Vba excel если ошибка то выполнить

Обработка ошибок в VBA Excel с помощью оператора On Error. Синтаксис выражений с оператором On Error. Пример кода с простым обработчиком ошибок.

On Error – это оператор, который используется для отслеживания ошибок во время исполнения кода VBA. При возникновении ошибки On Error передает информацию о ней в объект Err и включает программу обработки ошибок, начинающуюся с указанной строки.

В первую очередь, обработчик ошибок нужен для пользователей файлов Excel с кодами VBA. Любая ошибка приводит к прекращению выполнения программы, открытию редактора VBA с непонятным для пользователя сообщением или даже к полному зависанию приложения.

Обработчик ошибок позволяет завершить выполнение программы при возникновении ошибки и вывести сообщение пользователю с ее описанием.

Синтаксис выражений с On Error

Включает алгоритм обнаружения ошибок и, в случае возникновения ошибки, передает управление операторам обработчика ошибок с указанной в выражении строки. Stroka – это метка, после которой расположены операторы обработчика ошибок.

Включает алгоритм обнаружения ошибок и, в случае возникновения ошибки, передает управление оператору, следующему за оператором, вызвавшем ошибку.

Отключает любой включенный обработчик ошибок в текущей процедуре.

Простой обработчик ошибок

Шаблон простейшего обработчика ошибок:

Sub Primer() On Error GoTo Stroka     ‘Блок операторов процедуры Exit Sub Stroka:     MsgBox «Произошла ошибка: « & Err.Description End Sub

Оператор On Error GoTo размещается в начале процедуры, метка и обработчик ошибок – в конце процедуры. Название метки можно сменить на другое, в том числе на кириллице.

Оператор Exit Sub обеспечивает выход из процедуры, если блок операторов выполнен без ошибок. Для вывода описания ошибки используется свойство Description объекта Err.

Примеры обработки ошибок

Пример 1
Деление на ноль:

Sub Primer1() On Error GoTo Инструкция     Dim a As Double     a = 45 / 0 Exit Sub Instr:     MsgBox «Произошла ошибка: « & Err.Description End Sub

Результат выполнения кода VBA Excel с обработчиком ошибок:

Пример 2
Выход за границы диапазона:

Sub Primer2() On Error GoTo Instr     Dim myRange As Range     Set myRange = Range(«A1:D4»).Offset(—2) Exit Sub Instr:     MsgBox «Произошла ошибка: « & Err.Description End Sub

Результат выполнения кода VBA Excel с оператором On Error GoTo:

Пример использования выражений On Error Resume Next и On Error GoTo 0 смотрите в статье: Отбор уникальных значений с помощью Collection.

VBA Errors Cheat Sheet

Errors

See more VBA “Cheat Sheets” and free PDF Downloads

VBA Error Handling

VBA Error Handling refers to the process of anticipating, detecting, and resolving VBA Runtime Errors. The VBA Error Handling process occurs when writing code, before any errors actually occur.

VBA Runtime Errors are errors that occur during code execution. Examples of runtime errors include:

• Referencing a non-existent workbook, worksheet, or other object (Run-time Error 1004)
• Invalid data ex. referencing an Excel cell containing an error (Type Mismatch – Run-time Error 13)
• Attempting to divide by zero

VBA On Error Statement

Most VBA error handling is done with the On Error Statement. The On Error statement tells VBA what to do if it encounters an error. There are three On Error Statements:

• On Error GoTo 0
• On Error Resume Next
• On Error GoTo Line

On Error GoTo 0

On Error GoTo 0 is VBA’s default setting. You can restore this default setting by adding the following line of code:

On Error GoTo 0

When an error occurs with On Error GoTo 0, VBA will stop executing code and display its standard error message box.

