2 or Windows application had no
                                    starting address, which will usually
                                    cause the program to fail. High-level
                                    languages automatically specify a
                                    starting address.

                                    If you are writing an assembly-language
                                    program, specify a starting address with
                                    the END statement.

                                    DOS programs and dynamic-link libraries
                                    should never receive this message,
                                    regardless of whether they have starting
                                    addresses.

L4040                             stack size ignored for /TINY

                                    LINK ignores stack size if the /TINY
                                    option is used and if the stack segment
                                    has been defined in front of the code
                                    segment.

L4042                             cannot open old version

                                    The file specified in the OLD statement
                                    in the module-definition file could not
                                    be opened.

L4043                             old version not segmented executable
                                    format

                                    The file specified in the OLD statement
                                    in the module-definition file was not a
                                    valid OS/2 or Windows executable file.

L4045                             name of output file is filename

                                    LINK used the given filename for the
                                    output file.

                                    If the output filename is specified
                                    without an extension, LINK assumes the
                                    default extension .EXE. Creating a Quick
                                    library, DLL, or .COM file forces LINK
                                    to use a different extension:

/TINY option                      .COM

/Q option                         .QLB

LIBRARY statement                 .DLL

L4047                             Multiple code segments in module of
                                    overlaid program incompatible with /CO

                                    If there are multiple code segments
                                    defined in one object file by use of the
                                    C compiler #pragma alloc_text() and the
                                    program is built as an overlaid program,
                                    you can access the CodeView symbolic
                                    information for only the first code
                                    segment in an overlay. Symbolic
                                    information is not accessible for other
                                    code segments in the overlay.

L4050                             file not suitable for /EXEPACK; relink
                                    without

                                    LINK could not pack the file because the
                                    size of the packed load image plus
                                    packing overhead was larger than that of
                                    the unpacked load image.

L4051                             filename : cannot find library

                                    LINK could not find the given library
                                    file.

                                    One of the following may be a cause:

                                    ■ The specified file does not exist.
                                    Enter the name or full path
                                    specification of a library file.

                                    ■ The LIB environment variable is not
                                    set correctly. Check for incorrect
                                    directory specifications, mistyping, and
                                    a space, semicolon, or hidden character
                                    at the end of the line.

                                    ■ An earlier version of LINK is being
                                    run. Check the path environment variable
                                    and delete or rename earlier linkers.

L4053                             VM.TMP : illegal filename; ignored

                                    VM.TMP appeared as an object-file name.

                                    Rename the file and rerun LINK.

L4054                             filename : cannot find file

                                    LINK could not find the specified file.

                                    Enter a new filename, a new path
                                    specification, or both.

L4067                             changing default resolution for weak
                                    external symbol from oldresolution to
                                    newresolution

                                    LINK found conflicting default
                                    resolutions for a weak external. It
                                    ignored the first resolution and used
                                    the second.

L4068                             ignoring stack size greater than 64K

                                    A stack was defined with an invalid size.
                                    LINK assumed 64K.

L4069                             filename truncated to filename

                                    A filename specification exceeded the
                                    length allowed. LINK assumed the given
                                    filename.

L4070                             too many public symbols for sorting

                                    LINK uses the stack and all available
                                    memory in the near heap to sort public
                                    symbols for the /MAP option. This
                                    warning is issued if the number of
                                    public symbols exceeds the space
                                    available for them. In addition, the
                                    symbols are not sorted in the map file
                                    but are listed in an arbitrary order.

L4080                             changing substitute name for alias
                                    symbol from oldalias to newalias

                                    LINK found conflicting alias names. It
                                    ignored the first alias and used the
                                    second.


F.9  ML Error Messages

The error messages produced by the assembler fall into three categories:


    ■   Fatal error messages

    ■   Assembly error messages

    ■   Warning messages


The messages for each category are listed below in numerical order, with a
brief explanation of each error. To look up an error message, first
determine the message category, then find the error number. All messages
give the filename and line number where the error occurs.


Fatal Error Messages

Fatal error messages indicate a severe problem, one that prevents the
assembler from processing your program any further. These messages have the
following format:

filename (line) : fatal error A1xxx: messagetext

After the assembler displays a fatal-error message, it terminates without
producing an object file or checking for further errors.


Assembly Error Messages

Assembly error messages identify actual program errors. There messages
appear in the following format:

filename (line) : error A2xxx: messagetext

The assembler does not produce an object file for a source file that has
assembly errors in the program. When the assembler encounters such errors,
it attempts to recover from the error. If possible, it continues to process
the source file and produce error messages. If errors are too numerous or
too severe, the assembler stops processing.


Warning Messages

Warning messages are informational only; they do not prevent assembly and
linking. These messages appear in the following format:

filename (line) : warning A4xxx: messagetext


F.9.1  ML Fatal Errors

Number                            Message
────────────────────────────────────────────────────────────────────────────
A1000                             cannot open file: filename

                                    The assembler was unable to open a
                                    source, include, or output file.

                                    One of the following may be a cause:

                                    ■ The file does not exist.

                                    ■ The file is in use by another process.

                                    ■ The filename is not valid.

                                    ■ A read-only file with the output
                                    filename already exists.

                                    ■ Not enough file handles exist. In DOS,
                                    increase the number of file handles by
                                    changing the FILES setting in CONFIG.SYS
                                    to allow a larger number of open files.
                                    FILES=20 is the recommended setting.

                                    ■ The current drive is full.

                                    ■ The current directory is the root and
                                    is full.

                                    ■ The device cannot be written to.

                                    ■ The drive is not ready.

A1001                             I/O error closing file

                                    The operating system returned an error
                                    when the assembler attempted to close a
                                    file.

                                    This error can be caused by having a
                                    corrupt file system or by removing a
                                    disk before the file could be closed.

A1002                             I/O error writing file

                                    The assembler was unable to write to an
                                    output file.

                                    One of the following may be a cause:

                                    ■ The current drive is full.

                                    ■ The current directory is the root and
                                    is full.

                                    ■ The device cannot be written to.

                                    ■ The drive is not ready.

A1003                             I/O error reading file

                                    The assembler encountered an error when
                                    trying to read a file.

                                    One of the following may be a cause:

                                    ■ The disk has a bad sector.

                                    ■ The file-access attribute is set to
                                    prevent reading.

                                    ■ The drive is not ready.

A1004                             out of far memory, use /VM command-line
                                    option

                                    There was insufficient memory to
                                    assemble the program.

                                    One of the following may be a solution:

                                    ■ In DOS, use the /VM command-line
                                    option to enable virtual memory.

                                    ■ If you are using the NMAKE utility,
                                    try using NMK or assembling outside of
                                    NMAKE.

                                    ■ In PWB, try exiting and assembling
                                    using ML.

                                    ■ In OS/2, try increasing the swap space.

                                    ■ In DOS, remove
                                    terminate-and-stay-resident (TSR)
                                    software.

                                    ■ Change CONFIG.SYS to specify a lower
                                    number of buffers (the BUFFERS= command)
                                    and fewer drives (the LASTDRIVE=
                                    command).

                                    ■ Eliminate unnecessary INCLUDE
                                    directives.

A1005                             assembler limit : macro parameter name
                                    table full

                                    Too many parameters, locals, or macro
                                    labels were defined for a macro. There
                                    was no more room in the macro name table.

                                    Define shorter or fewer names, or remove
                                    unnecessary macros.

A1006                             invalid command-line option: option

                                    ML did not recognize the given parameter
                                    as an option.

A1007                             nesting level too deep

                                    The assembler reached its nesting limit.
                                    The limit is 20 levels except where
                                    noted otherwise.

                                    One of the following was nested too
                                    deeply:

                                    ■ A high-level directive such as .IF,
                                    .REPEAT, or .WHILE

                                    ■ A structure definition

                                    ■ A conditional-assembly directive

                                    ■ A procedure definition

                                    ■ A PUSHCONTEXT directive (The limit is
                                    10.)

                                    ■ A segment definition

                                    ■ An include file

                                    ■ A macro

A1008                             unmatched macro nesting

                                    Either a macro was not terminated before
                                    the end of the file, or the terminating
                                    directive ENDM was found outside of a
                                    macro block.

                                    One cause of this error is omission of
                                    the dot before .REPEAT or .WHILE.

A1009                             line too long

                                    A line in a source file exceeded the
                                    limit of 512 characters.

                                    If multiple physical lines are
                                    concatenated with the line-continuation
                                    character (  ), the resulting logical
                                    line is still limited to 512 characters.

A1010                             unmatched block nesting :

                                    A block beginning did not have a
                                    matching end, or a block end did not
                                    have a matching beginning. One of the
                                    following may be involved:

                                    ■ A high-level directive such as .IF,
                                    .REPEAT, or .WHILE

                                    ■ A conditional-assembly directive such
                                    as IF, REPEAT, or WHILE

                                    ■ A structure or union definition

                                    ■ A procedure definition

                                    ■ A segment definition

                                    ■ A POPCONTEXT directive

                                    ■ A conditional-assembly directive, such
                                    as an ELSE, ELSEIF, or ENDIF without a
                                    matching IF

A1011                             directive must be in control block

                                    The assembler found a high-level
                                    directive where one was not expected.
                                    One of the following directives was
                                    found:

                                    ■ .ELSE without .IF

                                    ■ .ENDIF without .IF

                                    ■ .ENDW without .WHILE

                                    ■ .UNTIL«CXZ» without .REPEAT

                                    ■ .CONTINUE without .WHILE or .REPEAT

                                    ■ .BREAK without .WHILE or .REPEAT

                                    ■ .ELSE following .ELSE

A1012                             error count exceeds 100; stopping
                                    assembly

                                    The number of nonfatal errors exceeded
                                    the assembler limit of 100.

                                    Nonfatal errors are in the range A2xxx.
                                    When warnings are treated as errors they
                                    are included in the count. Warnings are
                                    considered errors if you use the /Wx
                                    command-line option, or if you set the
                                    Warnings Treated as Errors option in the
                                    Macro Assembler Global Options dialog
                                    box of PWB.

A1013                             invalid numerical command-line argument
                                    : number

                                    The argument specified with an option
                                    was not a number or was an invalid
                                    number.

A1014                             too many arguments

                                    There was insufficient memory to hold
                                    all of the command-line arguments.

                                    This error usually occurs while
                                    expanding input filename wildcards (*
                                    and ?). To eliminate this error,
                                    assemble multiple source files
                                    separately.

A1015                             statement too complex

                                    The assembler ran out of stack space
                                    while trying to parse the specified
                                    statement.

                                    One or more of the following changes may
                                    eliminate this error:

                                    ■ Break the statement into several
                                    shorter statements.

                                    ■ Reorganize the statement to reduce the
                                    amount of parenthetical nesting.

                                    ■ If the statement is part of a macro,
                                    break the macro into several shorter
                                    macros.

A1016                             out of virtual memory

                                    The assembler was unable to allocate
                                    enough virtual memory to assemble this
                                    file.

                                    To eliminate this error, free some space
                                    on the drive specified by the TMP
                                    environment variable, or reassign TMP to
                                    a location where there is more free
                                    space. The assembler uses the current
                                    directory to store VM files if the TMP
                                    environment varible does not exist.

A1017                             out of near memory

                                    There was insufficient memory to
                                    assemble the program.

                                    One of the following may be a solution:

                                    ■ If you are using the NMAKE utility,
                                    try using NMK or assembling outside of
                                    NMAKE.

                                    ■ In PWB, try exiting and assembling
                                    using ML.

                                    ■ In OS/2, try increasing the swap space.

                                    ■ In DOS, remove
                                    terminate-and-stay-resident (TSR)
                                    software.

                                    ■ Change CONFIG.SYS to specify a lower
                                    number of buffers (the BUFFERS= command)
                                    and fewer drives (the LASTDRIVE=
                                    command).

                                    ■ Eliminate unnecessary INCLUDE
                                    directives.

A1018                             missing source filename

                                    ML could not find a file to assemble or
                                    pass to the linker.

                                    This error is generated when you give ML
                                    command-line options without specifying
                                    a filename to act upon. To assemble
                                    files that do not have a .ASM extension,
                                    use the /Ta command-line option.

                                    This error can also be generated by
                                    invoking ML with no parameters if the ML
                                    environment variable contains
                                    command-line options.

A1901                             Internal Assembler Error Contact
                                    Microsoft Product Support Services

                                    The MASM driver called ML.EXE, which
                                    generated a system error.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.


F.9.2  ML Errors

Number                            Message
────────────────────────────────────────────────────────────────────────────
A2000                             memory operand not allowed in context

                                    A memory operand was given to an
                                    instruction that cannot take a memory
                                    operand.

A2001                             immediate operand not allowed

                                    A constant or memory offset was given to
                                    an instruction that cannot take an
                                    immediate operand.

A2002                             cannot have more than one ELSE clause
                                    per IF block

                                    The assembler found an ELSE directive
                                    after an existing ELSE directive in a
                                    conditional-assembly block (IF block).

                                    Only one ELSE can be used in an IF block.
                                    An IF block begins with an IF, IFE, IFB,
                                    IFNB, IFDEF, IFNDEF, IFDIF, or IFIDN
                                    directive. There can be several ELSEIF
                                    statements in an IF block.

                                    One cause of this error is omission of
                                    an ENDIF statement from a nested IF
                                    block.

A2003                             extra characters after statement

                                    A directive was followed by unexpected
                                    characters.

A2004                             symbol type conflict : identifier

                                    The EXTERNDEF or LABEL directive was
                                    used on a variable, symbol, data
                                    structure, or label that was defined in
                                    the same module but with a different
                                    type.

A2005                             symbol redefinition : identifier

                                    The given nonredefinable symbol was
                                    defined in two places.

A2006                             undefined symbol : identifier

                                    An attempt was made to use a symbol that
                                    was not defined.

                                    One of the following may have occurred:

                                    ■ A symbol was not defined.

                                    ■ A field was not a member of the
                                    specified structure.

                                    ■ A symbol was defined in an include
                                    file that was not included.

                                    ■ An external symbol was used without an
                                    EXTERN or EXTERNDEF directive.

                                    ■ A symbol name was misspelled.

                                    ■ A local code label was referenced
                                    outside of its scope.

A2008                             syntax error :

                                    A token at the current location caused a
                                    syntax error.

                                    One of the following may have occurred:

                                    ■ A dot prefix was added to or omitted
                                    from a directive.

                                    ■ A reserved word (such as C or SIZE)
                                    was used as an identifier.

                                    ■ An instruction was used that was not
                                    available with the current processor or
                                    coprocessor selection.

                                    ■ A comparison run-time operator (such
                                    as ==) was used in a conditional
                                    assembly statement instead of a
                                    relational operator (such as EQ).

                                    ■ An instruction or directive was given
                                    too few operands.

                                    ■ An obsolete directive was used.

A2009                             syntax error in expression

                                    An expression on the current line
                                    contained a syntax error. This error
                                    message may also be a side-effect of a
                                    preceding program error.

A2010                             invalid type expression

                                    The operand to THIS or PTR was not a
                                    valid type expression.

A2011                             distance invalid for word size of
                                    current segment

                                    A procedure definition or a code label
                                    defined with LABEL specified an address
                                    size that was incompatible with the
                                    current segment size.

                                    One of the following occurred:

                                    ■ A NEAR16 or FAR16 procedure was
                                    defined in a 32-bit segment.

                                    ■ A NEAR32 or FAR32 procedure was
                                    defined in a 16-bit segment.

                                    ■ A code label defined with LABEL
                                    specified FAR16 or NEAR16 in a 32-bit
                                    segment.

                                    ■ A code label defined with LABEL
                                    specified FAR32 or NEAR32 in a 16-bit
                                    segment.

A2012                             PROC, MACRO, or macro repeat directive
                                    must precede LOCAL

                                    A LOCAL directive must be immediately
                                    preceded by a MACRO, PROC, macro repeat
                                    directive (such as REPEAT, WHILE, or FOR
                                    ), or another LOCAL directive.

A2013                             .MODEL must precede this directive

                                    A simplified segment directive or a
                                    .STARTUP or .EXIT directive was not
                                    preceded by a .MODEL directive.

                                    A .MODEL directive must specify the
                                    model defaults before a simplified
                                    segment directive, or a .STARTUP or
                                    .EXIT directive may be used.

A2014                             cannot define as public or external :
                                    identifier

                                    Only labels, procedures, and numeric
                                    equates can be made public or external
                                    using PUBLIC, EXTERN, or EXTERNDEF.
                                    Local code labels cannot be made public.

A2015                             segment attributes cannot change :
                                    attribute

                                    A segment was reopened with different
                                    attributes than it was opened with
                                    originally.

                                    When a SEGMENT directive opens a
                                    previously defined segment, the newly
                                    opened segment inherits the attributes
                                    the segment was defined with.

A2016                             expression expected

                                    The assembler expected an expression at
                                    the current location but found one of
                                    the following:

                                    ■ A unary operator without an operand

                                    ■ A binary operator without two operands

                                    ■ An empty pair of parentheses, ( ), or
                                    brackets, [ ]

A2017                             operator expected

                                    An expression operator was expected at
                                    the current location.

                                    One possible cause of this error is a
                                    missing comma between expressions in an
                                    expression list.

A2018                             invalid use of external symbol :
                                    identifier

                                    An attempt was made to compare the given
                                    external symbol using a relational
                                    operator.

                                    The comparison cannot be made because
                                    the value or address of an external
                                    symbol is not known at assembly time.

A2019                             operand must be RECORD type or field

                                    The operand following the WIDTH or MASK
                                    operator was not valid.

                                    The WIDTH operator takes an operand that
                                    is the name of a field or a record. The
                                    MASK operator takes an operand that is
                                    the name of a field or a record type.

A2020                             identifier not a record : identifier

                                    A record type was expected at the
                                    current location.

A2021                             record constants cannot span line breaks

                                    A record constant must be defined on one
                                    physical line. A line ended in the
                                    middle of the definition of a record
                                    constant.

A2022                             instruction operands must be the same
                                    size

                                    The operands to an instruction did not
                                    have the same size.

A2023                             instruction operand must have size

                                    At least one of the operands to an
                                    instruction must have a known size.

A2024                             invalid operand size for instruction

                                    The size of an operand was not valid.

A2025                             operands must be in same segment

                                    Relocatable operands used with a
                                    relational or minus operator were not
                                    located in the same segment.

A2026                             constant expected

                                    The assembler expected a constant
                                    expression at the current location. A
                                    constant expression is a numeric
                                    expression that can be resolved at
                                    assembly time.

A2027                             operand must be a memory expression

                                    The right operand of a PTR expression
                                    was not a memory expression.

                                    When the left operand of the PTR
                                    operator is a structure or union type,
                                    the right operand must be a memory
                                    expression.

A2028                             expression must be a code address

                                    An expression evaluating to a code
                                    address was expected.

                                    One of the following occurred:

                                    ■ SHORT was not followed by a code
                                    address.

                                    ■ NEAR PTR or FAR PTR was applied to
                                    something that was not a code address.

A2029                             multiple base registers not allowed

                                    An attempt was made to combine two base
                                    registers in a memory expression.

                                    For example, the following expressions
                                    cause this error:

                                    [bx+bp]

                                    [bx][bp]

                                    In another example, given the following
                                    definition:

                                    id1 proc arg1:byte

                                    either of the following lines causes
                                    this error:

                                    mov al, [bx].arg1

                                    lea ax, arg1[bx]

A2030                             multiple index registers not allowed

                                    An attempt was made to combine two index
                                    registers in a memory expression.

                                    For example, the following expressions
                                    cause this error:

                                    [si+di]

                                    [di][si]

A2031                             must be index or base register

                                    An attempt was made to use a register
                                    that was not a base or index register in
                                    a memory expression.

                                    For example, the following expressions
                                    cause this error:

                                    [ax]

                                    [bl]

A2032                             invalid use of register

                                    An attempt was made to use a register
                                    that was not valid for the intended use.