Often you will add an On Error GoTo 0 after adding On Error Resume Next error handling (next section):

Sub ErrorGoTo0()

On Error Resume Next
    ActiveSheet.Shapes("Start_Button").Delete
On Error GoTo 0

'Run More Code

End Sub

On Error Resume Next

On Error Resume Next tells VBA to skip any lines of code containing errors and proceed to the next line.

On Error Resume Next

Note: On Error Resume Next does not fix an error, or otherwise resolve it. It simply tells VBA to proceed as if the line of code containing the error did not exist. Improper use of On Error Resume Next can result in unintended consequences.

A great time to use On Error Resume Next is when working with objects that may or may not exist. For example, you want to write some code that will delete a shape, but if you run the code when the shape is already deleted, VBA will throw an error. Instead you can use On Error Resume Next to tell VBA to delete the shape if it exists.

On Error Resume Next
    ActiveSheet.Shapes("Start_Button").Delete
On Error GoTo 0

Notice we added On Error GoTo 0 after the line of code containing the potential error. This resets the error handling.

In the next section we’ll show you how to test if an error occurred using Err.Number, giving you more advanced error handling options.

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Err.Number, Err.Clear, and Catching Errors

Instead of simply skipping over a line containing an error, we can catch the error by using On Error Resume Next and Err.Number.

Err.Number returns an error number corresponding with the type of error detected. If there is no error, Err.Number = 0.

For example, this procedure will return “11” because the error that occurs is Run-time error ’11’.

Sub ErrorNumber_ex()

On Error Resume Next
ActiveCell.Value = 2 / 0
MsgBox Err.Number

End Sub

Error Handling with Err.Number

The true power of Err.Number lies in the ability to detect if an error occurred (Err.Number <> 0).  In the example below, we’ve created a function that will test if a sheet exists by using Err.Number.

Sub TestWS()
    MsgBox DoesWSExist("test")
End Sub

Function DoesWSExist(wsName As String) As Boolean
    Dim ws As Worksheet
    
    On Error Resume Next
    Set ws = Sheets(wsName)
    
    'If Error WS Does not exist
    If Err.Number <> 0 Then
        DoesWSExist = False
    Else
        DoesWSExist = True
    End If

    On Error GoTo -1
End Function

Note: We’ve added a On Error GoTo -1 to the end which resets Err.Number to 0 (see two sections down).

With On Error Resume Next and Err.Number, you can replicate the “Try” & “Catch” functionality of other programming languages.

On Error GoTo Line

On Error GoTo Line tells VBA to “go to” a labeled line of code when an error is encountered.  You declare the Go To statement like this (where errHandler is the line label to go to):

On Error GoTo errHandler

and create a line label like this:

errHandler:

Note: This is the same label that you’d use with a regular VBA GoTo Statement.

Below we will demonstrate using On Error GoTo Line to Exit a procedure.

On Error Exit Sub

You can use On Error GoTo Line to exit a sub when an error occurs.

You can do this by placing the error handler line label at the end of your procedure:

Sub ErrGoToEnd()

On Error GoTo endProc

'Some Code
    
endProc:
End Sub

or by using the Exit Sub command:

Sub ErrGoToEnd()

On Error GoTo endProc

'Some Code
GoTo skipExit
    
endProc:
Exit Sub

skipExit:

'Some More Code

End Sub

Err.Clear, On Error GoTo -1,  and Resetting Err.Number

After an error is handled, you should generally clear the error to prevent future issues with error handling.

After an error occurs, both Err.Clear and On Error GoTo -1 can be used to reset Err.Number to 0. But there is one very important difference: Err.Clear does not reset the actual error itself, it only resets the Err.Number.

What does that mean?  Using Err.Clear, you will not be able to change the error handling setting. To see the difference, test out this code and replace On Error GoTo -1 with Err.Clear:

Sub ErrExamples()

    On Error GoTo errHandler:
        
    '"Application-defined" error
    Error (13)
    
Exit Sub
errHandler:
    ' Clear Error
    On Error GoTo -1
    
    On Error GoTo errHandler2:
    
    '"Type mismatch" error
    Error (1034)
    
Exit Sub
errHandler2:
    Debug.Print Err.Description
End Sub

Typically, I recommend always using On Error GoTo -1, unless you have a good reason to use Err.Clear instead.

VBA On Error MsgBox

You might also want to display a Message Box on error.  This example will display different message boxes depending on where the error occurs:

Sub ErrorMessageEx()
 
Dim errMsg As String
On Error GoTo errHandler

    'Stage 1
    errMsg = "An error occured during the Copy & Paste stage."
    'Err.Raise (11)
    
    'Stage 2
    errMsg = "An error occured during the Data Validation stage."
    'Err.Raise (11)
     
    'Stage 3
    errMsg = "An error occured during the P&L-Building and Copy-Over stage."
    Err.Raise (11)
     
    'Stage 4
    errMsg = "An error occured while attempting to log the Import on the Setup Page"
    'Err.Raise (11)

    GoTo endProc
    
errHandler:
    MsgBox errMsg
   
endProc:
End Sub

Here you would replace Err.Raise(11) with your actual code.

VBA IsError

Another way to handle errors is to test for them with the VBA ISERROR Function. The ISERROR Function tests an expression for errors, returning TRUE or FALSE if an error occurs.

Sub IsErrorEx()
    MsgBox IsError(Range("a7").Value)
End Sub

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If Error VBA

You can also handle errors in VBA with the Excel IFERROR Function.  The IFERROR Function must be accessed by using the WorksheetFunction Class:

Sub IfErrorEx()

Dim n As Long
n = WorksheetFunction.IfError(Range("a10").Value, 0)

MsgBox n
End Sub

This will output the value of Range A10, if the value is an error, it will output 0 instead.

VBA Error Types

Runtime Errors

As stated above:

VBA Runtime Errors are errors that occur during code execution. Examples of runtime errors include:

• Referencing a non-existent workbook, worksheet, or other object
• Invalid data ex. referencing an Excel cell containing an error
• Attempting to divide by zero

You can “error handle” runtime errors using the methods discussed above.

Syntax Errors

VBA Syntax Errors are errors with code writing. Examples of syntax errors include:

• Mispelling
• Missing or incorrect punctuation

The VBA Editor identifies many syntax errors with red highlighting:

The VBA Editor also has an option to “Auto Syntax Check”:

When this is checked, the VBA Editor will generate a message box alerting you syntax errors after you enter a line of code:

I personally find this extremely annoying and disable the feature.

Compile Errors

Before attempting to run a procedure, VBA will “compile” the procedure. Compiling transforms the program from source code (that you can see) into executable form (you can’t see).

VBA Compile Errors are errors that prevent the code from compiling.

A good example of a compile error is a missing variable declaration:

Other examples include:

• For without Next
• Select without End Select
• If without End If
• Calling a procedure that does not exist

Syntax Errors (previous section) are a subset of Compile Errors.

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Debug > Compile

Compile errors will appear when you attempt to run a Procedure. But ideally, you would identify compile errors prior to attempting to run the procedure.

You can do this by compiling the project ahead of time. To do so, go to Debug > Compile VBA Project.

The compiler will “go to” the first error. Once you fix that error, compile the project again. Repeat until all errors are fixed.

You can tell that all errors are fixed because Compile VBA Project will be grayed out:

OverFlow Error

The VBA OverFlow Error occurs when you attempt to put a value into a variable that is too large. For example, Integer Variables can only contain values between -32,768 to 32,768. If you enter a larger value, you’ll receive an Overflow error:

Instead, you should use the Long Variable to store the larger number.

Other VBA Error Terms

VBA Catch Error

Unlike other programming languages, In VBA there is no Catch Statement. However, you can replicate a Catch Statement by using On Error Resume Next and If Err.Number <> 0 Then. This is covered above in Error Handling with Err.Number.