                                    One of the following occurred:

                                    ■ OFFSET was applied to a register. (
                                    OFFSET can be applied to a register
                                    under the M510 option.)

                                    ■ A special 386 register was used in an
                                    invalid context.

                                    ■ A register was cast with PTR to a type
                                    of invalid size.

                                    ■ A register was specified as the right
                                    operand of a segment override
                                    operator (:).

                                    ■ A register was specified as the right
                                    operand of a binary minus operator (-).

                                    ■ An attempt was made to multiply
                                    registers using the * operator.

                                    ■ Brackets ([ ]) were missing around a
                                    register that was added to something.

A2033                             invalid INVOKE argument : argument
                                    number

                                    The INVOKE directive was passed a
                                    special 386 register, or a register pair
                                    containing a byte register or special
                                    386 register. These registers are
                                    illegal with INVOKE.

A2034                             must be in segment block

                                    One of the following was found outside
                                    of a segment block:

                                    ■ An instruction

                                    ■ A label definition

                                    ■ A THIS operator

                                    ■ A $ operator

                                    ■ A procedure definition

                                    ■ An ALIGN directive

                                    ■ An ORG directive

A2035                             DUP too complex

                                    A declaration using the DUP operator
                                    resulted in a data structure with an
                                    internal representation that was too
                                    large.

A2036                             too many initial values for structure:
                                    structure

                                    The given structure was defined with
                                    more initializers than the number of
                                    fields in the type declaration of the
                                    structure.

A2037                             statement not allowed inside structure
                                    definition

                                    A structure definition contained an
                                    invalid statement.

                                    A structure cannot contain instructions,
                                    labels, procedures, control-flow
                                    directives, .STARTUP, or .EXIT.

A2038                             missing operand for macro operator

                                    The assembler found the end of a macro's
                                    parameter list immediately after the !
                                    or % operator.

A2039                             line too long

                                    A source-file line exceeded the limit of
                                    512 characters.

                                    If multiple physical lines are
                                    concatenated with the line- continuation
                                    character (  ), the resulting logical
                                    line is still limited to 512 characters.

A2040                             segment register not allowed in context

                                    A segment register was specified for an
                                    instruction that cannot take a segment
                                    register.

A2041                             string or text literal too long

                                    A string or text literal, or a macro
                                    function return value, exceeded the
                                    limit of 255 characters.

A2042                             statement too complex

                                    A statement was too complex for the
                                    assembler to parse.

                                    Reduce either the number of tokens or
                                    the number of forward-referenced
                                    identifiers.

A2043                             identifier too long

                                    An identifier exceeded the limit of 247
                                    characters.

A2044                             invalid character in file

                                    The source file contained a character
                                    outside a comment, string, or literal
                                    that was not recognized as an operator
                                    or other legal character.

A2045                             missing angle bracket or brace in
                                    literal

                                    An unmatched angle bracket (either < or
                                    >) or brace (either { or }) was found in
                                    a literal constant or an initializer.

                                    One of the following occurred:

                                    ■ A pair of angle brackets or braces was
                                    not complete.

                                    ■ An angle bracket was intended to be
                                    literal, but it was not preceded by an
                                    exclamation point (!) to indicate a
                                    literal character.

A2046                             missing single or double quotation mark
                                    in string

                                    An unmatched quotation mark (either ' or
                                    ") was found in a string.

                                    One of the following may have occurred:

                                    ■ A pair of quotation marks around a
                                    string was not complete.

                                    ■ A pair of quotation marks around a
                                    string was formed of one single and one
                                    double quotation mark.

                                    ■ A single or double quotation mark was
                                    intended to be literal, but the
                                    surrounding quotation marks were the
                                    same kind as the literal one.

A2047                             empty (null) string

                                    A string consisted of a delimiting pair
                                    of quotation marks and no characters
                                    within.

                                    For a string to be valid, it must
                                    contain 1-255 characters.

A2048                             nondigit in number

                                    A number contained a character that was
                                    not in the set of characters used by the
                                    current radix (base).

                                    This error can occur if a B or D radix
                                    specifier is used when the default radix
                                    is one that includes that letter as a
                                    valid digit.

A2049                             syntax error in floating-point constant

                                    A floating-point constant contained an
                                    invalid character.

A2050                             real or BCD number not allowed

                                    A floating-point (real) number or binary
                                    coded decimal (BCD) constant was used
                                    other than as a data initializer.

                                    One of the following occurred:

                                    ■ A real number or a BCD was used in an
                                    expression.

                                    ■ A real number was used to initialize a
                                    directive other than DWORD, QWORD, or
                                    TBYTE.

                                    ■ A BCD was used to initialize a
                                    directive other than TBYTE.

A2051                             text item required

                                    A literal constant or text macro was
                                    expected.

                                    One of the following was expected:

                                    ■ A literal constant, which is text
                                    enclosed in < >

                                    ■ A text macro name

                                    ■ A macro function call

                                    ■ A % followed by a constant expression

A2052                             forced error

                                    The conditional-error directive .ERR or
                                    .ERR1 was used to generate this error.

A2053                             forced error : value equal to 0

                                    The conditional-error directive .ERRE
                                    was used to generate this error.

A2054                             forced error : value not equal to 0

                                    The conditional-error directive .ERRNZ
                                    was used to generate this error.

A2055                             forced error : symbol not defined

                                    The conditional-error directive .ERRNDEF
                                    was used to generate this error.

A2056                             forced error : symbol defined

                                    The conditional-error directive .ERRDEF
                                    was used to generate this error.

A2057                             forced error : string blank

                                    The conditional-error directive .ERRB
                                    was used to generate this error.

A2058                             forced error : string not blank

                                    The conditional-error directive .ERRNB
                                    was used to generate this error.

A2059                             forced error : strings equal

                                    The conditional-error directive .ERRIDN
                                    or .ERRIDNI was used to generate this
                                    error.

A2060                             forced error : strings not equal

                                    The conditional-error directive .ERRDIF
                                    or .ERRDIFI was used to generate this
                                    error.

A2061                             [[ELSE]]IF2/.ERR2 not allowed :
                                    single-pass assembler

                                    A directive for a two-pass assembler was
                                    found.

                                    The Microsoft Macro Assembler (MASM) is
                                    a one-pass assembler. MASM does not
                                    accept the IF2, ELSEIF2, and .ERR2
                                    directives.

                                    This error also occurs if an ELSE
                                    directive follows an IF1 directive.

A2062                             expression too complex for .UNTILCXZ

                                    An expression used in the condition that
                                    follows .UNTILCXZ was too complex.

                                    The .UNTILCXZ directive can take only
                                    one expression, which can contain only
                                    == or !=. It cannot take other
                                    comparison operators or more complex
                                    expressions using operators such as ||.

A2063                             can ALIGN only to power of 2 :
                                    expression

                                    The expression specified with the ALIGN
                                    directive was invalid.

                                    The ALIGN expression must be a power of
                                    2 between 2 and 256, and must be less
                                    than or equal to the alignment of the
                                    current segment, structure, or union.

A2064                             structure alignment must be 1, 2, or 4

                                    The alignment specified in a structure
                                    definition was invalid.

A2065                             expected : token

                                    The assembler expected the given token.

A2066                             incompatible CPU mode and segment size

                                    An attempt was made to open a segment
                                    with a USE16, USE32, or FLAT attribute
                                    that was not compatible with the
                                    specified CPU, or to change to a 16-bit
                                    CPU while in a 32-bit segment.

                                    The USE32 and FLAT attributes must be
                                    preceded by one of the following
                                    processor directives: .386, .386C, .386P,
                                    .486, or .486P.

A2067                             LOCK must be followed by a memory
                                    operation

                                    The LOCK prefix preceded an invalid
                                    instruction. No instruction can take the
                                    LOCK prefix unless one of its operands
                                    is a memory expression.

A2068                             instruction prefix not allowed

                                    One of the prefixes REP, REPE, REPNE, or
                                    LOCK preceded an instruction for which
                                    it was not valid.

A2069                             no operands allowed for this instruction

                                    One or more operands were specified with
                                    an instruction that takes no operands.

A2070                             invalid instruction operands

                                    One or more operands were not valid for
                                    the instruction they were specified with.

A2071                             initializer too large for specified size

                                    An initializer value was too large for
                                    the data area it was initializing.

A2072                             cannot access symbol in given segment or
                                    group: identifier

                                    The given identifier cannot be addressed
                                    from the segment or group specified.

A2073                             operands have different frames

                                    Two operands in an expression were in
                                    different frames.

                                    Subtraction of pointers requires the
                                    pointers to be in the same frame.
                                    Subtraction of two expressions that have
                                    different effective frames is not
                                    allowed. An effective frame is
                                    calculated from the segment, group, or
                                    segment register.

A2074                             cannot access label through segment
                                    registers

                                    An attempt was made to access a label
                                    through a segment register that was not
                                    assumed to its segment or group.

A2075                             jump destination too far [: by `n'
                                    bytes]

                                    The destination specified with a jump
                                    instruction was too far from the
                                    instruction.

                                    One of the following may be a solution:

                                    ■ Enable the LJMP option.

                                    ■ Remove the SHORT operator. If SHORT
                                    has forced a jump that is too far, n is
                                    the number of bytes out of range.

                                    ■ Rearrange code so that the jump is no
                                    longer out of range.

A2076                             jump destination must specify a label

                                    A direct jump's destination must be
                                    relative to a code label.

A2077                             instruction does not allow NEAR indirect
                                    addressing

                                    A conditional jump or loop cannot take a
                                    memory operand. It must be given a
                                    relative address or label.

A2078                             instruction does not allow FAR indirect
                                    addressing

                                    A conditional jump or loop cannot take a
                                    memory operand. It must be given a
                                    relative address or label.

A2079                             instruction does not allow FAR direct
                                    addressing

                                    A conditional jump or loop cannot be to
                                    a different segment or group.

A2080                             jump distance not possible in current
                                    CPU mode

                                    A distance was specified with a jump
                                    instruction that was incompatible with
                                    the current processor mode.

                                    For example, 48-bit jumps require .386
                                    or above.

A2081                             missing operand after unary operator

                                    An operator required an operand, but no
                                    operand followed.

A2082                             cannot mix 16- and 32-bit registers

                                    An address expression contained both 16-
                                    and 32-bit registers.

                                    For example, the following expression
                                    causes this error:

                                    [bx+edi]

A2083                             invalid scale value

                                    A register scale was specified that was
                                    not 1, 2, 4, or 8.

A2084                             constant value too large

                                    A constant was specified that was too
                                    big for the context in which it was used.

A2085                             instruction or register not accepted in
                                    current CPU mode

                                    An attempt was made to use an
                                    instruction, register, or keyword that
                                    was not valid for the current processor
                                    mode.

                                    For example, 32-bit registers require
                                    .386 or above. Control registers such as
                                    CR0 require privileged mode .386P or
                                    above. This error will also be generated
                                    for the NEAR32, FAR32, and FLAT keywords,
                                    which require .386 or above.

A2086                             reserved word expected

                                    One or more items in the list specified
                                    with a NOKEYWORD option were not
                                    recognized as reserved words.

A2087                             instruction form requires 80386/486

                                    An instruction was used that was not
                                    compatible with the current processor
                                    mode.

                                    One of the following processor
                                    directives must precede the instruction:
                                    .386, .386C, .386P, .486, or .486P.

A2088                             END directive required at end of file

                                    The assembler reached the end of the
                                    main source file and did not find an
                                    .END directive.

A2089                             too many bits in RECORD : identifier

                                    One of the following occurred:

                                    ■ Too many bits were defined for the
                                    given record field.

                                    ■ Too many total bits were defined for
                                    the given record.

                                    The size limit for a record or a field
                                    in a record is 16 bits when doing 16-bit
                                    arithmetic or 32 bits when doing 32-bit
                                    arithmetic.

A2090                             positive value expected

                                    A positive value was not found in one of
                                    the following situations:

                                    ■ The starting position specified for
                                    SUBSTR or @SubStr

                                    ■ The number of data objects specified
                                    for COMM

                                    ■ The element size specified for COMM

A2091                             index value past end of string

                                    An index value exceeded the length of
                                    the string it referred to when used with
                                    INSTR, SUBSTR, @InStr, or @SubStr.

A2092                             count must be positive or zero

                                    The operand specified to the SUBSTR
                                    directive, @SubStr macro function, SHL
                                    operator, SHR operator, or DUP operator
                                    was negative.

A2093                             count value too large

                                    The length argument specified for SUBSTR
                                    or @SubStr exceeded the length of the
                                    specified string.

A2094                             operand must be relocatable

                                    An operand was not relative to a label.

                                    One of the following occurred:

                                    ■ An operand specified with the END
                                    directive was not relative to a label.

                                    ■ An operand to the SEG operator was not
                                    relative to a label.

                                    ■ The right operand to the minus
                                    operator was relative to a label, but
                                    the left operand was not.

                                    ■ The operands to a relational operator
                                    were either not both integer constants
                                    or not both memory operands. Relational
                                    operators can take operands that are
                                    both addresses or both non-addresses but
                                    not one of each.

A2095                             constant or relocatable label expected

                                    The operand specified must be a constant
                                    expression or a memory offset.

A2096                             segment, group, or segment register
                                    expected

                                    A segment or group was expected but was
                                    not found.

                                    One of the following occurred:

                                    ■ The left operand specified with the
                                    segment override operator (:) was not a
                                    segment register (CS, DS, SS, ES, FS, or
                                    GS), group name, segment name, or
                                    segment expression.

                                    ■ The ASSUME directive was given a
                                    segment register without a valid segment
                                    address, segment register, group, or the
                                    special FLAT group.

A2097                             segment expected : identifier

                                    The GROUP directive was given an
                                    identifier that was not a defined
                                    segment.

A2098                             invalid operand for OFFSET

                                    The expression following the OFFSET
                                    operator must be a memory expression or
                                    an immediate expression.

A2099                             invalid use of external absolute

                                    An attempt was made to subtract a
                                    constant defined in another module from
                                    an expression.

                                    You can avoid this error by placing
                                    constants in include files rather than
                                    making them external.

A2100                             segment or group not allowed

                                    An attempt was made to use a segment or
                                    group in a way that was not valid.
                                    Segments or groups cannot be added.

A2101                             cannot add two relocatable labels

                                    An attempt was made to add two
                                    expressions that were both relative to a
                                    label.

A2102                             cannot add memory expression and code
                                    label

                                    An attempt was made to add a code label
                                    to a memory expression.

A2103                             segment exceeds 64K limit

                                    A 16-bit segment exceeded the size limit
                                    of 64K.

A2104                             invalid type for data declaration : type

                                    The given type was not valid for a data
                                    declaration.

A2105                             HIGH and LOW require immediate operands

                                    The operand specified with either the
                                    HIGH or the LOW operator was not an
                                    immediate expression.

A2107                             cannot have implicit far jump or call to
                                    near label

                                    An attempt was made to make an implicit
                                    far jump or call to a near label in
                                    another segment.

A2108                             use of register assumed to ERROR

                                    An attempt was made to use a register
                                    that had been assumed to ERROR with the
                                    ASSUME directive.

A2109                             only white space or comment can follow
                                    backslash

                                    A character other than a semicolon (;)
                                    or a white-space character (spaces or
                                    TAB characters) was found after a
                                    line-continuation character (  ).

A2110                             COMMENT delimiter expected

                                    A delimiter character was not specified
                                    for a COMMENT directive.

                                    The delimiter character is specified by
                                    the first character that is not white
                                    space (spaces or TAB characters) after
                                    the COMMENT directive. The comment
                                    consists of all text following the
                                    delimiter until the end of the line
                                    containing the next appearance of the
                                    delimiter.

A2111                             conflicting parameter definition

                                    A procedure defined with the PROC
                                    directive did not match its prototype as
                                    defined with the PROTO directive.

A2112                             PROC and prototype calling conventions
                                    conflict

                                    A procedure was defined in a prototype
                                    (using the PROTO, EXTERNDEF, or EXTERN
                                    directive), but the calling convention
                                    did not match the corresponding PROC
                                    directive.

A2113                             invalid radix tag

                                    The specified radix was not a number in
                                    the range 2-16.

A2114                             INVOKE argument type mismatch : argument
                                    number

                                    The type of the arguments passed using
                                    the INVOKE directive did not match the
                                    type of the parameters in the prototype
                                    of the procedure being invoked.

A2115                             invalid coprocessor register

                                    The coprocessor index specified was
                                    negative or greater than 7.

A2116                             instructions and initialized data not
                                    allowed in AT segments

                                    An instruction or initialized data was
                                    found in a segment defined with the AT
                                    attribute.

                                    Data in AT segments must be declared
                                    with the ? initializer.

A2117                             /AT option requires TINY memory model

                                    The /AT option was specified on the
                                    assembler command line, but the program
                                    being assembled did not specify the TINY
                                    memory model with the .MODEL directive.

                                    This error is only generated for modules
                                    that specify a start address or use the
                                    .STARTUP directive.

A2118                             cannot have segment address references
                                    with TINY model

                                    An attempt was made to reference a
                                    segment in a TINY model program.

                                    All TINY model code and data must be
                                    accessed with NEAR addresses.

A2119                             language type must be specified

                                    A procedure definition or prototype was
                                    not given a language type.

                                    A language type must be declared in each
                                    procedure definition or prototype if a
                                    default language type is not specified.
                                    A default language type is set using
                                    either the .MODEL directive, OPTION LANG,
                                    or the ML command-line options /Gc or
                                    /Gd.

A2120                             PROLOGUE must be macro function

                                    The identifier specified with the OPTION
                                    PROLOGUE directive was not recognized as
                                    a defined macro function.

                                    The user-defined prologue must be a
                                    macro function that returns the number
                                    of bytes needed for local varaiables and
                                    any extra space needed for the macro
                                    function.

A2121                             EPILOGUE must be macro procedure

                                    The identifier specified with the OPTION
                                    EPILOGUE directive was not recognized as
                                    a defined macro procedure.

                                    The user-defined epilogue macro cannot
                                    return a value.

A2122                             alternate identifier not allowed with
                                    EXTERNDEF

                                    An attempt was made to specify an
                                    alternate identifier with an EXTERNDEF
                                    directive.

                                    You can specify an optional alternate
                                    identifier with the EXTERN directive but
                                    not with EXTERNDEF.

A2123                             text macro nesting level too deep

                                    A text macro was nested too deeply. The
                                    nesting limit for text macros is 40.

A2125                             missing macro argument

                                    A required argument to @InStr, @SubStr,
                                    or a user-defined macro was not
                                    specified.

A2126                             EXITM used inconsistently

                                    The EXITM directive was used both with
                                    and without a return value in the same
                                    macro.

                                    A macro procedure returns a value; a
                                    macro function does not.

A2127                             macro function argument list too long

                                    There were too many characters in a
                                    macro function's argument list. This
                                    error applies also to a prologue macro
                                    function called implicitly by the PROC
                                    directive.

A2129                             VARARG parameter must be last parameter

                                    A parameter other than the last one was
                                    given the VARARG attribute.

                                    The :VARARG specification can be applied
                                    only to the last parameter in a
                                    parameter list for macro and procedure
                                    definitions and prototypes. You cannot
                                    use multiple :VARARG specifications in a
                                    macro.

A2130                             VARARG parameter not allowed with LOCAL

                                    An attempt was made to specify :VARARG
                                    as the type in a procedure's LOCAL
                                    declaration.

A2131                             VARARG parameter requires C calling
                                    convention

                                    A VARARG parameter was specified in a
                                    procedure definition or prototype, but
                                    the C, SYSCALL, or STDCALL calling
                                    convention was not specified.

A2132                             ORG needs a constant or local offset

                                    The expression specified with the ORG
                                    directive was not valid.

                                    ORG requires an immediate expression
                                    with no reference to an external label
                                    or to a label outside the current
                                    segment.

A2133                             register value overwritten by INVOKE

                                    A register was passed as an argument to
                                    a procedure, but the code generated by
                                    INVOKE to pass other arguments destroyed
                                    the contents of the register.

                                    The AX, AL, AH, EAX, DX, DL, DH, and EDX
                                    registers may be used by the assembler
                                    to perform data conversion.

                                    Use a different register.

A2134                             structure too large to pass with INVOKE
                                    : argument number

                                    An attempt was made with INVOKE to pass
                                    a structure that exceeded 255 bytes.

                                    Pass structures by reference if they are
                                    larger than 255 bytes.

A2136                             too many arguments to INVOKE

                                    The number of arguments passed using the
                                    INVOKE directive exceeded the number of
                                    parameters in the prototype for the
                                    procedure being invoked.

A2137                             too few arguments to INVOKE

                                    The number of arguments passed using the
                                    INVOKE directive was fewer than the
                                    number of required parameters specified
                                    in the prototype for the procedure being
                                    invoked.

A2138                             invalid data initializer

                                    The initializer list for a data
                                    definition was invalid.

                                    This error can be caused by using the R
                                    radix override with too few digits.

A2140                             RET operand too large

                                    The operand specified to RET, RETN, or
                                    RETF exceeded two bytes.

A2141                             too many operands to instruction

                                    Too many operands were specified with a
                                    string control instruction.

A2142                             cannot have more than one .ELSE clause
                                    per .IF block

                                    The assembler found more than one .ELSE
                                    clause within the current .IF block.

                                    Use .ELSEIF for all but the last block.

A2143                             expected data label

                                    The LENGTHOF, SIZEOF, LENGTH, or SIZE
                                    operator was applied to a non-data label,
                                    or the SIZEOF or SIZE operator was
                                    applied to a type.

A2144                             cannot nest procedures

                                    An attempt was made to nest a procedure
                                    containing a parameter, local variable,
                                    USES clause, or a statement that
                                    generated a new segment or group.

A2145                             EXPORT must be FAR : procedure

                                    The given procedure was given EXPORT
                                    visibility and NEAR distance.

                                    All EXPORT procedures must be FAR. The
                                    default visibility may have been set
                                    with the OPTION PROC:EXPORT statement or
                                    the SMALL or COMPACT memory models.

A2146                             procedure declared with two visibility
                                    attributes : procedure

                                    The given procedure was given
                                    conflicting visibilities.

                                    A procedure was declared with two
                                    different visibilities (PUBLIC, PRIVATE,
                                    or EXPORT). The PROC and PROTO
                                    statements for a procedure must have the
                                    same visibility.

A2147                             macro label not defined : macrolabel

                                    The given macro label was not found.

                                    A macro label is defined with :
                                    macrolabel.

A2148                             invalid symbol type in expression :
                                    identifier

                                    The given identifier was used in an
                                    expression in which it was not valid.

                                    For example, a macro procedure name is
                                    not allowed in an expression.

A2149                             byte register cannot be first operand

                                    A byte register was specified to an
                                    instruction that cannot take it as the
                                    first operand.

A2150                             word register cannot be first operand

                                    A word register was specified to an
                                    instruction that cannot take it as the
                                    first operand.

A2151                             special register cannot be first operand

                                    A special register was specified to an
                                    instruction that cannot take it as the
                                    first operand.

A2152                             coprocessor register cannot be first
                                    operand

                                    A coprocessor (stack) register was
                                    specified to an instruction that cannot
                                    take it as the first operand.

A2153                             cannot change size of expression
                                    computations

                                    An attempt was made to set the
                                    expression word size when the size had
                                    been already set using the EXPR16,
                                    EXPR32, SEGMENT:USE32, or SEGMENT:FLAT
                                    option or the .386 or higher processor
                                    selection directive.

A2154                             syntax error in control-flow directive

                                    The condition for a control-flow
                                    directive (such as .IF or .WHILE)
                                    contained a syntax error.

A2155                             cannot use 16-bit register with a 32-bit
                                    address

                                    An attempt was made to mix 16-bit and
                                    32-bit offsets in an expression.

                                    Use a 32-bit register with a symbol
                                    defined in a 32-bit segment.

                                    For example, if  id1  is defined in a
                                    32-bit segment, the following causes
                                    this error:

                                    id1[bx]

A2156                             constant value out of range

                                    An invalid value was specified for the
                                    PAGE directive.

                                    The first parameter of the PAGE
                                    directive can be either 0 or a value in
                                    the range 10-255. The second parameter
                                    of the PAGE directive can be either 0 or
                                    a value in the range 60-255.

A2157                             missing right parenthesis

                                    A right parenthesis, ), was missing from
                                    a macro function call.

                                    Be sure that parentheses are in pairs if
                                    nested.

A2158                             type is wrong size for register

                                    An attempt was made to assume a
                                    general-purpose register to a type with
                                    a different size than the register.

                                    For example, the following pair of
                                    statements causes this error:

                                    ASSUME bx:far ptr byte ; far pointer is
                                    4 or 6 bytes
                                    ASSUME al:word         ; al is a byte
                                    reg, cannot hold word

A2159                             structure cannot be instanced

                                    An attempt was made to create an
                                    instance of a structure when there were
                                    no fields or data defined in the
                                    structure definition or when ORG was
                                    used in the structure definition.

A2160                             non-benign structure redefinition :
                                    label incorrect

                                    A label given in a structure
                                    redefinition either did not exist in the
                                    original definition or was out of order
                                    in the redefinition.

A2161                             non-benign structure redefinition : too
                                    few labels

                                    Not enough members were defined in a
                                    structure redefinition.

A2162                             OLDSTRUCT/NOOLDSTRUCT state cannot be
                                    changed

                                    Once the OLDSTRUCTS or NOOLDSTRUCTS
                                    option has been specified and a
                                    structure has been defined, the
                                    structure scoping cannot be altered or
                                    respecified in the same module.

A2163                             non-benign structure redefinition :
                                    incorrect initializers

                                    A STRUCT or UNION was redefined with a
                                    different initializer value.

                                    When structures and unions are defined
                                    more than once, the definitions must be
                                    identical. This error can be caused by
                                    using a variable as an initializer and
                                    having the value of the variable change
                                    between definitions.

A2164                             non-benign structure redefinition : too
                                    few initializers

                                    A STRUCT or UNION was redefined with too
                                    few initializers.

                                    When structures and unions are defined
                                    more than once, the definitions must be
                                    identical.

A2165                             non-benign structure redefinition :
                                    label has incorrect offset

                                    The offset of a label in a redefined
                                    STRUCT or UNION differs from the
                                    original definition.

                                    When structures and unions are defined
                                    more than once, the definitions must be
                                    identical. This error can be caused by a
                                    missing member or by a member that has a
                                    different size than in its original
                                    definition.

A2166                             structure field expected

                                    The right-hand side of a dot operator (.)
                                    is not a structure field.

                                    This error may occur with some code
                                    acceptable to previous versions of the
                                    assembler. To enable the old behavior,
                                    use OPTION OLDSTRUCTS, which is
                                    automatically enabled by OPTION M510 or
                                    the /Zm command-line option.

A2167                             unexpected literal found in expression

                                    A literal was found where an expression
                                    was expected.

                                    One of the following may have occurred:

                                    ■ A literal was used as an initializer

                                    ■ A record tag was omitted from a record
                                    constant

A2169                             divide by zero in expression

                                    An expression contains a divisor whose
                                    value is equal to zero.

                                    Check that the syntax of the expression
                                    is correct and that the divisor (whether
                                    constant or variable) is correctly
                                    initialized.

A2170                             directive must appear inside a macro

                                    A GOTO or EXITM directive was found
                                    outside the body of a macro.

A2171                             cannot expand macro function

                                    A syntax error prevented the assembler
                                    from expanding the macro function.

A2172                             too few bits in RECORD

                                    There was an attempt to define a record
                                    field of 0 bits.

A2173                             macro function cannot redefine itself

                                    There was an attempt to define a macro
                                    function inside the body of a macro
                                    function with the same name. This error
                                    can also occur when a member of a chain
                                    of macros attempts to redefine a
                                    previous member of the chain.

A2175                             invalid qualified type

                                    An identifier was encountered in a
                                    qualified type that was not a type,
                                    structure, record, union, or prototype.

A2176                             floating point initializer on an integer
                                    variable

                                    An attempt was made to use a
                                    floating-point initializer with DWORD,
                                    QWORD, or TBYTE. Only integer
                                    initializers are allowed.

A2177                             nested structure improperly initialized

                                    The nested structure initialization
                                    could not be resolved.

                                    This error can be caused by using
                                    different beginning and ending
                                    delimiters in a nested structure
                                    initialization.

A2178                             invalid use of FLAT

                                    There was an ambiguous reference to FLAT
                                    as a group.

                                    This error is generated when there is a
                                    reference to FLAT instead of a FLAT
                                    subgroup. For example,

                                    mov    ax, FLAT               ;
                                    Generates A2178
                                    mov    ax, SEG FLAT:_data     ; Correct

A2179                             structure improperly initialized

                                    There was an error in a structure
                                    initializer.

                                    One of the following occurred:

                                    ■ The initializer is not a valid
                                    expression.

                                    ■ The initializer is an invalid DUP
                                    statement.

A2180                             improper list initialization

                                    In a structure, there was an attempt to
                                    initialize a list of items with a value
                                    or list of values of the wrong size.

A2181                             initializer must be a string or single
                                    item

                                    There was an attempt to initialize a
                                    structure element with something other
                                    than a single item or string.

                                    This error can be caused by omitting
                                    braces ({ }) around an initializer.

A2182                             initializer must be a single item

                                    There was an attempt to initialize a
                                    structure element with something other
                                    than a single item.

                                    This error can be caused by omitting
                                    braces ({ }) around an initializer.

A2183                             initializer must be a single byte

                                    There was an attempt to initialize a
                                    structure element of byte size with
                                    something other than a single byte.

A2184                             improper use of list initializer

                                    The assembler did not expect an opening
                                    brace ({) at this point.

A2185                             improper literal initialization

                                    A literal structure initializer was not
                                    properly delimited.

                                    This error can be caused by missing
                                    angle brackets (< >) or braces ({ })
                                    around an initializer or by extra
                                    characters after the end of an
                                    initializer.

A2186                             extra characters in literal
                                    initialization

                                    A literal structure initializer was not
                                    properly delimited.

                                    One of the following may have occurred:

                                    ■ There were missing or mismatched angle
                                    brackets (< >) or braces ({ }) around an
                                    initializer.

                                    ■ There were extra characters after the
                                    end of an initializer.

                                    ■ There was a syntax error in the
                                    structure initialization.

A2187                             must use floating point initializer

                                    A variable declared with the REAL4,
                                    REAL8, and REAL10 directives must be
                                    initialized with a floating-point number
                                    or a question mark (?).

                                    This error can be caused by giving an
                                    initializer in integer form (such as 18)
                                    instead of in floating-point form (18.0).

A2188                             cannot use .EXIT for OS_OS2 with .8086

                                    The INVOKE generated by the .EXIT
                                    statement under OS_OS2 requires the .186
                                    (or higher) directive, since it must be
                                    able to use the PUSH instruction to push
                                    immediates directly.

A2189                             invalid combination with segment
                                    alignment

                                    The alignment specified by the ALIGN or
                                    EVEN directive was greater than the
                                    current segment alignment as specified
                                    by the SEGMENT directive.

A2190                             INVOKE requires prototype for procedure

                                    The INVOKE directive must be preceded by
                                    a PROTO statement for the procedure
                                    being called.

                                    When using INVOKE with an address rather
                                    than an explicit procedure name, you
                                    must precede the address with a pointer
                                    to the prototype.

A2191                             cannot include structure in self

                                    You cannot reference a structure
                                    recursively (inside its own definition).

A2192                             symbol language attribute conflict

                                    Two declarations for the same symbol
                                    have conflicting language attributes
                                    (such as C and PASCAL). The attributes
                                    should be identical or compatible.

A2193                             non-benign COMM redefinition

                                    A variable was redefined with the COMM
                                    directive to a different language type,
                                    distance, size, or instance count.

                                    Multiple COMM definitions of a variable
                                    must be identical.

A2194                             COMM variable exceeds 64K

                                    A variable declared with the COMM
                                    directive in a 16-bit segment was
                                    greater than 64K.

A2195                             parameter or local cannot have void type

                                    The assembler attemped to create an
                                    argument or create a local without a
                                    type.

                                    This error can be caused by declaring or
                                    passing a symbol followed by a colon
                                    without specifying a type or by using a
                                    user-defined type defined as void.

A2196                             cannot use TINY model with OS_OS2

                                    A .MODEL statement specified the TINY
                                    memory model and the OS_OS2 operating
                                    system. The tiny memory model is not
                                    allowed under OS/2.

A2197                             expression size must be 32-bits

                                    There was an attempt to use the 16-bit
                                    expression evaluator in a 32-bit segment.
                                    In a 32-bit segment (USE32 or FLAT), you
                                    cannot use the default 16-bit expression
                                    evaluator (OPTION EXPR16).

A2198                             .EXIT does not work with 32-bit segments

                                    The .EXIT directive cannot be used in a
                                    32-bit segment; it is valid only under
                                    MS-DOS and OS/2 1.x.

A2199                             .STARTUP does not work with 32-bit
                                    segments

                                    The .STARTUP directive cannot be used in
                                    a 32-bit segment; it is valid only under
                                    MS-DOS and OS/2 1.x.

A2200                             ORG directive not allowed in unions

                                    The ORG directive is not valid inside a
                                    UNION definition.

                                    You can use the ORG directive inside
                                    STRUCT definitions, but it is
                                    meaningless inside a UNION.

A2201                             scope state cannot be changed

                                    Both OPTION SCOPED and OPTION NOSCOPED
                                    statements occurred in a module. You
                                    cannot switch scoping behavior in a
                                    module.

                                    This error may be caused by an OPTION
                                    SCOPED or OPTION NOSCOPED statement in
                                    an include file.

A2901                             cannot run ML.EXE

                                    The MASM driver could not spawn ML.EXE.

                                    One of the following may have occurred:

                                    ■ ML.EXE was not in the path.

                                    ■ The READ attribute was not set on
                                    ML.EXE.

                                    ■ There was not enough memory.


F.9.3  ML Warnings

Number                            Message
────────────────────────────────────────────────────────────────────────────
A4000                             cannot modify READONLY segment

                                    An attempt was made to modify an operand
                                    in a segment marked with the READONLY
                                    attribute.

A4002                             non-unique STRUCT/UNION field used
                                    without qualification

                                    A STRUCT or UNION field can be
                                    referenced without qualification only if
                                    it has a unique identifier.

                                    This conflict can be resolved either by
                                    renaming one of the structure fields to
                                    make it unique or by fully specifying
                                    both field references.

                                    The NONUNIQUE keyword requires that all
                                    references to the elements of a STRUCT
                                    or UNION be fully specified.

A4003                             start address on END directive ignored
                                    with .STARTUP

                                    Both .STARTUP and a program load address
                                    (optional with the END directive) were
                                    specified. The address specification
                                    with the END directive was ignored.

A4004                             cannot ASSUME CS

                                    An attempt was made to assume a value
                                    for the CS register. CS is always set to
                                    the current segment or group.

A4006                             too many arguments in macro call

                                    There were more arguments given in the
                                    macro call than there were parameters in
                                    the macro definition.

A4007                             option untranslated, directive required
                                    : option

                                    There is no ML command-line equivalent
                                    for the given MASM option. The desired
                                    behavior can be obtained by using a
                                    directive in the source file.

Option                  Directive
────────────────────────────────────────────────────────────────────────────
/A                      .ALPHA
/P                      OPTION READONLY
/S                      .SEQ

A4008                             invalid command-line option value,
                                    default is used : option

                                    The value specified with the given
                                    option was not valid. The option was
                                    ignored, and the default was assumed.

A4009                             virtual memory not available : /VM
                                    ignored

                                    The assembler was unable to initialize
                                    virtual memory.

                                    You may be able to fix this error by
                                    freeing memory being used by RAM disks,
                                    caches, or TSR programs.

A4010                             insufficent memory for /EP : /EP ignored

                                    There is not enough memory to generate a
                                    first-pass listing.

A4011                             expected '>' on text literal

                                    A macro was called with a text literal
                                    argument that was missing a closing
                                    angle bracket.

A4012                             multiple .MODEL directives found :
                                    .MODEL ignored

                                    More than one .MODEL directive was found
                                    in the current module. Only the first
                                    .MODEL statement is used.

A4910                             cannot open file: filename

                                    The given filename could not be in the
                                    current path.

                                    Make sure that filename was copied from
                                    the distribution disks and is in the
                                    current path.

A5000                             @@: label defined but not referenced

                                    A jump target was defined with the @@:
                                    label, but the target was not used by a
                                    jump instruction.

                                    One common cause of this error is
                                    insertion of an extra @@: label between
                                    the jump and the @@: label that the jump
                                    originally referred to.

A5001                             expression expected, assume value 0

                                    There was an IF, ELSEIF, IFE, IFNE,
                                    ELSEIFE, or ELSEIFNE directive without
                                    an expression to evaluate. The assembler
                                    assumes a 0 for the comparison
                                    expression.

A5002                             externdef previously assumed to be
                                    external

                                    The OPATTR or .TYPE operator was applied
                                    to a symbol after the symbol was used in
                                    an EXTERNDEF statement but before it was
                                    declared. These operators were used on a
                                    line where the assembler assumed that
                                    the symbol was external.

A5003                             length of symbol previously assumed to
                                    be different

                                    The LENGTHOF, LENGTH, SIZEOF, or SIZE
                                    operator was applied to a symbol after
                                    the symbol was used in an EXTERNDEF
                                    statement but before it was declared.
                                    These operators were used on a line
                                    where the assembler assumed that the
                                    symbol had a different length and size.

A5004                             symbol previously assumed to not be in a
                                    group

                                    A symbol was used in an EXTERNDEF
                                    statement outside of a segment and then
                                    was declared inside a segment.

A5005                             types are different

                                    The type given by an INVOKE statement
                                    differed from that given in the
                                    procedure prototype. The assembler
                                    performed the appropriate type
                                    conversion.

A6001                             no return from procedure

                                    A PROC statement generated a prologue,
                                    but there was no RET or IRET instruction
                                    found inside the procedure block.

A6003                             conditional jump lengthened

                                    A conditional jump was encoded as a
                                    reverse conditional jump around a near
                                    unconditional jump.

                                    You may be able to rearrange code to
                                    avoid the longer form.


F.10  NMAKE Error Messages

This section lists error messages generated by the Microsoft Program
Maintenance Utility (NMAKE):


    ■   Fatal errors (U10xx) cause NMAKE to stop execution.

    ■   Fatal errors (U14xx) cause NMK to stop execution.

    ■   Errors (U2xxx) do not stop execution but prevent NMAKE from completing
        the make process.

    ■   Warnings (U4xxx) indicate possible problems in the make process.



F.10.1  NMAKE Fatal Errors

Number                            NMAKE Error Message
────────────────────────────────────────────────────────────────────────────
U1000                             syntax error : ')' missing in macro
                                    invocation

                                    A left parenthesis ( ( ) appeared
                                    without a matching right parenthesis ( )
                                    ) in a macro invocation. The correct
                                    form is $(name), or $n for one-character
                                    names.

U1001                             syntax error : illegal character
                                    character in macro

                                    A nonalphanumeric character other than
                                    an underscore (_) appeared in a macro.

U1002                             syntax error : invalid macro invocation
                                    '$'

                                    A single dollar sign ($) appeared
                                    without a macro name associated with it.

                                    The correct form is $(name). To use a
                                    dollar sign in the file, type it twice (
                                    $$) or precede it with a caret (^).