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VBA Ignore Error

To ignore errors in VBA, simply use the On Error Resume Next statement:

On Error Resume Next

However, as mentioned above, you should be careful using this statement as it doesn’t fix an error, it just simply ignores the line of code containing the error.

VBA Throw Error / Err.Raise

To through an error in VBA, you use the Err.Raise method.

This line of code will raise Run-time error ’13’: Type mismatch:

Err.Raise (13)

VBA Error Trapping

VBA Error Trapping is just another term for VBA Error Handling.

VBA Error Message

A VBA Error Message looks like this:

When you click ‘Debug’, you’ll see the line of code that is throwing the error:

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VBA Error Handling in a Loop

The best way to error handle within a Loop is by using On Error Resume Next along with Err.Number to detect if an error has occurred (Remember to use Err.Clear to clear the error after each occurrence).

The example below will divide two numbers (Column A by Column B) and output the result into Column C. If there’s an error, the result will be 0.

Sub test()
Dim cell As Range

On Error Resume Next
For Each cell In Range("a1:a10")

    'Set Cell Value
    cell.Offset(0, 2).Value = cell.Value / cell.Offset(0, 1).Value
    
    'If Cell.Value is Error then Default to 0
    If Err.Number <> 0 Then
         cell.Offset(0, 2).Value = 0
         Err.Clear
    End If
 Next
End Sub

VBA Error Handling in Access

All of the above examples work exactly the same in Access VBA as in Excel VBA.

Function DelRecord(frm As Form)
'this function is used to delete a record in a table from a form
   On Error GoTo ending
   With frm
      If .NewRecord Then
         .Undo
         Exit Function
      End If
   End With
   With frm.RecordsetClone
      .Bookmark = frm.Bookmark
      .Delete
      frm.Requery
   End With
   Exit Function
   ending:
   End
End Function

In a VBA code, there may be some errors like syntax errors, compilation errors, or runtime errors so we need to handle these errors. Suppose there is a code of 200 lines and the code has an error it’s very difficult to find an error in the code of 200 lines so it’s better to handle the error where we are expecting some error in our code. There are many errors handling methods in VBA which we will discuss in this article but before that, we will discuss types of error.

VBA Errors

Syntax Error

This error will occur if any syntax is not correctly written in the code then VBA will display an error message.

Examples of Syntax Error

Compilation Error

When there is a statement where there is an error in more than one line of its statement then VBA will display an error message. In the following example, a for loop is written without Next which is a compilation error

Runtime Error

A code that is written perfectly but an error occurs at the time of execution. For example, if a file address is attached to the code which doesn’t exist or when a number is divided by zero a case runtime error occurs.

Logical Error

The compiler can not highlight the logical errors but it will give a wrong output. The code will run without any error but the output will come wrong. In case of a large number of codes, it is difficult to identify the logical errors we need to press “F8” it will run the code one line at a time and we can identify the mistakes for which we are getting the wrong output. The following code is written to the difference between two numbers where we are getting the summation of two numbers.

Here, we can identify our logical error that instead of “-” we have written “+”

Expected Vs Unexpected Errors

• Expected Errors: Where we are expecting to get an error, there we write our own code to handle the error.
• Unexpected Errors: Where we don’t need to write our own code we have VBA error handling statements to handle the errors

Types of Error Handling Statements

On Error

It is used to handle errors that occur during run time.

• On Error GoTo 0: This statement will show an error message that a number or a variable is divided by zero.

• On Error Resume Next: It tells VBA if it gets a run time error then don’t show the error message simply resume to the next statement.

• On Error GoTo [label]: If it gets an error then it will go to the specific statement which we will mention in the “label” part.

The Err Object

When an error occurs an err object is created with help of that we can get the type of error and error number.

The Er1 Function 

It is used to get the line number of the error.

Err.Raise

We can create our own errors with the help of this method.

Syntax: Err. Raise [Number of the error],[Source of the error], [Description of the error]

From 1-512, number of errors is reserved by VBA. So, we can use anything from 513 to 65535.

Err.Clear

It is used to clear the number and type of the error from the Err.Object.

Error Function

It is used to print the description of the error from its number.

“Abort, Retry, Fail?” – MS-DOS error message circa 1986

This post provides a complete guide to VBA Error Handing. If you are looking for a quick summary then check out the quick guide table in the first section.

If you are looking for a particular topic on VBA Error Handing then check out the table of contents below(if it’s not visible click on the post header).

If you are new to VBA Error Handling, then you can read the post from start to finish as it is laid out in logical order.

A Quick Guide to Error Handing

Item	Description
On Error Goto 0	When error occurs, the code stops and displays the error.
On Error Goto -1	Clears the current error setting and reverts to the default.
On Error Resume Next	Ignores the error and continues on.
On Error Goto [Label]	Goes to a specific label when an error occurs. This allows us to handle the error.
Err Object	When an error occurs the error information is stored here.
Err.Number	The number of the error. (Only useful if you need to check a specific error occurred.)
Err.Description	Contains the error text.
Err.Source	You can populate this when you use Err.Raise.
Err.Raise	A function that allows you to generate your own error.
Error Function	Returns the error text from an error number. Obsolete.
Error Statement	Simulates an error. Use Err.Raise instead.

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Introduction

Error Handling refers to code that is written to handle errors which occur when your application is running. These errors are normally caused by something outside your control like a missing file, database being unavailable, data being invalid etc.

If we think an error is likely to occur at some point, it is good practice to write specific code to handle the error if it occurs and deal with it.

For all other errors, we use generic code to deal with them. This is where the VBA error handling statement comes into play. They allow our application to deal gracefully with any errors we weren’t expecting.

To understand error handling we must first understand the different types of errors in VBA.

VBA Errors

There are three types of errors in VBA:

1. Syntax
2. Compilation
3. Runtime

We use error handling to deal with runtime errors. Let’s have a look at each of these error types so that it is clear what a runtime error is.

Syntax Errors

If you have used VBA for any length of time you will have seen a syntax error. When you type a line and press return, VBA will evaluate the syntax and if it is not correct it will display an error message.

For example if you type If and forget the Then keyword, VBA will display the following error message

Some examples of syntax errors are

' then is missing
If a > b

' equals is missing after i
For i 2 To 7

' missing right parenthesis
b = left("ABCD",1

Syntax errors relate to one line only. They occur when the syntax of one line is incorrect.

Note: You can turn off the Syntax error dialog by going to Tools->Options and checking off “Auto Syntax Check”. The line will still appear red if there is an error but the dialog will not appear.

Compilation Errors

Compilation errors occur over more than one line. The syntax is correct on a single line but is incorrect when all the project code is taken into account.

Examples of compilation errors are:

• If statement without corresponding End If statement
• For without Next
• Select without End Select
• Calling a Sub or Function that does not exist
• Calling a Sub or Function with the wrong parameters
• Giving a Sub or Function the same name as a module
• Variables not declared(Option Explicit must be present at the top of the module)

The following screenshot shows a compilation error that occurs when a For loop has no matching Next statement.

Using Debug->Compile

To find compilation errors, we use Debug->Compile VBA Project from the Visual Basic menu.

When you select Debug->Compile, VBA displays the first error it comes across.

When this error is fixed, you can run Compile again and VBA will then find the next error.

Debug->Compile will also include syntax errors in it’s search which is very useful.

If there are no errors left and you run Debug->Compile , it may appear that nothing happened. However, “Compile” will be grayed out in the Debug menu. This means your application has no compilation errors at the current time.

Debug->Compile Error Summary

• Debug->Compile finds compilation(project wide) errors.
• It will also find syntax errors.
• It finds one error each time you use it.
• When there are no compilation errors left the Compile option will appear grayed out in the menu.