U1003                             syntax error : '=' missing in macro

                                    The equal sign (=) was missing in a
                                    macro definition.

                                    The correct form is

                                    macroname=string

U1004                             syntax error : macro name missing

                                    A macro invocation appeared without a
                                    name.

                                    The correct form is

                                    $(name)

U1005                             syntax error : text must follow ':' in
                                    macro

                                    A string substitution was specified for
                                    a macro, but the string to be changed in
                                    the macro was not specified.

U1006                             syntax error : missing closing double
                                    quotation mark

                                    An opening double quotation mark (")
                                    appeared without a closing double
                                    quotation mark.

U1007                             double quotation mark not allowed in
                                    name

                                    The specified target name or filename
                                    contained a double quotation mark (").

                                    Double quotation marks can surround a
                                    filename but cannot be contained  within
                                    it.

U1017                             unknown directive !directive

                                    The directive specified is not one of
                                    the recognized directives.

U1018                             directive and/or expression part missing

                                    The directive was incompletely specified.

                                    The expression part of the directive is
                                    required.

U1019                             too many nested !IF blocks

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1020                             end-of-file found before next directive

                                    A directive, such as !ENDIF, was missing.

U1021                             syntax error : !ELSE unexpected

                                    An !ELSE directive was found that was
                                    not preceded by !IF, !IFDEF, or !IFNDEF,
                                    or the directive was placed in a
                                    syntactically incorrect place.

U1022                             missing terminating character for
                                    string/program invocation : char

                                    The closing double quotation mark (") in
                                    a string comparison in a directive was
                                    missing, or the closing bracket ( ] ) in
                                    a program invocation in a directive was
                                    missing.

U1023                             syntax error in expression

                                    An expression was invalid.

                                    Check the allowed operators and operator
                                    precedence.

U1024                             illegal argument to !CMDSWITCHES

                                    An unrecognized command switch was
                                    specified.

U1031                             filename missing (or macro is null)

                                    An include directive was found, but the
                                    name of the file to be included was
                                    missing, or the macro expanded to
                                    nothing.

U1033                             syntax error : string unexpected

                                    The given string is not part of the
                                    valid syntax for a description file.

U1034                             syntax error : separator missing

                                    The colon (:) that separates targets and
                                    dependents is missing.

U1035                             syntax error : expected ':' or '='
                                    separator

                                    Either a colon (:), implying a
                                    dependency line, or an equal sign (=),
                                    implying a macro definition, was
                                    expected.

U1036                             syntax error : too many names to left of
                                    '='

                                    Only one string is allowed to the left
                                    of a macro definition.

U1037                             syntax error : target name missing

                                    A colon (:) was found before a target
                                    name was found.

                                    At least one target is required.

U1038                             internal error : lexer

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1039                             internal error : parser

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1040                             internal error : macro expansion

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1041                             internal error : target building

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1042                             internal error : expression stack
                                    overflow

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1043                             internal error : temp file limit
                                    exceeded

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1044                             internal error : too many levels of
                                    recursion building a target

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1045                             internal error message

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1046                             internal error : out of search handles

                                    This error occurs under OS/2 when there
                                    are not enough search handles for NMAKE
                                    to run.

U1049                             macro or inline file too long (maximum
                                    64K)

                                    An inline file or a macro exceeded the
                                    limit of 64K.

U1050                             user-specified text

                                    The message specified with the !ERROR
                                    directive was displayed.

U1051                             out of memory

                                    The program ran out of space in the far
                                    heap.

                                    Split the description file into smaller
                                    and simpler pieces.

U1052                             file filename not found

                                    The file was not found.

                                    Check the specification of the filename
                                    in the description file.

U1053                             file filename unreadable

                                    The file cannot be read.

                                    The following are possible causes of
                                    this error:

                                    ■ The file does not have appropriate
                                    attributes for reading.

                                    ■ A bad area exists on disk.

                                    ■ A bad file-allocation table exists.

                                    ■ The file is locked.

U1054                             cannot create inline file filename

                                    NMAKE failed in its attempt to create
                                    the given file.

                                    The following are possible causes of
                                    this error:

                                    ■ The file already exists with a
                                    read-only attribute.

                                    ■ There is insufficient disk space to
                                    create the file.

U1055                             out of environment space

                                    The environment space limit was reached.

                                    Restart the program with a larger
                                    environment space or with fewer
                                    environment variables.

U1056                             cannot find command processor

                                    The command processor was not found.

                                    NMAKE uses COMMAND.COM or CMD.EXE as a
                                    command processor to execute commands.
                                    It looks for the command processor first
                                    by the full pathname given by the
                                    COMSPEC environment variable. If COMSPEC
                                    does not exist, NMAKE searches the
                                    directories specified by the PATH
                                    environment variable.

U1057                             cannot delete temporary file filename

                                    NMAKE failed to delete the temporary
                                    inline file.

U1058                             terminated by user

                                    Execution of NMAKE was aborted by CTRL+C
                                    or CTRL+BREAK.

U1060                             unable to close file : filename

                                    NMAKE encountered an error while closing
                                    a file.

                                    One of the following may have occurred:

                                    ■ The file is a read-only file.

                                    ■ There is a locking or sharing
                                    violation.

                                    ■ The disk is full.

U1061                             /F option requires a filename

                                    The /F command-line option requires the
                                    name of the description file to be
                                    specified.

                                    To use standard input, specify '-' as
                                    the filename.

                                    One cause of this error is omitting the
                                    space between /F and the filename.

U1062                             missing filename with /X option

                                    The /X command-line option requires the
                                    name of the file to which diagnostic
                                    error output should be redirected.

                                    To use standard output, specify '-' as
                                    the output filename.

U1063                             missing macro name before '='

                                    NMAKE detected an equal sign (=) without
                                    a preceding name.

                                    This error can occur in a recursive call
                                    when the macro corresponding to the
                                    macro name expands to nothing.

U1064                             MAKEFILE not found and no target
                                    specified

                                    No description file was found, and no
                                    target was specified.

                                    A description file can be specified
                                    either with the /F option or in a file
                                    named MAKEFILE. Note that NMAKE can
                                    create a target using an inference rule
                                    even if no description file is specified.

U1065                             invalid option option

                                    The option specified is not a valid
                                    option for NMAKE.

U1066                             option /N not supported; use NMAKE /N

                                    NMK does not support the /N option. Run
                                    NMAKE with the /N option.

U1070                             cycle in macro definition macroname

                                    A circular definition was detected in
                                    the given macro definition.

                                    Circular definitions are invalid.

U1071                             cycle in dependency tree for target
                                    targetname

                                    A circular dependency was detected in
                                    the dependency tree for the given target.

                                    Circular dependencies are invalid.

U1072                             cycle in include files : filename

                                    A circular inclusion was detected in the
                                    given include file. This file includes a
                                    file which eventually includes this file.

U1073                             don't know how to make targetname

                                    The specified target does not exist, and
                                    there are no commands to execute or
                                    inference rules given for it.

U1074                             macro definition too long

                                    The value of a macro definition
                                    overflowed an internal buffer.

U1075                             string too long

                                    The text string overflowed an internal
                                    buffer.

U1076                             name too long

                                    The macro name, target name, or
                                    build-command name overflowed an
                                    internal buffer.

                                    Macro names cannot exceed 128 characters.

U1077                             program : return code value

                                    The given program invoked from NMAKE
                                    failed, returning the given exit code.

U1078                             constant overflow at directive

                                    A constant in the directive's expression
                                    was too big.

U1079                             illegal expression : divide by zero

                                    An expression tried to divide by zero.

U1080                             operator and/or operand usage illegal

                                    The expression incorrectly used an
                                    operator or operand.

                                    Check the allowed set of operators and
                                    their order of precedence.

U1081                             program : program not found

                                    NMAKE could not find the given program
                                    in order to run it.

                                    Make sure that the program is in the
                                    current path and has the correct
                                    extension.

U1082                             command : cannot execute command; out of
                                    memory

                                    NMAKE cannot execute the given command
                                    because there is not enough memory.

                                    Free some memory and run NMAKE again.

U1083                             target macro $(macroname) expands to
                                    nothing

                                    A target was specified as a macro name
                                    that has not been defined or has null
                                    value.

                                    NMAKE cannot process a null target.

U1084                             cannot create temporary file filename

                                    NMAKE was unable to create a temporary
                                    file it needed for processing the
                                    description file.

                                    The following are possible causes of
                                    this error:

                                    ■ The file already exists with a
                                    read-only attribute.

                                    ■ There is insufficient disk space to
                                    create the file.

                                    ■ The TMP environment variable was set
                                    to an invalid directory or path.

U1085                             cannot mix implicit and explicit rules

                                    A regular target was specified along
                                    with the target for a rule.

                                    A rule has the form

                                    .fromext.toext

U1086                             inference rule cannot have dependents

                                    Dependents are not allowed when an
                                    inference rule is being defined.

U1087                             cannot have : and :: dependents for same
                                    target

                                    A target cannot have both a single-colon
                                    (:) and a double-colon (::) dependency.

U1088                             invalid separator '::' on inference rule

                                    Inference rules can use only a
                                    single-colon (:) separator.

U1089                             cannot have build commands for directive
                                    targetname

                                    Directives (for example, .PRECIOUS or
                                    .SUFFIXES) cannot have build commands
                                    specified.

U1090                             cannot have dependents for directive
                                    targetname

                                    The specified directive (for example,
                                    .SILENT or .IGNORE) cannot have a
                                    dependent.

U1091                             invalid suffixes in inference rule

                                    The suffixes being used in the inference
                                    rule are not part of the .SUFFIXES list.

U1092                             too many names in rule

                                    An inference rule cannot have more than
                                    one pair of extensions.

U1093                             cannot mix special pseudotargets

                                    It is illegal to list two or more
                                    pseudotargets together.

U1094                             syntax error : only (NO)KEEP allowed
                                    here

                                    Something other than KEEP or NOKEEP
                                    appeared at the end of the syntax for
                                    creating an inline file.

                                    The syntax for generating an inline file
                                    allows an action to be specified after
                                    the second pair of angle brackets. Valid
                                    actions are KEEP and NOKEEP. Any other
                                    specification is invalid.

                                    The KEEP option specifies that NMAKE
                                    should leave the inline file on disk.
                                    The NOKEEP option causes NMAKE to delete
                                    the file before exiting. The default is
                                    NOKEEP.

U1095                             expanded command line commandline too
                                    long

                                    After macro expansion, the command line
                                    shown exceeded the length limit for
                                    command lines for the operating system.

                                    DOS permits up to 128 characters on a
                                    command line.

                                    If the command is for a program that can
                                    accept command-line input from a file,
                                    change the command and supply input from
                                    either a file on disk or an inline file.
                                    For example, LINK and LIB accept input
                                    from a response file.

U1096                             cannot open file filename

                                    The given file could not be opened,
                                    either because the disk was full or
                                    because the file has been set to be
                                    read-only.

U1097                             extmake syntax usage error, no dependent

                                    No dependent was given.

                                    In extmake syntax, the target under
                                    consideration must have either an
                                    implicit dependent or an explicit
                                    dependent.

U1098                             extmake syntax in string incorrect

                                    The part of the string shown contains an
                                    extmake syntax error.

U1099                             stack overflow

                                    The description file being processed was
                                    too complex for the current stack
                                    allocation in NMAKE.

                                    NMAKE has a default allocation of 0x3000
                                    (12K).

                                    To increase NMAKE's stack allocation,
                                    run the EXEHDR utility with a larger
                                    stack option:

                                    EXEHDR /STACK:stacksize

                                    where stacksize is a number greater than
                                    the current stack allocation in NMAKE.

U1450                             could not execute NMAKE.EXE

                                    NMK was not able to locate and execute
                                    the NMAKE utility. Make sure this file
                                    is on your path.

U1451                             out of memory

                                    There was not enough available memory to
                                    complete the operation.

                                    One of the following may be a cause:

                                    ■ There are too many TSR programs
                                    installed. Remove some TSRs.

                                    ■ A previous command did not release
                                    memory when it terminated. This can
                                    happen if you attempt to run a TSR from
                                    within NMK.

                                    ■ There are too many active command
                                    shells. Close the current shell by
                                    entering  EXIT  at the operating-system
                                    prompt.

U1452                             COMSPEC not defined

                                    The COMSPEC environment variable is not
                                    defined

                                    NMK requires COMSPEC to be set to the
                                    full pathname of the operating-system
                                    command processor.

U1453                             error reading script file

                                    NMK encountered an error while reading
                                    the script file, which contains commands
                                    to execute during a shell or build
                                    operation.

                                    This can be caused by a CTRL+BREAK or a
                                    disk error while reading the script file.

U1454                             command could not execute

                                    NMK was unable to execute the given
                                    command.

                                    One of the following may have occurred:

                                    ■ There was not enough available memory
                                    to execute the command. A previous
                                    command may not have released memory
                                    when it ended. This can happen if you
                                    attempt to run a TSR from within NMK.

                                    ■ The operating system denied access to
                                    the file: it is in use by another
                                    program.

                                    ■ The executable file is corrupt.

U1455                             bad command or file name

                                    An operating-system command or
                                    executable program could not be executed.

                                    Either the command was spelled
                                    incorrectly, or it does not exist on the
                                    paths specified in the PATH environment
                                    variable.


F.10.2  NMAKE Errors

Number                            NMAKE Error Message
────────────────────────────────────────────────────────────────────────────
U2001                             no more file handles (too many files
                                    open)

                                    NMAKE could not find a free file handle.

                                    One of the following may be a solution:

                                    ■ Reduce recursion in the build
                                    procedures.

                                    ■ In DOS, increase the number of file
                                    handles by changing the FILES setting in
                                    CONFIG.SYS to allow a larger number of
                                    open files. FILES=20 is the recommended
                                    setting.


F.10.3  NMAKE Warnings

Number                            NMAKE Warning
────────────────────────────────────────────────────────────────────────────
U4001                             command file can be invoked only from
                                    command line

                                    A command file cannot be invoked from
                                    within another command file. The
                                    invocation was ignored.

                                    The command file must contain the entire
                                    remaining command line.

U4002                             resetting value of special macro
                                    macroname

                                    The value of a macro such as $(MAKE) was
                                    changed within a description file.

U4003                             no match found for wildcard filename

                                    There are no filenames that match the
                                    specified target or dependent file with
                                    the wildcard characters asterisk (*) and
                                    question mark (?).

U4004                             too many rules for target targetname

                                    Multiple blocks of build commands were
                                    specified for a target using single
                                    colons (:) as separators.

                                    To use multiple dependency blocks for
                                    the same target, specify a pair of
                                    colons (::) as the separator.

U4005                             ignoring rule rule (extension not in
                                    .SUFFIXES)

                                    The rule was ignored because the
                                    suffix(es) in the rule are not listed in
                                    the .SUFFIXES list.

U4006                             special macro undefined : macroname

                                    The special macro name is undefined and
                                    expands to nothing.

U4007                             filename filename too long; truncating
                                    to 8.3

                                    The base name of the given file has more
                                    than eight characters, or the extension
                                    has more than three characters. NMAKE
                                    truncated the name to an eight-
                                    character base and a three-character
                                    extension.

                                    You can use long filenames supported by
                                    HPFS under OS/2 by enclosing the name in
                                    double quotation marks.

U4008                             removed target target

                                    Execution of NMAKE was interrupted while
                                    NMAKE was trying to build the given
                                    target, and therefore the target was
                                    incomplete. Because the target was not
                                    specified in the .PRECIOUS list, NMAKE
                                    has deleted it.

U4009                             duplicate inline file filename

                                    The given filename is the same as the
                                    name of an earlier inline file.

                                    Reuse of this name caused the earlier
                                    file to be overwritten. This will
                                    probably cause unexpected results.


F.11  PWB.COM Error Messages

This section lists fatal error messages generated by the DOS Microsoft
Programmer's WorkBench (PWB.COM). PWB errors (U13xx) prevent PWB from
starting up, or returning from a build or operating-system shell.

Number                            PWB Error Message
────────────────────────────────────────────────────────────────────────────
U1350                             Could not execute PWBED.EXE

                                    PWB.COM could not find or load PWBED.EXE.

                                    Make sure your system has the following
                                    configuration:

                                    ■ Make sure PWBED.EXE can be found on
                                    the path specified in the PATH
                                    environment variable and that there is
                                    sufficient memory to operate PWB.

                                    ■ Check that your environment contains
                                    the recommended settings from the
                                    NEW-VARS.BAT file created by the SETUP
                                    program when you installed PWB.

                                    PWBED.EXE is the executable file for the
                                    PWB editor and environment. PWB.COM
                                    processes the command line on start-up
                                    and handles all system-level commands
                                    when building projects and executing
                                    Shell, User, Print, and Compile commands.

U1351                             out of memory

                                    There is not enough available memory to
                                    complete the operation.

                                    Some possible causes for this error are

                                    ■ You may have too many TSR programs
                                    installed. Remove some TSRs.

                                    ■ A previous command may not have
                                    released memory when it terminated. This
                                    can happen if you attempt to run a TSR
                                    from within PWB.

                                    ■ You may have too many active command
                                    shells. Leave the current shell with the
                                    operating-system Exit command.

U1352                             COMSPEC not defined

                                    The COMSPEC environment variable is not
                                    set.

                                    PWB requires COMSPEC to be set to the
                                    full pathname of the operating-system
                                    command processor.

U1353                             error reading script file

                                    PWB.COM encountered an error while
                                    reading the file that contains a script
                                    of commands to execute during a shell or
                                    build operation.

                                    This can be caused by a CTRL+BREAK or a
                                    disk error while reading the script file.

U1354                             could not execute

                                    PWB.COM was unable to execute the given
                                    command.

                                    Some possible causes for this error are

                                    ■ The executable file for the command
                                    was not found.

                                    ■ The pathname of the command was not
                                    found.

                                    ■ The operating system denied access to
                                    the file: it is in use by another
                                    program.

                                    ■ There is not enough available memory
                                    to execute the command.

    A previous command may not have released memory when it terminated. This
    can happen if you attempt to run a TSR from within PWB.


    ■   The environment is corrupt.

    ■   The executable file is corrupt.


U1355                             Bad Command or Filename

                                    An operating-system command or
                                    executable program could not be executed.

                                    The command may be spelled incorrectly,
                                    or it does not exist on the path
                                    specified in the PATH environment
                                    variable. Make sure that your
                                    environment contains the recommended
                                    settings from the NEW-VARS.BAT file
                                    created by the SETUP program when you
                                    installed PWB.


F.12  PWBRMAKE Error Messages

This section lists error messages generated by the Microsoft PWBRMAKE
Utility (PWBRMAKE):


    ■   Fatal errors (U15xx) cause PWBRMAKE to stop execution.

    ■   Warnings (U45xx) indicate possible problems in the operation of
        PWBRMAKE.



F.12.1  PWBRMAKE Fatal Errors

Number                            PWBRMAKE Error Message
────────────────────────────────────────────────────────────────────────────
U1500                             UNKNOWN ERROR Contact Microsoft Product
                                    Support Services

                                    PWBRMAKE detected an unknown error
                                    condition.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U1501                             unknown character character in option
                                    option

                                    PWBRMAKE did not recognize the given
                                    character specified for the given option.

U1502                             incomplete specification for option
                                    option

                                    The given option did not contain the
                                    complete specification that PWBRMAKE
                                    expected.

U1503                             cannot write to file filename

                                    PWBRMAKE could not write to the given
                                    file.

                                    One of the following may have occurred:

                                    ■ The disk was full.

                                    ■ A hardware error occurred.

U1504                             cannot position in file filename

                                    PWBRMAKE could not move to a location in
                                    the given file.

                                    One of the following may have occurred:

                                    ■ The disk was full.

                                    ■ A hardware error occurred.

                                    ■ The file was truncated. Truncation can
                                    occur if the compiler runs out of disk
                                    space or is interrupted when it is
                                    creating the .SBR file.