Debug->Compile Usage

You should always use Debug->Compile before you run your code. This ensures that your code has no compilation errors when you run it.

If you do not run Debug->Compile then VBA may find compile errors when it runs. These should not be confused with Runtime errors.

Runtime Errors

Runtime errors occur when your application is running. They are normally outside of your control but can be caused by errors in your code.

For example, imagine your application reads from an external workbook. If this file gets deleted then VBA will display an error when your code tries to open it.

Other examples of runtime errors are

• a database not being available
• the user entering invalid data
• a cell containing text instead of a number

As we have seen, the purpose of error handling is to deal with runtime errors when they occur.

Expected Versus Unexpected Errors

When we think a runtime error could occur we put code in place to handle it. For example, we would normally put code in place to deal with a file not being found.

The following code checks if the file exists before it tries to open it. If the file does not exist then a user friendly message is displayed and the code exits the sub.

' https://excelmacromastery.com/
Sub OpenFile()
    
    Dim sFile As String
    sFile = "C:docsdata.xlsx"
    
    ' Use Dir to check if file exists
    If Dir(sFile) = "" Then
        ' if file does not exist display message
        MsgBox "Could not find the file " & sFile
        Exit Sub
    End If
    
    ' Code will only reach here if file exists
    Workbooks.Open sFile
    
End Sub

When we think an error is likely to occur at some point, it is good practice to add code to handle the situation. We normally refer to these errors as expected errors.

If we don’t have specific code to handle an error it is considered an unexpected error. We use the VBA error handling statements to handle the unexpected errors.

Runtime Errors that are not VBA Errors

Before we look at the VBA Handling there is one type of error we must mention. Some runtime errors are not considered errors by VBA but only by the user.

Let me explain this with an example. Imagine you have an application that requires you to add the values in the variables a and b

result = a + b

Let’s say you mistakenly use an asterisk instead of the plus sign

result = a * b

This is not a VBA error. Your code syntax is perfectly legal. However, from your requirements point of view it is an error.

These errors cannot be dealt with using error handling as they obviously won’t generate any error. You can deal with these errors using Unit Testing and Assertions. I have an in-depth post about using VBA assertions – see How to Make Your Code BulletProof.

The On Error Statement

As we have seen there are two ways to treat runtime errors

1. Expected errors – write specific code to handle them.
2. Unexpected errors – use VBA error handling statements to handle them.

The VBA On Error statement is used for error handling. This statement performs some action when an error occurs during runtime.

There are four different ways to use this statement

1. On Error GoTo 0 – the code stops at the line with the error and displays a message.
2. On Error Resume Next – the code moves to next line. No error message is displayed.
3. On Error GoTo [label] – the code moves to a specific line or label. No error message is displayed. This is the one we use for error handling.
4. On Error GoTo -1 – clears the current error.

Let’s look at each of these statements in turn.

On Error GoTo 0

This is the default behavior of VBA. In other words, if you don’t use On Error then this is the behavior you will see.

When an error occurs, VBA stops on the line with the error and displays the error message. The application requires user intervention with the code before it can continue. This could be fixing the error or restarting the application. In this scenario no error handling takes place.

Let’s look at an example. In the following code, we have not used any On Error line so VBA will use the On Error GoTo 0 behavior by default.

' https://excelmacromastery.com/
Sub UsingDefault()

    Dim x As Long, y As Long
    
    x = 6
    y = 6 / 0
    x = 7

End Sub

The second assignment line results in a divide by zero error. When we run this code we will get the error message shown in the screenshot below

When the error appears you can choose End or Debug

If you select End then the application simply stops.
If you select Debug the application stops on the error line as the screenshot below shows

This behaviour is fine when you are writing VBA code as it shows you the exact line with the error.

This behavior is unsuitable for an application that you are given to a user. These errors look unprofessional and they make the application look unstable.

An error like this is essentially the application crashing. The user cannot continue on without restarting the application. They may not use it at all until you fix the error for them.