U1505                             cannot read from file filename

                                    PWBRMAKE could not read from the given
                                    file.

                                    One of the following may have occurred:

                                    ■ The file was corrupt.

                                    ■ The file was truncated. Truncation can
                                    occur if the compiler runs out of disk
                                    space or is interrupted when it is
                                    creating the .SBR file.

U1506                             cannot open file filename

                                    PWBRMAKE could not open the given file.

                                    One of the following may have occurred:

                                    ■ No more file handles were available.
                                    In DOS, increase the number of file
                                    handles by changing the FILES setting in
                                    CONFIG.SYS to allow a larger number of
                                    open files. FILES=20 is the recommended
                                    setting.

                                    ■ The file was locked by another process.

                                    ■ The disk was full.

                                    ■ A hardware error occurred.

                                    ■ The specified output file had the same
                                    name as an existing subdirectory.

U1507                             cannot open temporary file filename

                                    PWBRMAKE could not open one of its
                                    temporary files.

                                    One of the following may have occurred:

                                    ■ No more file handles were available.
                                    In DOS, increase the number of file
                                    handles by changing the FILES setting in
                                    CONFIG.SYS to allow a larger number of
                                    open files. FILES=20 is the recommended
                                    setting.

                                    ■ The TMP environment variable was not
                                    set to a valid drive and directory.

                                    ■ The disk was full.

U1508                             cannot delete temporary file filename

                                    PWBRMAKE could not delete one of its
                                    temporary files.

                                    One of the following may have occurred:

                                    ■ Another process had the file open.

                                    ■ A hardware error occurred.

U1509                             out of heap space

                                    PWBRMAKE ran out of memory.

                                    One of the following may be a solution:

                                    ■ Reduce the memory that PWBRMAKE will
                                    require by using one or more options.
                                    Use /Ei or /Es to eliminate some input
                                    files. Use /Em to eliminate macro bodies.

                                    ■ Free some memory by removing
                                    terminate-and-stay-resident (TSR)
                                    software.

                                    ■ Reconfigure the EMM driver.

                                    ■ Change CONFIG.SYS to specify a lower
                                    number of buffers (the BUFFERS command)
                                    and fewer drives (the LASTDRIVE command).

U1510                             corrupt .SBR file filename

                                    The given .SBR file is corrupt or does
                                    not have the expected format.

                                    Recompile to regenerate the .SBR file.

U1511                             invalid response file specification

                                    PWBRMAKE did not understand the
                                    command-line specification for the
                                    response file. The specification was
                                    probably wrong or incomplete.

                                    For example, the following specification
                                    causes this error:

                                    pwbrmake @

U1512                             database capacity exceeded

                                    PWBRMAKE could not build a database
                                    because the number of definitions,
                                    references, modules, or other
                                    information exceeded the limit for a
                                    database.

                                    One of the following may be a solution:

                                    ■ Exclude some information using the /Em,
                                    /Es, or /Ei option.

                                    ■ Omit the /Iu option if it was used.

                                    ■ Divide the list of .SBR files and
                                    build multiple databases.

U1513                             nonincremental update requires all .SBR
                                    files

                                    An attempt was made to build a new
                                    database, but one or more of the
                                    specified .SBR files was truncated. This
                                    message is always preceded by warning
                                    U4502, which will give the name of the
                                    .SBR file that caused the error.

                                    PWBRMAKE can process a truncated, or
                                    zero-length, .SBR file only when a
                                    database already exists and is being
                                    incrementally updated.

                                    One of the following may be a cause:

                                    ■ The database was deleted.

                                    ■ The wrong database name was specified.

                                    ■ The database file was corrupted,
                                    requiring a full build.

U1514                             all .SBR files truncated and not in
                                    database

                                    None of the .SBR files specified for an
                                    update was a part of the original
                                    database. This message is always
                                    preceded by warning U4502, which will
                                    give the name of the .SBR file that
                                    caused the error.

                                    One of the following may be a cause:

                                    ■ The wrong database name was specified.

                                    ■ The database file was corrupted,
                                    requiring a full build.


F.12.2  PWBRMAKE Warnings

Number                            PWBRMAKE Warning
────────────────────────────────────────────────────────────────────────────
U4500                             UNKNOWN WARNING Contact Microsoft
                                    Product Support Services

                                    An unknown error condition was detected
                                    by PWBRMAKE.

                                    Note the circumstances of the error and
                                    notify Microsoft Corporation by
                                    following the instructions on the
                                    Microsoft Product Assistance Request
                                    form at the back of one of your manuals.

U4501                             ignoring unknown option option

                                    PWBRMAKE did not recognize the given
                                    option and ignored it.

U4502                             truncated .SBR file filename not in
                                    database

                                    The given zero-length .SBR file,
                                    specified during a database update, was
                                    not originally part of the database.

                                    If a zero-length file not part of the
                                    original build of the database is
                                    specified during a rebuild of that
                                    database, PWBRMAKE issues this warning.
                                    One of the following may be a cause:

                                    ■ The wrong database name was specified.

                                    ■ The database was deleted. (Error U1513
                                    will result.)

                                    ■ The database file was corrupted,
                                    requiring a full build.









Glossary
────────────────────────────────────────────────────────────────────────────

8087, 80287, or 80387 coprocessor
Intel chips that perform high-speed floating-point and binary coded decimal
number processing. Also called math coprocessors. Floating-point
instructions are supported directly by the 80486 processor.

address
The memory location of a data item or procedure, or an expression that
evaluates to an address. The expression can represent just the offset (in
which case the default segment is assumed), or it can be in segment:offset
format.

address constant
In an assembly-language instruction, an immediate operand derived by
applying the SEG or OFFSET operator to an identifier.

address range
A range of memory bounded by two addresses.

addressing modes
The various ways a memory address or device I/O address can be generated.
See far address, near address.

aggregate types
Data types containing more than one element, such as arrays, structures, and
unions.

animate
A debugging feature in which each line in a running program is highlighted
as it executes. The Animate command from the CodeView debugger Run menu
turns on animation.

API (application program interface)
A set of system-level routines that can be used in an application program
for tasks such as basic input/output and file management. In a
graphics-oriented operating environment like Microsoft Windows, high-level
support for video graphics output is part of the Windows graphical API. See
Family application program interface.

arg
In PWB, a function modifier that introduces an argument or an editing
function. The argument may be of any type and is passed to the next function
as input. For example, the PWB command  Arg textarg Copy  passes the text
argument  textarg  to the function  Copy.

argument
A value passed to a procedure or function. See parameter.

array
An ordered set of continuous elements of the same type.

ASCII (American Standard Code for Information Interchange)
A widely used coding scheme where one-byte numeric values represent letters,
numbers, symbols, and special characters. There are 256 possible codes. The
first 128 codes are standardized; the remaining 128 are special characters
defined by the computer manufacturer.

assembler
A program that converts a text file containing mnemonically coded
microprocessor instructions into the corresponding binary machine code. MASM
is an assembler. See compiler.

assembly language
A programming language in which each line of source code corresponds to a
specific microprocessor instruction. Assembly language gives the programmer
full access to the computer's hardware and produces the most compact,
fastest executing code. See high-level language.

assembly mode
The mode in which the CodeView debugger displays the assembly- language
equivalent of the high-level code being executed. CodeView obtains the
assembly-language code by disassembling the executable file. See source
mode.

base address
The starting address of a stack frame. Base addresses are usually stored in
the BP register.

base name
The portion of the filename that precedes the extension. For example, SAMPLE
is the base name of the file SAMPLE.ASM.

BCD (binary coded decimal)
A way of representing decimal digits where four bits of one byte are a
decimal digit, coded as the equivalent binary number.

binary
Referring to the base-2 counting system, whose digits are 0 and 1.

binary expression
A Boolean expression consisting of two operands joined by a binary operator
and resolving to a binary number.

binary file
A file that contains numbers in binary form (as opposed to ASCII characters
representing the same numbers). For example, a program file is a binary
file.

binary operator
A Boolean operator that takes two arguments. The AND and OR operators in
assembly language are examples of binary operators.

BIOS (Basic Input/Output System)
The software in a computer's ROM which forms a hardware- independent
interface between the CPU and its peripherals (for example, keyboard, disk
drives, video display, I/O ports).

bit
Short for binary digit. The basic unit of binary counting. Logically
equivalent to decimal digits, except that bits can have a value of 0 or 1,
whereas decimal digits can range from 0 through 9.

breakpoint
A user-defined condition that pauses program execution while debugging.
CodeView can set breakpoints at a specific line of code, for a specific
value of a variable, or for a combination of these two conditions.

buffer
A reserved section of memory that holds data temporarily, most often during
input/output operations.

byte
The smallest unit of measure for computer memory and data storage. One byte
consists of eight bits and can store one 8-bit character (a letter, number,
punctuation mark, or other symbol). It can represent unsigned values from 0
to 255 or signed values between -128 and +127.

C calling convention
The convention that follows the order used by C─that is, pushing arguments
onto the stack from right to left, or in reverse order from the way they are
declared in the MASM procedure. The C calling convention permits a variable
number of arguments to be passed.

chaining (to an interrupt)
Installing an interrupt handler that shares control of an interrupt with
other handlers. Control passes from one handler to the next until a handler
breaks the chain by terminating through an IRET instruction. See interrupt
handler.

character string
A group of characters enclosed in single quotation marks (' ') or double
quotation marks (" ").

child process
In protected mode, a new process created by a currently executing process
(its parent process).

clipboard
In PWB, a section of memory that holds text deleted with the Copy, Ldelete,
or Sdelete functions. Any text attached to the clipboard deletes text
already there. The Paste function inserts text from the clipboard at the
current cursor position.

.COM
The filename extension for executable files that have a single segment
containing both code and data. Tiny model produces .COM files.

combine type
The segment-declaration specifier (AT, COMMON, MEMORY, PUBLIC, or STACK)
which tells the linker to combine all segments of the same type. Segments
without a combine type are private and are placed in separate physical
segments.

compact
A memory model with multiple data segments but only one code segment.

compiler
A program that translates source code into machine language. Usually applied
only to high-level languages, such as Basic, Pascal,  FORTRAN, or C. See
assembler.

constant
A value that does not change during program execution. A variable, on the
other hand, is a value that can─and usually does─change. See symbolic
constant.

constant expression
Any expression that evaluates to a constant. It may include integer
constants, character constants, floating-point constants, or other constant
expressions.

debugger
A utility program that allows the programmer to execute a program one line
at a time and view the contents of registers and memory in order to help
locate the source of bugs or other problems. Examples are CodeView and
Symdeb.

declaration
A construct that associates the name and the attributes of a variable,
function, or type. See variable declaration.

default
A setting or value that is assumed unless specified otherwise.

definition
A construct that initializes and allocates storage for a variable, or that
specifies either code labels or the name, formal parameters, body, and
return type of a procedure. See type definition.

device driver
A program that transforms I/O requests into the operations necessary to make
a specific piece of hardware fulfill that request.

Dialog Command window
The window at the bottom of the CodeView screen where dialog com- mands can
be entered, and previously entered dialog commands can be reviewed.

direct memory operand
In an assembly-language instruction, a memory operand that refers to the
contents of an explicitly specified memory location.

directive
An instruction that controls the assembler's state.

displacement
In an assembly-language instruction, a constant value added to an effective
address. This value often specifies the starting address of a variable, such
as an array or multidimensional table.

DLL
See dynamic-link library.

double-click
To rapidly press and release a mouse button twice while pointing the mouse
cursor at an object on the screen.

double precision
A real (floating-point) value that occupies eight bytes of memory (MASM type
REAL8). Double-precision values are accurate to 15 or 16 digits.

doubleword
A four-byte word (MASM type DWORD).

drag
To move the mouse while pointing at an object and holding down one of the
mouse buttons.

dump
To display the contents of memory at a specified memory range.

dynamic linking
The resolution of external references at load time or run time (rather than
link time). Dynamic linking allows the called subroutines to be packaged,
distributed, and maintained independently of their callers. OS/2 extends the
dynamic-link mechanism to serve as the primary method by which all system
and nonsystem services are obtained.

dynamic-link library (DLL)
A file, in a special format, that contains the binary code for a group of
dynamically linked routines.

dynamic-link routine
A routine that can be linked at load time or run time.

environment block
The section of memory containing the DOS environment variables.

errorlevel code
See exit code.

.EXE
The filename extension for a program that can be loaded and executed by the
computer. The small, compact, medium, large, huge, and flat models generate
.EXE files. See .COM, tiny.

exit code
A code returned by a program to the operating system. This usually indicates
whether the program ran successfully.

expanded memory
Increased memory available after adding an EMS (Expanded Memory
Specification) board to an 8086 or 80286 machine. Expanded memory can be
simulated in software. The EMS board can increase memory from 1 megabyte to
8 megabytes by swapping segments of high-end memory into lower memory.
Applications must be written to the EMS standard in order to make use of
expanded memory. See extended memory.

expression
Any valid combination of mathematical or logical variables, constants,
strings, and operators that yields a single value.

extended memory
Physical memory above 1 megabyte that can be addressed by 80286-80486
machines in protected mode. Adding a memory card adds extended memory. On
80386-based machines, extended memory can be made to simulate expanded
memory by using a memory- management program.

extension
The part of a filename (of up to three characters) that follows the period
(.). An extension is not required but is usually added to differentiate
similar files. For example, the source-code file MYPROG.ASM is assembled
into the object file MYPROG.OBJ, which is linked to produce the executable
file MYPROG.EXE.

external variable
A variable declared in one module and referenced in another module.

Family Application Program Interface (Family API)
    A standard execution environment under MS-DOS (R) (versions 2.x and later)
and OS/2. The programmer can use the Family API to create an application
that uses a subset of OS/2 functions (but a superset of MS-DOS 3.x
functions).

far address
A memory location specified with a segment value plus an offset from the
start of that segment. Far addresses require four bytes─two for the segment
and two for the offset. See near address.

field
One of the components of a structure, union, or record variable.

fixup
The linking process that supplies addresses for procedure calls and variable
references.

flags register
A register containing information about the status of the CPU and the
results of the last arithmetic operation performed by the CPU.

flat
A nonsegmented linear address space. Selectors in flat model can address the
entire four gigabytes of addressable memory space. See  segment, selector.

formal parameters
The variables that receive values passed to a function when the function is
called.

forward declaration
A function declaration that establishes the attributes of a symbol so that
it can be referenced before it is defined, or called from a different source
file.

frame
The segment, group, or segment register that specifies the segment portion
of an address.

General-Protection (GP) fault
An error that occurs in protected mode when a program accesses invalid
memory locations or accesses valid locations in an invalid way (such as
writing into ROM areas).

gigabyte
1,024 megabytes, or 1,073,741,824 bytes.

global
See visibility.

global constant
A constant available throughout a module. Symbolic constants defined in the
module-level code are global constants.

global data segment
A data segment that is shared among all instances of a dynamic-link routine;
in other words, a single segment that is accessible to all processes that
call a particular dynamic-link routine.

global variable
A variable that is available (visible) across multiple modules.

granularity
The degree to which library procedures can be linked as individual blocks of
code. In Microsoft libraries, granularity is at the object-file level. If a
single object file containing three procedures is added to a library, all
three procedures will be linked with the main program even if only one of
them is actually called.

group
A collection of individually defined segments that have the same segment
base address.

handle
An arbitrary value that an operating system supplies to a program (or vice
versa) so that the program can access system resources, files, peripherals,
and so forth, in a controlled fashion.

hexadecimal
The base-16 numbering system whose digits are 0 through F (the letters A
through F represent the decimal numbers 10 through 15). This is often used
in computer programming because it is easily converted to and from the
binary (base-2) numbering system the computer itself uses.

high-level language
A programming language that expresses operations as mathematical or logical
relationships which the language's compiler then converts into machine code.
This contrasts with assembly language, in which the program is written
directly as a sequence of explicit microprocessor instructions. Basic, C,
COBOL, FORTRAN, and Pascal are examples of high-level languages. See
assembly language, compiler.

hooking (an interrupt)
Replacing an address in the interrupt vector table with the address of
another interrupt handler. See interrupt handler, interrupt vector table,
unhooking (an interrupt).

huge
A memory model (similar to large model) with more than one code segment and
more than one data segment. However, individual data items can be larger
than 64K, spanning more than one segment. See large.

identifier
A name that identifies a register or memory location.

IEEE format
A standard created by the Institute of Electrical and Electronics Engineers
for representing floating-point numbers, performing math with them, and
handling underflow/overflow conditions. The 8087 family of coprocessors and
the emulator package implement this format.

immediate expression
An expression that evaluates to a number that can either be a component of
an address or the entire address.

immediate operand
In an assembly-language instruction, a constant operand that is specified at
assembly time and stored in the program file as part of the instruction
opcode.

include file
A text file with the .INC extension whose contents are inserted into the
source-code file and immediately assembled.

indirect memory operand
In an assembly- language instruction, a memory operand whose value is
treated as an address that points to the location of the desired data.

instruction
The unit of binary information that a CPU decodes and executes. In assembly
language, instruction refers to the mnemonic (such as LDS or SHL) that the
assembler converts into machine code.

instruction prefix
See prefix.

interrupt
Instructions that cause a new sequence of actions to take place.

interrupt handler
A routine that receives processor control when a specific interrupt occurs.

interrupt service routine
See interrupt handler.

interrupt vector
An address that points to an interrupt handler.

interrupt vector table
A table maintained by the operating system. It contains addresses (vectors)
of current interrupt handlers. When an interrupt occurs, the CPU branches to
the address in the table that corresponds to the interrupt's number. See
interrupt handler.

keyword
A word with a special, predefined meaning for the assembler. In MASM 6.0,
keywords cannot be used as identifiers.

kilobyte (K)
1,024 bytes.

label
A symbol (identifier) representing the address of a code label or data
objects.

language type
The specifier that establishes the naming and calling conventions for a
procedure. These are BASIC, C, FORTRAN, PASCAL, STDCALL, and SYSCALL.

large
A memory model with more than one code segment and more than one data
segment, but with no individual data item larger than 64K (a single
segment). See huge.

library
A file with the .LIB extension that stores modules of compiled code (object
files). The linker extracts modules from the library and combines them with
other object modules to create executable program files.

linked list
A data structure in which each entry includes a pointer to the location of
the adjoining entries.

linking
The process in which the linker resolves all external references by
searching the run-time and user libraries, and then computes absolute offset
addresses for these references. The linking process results in a single
executable file.

local constant
A constant whose scope is limited to a procedure or a module.

local variable
A variable whose scope is confined to a particular unit of code, such as
module-level code, or a procedure. See module-level code.

logical device
A symbolic name for a device that can be mapped to a physical (actual)
device.

logical line
A complete program statement in source code, including the initial line of
code and any extension lines.

low-level input and output routines
Run-time library routines that perform unbuffered, unformatted input/output
operations.

LSB (least-significant bit)
The bit lowest in memory in a binary number.

machine code
The binary numbers that a microprocessor interprets as program instructions.
See instruction.

macro
A block of text or instructions that has been assigned an identifier. When
the assembler sees this identifier in the source code, it substitutes the
related text or instructions and assembles them.

main module
The module containing the point where program execution begins (the
program's entry point). See module.

math coprocessor
See 8087, 80287, or 80387 coprocessor.

medium
A memory model with multiple code segments but only one data segment.

megabyte
1,024 kilobytes or 1,048,576 bytes.

member
One of the elements of a structure or union; also called a field.

memory address
A number through which a program can reference a location in memory.

memory map
A representation of where in memory the computer expects to find certain
types of information.

memory model
A convention for specifying the number and types of code and data segments
in a module. See tiny, small, medium, compact, large, huge, and flat.

memory operand
An operand that specifies a memory location.

meta
A prefix that modifies the subsequent PWB function.

mnemonic
A word, abbreviation, or acronym that replaces something too complex to
remember or type easily. For example, ADC is the mnemonic for the 8086's
add-with-carry instruction. The assembler converts it into machine (binary)
code, so it is not necessary to remember or calculate the binary form.

module
A discrete group of statements. Every program has at least one module (the
main module). In most cases, a module is the same as a source file.

module-level code
Program statements within any module that are outside procedure definitions.

MSB (most-significant bit)
The bit farthest to the left in a binary number. It represents 2(n-1), where
n is the number of bits in the number.

multitasking operating system
An operating system in which two or more programs, processes, or threads can
execute simultaneously.

naming convention
The way the compiler or assembler alters the name of a routine before
placing it into an object file.

NAN
Acronym for "not a number." The math coprocessors generate NANs when the
result of an operation cannot be represented in IEEE format. For example, if
two numbers being multiplied have a product larger than the maximum value
permitted, the coprocessor returns a NAN instead of the product.

near address
A memory location specified by the offset from the start of the value in a
segment register. A near address requires only two bytes. See far address.

nonreentrant
See reentrant procedure.

null character
The ASCII character encoded as the value 0.

null pointer
A pointer to nothing, expressed as the value 0.

.OBJ
Default filename extension for an object file.

object file
A file (normally with the extension .OBJ) produced by assembling source
code. It contains relocatable machine code. The linker combines object files
with run-time and library code to create an executable file.

offset
The number of bytes from the beginning of a segment to a particular byte
within that segment.

opcode
The binary number that represents a specific microprocessor instruction.

operand
A constant or variable value that is manipulated in an expression or
instruction.

operator
One or more symbols that specify how the operand or operands of an
expression are manipulated.

option
A variable that modifies the way a program performs. Options can appear on
the command line, or they can be part of an initialization file (such as
TOOLS.INI). An option is sometimes called a switch.

OS/2
A multitasking operating system for the 80286-80486 family of personal
computers.

output screen
The CodeView screen that displays program output. Choosing the Output
command from the View menu or pressing F4 switches to this screen.

overflow
An error that occurs when the value assigned to a numeric variable falls
outside the allowable range for that variable's type.

overlay
A program component loaded into memory from disk only when needed. This
technique reduces the amount of free RAM needed to run the program.

parameter
The name given in a procedure definition to a variable that is passed to the
procedure. See argument.

passing by reference
Transferring the address of an argument to a procedure. This allows the
procedure to modify the argument's value.

passing by value
Transferring the value (rather than the address) of an argument to a
procedure. This prevents the procedure from changing the argument's original
value.

physical memory
The hardware addresses of the actual RAM or ROM present in the computer.

physical segment
The hardware address of a segment.

pointer
A variable containing the address or relative offset of another variable.

precedence
The relative position of an operator in the hierarchy that determines the
order in which expression elements are evaluated.

preemptive
Having the power to take precedence over another event.

prefix
A keyword (LOCK, REP, REPE, REPNE, REPNZ, or REPZ) that modifies the
behavior of an instruction. MASM 6.0 checks to be sure the prefix is
compatible with the instruction.

private
Data items and routines local to the module in which they are defined. They
cannot be accessed outside that module. See public.

privilege level
A hardware-supported feature of the 80286-80486 processors which allows the
programmer to specify the exclusivity of a program  or process. Programs
running at low-numbered privilege levels can access data or resources at
higher-numbered privilege levels, but the reverse is not true. This feature
reduces the possibility that malfunctioning code will corrupt data or crash
the operating system.

privileged mode
The term applied to privilege level 0. This privilege level should only be
used by the OS/2 kernel and device drivers. Special privileged instructions
are enabled by .286P, .386P, and .486P. This feature should not be confused
with protected mode.

procedure call
An expression that invokes a procedure and passes actual arguments (if any)
to the procedure.

procedure definition
A definition that specifies a procedure's name, its formal parameters, the
declarations and statements that define what it does, and (optionally) its
return type and storage class.

procedure prototype
A procedure declaration that includes a list of the names and types of
formal parameters following the procedure name.

process
Generally, any executing program or code unit. This term implies that the
program or unit is one of a group of processes executing independently.

Program Segment Prefix (PSP)
A 256-byte data structure at the base of the memory block allocated to a
transient program. It contains linkages to DOS and data from DOS that the
program can use or ignore.

protected mode
The 80286-80486 operating mode that permits multiple processes to run and
not interfere with each other. This feature should not be confused with
privileged mode.

public
Data items and procedures that can be accessed outside the module in which
they are defined. See private.

qualifiedtype
A user-defined type consisting of an existing MASM type (intrinsic,
structure, union, or record), or a previously defined TYPEDEF type, together
with its language or distance attributes.

radix
The base of a number system. The default radix for MASM and CodeView is 10.

RAM (random-access memory)
Computer memory that can both be written to and read from. RAM data is
volatile; it is usually lost when the computer is turned off. Programs are
loaded into and executed from RAM. See ROM.

real mode
The normal operating mode of the 8086 family of processors. Addresses
correspond to physical (not mapped) memory locations, and there is no
mechanism to keep one application from accessing or modifying the code or
data of another. See protected mode.

record
A MASM variable that consists of a sequence of bit values.

reentrant procedure
A procedure that can be safely interrupted during its execution and
restarted from its beginning in response to a call from a preemptive
process. After servicing the preemptive call, the procedure continues
execution at the point at which it was interrupted.

register operand
In an assembly-language instruction, an operand that is stored in the
register specified by the instruction.

register window
The optional CodeView window in which the CPU registers and the flag
register bits are displayed.

registers
Memory locations in the processor that temporarily store data, addresses,
and logical values.

regular expression
A text expression that specifies a pattern of text to be matched (as opposed
to matching specific characters).

relocatable
Not having an absolute address. The assembler does not know where the label,
data, or code will be located in memory, so it generates a fixup record. The
linker provides the address.

return value
The value returned by a function.

ROM (read-only memory)
Computer memory that can only be read from and cannot be modified. ROM data
is permanent; it is not lost when the machine is turned off. A computer's
ROM often contains BIOS routines and parts of the operating system. See RAM.

routine
A generic term for a procedure or function.

run-time dynamic linking
The act of establishing a link when a process is started or is running.

run-time error
A math or logic error that can be detected only when the program runs.
Examples of run-time errors are dividing by a variable whose value is zero
or calling a DLL function that doesn't exist.

scope
The range of statements over which a variable or constant can be referenced
by name. See global constant, global variable, local constant, local
variable.

screen swapping
A screen-exchange method that uses buffers to store the debugging and output
screens. When you request the other screen, the two buffers are exchanged.
This method is slower than flipping (the other screen-exchange method), but
it works with most adapters and most types of programs.

scroll bars
The bars that appear at the right side and bottom of a window and some list
boxes. Dragging the mouse on the scroll bars allows scrolling through the
contents of a window or text box.

segment
A section of memory, limited to 64K with 16-bit segments or 4 gigabytes with
32-bit segments, containing code or data. Also refers to the starting
address of that memory area.

sequential mode
The mode in CodeView in which no windows are available. Input and output
scroll down the screen, and the old output scrolls off the top of the screen
when the screen is full. You cannot examine previous commands after they
scroll off the top. This mode is required with computers that are not IBM
compatible.

selector
An address segment component supplied by a protected-mode operating system
(such as OS/2). Programs that attempt to modify or directly manipulate these
values may crash or cause system malfunctions.

shared memory
A memory segment that can be accessed simultaneously by more than one
process.

shell escape
A method of gaining access to the operating system without leaving CodeView
or losing the current debugging context. It is possible to execute DOS
commands, then return to the debugger.

sign extended
The process of widening (for example, going from a byte to a word, or a word
to a doubleword) a negative integer while retaining its correct value and
sign.

signed integer
A binary integer that uses the most-significant bit to represent signed
quantities. If this bit is one, the number is negative; if zero, the number
is non-negative. See two's complement, unsigned integer.

single precision
A real (floating-point) value that occupies four bytes of memory.
Single-precision values are accurate to six or seven decimal places.

single-tasking environment
An environment in which only one program runs at a time. DOS is a
single-tasking environment.

small
A memory model with only one code segment and only one data segment.

source file
A text file containing symbols that define the program.

source mode
The mode in which CodeView displays the assembly-language source code that
represents the machine code currently being executed.

stack
A dynamically shrinking and expanding area of memory in which data items are
stored consecutively and removed on a last-in, first-out basis. A stack can
be used to pass parameters to procedures.

stack frame
The portion of a stack containing a particular procedure's local variables
and parameters.

stack probe
A short routine called on entry to a function to verify that there is enough
room in the program stack to allocate local variables required by the
function and, if so, to allocate those variables.

stack switching
Changing pointers (usually the SS:SP register) to point to another stack or
stack frame.

stack trace
A symbolic representation of the functions that are being executed to reach
the current instruction address. As a function is executed, the function
address and any function arguments are pushed on the stack. Therefore,
tracing the stack shows the active functions and their arguments.

standard error
The device to which a program can send error messages. The display is
normally standard error.

standard input
The device from which a program reads its input. The keyboard is normally
standard input.

standard output
The device to which a program can send its output. The display is normally
standard output.

statement
A combination of labels, data declarations, directives, or instructions that
the assembler can convert into machine code.

static linking
The combining of multiple object and library files into a single executable
file with all external references resolved. See dynamic linking.

status bar
The line at the bottom of the PWB or CodeView screen. The status bar
displays text position, keyboard status, current context of execution, and
other program information.

STDCALL
A calling convention that uses caller stack cleanup if the VARARG keyword is
specified. Otherwise the called routine must clean up the stack.

string
A contiguous sequence of characters identified with a symbolic name.

string literal
A string of characters and escape sequences delimited by single quotation
marks (' ') or double quotation marks (" ").

structure
A set of elements or fields, which may be of different types, grouped under
a single name.

structure member
One of the elements of a structure. Also called a field.

switch
See option.

symbol
A name that identifies a memory location (usually for data).

symbolic constant
A constant represented by a symbol rather than the constant itself. Symbolic
constants are defined with EQU statements. They make a program easier to
read and modify.

SYSCALL
A language type for a procedure. Its conventions are identical to C's,
except no underscore is prefixed to the name. All OS/2 version 2.0 functions
use the SYSCALL language type.

tag
The name assigned to a structure, union, or enumeration type.

task
See process.

text
Ordinary, readable characters, including the uppercase and lowercase letters
of the alphabet, the numerals 0 through 9, and punctuation marks.

text box
In PWB, a box where you type information needed to carry out a command. A
text box appears within a dialog box. The text box may be blank or contain a
default entry.

tiny
Memory model with a single segment for both code and data. This limits the
total program size to 64K. Tiny programs have the filename extension .COM.

toggle
A function key or menu selection that turns a feature off if it is on, or on
if it is off. Used as a verb, "toggle" means to reverse the status of a
feature.

TOOLS.INI
A file containing initialization information for many of the Microsoft
utilities, including PWB.

two's complement
A form of base-2 notation in which negative numbers are formed by inverting
the bit values of the equivalent positive number and adding 1 to the result.

type
A description of a set of values and a valid set of operations on items of
that type. For example, a variable of type BYTE can have any of a set of
integer values within the range specified for the type on a particular
machine.

type checking
An operation in which the assembler verifies that the operands of an
operator are valid or that the actual arguments in a function call are of
the same types as the function definition's parameters.

type definition
The storage format and attributes for a data unit.

unary expression
An expression consisting of a single operand preceded or followed by a unary
operator.

unary operator
An operator that acts on a single operand, such as NOT.

underflow
An error condition that occurs when a calculation produces a result too
small for the computer to represent.

unhooking (an interrupt)
The act of removing your interrupt handler and restoring the original
vector. See hooking (an interrupt).

union
A set of values (in fields) of different types that occupy the same storage
space.

unresolved external
See unresolved reference.

unresolved reference
A reference to a global or external variable or function that cannot be
found, either in the modules being linked or in the libraries linked with
those modules. An unresolved reference causes a fatal link error.

unsigned integer
A positive binary integer; all its bits represent the magnitude of the
number. See signed integer.

user-defined type
A data type defined by the user. It is usually a structure, union, record,
or pointer.

variable declaration
A statement that initializes and allocates storage for a variable of a given
type.

virtual disk
A portion of the computer's random access memory reserved for use as a
simulated disk drive. Also called an electronic disk or RAM disk. Unless
saved to a physical disk, the contents of a virtual disk are lost when the
computer is turned off.

virtual memory
Memory space allocated on a disk, rather than in RAM. Virtual memory allows
large data structures that would not fit in conventional memory, at the
expense of slow access.

visibility
The characteristic of a variable or function that describes the parts of the
program in which it can be accessed. An item has global visibility if it can
be referenced in every source file constituting the program. Otherwise, it
has local visibility.

watch window
The window in CodeView that displays watch statements and their values. A
variable or expression is watchable only while execution is occurring in the
section of the program (context) in which the item is defined.

window
A discrete area of the screen in PWB or CodeView used to display part of a
file or to enter statements.

window commands
Commands that work only in CodeView's window mode. Window commands consist
of function keys, mouse selections, CTRL and ALT key combinations, and
selections from pop-up menus.

window mode
The mode in which CodeView displays separate windows, which can change
independently. CodeView has mouse support and a wide variety of window
commands in window mode.

word
A data unit containing 16 bits (two bytes). It can store values from 0 to
65,535 (or -32,768 to +32,767).





INDEX
──────────────────────────────────────────────────────────────────────────



@@: (anonymous label)
{ } (brackets)
{} (curly braces)
    structures and unions
:: (double colon)
;; (double semicolon)
« » (index operator)
( ) (parentheses)
/? option, LINK
@ (at sign)

        (at sign);H2INC, used with
        (at sign);HELPMAKE, used with
        (at sign);predefined symbols
 (backslash character)
    MASM code
    NMAKE macros
    PWB macros
: (colon)
$ (current address operator)
$ (dollar sign)
. (dot operator)
" (double quotation marks)
% (expansion operator)
 (line-continuation character)
! (literal-character operator)
+ (plus operator)
? (question mark initializer)
    array elements
    variables
: (segment-override operator)
; (semicolon);comments
; (semicolon);LINK, used with
' (single quotation mark)
. (structure-member operator)
& (substitution operator)
.186 directive
.286 directive
.286P directive
.287 directive
.386 directive
    FLAT, with
    processor mode, specifying
    segment mode, setting
.386P directive
.387 directive
.486 directive
    FLAT, with
    processor mode, specifying
    segment mode, setting
.486P directive
80186 processor
80188 processor
80286 processor
80287 math coprocessor
80386 processor
80387 math coprocessor
80486 processor
.8086 directive
8086-based processors
.8087 directive
8087 math coprocessor
8088 processor
<<<< ra (angle brackets)
    default parameters
    epilogues
    FOR loops
    FORC loops
    macro text delimiters
    prologues
    records
    structures and unions

    A
/A option, LINK
AAA instruction
AAD instruction
AAM instruction
AAS instruction
ABS operand
ADC instruction
ADD instruction
ADDR operator
Address range
Addresses
    base
    constant
    defined
    displacement of
    dynamic
    effective
    errors in
    far
    near
    physical
    registers, loading into
    relocatable
    segmented
Addressing modes
    defined
    direct registers, used in
    indirect registers, used in
    scaling operands
    specifying
Aliases
ALIGN directive
Align types
/ALIGNMENT option, LINK
.ALPHA directive
AND instruction
Angle brackets (<<<< ra)
    default parameters
    epilogues
    FOR loops
    FORC loops
    macro text delimiters
    prologues
    structures and unions
Anonymous label (@@:)
API (Application Program Interface)
Applications
    bound
    dual-mode
    OS/2. See OS/2 applications
Architecture
    segmented
    unsegmented
Arg function, PWB
Arguments
    defined
    mixed-language programs, passing in
    qualifiedtype, with
    stack, on
Arrays
    accessing elements in
    declaring
    defined
    defining
    DUP, declaring with
    instructions for processing
    length of
    multiple-line declarations for
    number of bytes in
    referencing
    size of elements
ASCII
Assembler
Assembly-time variables
Assembly
    actions during
    conditional. See Conditional assembly
    INCLUDE files
    language
    book list
    defined
    mixed-language programs
    listing files. See Listing files
    mode
    two-pass
ASSUME directive
    .MODEL, .STACK, generated with
    code segments, changing
    correct stack, accessing
    enhancements
    general-purpose registers
    segment registers, setting
AT address combine type
/AT command-line option, ML
At sign (@)

    );H2INC, used with
    );HELPMAKE, used with
    );predefined symbols

    B
/B option, LINK
Backslash character ()
    MASM code
    NMAKE macros
    PWB macros
Base Pointer (BP) register
Basic/MASM programs
/BATCH option, LINK
Bias
Binary Coded Decimals
    calculating with
    defined
    defining
    instructions for
    packed
    unpacked
Binary expression
Binary file
Binary operator
BIND utility
    described
    error messages
Bits
    defined
    mask
    rotating
    shifting
BNF grammar
Bound applications
BOUND instruction
BP (Base Pointer) register
Brackets ({ })
.BREAK directive
BSF instruction
BSR instruction
BYTE align type
BYTE directive
Byte

    C
C calling convention
C function prototypes
C header files
C/MASM programs
CALL instruction
Calling conventions
    (list)
    C
    directives, specifying with
    mixed-language programming
    OS/2
    Pascal
    STDCALL
    SYSCALL
CARRY? operand
Case sensitivity
    enforcing
    macro functions, predefined
    MASM statements
    radix specifiers
    reserved words
    specifying
    command-line options, in
    language type
    OPTION directive, in
    symbols, predefined
CASEMAP:ALL argument, OPTION directive
CASEMAP:NONE argument, OPTION directive
CASEMAP:NOTPUBLIC argument, OPTION directive
CATSTR directive
@CatStr predefined symbol
CBW instruction
CDQ instruction
Chaining to interrupts
Character string
CLC instruction
CLI instruction
Client program
CMC instruction
CMP instruction
CMPS instruction
CMPSB instruction
/CO option, LINK
.CODE directive
CODE statement, LINK
Code, near or far
@CodeSize predefined symbol
/CODEVIEW option, LINK
CodeView
    8087 window
    animation
    arrays and strings, viewing
    breakpoints
    C expression evaluator
    calling procedures
    Command window
    command-line arguments
    command-line options (list)
    CURRENT.STS file
    data display format
    data, viewing
Codeview
    data, viewing
CodeView
    debugging techniques
    display mode
    displaying
    dynamic replay
    error messages
    expanded/extended memory
    limitations under OS/2
    live expressions
    Local window
    memory and registers
    Memory window
    multiple windows
    OS/2 programs, compiling
    output screen
    pointers, defining with TYPEDEF
    printing from
    program execution
    Quick Watch command
    Radix command
    redirecting I/O
    Register window
    replaying sessions
    single-stepping
    source mode
    Source window
    status bar
    structures, viewing
    TOOLS.INI file
    Watch window
    windows
    commands
    described
    mode
.COM files
    defined
    initial IP, setting
    relocatable segment expression, lacking
    tiny model, using
Combine types
    (list)
    defined
COMM directive
Command-line driver, ML
Command-line options
    CodeView
    H2INC
    HELPMAKE
    LINK
    listing file options (list)
    ML
    NMAKE
COMMENT directive
Comments
    extended lines, in
    macros, in
    source code, in
COMMON combine type
Communal variables
Compiler
Conditional assembly
    assembly behavior, changing
    conditions, testing for
    directives
    pointers, with
Conditional-error directives (table)
.CONST directive
Constants
    address
    defined
    expressions
    global
    immediate
    integer
    local
    size of
    size
    symbolic
.CONTINUE directive
Coprocessors
    architecture
    control registers
    data format in registers
    defined
    described
    instructions
    arithmetic
    data transfer
    described
    list
    overview
    program control
    memory access
    operand formats
    classical stack
    memory
    overview
    register
    register-pop
    specifying
    status word register
    steps for using
/Cp command-line option, ML
/CP option, LINK
/CPARMAXALLOC option, LINK
@Cpu predefined symbol
Curly braces ({})
    structures and unions, with
Current address operator ($)
@CurSeg predefined symbol
CWD instruction
CWDE instruction

    D
DAA instruction
DAS instruction
.DATA directive
@data predefined symbol
DATA statement, LINK
Data types
    arrays. See Arrays
    attributes for
    Binary Coded Decimals
    CodeView
    defined
    defining
    directives
    floating-point
    initializers, as
    integers, allocating memory for
    new features, MASM 6.0
    qualifiedtypes
    real
    signed
    strings. See Strings
    structures
    TYPEDEF
    unions
    user-defined
Data-sharing methods
Data
    near or far
.DATA? directive
@DataSize predefined symbol
DB directive
DD directive
Debugger
DEC instruction
Default setting or value
Definition
Dependent, description block
DESCRIPTION statement, LINK
Device driver
DF directive
DGROUP group name
    .MODEL, defined by
    DOS programs, for
    DS registers, initializing to
    memory, allocating
    near data, accessing
    OS/2 programs for
    segment
    order
    placement
Direct memory operands
    defined
    loading offset of
    overview
Directives
    .186
    .286
    .286P
    .287
    .386. See .386 directive
    .386P
    .387
    .486. See .486 directive
    .486P
    .8086
    .8087
    .ALPHA
    .BREAK
    .CODE
    .CONST
    .CONTINUE
    .DATA
    .DATA?
    .DOSSEG
    .ELSE
    .ELSEIF
    .ENDIF
    .ENDW
    .ERR
    .ERR1
    .ERR2
    .ERRB
    .ERRDEF
    .ERRDIF
    .ERRE
    .ERRIDN
    .ERRNB
    .ERRNDEF
    .ERRNZ
    .EXIT
    .FARDATA
    .FARDATA?
    .IF
    .LIST
    .LISTMACRO
    .LISTMACROALL
    .MODEL. See .MODEL directive
    .NO87
    .RADIX
    .REPEAT
    .SEQ
    .STACK. See STACK directive
    .STARTUP. See .STARTUP directive
    .UNTIL
    .UNTILCXZ
    .WHILE
    = (equal)
    ALIGN
    ASSUME. See ASSUME directive
    BYTE
    CATSTR
    COMM
    COMMENT
    conditional assembly
    conditional error
    data declarations, for
    data types, for
    DB
    DD
    decision
    defined
    DF
    DQ
    DT
    DW
    DWORD
    ECHO
    ELSE
    ELSEIF
    ELSEIF1
    ELSEIF2
    ELSEIFE
    END
    ENDIF
    ENDS
    EQU
    EVEN
    EXITM
    EXTERN. See EXTERN directive
    EXTERNDEF. See EXTERNDEF directive
    FARDATA
    floating-point
    FOR
    FORC
    FWORD
    GROUP
    IF
    IF1
    IF2
    IFB
    IFDEF
    IFDIF
    IFE
    IFIDN
    IFNB
    IFNDEF
    INCLUDE
    INCLUDELIB
    INSTR
    INVOKE. See INVOKE directive
    LABEL
    LENGTHOF. See LENGTHOF directive
    LOCAL
    loop-generating
    OPTION. See OPTION directive
    ORG
    PAGE
    POPCONTEXT
    PROC
    PROTO. See PROTO directive
    PUBLIC
    PUSHCONTEXT
    QWORD
    REAL10
    REAL4
    REAL8
    renamed in MASM 6.0
    REPEAT
    SBYTE
    SDWORD
    segment order, controlling
    SEGMENT
    SIZEOF. See SIZEOF directive
    SIZESTR
    SUBSTR
    SUBTITLE
    SWORD
    TBYTE
    TEXTEQU. See TEXTEQU directive
    TITLE
    TYPE. See TYPE directive
    TYPEDEF. See TYPEDEF directive
    WHILE
    WORD
Displacement
Distance attributes
DIV instruction
Division
    instructions, with
    shift operations, with
DLLs
    .MODEL, with
    advantages of
    building
    client program
    data segments, changing
    defined
    example
    exporting
    FARSTACK
    floating-point operations
    generating
    IMPLIB
    initialization code
    linking
    module attributes
    module-definition files
    NEARSTACK
    programming requirements
    re-entrance
    segments in
    stacks in
    termination code
    using
/DO option, LINK
Document conventions
Dollar sign ($)
DOS applications, differences from OS/2 applications
DOS Interrupts
DOS operating system
.DOSSEG directive
/DOSSEG option, LINK
Dot operator (.)
DOTNAME argument, OPTION directive
Double colon (::)
Double quotation marks (")
Double semicolon (
    ;)
Doublewords
DQ directive
/DS option, LINK
/DSALLOCATE option, LINK
DT directive
Dual-mode applications
Dump, memory
DUP operator
    arrays, with
    record variables, with
    structures and unions, with
DW directive
DWORD align type
DWORD directive
Dynamic linking
    defined
    run-time
Dynamic-link routines

    E
/E option, LINK
80186 processor
80188 processor
80286 processor
80287 math coprocessor
80386 processor
80387 math coprocessor
80486 processor
.8086 directive
8086-based processors
.8087 directive
8087 math coprocessor
8088 processor
ECHO directive
ELSE directive
.ELSE directive
ELSEIF directive
.ELSEIF directive
EMULATOR argument, OPTION directive
Emulator libraries
Encoding options, HELPMAKE
END directive
ENDIF directive
.ENDIF directive
ENDS directive
.ENDW directive
ENTER instruction
Environment
    block
    target
    variables
    INCLUDE
    LINK
    returning values of
/EP command-line option, ML
EPILOGUE argument OPTION directive
EPILOGUE argument, OPTION directive
Epilogue code
    defined
    macros
    PROC statement, specifying arguments in
    procedures, with
    RET instruction
    standard
    user-defined
EQU directive
Equal directive (=)
.ERR directive
.ERRB directive
.ERRDEF directive
.ERRDIF directive
.ERRE directive
.ERRIDN directive
.ERRNB directive
.ERRNDEF directive
.ERRNZ directive
Error messages
    BIND
    CodeView
    EXEHDR
    H2INC
    HELPMAKE
    IMPLIB
    LIB
    LINK
    ML
    NMAKE
    overview
    PWB
    PWBRMAKE
ERROR operand
Errors
    general-protection fault
    run-time
    standard
EVEN directive
Executable (.EXE) files
    controlling size of
    defined
EXEHDR utility
    described
    error messages
/EXEPACK option, LINK
EXETYPE statement, LINK
Exit codes
    applications with
    defined
    LINK
    NMAKE
.EXIT directive
EXITM directive
Expansion operator (%)
EXPORT operand
EXPORTS statement, LINK
EXPR16 argument, OPTION directive
EXPR32 argument, OPTION directive
Expressions
    assembly-time evaluation
    binary
    constant
    defined
    immediate
    loop conditions, evaluating
    OPTION M510 behavior
    order of evaluation
    regular
    size
    unary
    word size
Extension, filename
EXTERN directive
    data-sharing
    executable file size, limiting
    module-specific
    overview
    positioning
    procedure prototypes, declaring
External declarations
External variables
EXTERNDEF directive
    data-sharing
    H2INC, generated by
    overview
    positioning
    procedure prototypes, declaring
    symbols, declaring

    F
/F, option, LINK
.486 directive
    FLAT, with
    processor mode, specifying
    segment mode, setting
.486P directive
Family API (Application Program Interface)
Far address
Far code
Far data
FAR operator
Far pointer
/FARCALLTRANSLATION option, LINK
.FARDATA directive
.FARDATA? directive
FARSTACK operand
    DOS program, initializing
    example
    grouping
    OS2 program, initializing
    special cases, setting for
Farwords
FCOM instruction
Fields
    defined
    statements, in
Files
    .COM
    defined
    initial IP, setting
    relocatable segment expression, lacking
    tiny model, using
    .EXE
    .LIB
    .OBJ
    base name
    binary
    executable
    extensions
    line numbers
    naming
    object
    source
First pass listings
Fixup
/Fl command-line option, ML
Flags
    CARRY?
    operands, as
    OVERFLOW?
    PARITY?
    SIGN?
    stack, saving on
    ZERO?
FLAT operand
FLD1 instruction
FLDZ instruction
Floating-point
    calculations
    constants
    decimal form
    encoded hexadecimal format
    syntax for defining
    emulation
    instructions
    arithmetic
    controlling
    data transfer
    not emulated (list)
    program control
    operations
    values
    double precision
    single precision
    variables
    .MSFLOAT format
    IEEE format
    Microsoft binary format
    ranges
FOR directive
FORC directive
FORCEFRAME operand
Formal parameters
FORTRAN/MASM programs
Forward declaration
/Fpi command-line option, ML
Frame
FS register
FTST instruction
Full segment definitions
    described
    segment registers, initializing
    segments, specifying
    using
Functions, Arg
FWORD directive
FXCH instruction

    G
General-Protection (GP) fault
Gigabyte
Global
    constant
    data segment
    variables
Granularity
GROUP directive
Groups
    defined
    DGROUP
    GROUP directive
    linking procedures, used in
    SEG operator, returned by
GS register

    H
H2INC
    C data types (list)
    command-line options (lists)
    converting
    C bit fields
    C enumerations
    C type definitions
    comments
    constants
    function prototypes
    nested structures
    pointers
    records
    structures
    unions
    variables
    error messages
    fastcall
    function prototypes, writing
    naming considerations
    overview
    predefined constants (list)
    syntax
    type definitions
Handle
/HE option, LINK
HEAPSIZE statement, LINK
Help delimiter (ra)
/HELP option, LINK
HELPMAKE
    command-line options (lists)
    error messages
    file formats
    minimally formatted ASCII
    QuickHelp format
    Rich Text Format (RTF)
    unformatted ASCII
    help database
    creating
    formats
    help files
    context prefixes
    local contexts
    organizational conventions
    overview
    structure
    hyperlinks
    creating
    defined
    Microsoft product context prefixes (list)
    options
    decoding (list)
    encoding (list)
    help (list)
    QuickHelp
    cross-references
    dot commands (list)
    example
    format
    formatting flags (list)
    standard .h contexts (list)
    syntax
Hexadecimal
/HI option, LINK
HIGH operator
/HIGH option, LINK
High-level language
HIGHWORD operator
Hooking (an interrupt)

    I
/I command-line option, ML
Identifiers
    ABS, using
    defined
    naming restrictions
    % character
    dot operator (.)
    length
    OPTION DOTNAME
    OPTION NOKEYWORD
IDIV instruction
IEEE format
IF directive
.IF directive
IFB directive
IFDEF directive
IFDIF directive
IFE directive
IFIDN directive
IFNB directive
IFNDEF directive
Immediate operands
IMPLIB utility
    described
    error messages
Import libraries
IMPORTS statement, LINK
IMUL instruction
IN instruction
INC instuction
/INC option, LINK
INCLUDE directive
INCLUDE environment variables
Include files
    assembling
    defined
    nested
    overview
INCLUDELIB directive
/INCREMENTAL option, LINK
Index operator ({ })
Indirect memory operands
/INF option, LINK
Inference rules, NMAKE
/INFORMATION option, LINK
Initializers
    allocating
    directives for
    multiple-line
INSTR directive
@InStr predefined symbol
Instruction Pointer (IP) register
Instructions
    (list)
    AAA
    AAD
    AAM
    AAS
    ADC
    ADD
    AND
    arithmetic
    bit-test
    BOUND
    BSF
    BSR
    CALL
    CBW
    CDQ
    CLC
    CLI
    CMC
    CMP
    CMPS
    CMPSB
    conditional-jump
    coprocessor
    CWD
    CWDE
    DAA
    DAS
    DEC
    default segments, requiring
    defined
    DIV
    encodings, changes to
    ENTER
    ESC
    FCOM
    FLD1
    FLDZ
    floating-point. See Floating-point, instructions
    FTST
    FXCH
    IDIV
    IMUL
    IN
    INC
    INT
    INTO
    JCXZ
    JECXZ
    JMP
    JO
    jump
    LAHF
    LDS
    LEA
    LEAVE
    LES
    LOCK
    LODS
    logical
    LOOP
    LOOPE
    LOOPNE
    LOOPNZ
    LOOPZ
    MOV
    MOVS
    MOVSX
    MOVZX
    MUL
    NOP
    NOT
    obsolete
    operands for
    OR
    OUT
    POP
    POPA
    POPAD
    POPF
    POPFD
    privileged
    PUSH
    PUSHA
    PUSHAD
    PUSHF
    PUSHFD
    RCL
    RCR
    REP
    REPE
    REPNE
    REPNZ
    REPZ
    RET. See RET instruction
    RETF
    RETN
    ROL
    ROR
    SAL
    SAR
    SBB
    SCAS
    SHL
    SHR
    STC
    STI
    STOS
    SUB
    TEST
    XCHG
    XLAT
    XLATB
    XOR
INT instruction
Integers
    adding
    allocating memory for
    Binary Coded Decimals (BCD)
    bit operations on
    constants, defining
    dividing
    exchanging
    hexadecimal
    initializing
    memory format
    moving
    multiplying
    operations with
    popping off stack
    pushing onto stack
    radix specifiers for
    sign-extending
    signed
    size of
    stack
    subtracting
    translating
    types, defining
    unsigned
    value range
@Interface predefined symbol
Interrupt descriptor table
Interrupt handler
Interrupt vector
Interrupt-enable flag
Interrupts
    chaining to
    CLI instruction
    defined
    INT instruction
    operation
    overview
    redefining
    routines
    STI instruction
    unhooking
INTO instruction
INVOKE directive
    actions
    ADDR, invoking
    arguments, widening
    error detection
    far addresses, invoking
    generated code, checking
    indirect procedure calls
    mixed-language programs
    OS/2 system calls
    procedures, calling
    type conversions
IRET instruction

    J
JCXZ instruction
JECXZ instruction
JMP instruction
JO instruction
Jumps
    anonymous
    automatic
    conditional
    bit status
    comparisons
    extending
    flag status
    instructions (list)
    overview
    directives for
    extension, automatic
    instructions
    optimization, automatic
    overview
    unconditional
    indirect operands
    jump tables
    overview

    K
Keywords
Kilobyte

    L
LABEL directive
Labels
    anonymous
    code
    length
    OPTION M510 behavior
    OPTION NOSCOPED
    procedures, in
    referencing
    size
    visibility
    defined
LAHF instruction
LANGUAGE argument, OPTION directive
Language attributes
    .MODEL directive, with
    OPTION directive, with
LANGUAGE:BASIC argument, OPTION directive
LANGUAGE:C argument, OPTION directive
LANGUAGE:FORTRAN argument, OPTION directive
LANGUAGE:PASCAL argument, OPTION directive
LANGUAGE:STDCALL argument, OPTION directive
LANGUAGE:SYSCALL argument, OPTION directive
LDS instruction
LEA instruction
LEAVE instruction
LENGTH operator
LENGTHOF directive
    number of items, returning
    structures, defining
    unions, with
LES instruction
/LI option, LINK
LIB utility, error messages
Libraries
    defined
    emulator
    import
    linking. See LINK, specifying libraries
    overview
    source files, specifying in
Library files
LIBRARY statement, LINK
Line-continuation character
/LINENUMBERS option, LINK
LINK
    alignment types
    combine types
    command-line options
    command-line options. See also individual entries
    DOS executables, producing
    environment variable
    error messages
    exit codes (list)
    groups
    libraries, specifying
    module-definition files. See Module-definition files
    object file search order
    output files
    overlays under DOS
    overview
    prompts
    PWB, invoking in
    response files
    running
    syntax
    temporary files
Linked list
Linking
    actions during
    defined
    dynamic
    segment order in
    static
.LIST directive
Listing files
    .LIST
    .LISTMACRO
    .LISTMACROALL
    code generated
    command-line options
    directives
    error messages
    examples
    first pass
    generating
    options (list)
    page format, controlling
    PAGE
    PWB options
    reading
    SUBTITLE
    symbols used in (list)
    tables in
    TITLE
.LISTMACRO directive
.LISTMACROALL directive
Literal-character operator (!)
LJMP argument, OPTION directive
LOADDS operand
Loading, actions during
Local constants
LOCAL directive
Local variables
    creating
    defined
    loading addresses of
    procedures, in
Local window, CodeView
LOCK instruction
LODS instruction
Logical device
Logical instruction
Logical line
Lookup tables
LOOP instruction
LOOPE instruction
LOOPNE instruction
LOOPNZ instruction
Loops
    conditions
    expression evaluation
    precedence
    PTR operator in
    relational operators for (list)
    signed operands
    writing
    controlling
    .BREAK
    .CONTINUE
    directives that generate
    .REPEAT
    .WHILE
    instructions (list)
    macros
    FOR
    FORC
    REPEAT
    WHILE
LOOPZ instruction
LOW operator
LOWWORD operator
LROFFSET operator

    M
/M option, LINK
M510 argument, OPTION directive
    compatibility with MASM 5.1
    expression word size, setting
    macro behavior
    structures, with
Machine code
Macros
    .LISTMACRO
    .LISTMACROALL
    arguments
    commas
    quotation marks
    calling
    checking argument types with
    comments (;;)
    defined
    expansion
    functions
    defined
    epilogues
    EXITM
    prologues
    returning values
    listing file directives
    local symbols in
    loops
    FOR
    FORC
    REPEAT
    WHILE
    MASM 5.1 behavior
    nested
    new features
    NMAKE. See NMAKE, macros
    operators
    (list)
    behavior in macro functions
    expansion (%)
    literal-character (!)
    substitution (&)
    OPTION OLDMACROS
    parameters
    default values
    procedure parameters, compared to
    required
    substitution
    passing arguments to
    predefined string functions
    procedures
    defined
    functions, compared to
    PWB. See PWB macros
    recursive
    redefining
    string operations
    text
    defined
    forward referencing
    numeric equates, compared to
    OPTION M510 behavior
    VARARG keyword
    writing
Mantissa
Map files, creating
/MAP option, LINK
MASK operator
Mask
    defined
    logic instructions, with
    record operators, with
MASM 5.1 compatibility
    address fixups
    macro behavior
    OPTION directive, specifying
    overview
    structures
    updating code
MASM utility
Megabyte
Members
MEMORY combine type
Memory models
    attributes
    compact
    default segment names (list)
    defined
    described
    determining
    far code segments
    far data segments
    flat
    huge
    large
    medium
    model-independent code
    near code segments
    small
    specifying in PROC statement
    tiny
Memory window, CodeView
Memory
    access, dynamic
    address
    allocation
    dump
    expanded
    extended
    map
    operand
    physical
    shared
    virtual
Meta function, PWB
Microsoft Advisor
Minus operator (-)
Mixed-language programming
    argument passing
    assembly procedures
    Basic/MASM programs
    C prototypes, converting with H2INC
    C/MASM programs
    calling conventions
    (list)
    Basic
    C
    FORTRAN
    Pascal
    STDCALL
    SYSCALL
    column-major order
    compatible data types
    Basic (list)
    C (list)
    FORTRAN (list)
    Pascal (list)
    QuickPascal (list)
    external data
    FORTRAN/MASM programs
    initialization code
    INVOKE, using
    naming conventions
    overview
    Pascal/MASM programs
    QuickPascal/MASM programs
    register preservation
    row-major order
ML
    Command-line options
    /AT
    /Cp
    /EP
    /Fl
    /Fpi
    /I
    /SG
    /X
    /Zm
    /Zp
    overview
    error messages
Mnemonic
.MODEL directive
    attributes
    DGROUP
    language types, specifying
    memory model, defining
    mode default
    operating system, specifying
    overview
    positioning
    simplified segment directives
    stack type, specifying
@model predefined symbol
@Model predefined symbol
Module statements
Module-definition files
    described
    DLLs, with
    module statements (list)
    OS/2 applications
    overview
    reserved words (list)
    rules for
    search order, LINK
    statements
    CODE
    DATA
    DESCRIPTION
    EXETYPE
    EXPORTS
    HEAPSIZE
    IMPORTS
    LIBRARY
    NAME
    OLD
    PROTMODE
    REALMODE
    SEGMENTS
    STACKSIZE
    STUB
    syntax
Module-level code
Modules
Modules, main
MOV instruction
MOVS instruction
MOVSX instruction
MOVZX instruction
MUL instruction
Multiple-module programs
    alternatives to include files, using
    COMM, using
    data-sharing methods, selecting
    declaring symbols public and external
    EXTERN with library routines, using
    external declarations, positioning
    EXTERNDEF, using
    include files, assembling
    libraries, developing
    modules, organizing
    PROTO, using
    PUBLIC and EXTERN, using
    sharing symbols with include files
Multiplex interrupt
Multiplication
    instructions, with
    shift operations, with
Multitasking operating system

    N
NAME statement, LINK
Naming conventions
    (list)
    defined
    directives, specifying with
    mixed-language programming
    OPTION M510 behavior
    OS/2 system calls
Naming restrictions
NAN (Not A Number)
NEAR operator
NEARSTACK operand
    ASSUME statement, with
    default stack type, as
    described
    OS/2, with
New features, MASM 6.0
NMAKE
    command file
    command-line options (table)
    description files
    command modifiers (table)
    comments in
    creating
    described
    directives in
    filename components, extracting
    inference rules in
    macros in
    macros
    multiple description blocks in
    predefined inference rules (list)
    preprocessing directives, executing with
    pseudotargets in
    sample
    special characters in
    error messages
    exit codes, using with
    inline files
    macros
    command (list)
    filename (list)
    multiple-line
    options (list)
    recursive (list)
    special
    user-defined
    MAKE, differences from
    NMK, using
    overview
    sequence of operations
    syntax
    TOOLS.INI, customizing
.NO87 directive
/NOD option, LINK
/NODEFAULTLIBRARYSEARCH, option, LINK
NODOTNAME argument, OPTION directive
/NOE option, LINK
NOEMULATOR argument, OPTION directive
/NOEXTDICTIONARY option, LINK
/NOF option, LINK
/NOFARCALLTRANSLATION option, LINK
/NOG option, LINK
/NOGROUPASSOCIATION option, LINK
/NOI option, LINK
/NOIGNORECASE option, LINK
NOKEYWORD argument, OPTION directive
    identifiers
    label names
    symbol names
/NOL option, LINK
NOLJMP argument, OPTION directive
/NOLOGO option, LINK
NOM510 argument, OPTION directive
/NON option, LINK
/NONULLSDOSSEG option, LINK
NONUNIQUE operand
NOOLDMACROS argument, OPTION directive
NOOLDSTRUCTS argument, OPTION directive
/NOP option, LINK
/NOPACKCODE option, LINK
NOREADONLY argument, OPTION directive
NOSCOPED argument, OPTION directive
NOSIGNEXTEND argument, OPTION directive
NOT instruction
NOTHING operand
Null characters
Null pointers
Numeric equates, compared to text macros

    O
/O option, LINK
.186 directive
Object files
OFFSET operator
OFFSET:FLAT argument, OPTION directive
OFFSET:GROUP argument, OPTION directive
OFFSET:SEGMENT argument, OPTION directive
Offsets
    accessing data with
    addresses
    defined
    described
    determining
    fixups for
OLD statement, LINK
OLDMACROS argument, OPTION directive
OLDSTRUCTS argument, OPTION directive
    MASM 5.1 compatibility
    structures, with
OPATTR operator
Opcode
Operands
    ABS
    defined
    direct memory
    FAR
    immediate
    indirect memory
    memory
    NEAR
    register
    registers
    size
    USE16
    USE32
Operating systems
    .MODEL, specifying with
    multitasking
    OS_DOS, OS_OS2, specifying
    types. See DOS, OS/2 operating systems
Operators
    .TYPE
    ADDR
    binary
    current address ($)
    defined
    dot (.)
    DUP. See DUP operator
    EQ
    expansion (%)
    expressions, in
    FAR
    HIGH
    HIGHWORD
    index(« »)
    instructions, compared to
    LENGTH
    literal-character (!)
    LOW
    LOWWORD
    LROFFSET
    macro
    MASK
    minus (-)
    NE
    NEAR
    OFFSET
    OFFSET. See OFFSET operator
    OPATTR
    plus (+)
    precedence
    PTR. See PTR operator
    relational (list)
    relational
    SEG
    segment-override (:)
    SHORT
    SIZE
    SIZEOF
    structure-member (.)
    substitution (&)
    TYPE
    unary
    WIDTH
OPTION directive
    CASEMAP
    described
    DOTNAME
    emulation mode
    EMULATOR
    EPILOGUE
    EXPR16. See EXPR16 argument, OPTION directive
    EXPR32. See EXPR32 argument, OPTION directive
    language types, specifying
    LANGUAGE
    list of arguments for
    LJMP
    M510. See M510 argument, OPTION directive
    NODOTNAME
    NOEMULATOR
    NOKEYWORD. See NOKEYWORD argument, OPTION directive
    NOLJMP
    NOM510
    NOOLDMACROS
    NOOLDSTRUCTS
    NOREADONLY
    NOSCOPED
    NOSIGNEXTEND
    OFFSET
    OLDMACROS
    OLDSTRUCTS. See OLDSTRUCTS argument, OPTION directive
    PROC
    procedure use
    PROLOGUE
    READONLY
    SCOPED
    using
Options
OR instruction
Ordinal position
ORG directive
OS/2 applications
    binding
    building
    calling convention
    differences from DOS applications
    DosExit, using
    example
    FARSTACK, using
    INCLUDELIB, using
    INVOKE, using
    NEARSTACK, using
    OS2.LIB, using
    overview
    register initialization
    segment selectors
    system calls
    target processors
OS/2 operating system
OS/2 system calls
OS2.INC
OS2.LIB
OS_DOS operand
OS_OS2 operand
OUT instruction
Overflow
OVERFLOW? flag
Overlay
/OVERLAYINTERRUPT option, LINK

    P
/PACKC option, LINK
/PACKCODE option, LINK
/PACKD option, LINK
/PACKDATA option, LINK
/PADC option, LINK
/PADCODE option, LINK
/PADD option, LINK
/PADDATA option, LINK
PAGE align type
PAGE directive
PARA align type
Parameters
Parentheses «( )»
PARITY? operand
Pascal calling convention
Pascal/MASM programs
Passing by reference
Passing by value
/PAU option, LINK
/PAUSE option, LINK
Physical line
Physical memory
Plus operator (+)
/PM option, LINK
/PMTYPE option, LINK
Pointer variables
Pointers
    accessing data with
    arguments, as
    copying
    defined
    far
    H2INC, translated by
    initializing
    location
    null
    operations
    TYPEDEF, defined with
    types, to
    variable
POP instruction
POPA instruction
POPAD instruction
POPCONTEXT directive
POPF instruction
POPFD instruction
Precedence
    defined
    operators
Predefined functions for macros
Predefined string functions

    CatStr
    InStr
    SizeStr
    SubStr
Predefined symbols
    (list)

    Codesize
    Cpu
    CurSeg
    data
    Datasize
    Interface
    Model
    stack
    Wordsize
    case sensitivity
    new to MASM 6.0 (list)
Preemptive
Prefix
PRIVATE combine type
PRIVATE operand
Private
Privilege levels
Privileged mode
Problems, reporting
PROC directive
PROC:EXPORT argument, OPTION directive
PROC:PRIVATE argument, OPTION directive
PROC:PUBLIC argument, OPTION directive
Procedures definition
Procedures
    arguments
    far pointers
    near addresses
    passing
    pointers
    type conversions
    CALL instruction
    calls
    defined
    indirect
    optimizing
    defining
    epilogues
    EXTERNDEF directive
    include files, in
    INVOKE directive
    libraries
    local variables
    macro. See Macros, procedures
    new features
    OPTION PROC
    overview
    parameters
    declaring
    variable numbers of
    PROC attributes, specifying
    prologues
    PROTO directive
    prototypes
    defined
    writing
    reentrant
    RET instruction
    RETF instruction
    RETN instruction
    syntax description
    VARARG keyword
    visibility
Process
Processors
    .MODEL directive
    8086-based
    modes, determining
    target
Product assistance
Program Segment Prefix (PSP)
Programming, MASM 6.0 practices
Programs
    exiting
    mixed-language
    multiple-module. See Multiple-module programs
    starting
PROLOGUE argument, OPTION directive
Prologue code
    arguments, specifying
    code labels in
    defined
    macros for
    standard
    user-defined
Protected mode
    defined
    described
PROTMODE statement, LINK
PROTO directive
    H2INC, generated by
    include file, in
    procedure prototypes, defined with
    procedure prototypes, writing
Prototypes
    H2INC, converted by
    procedure
    defined
    directives for
    overview
    qualifiedtypes, defined with
PTR operator
    example
    OPTION M510 behavior
    pointer to type, as
    signed number, specifying
    size, of
    size, specifying
    TYPEDEF, used with
PUBLIC combine type
PUBLIC directive
Public
PUSH instruction
PUSHA instruction
PUSHAD instruction
PUSHCONTEXT directive
PUSHF instruction
PUSHFD instruction
PWB
    arg function
    editor options
    error messages
    extensions, loading
    key assignments
    macros
    arguments
    conditional (list)
    interactive
    overview
    recording
    response operators (list)
    syntax
    temporary
    meta function
    options, setting
    pseudofile
    regular expressions
    status bar
    text box
    TOOLS.INI
    feature or function, changing
    macros, writing
    switches, setting
PWBRMAKE utility, error messages

    Q
/Q option, LINK
Quadwords
Qualifiedtypes
    BNF grammar, defined by
    defined
    pointers, defining
    prototypes, as
    rules for use
    where to use
Question mark initializer ( ? )
    array elements
    variables
QuickHelp
    cross-references
    dot commands (list)
    example
    format. See HELPMAKE, QuickHelp format
    formatting flags (list)
/QUICKLIBRARY option, LINK
QuickPascal/MASM programs
Quotation marks (' or ")
QWORD directive

    R
ra (help delimiter)
.RADIX directive
Radix specifiers
    (list)
    OPTION M510 behavior
Radix
Range, address
RCL instruction
RCR instruction
Re-entrant DLL
Read-only code
READONLY argument, OPTION directive
READONLY operand
Real mode
    defined
    described
REAL10 directive
REAL4 directive
REAL8 directive
REALMODE statement, LINK
Records
    defined
    field ranges
    H2INC, generated by
    LENGTH operator
    LENGTHOF directive
    MASK operator
    SIZEOF directive
    syntax
    TYPE directive
    WIDTH operator
Recursive macros
Reentrant procedure
Register operands
Register window, CodeView
Registers
    (list)
    16-bit
    base
    coprocessor
    copying pairs of
    defined
    division (table)
    Eflags
    extended
    flags
    FS
    general purpose
    GS
    index
    indirect addressing
    indirect operands
    initializing
    Instruction Pointer. See Instruction Pointer (IP) registers
    loading addresses into
    mixed 16-bit, 32-bit
    pointers as
    scaling
    segments. See Segment registers
    Stack Pointer (SP)
    Stack Segment (SS)
    stack, saving on
    types, defined with ASSUME
Relational operators (list)
Relocatable
    addresses
    data
    defined
    expressions
REP instruction
REPE instruction
Repeat blocks
.REPEAT directive
REPEAT directive
REPNE instruction
REPNZ instruction
Reporting problems
REPZ instruction
Reserved words
    (list)
    described
    OPTION M510 behavior
    OPTION NOKEYWORD
Response files, LINK
RET instruction
    epilogue code, generating
    instruction encodings, changes to
    PROC, with
RETF instruction
RETN instruction
Return values
ROL instruction
ROR instruction
Rotate instructions
Routines
    defined
    dynamic-link
    interrupt
    low-level I/O
Run-time error

    S
SAL instruction
SAR instruction
SBB instruction
SBYTE directive
Scaling factor
Scaling index registers
SCAS instruction
SCAS Instruction
Scope
SCOPED argument, OPTION directive
Screen swapping
Scroll bars
SDWORD directive
/SE option, LINK
SEG operator
Segment arithmetic
SEGMENT directive
Segment registers
    assigning
    ASSUME directive
    changing
    default
    described
    DOS, under
    FS
    GS
    initializing
    near code
    OS/2, under
    restoring
    segment-override operator (:)
Segment selectors
Segment-override operator (:)
SEGMENT:FLAT argument, OPTION directive
SEGMENT:USE16 argument, OPTION directive
SEGMENT:USE32 argument, OPTION directive
Segmented architecture
/SEGMENTS option, LINK
SEGMENTS statement, LINK
Segments
    32-bit
    accessing data with
    addresses
    aligning
    alignment types
    attributes
    class names
    class types
    code
    creating
    far
    memory model support for
    near
    combine types
    combining
    current
    data
    creating
    default
    far
    global
    memory model support for
    near
    default names for (list)
    defined
    defining. See full segment definitions, simplified segment directives
    described
    determining order of
    determining position of
    determining size of
    fixups for
    full segment definitions, defining
    groups, defining
    initializing
    location of
    naming
    order
    ordering with the linker
    physical
    protection
    READONLY
    selector
    simplified segment directives, defining
    size, determining
    types
    USE16
    USE32
    values
    word size, setting
Selector
Semicolon (
    );comments
    );LINK, used with
.SEQ directive
Sequential mode
Shell escape, CodeView
Shift instructions
SHL instruction
SHORT operator
SHR instruction
Sign extended
Sign-extending integers
SIGN? operand
Signed data
Simplified segment directives
    .MODEL, defining with
    code segments, creating
    code, starting and ending
    data segments, creating
    described
    language convention, choosing
    memory model, defining
    operating system, specifying
    processor, specifying
    segment registers, initializing
    stack distance, setting
    stack, creating
    using
Single quotation mark (')
Single-tasking environment
Size attribute, segments
    FLAT
    USE16
    USE32
SIZEOF directive
    arrays, with
    records, with
    strings, with
    structures, with
    unions, with
SIZEOF operator
SIZESTR directive
@SizeStr predefined symbol
Source code, statements in
Source mode, CodeView
Source window, CodeView
SP (Stack Pointer) register
SS (Stack Segment) register
/ST option, LINK
STACK combine type
.STACK directive
    ASSUME
    described
    segment registers, setting
Stack distance
Stack frame
/STACK option, LINK
Stack Pointer (SP) register
@stack predefined symbol
Stack Segment (SS) register
STACK
Stacks
    creating
    defined
    described
    distance, specifying
    far
    FARSTACK
    local variables on
    near
    NEARSTACK
    operations with
    operators with
    passing arguments on
    pointer
    POP instructions
    probe
    PUSH instructions
    saving flags on
    saving registers on
    segment register
    separate
    switching
    trace
    variables. See Local variables
STACKSIZE statement, LINK
Standard error
Standard input
Standard output
.STARTUP directive
    described
    initializing segments
    program, starting
    segment address
Startup routine
Statements
    case sensitivity
    defined
    module
    defined
    listed
    rules for
    syntax
Status flags, saving
STC instruction
STDCALL calling convention
STI instruction
STOS instruction
String literal
Strings
    $-terminated
    character
    compatibility with high-level languages
    declaring
    defined
    defining
    directives for manipulating
    initializing
    instructions
    processing, for
    requirements (table)
    length of
    length-specified
    multiple-line declarations for
    null-terminated
    overview
    predefined functions for macros
    predefined functions for macros. See also Predefined string functions
    register pairs, with
    size of
    type of
STRUCT directive
Structure-member operator (.)
Structures
    alignment of fields
    array initializers
    arrays
    compatibility with MASM 5.1
    current address operator ($)
    default field values
    defined
    fields, accessing
    fields, initializing
    fields, naming
    fields
    naming
    H2INC, generated by
    initializers, as
    LENGTHOF directive
    MASM 5.1 behavior
    members
    memory allocation for
    nested
    new features
    OPTION M510 behavior
    OPTION OLDSTRUCTS
    redefinition of
    referencing fields in
    SIZEOF directive
    steps for using
    string initializers
    syntax
    types, declaring
    variables, defining
    TYPE directive
STUB statement, LINK
SUB instruction
Substitution operator (&)
SUBSTR directive
@SubStr predefined symbol
SUBTITLE directive
SWORD directive
Symbol table, listing files
Symbols
    declaring public and external
    defined
    external
    naming
    predefined
Syntax, MASM 6.0 statements
SYSCALL calling convention
System date
System time

    T
/T option, LINK
.286 directive
.286P directive
.287 directive
.386 directive
    FLAT, with
    processor mode, specifying
    segment mode, setting
.386P directive
.387 directive
Tables, lookup
Tags
Target environment
TBYTE directive
TEST instruction
Text
TEXTEQU directive
    aliases
    CATSTR, compared with
    H2INC, generated by
/TINY option, LINK
TITLE directive
Toggle
TOOLS.INI
    CodeView
    defined
    NMAKE
    PWB
Trap flag
TSRs
    active
    described
    DOS functions, calling
    DOS functions, interrupting
    interrupt handlers in
    deinstalling
    described
    DOS internal stacks (lists)
    errors, trapping
    examples
    ALARM.ASM
    SNAP.ASM
    existing data, preserving
    hardware events, auditing
    interrupt handlers
    monitoring
    Critical Error flag
    system status
    multiplex interrupt
    passive
    segmented addresses, with
Type checking
Type definition
TYPE directive
    arrays, with
    records, with
    string, with
    structures, with
    unions, with
.TYPE operator
TYPE operator
TYPEDEF directive
    aliases, created by
    BNF, from
    CodeView information for
    data types, defining
    H2INC, generated by
    indirect operands, defining
    pointers, defined by
    procedure declarations, for
    procedure prototypes
    qualifiedtypes
Types

    U
Unary expression
Unary operator
Unconditional jumps, optimizing
Underflow
Unhooking interrupts
Unions
    arrays as initializers
    arrays of
    defined
    fields
    H2INC, generated by
    LENGTHOF directive
    memory allocation
    nested
    referencing fields in
    SIZEOF directive
    steps for using
    strings as initializers
    TYPE directive
    types, declaring
    variables, defining
Unpacked BCD numbers
Unresolved reference
Unsegmented architecture
.UNTIL directive
.UNTILCXZ directive
USE16 operand
USE32 operand
User-defined types
USES in PROC statement
Utilities
    BIND
    EXEHDR
    H2INC
    HELPMAKE
    IMPLIB
    LINK
    MASM
    ML
    NMAKE
    NMK

    V
VARARG keyword
    macros
    macros, used in
    procedures, used with
Variable declaration
Variables
    assembly-time
    communal
    environment
    external
    floating-point
    global
    initializing
    integers, allocating memory for
    local address, loading
    local. See Local variables
    naming restrictions
    pointer. See Pointer variables
    stack. See Local variables
Virtual disk
Virtual memory
Visibility
    defined
    PROC statement
    scope, within

    W
/W option, LINK
/WARNFIXUP option, LINK
Watch window, CodeView
.WHILE directive
WHILE directive
WIDTH operator
Windows
    commands
    defined
    Local
    manipulating
    Memory
    multiple
    programming
    Register
    Source
    Watch
WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML


WORD align type
WORD directive
Word size
    default
    expressions, in
Word
@WordSize predefined symbol

    X
/X command-line option, ML
XCHG instruction
XLAT instruction
XLATB instruction
XOR instruction

    Z
ZERO? operand
/Zm command-line option, ML
/Zp command-line option, ML