By using On Error GoTo [label] we can give the user a more controlled error message. It also prevents the application stopping. We can get the application to perform in a predefined manner.

On Error Resume Next

Using On Error Resume Next tells VBA to ignore the error and continue on.

There are specific occasions when this is useful. Most of the time you should avoid using it.

If we add Resume Next to our example Sub then VBA will ignore the divide by zero error

' https://excelmacromastery.com/
Sub UsingResumeNext()

    On Error Resume Next
    
    Dim x As Long, y As Long
    
    x = 6
    y = 6 / 0
    x = 7

End Sub

It is not a good idea to do this. If you ignore the error, then the behavior can be unpredictable. The error can affect the application in multiple ways.You could end up with invalid data. The problem is that you aren’t aware that something went wrong because you have suppressed the error.

The code below is an example of where using Resume Next is valid

' https://excelmacromastery.com/
Sub SendMail()

   On Error Resume Next
   
    ' Requires Reference:
    ' Microsoft Outlook 15.0 Object Library
    Dim Outlook As Outlook.Application
    Set Outlook = New Outlook.Application

    If Outlook Is Nothing Then
        MsgBox "Cannot create Microsoft Outlook session." _
                   & " The email will not be sent."
        Exit Sub
    End If
    
End Sub

In this code we are checking to see if Microsoft Outlook is available on a computer. All we want to know is if it is available or not. We are not interested in the specific error.

In the code above, we continue on if there is an error. Then in the next line we check the value of the Outlook variable. If there has been an error then the value of this variable will be set to Nothing.

This is an example of when Resume could be useful. The point is that even though we use Resume we are still checking for the error. The vast majority of the time you will not need to use Resume.

On Error GoTo [label]

This is how we use Error Handling in VBA. It is the equivalent of the Try and Catch functionality you see in languages such as C# and Java.

When an error occurs you send the error to a specific label. It is normally at the bottom of the sub.

Let’s apply this to the sub we have been using

' https://excelmacromastery.com/
Sub UsingGotoLine()

    On Error GoTo eh
    
    Dim x As Long, y As Long
    
    x = 6
    y = 6 / 0
    x = 7
    
Done:
    Exit Sub
eh:
    MsgBox "The following error occurred: " & Err.Description
End Sub

The screenshot below shows what happens when an error occurs

VBA jumps to the eh label because we specified this in the On Error Goto line.

Note 1: The label we use in the On…GoTo statement, must be in the current Sub/Function. If not you will get a compilation error.

Note 2: When an error occurs when using On Error GoTo [label], the error handling returns to the default behaviour i.e. The code will stop on the line with the error and display the error message. See the next section for more information about this.

On Error GoTo -1

This statement is different than the other three. It is used to clear the current error rather than setting a particular behaviour.

When an error occurs using On Error GoTo [label], the error handling behaviour returns to the default behaviour i.e. “On Error GoTo 0”. That means that if another error occurs the code will stop on the current line.

This behaviour only applies to the current sub. Once we exit the sub, the error will be cleared automatically.

Take a look at the code below. The first error will cause the code to jump to the eh label. The second error will stop on the line with the 1034 error.

' https://excelmacromastery.com/
Sub TwoErrors()

    On Error Goto eh
        
    ' generate "Type mismatch" error
    Error (13)

Done:
    Exit Sub
eh:
    ' generate "Application-defined" error
    Error (1034)
End Sub

If we add further error handling it will not work as the error trap has not been cleared.

In the code below we have added the line

On Error Goto eh_other

after we catch the first error.

This has no effect as the error has not been cleared. In other words the code will stop on the line with the error and display the message.

' https://excelmacromastery.com/
Sub TwoErrors()

    On Error Goto eh
        
    ' generate "Type mismatch" error
    Error (13)

Done:
    Exit Sub
eh:
    On Error Goto eh_other
    ' generate "Application-defined" error
    Error (1034)
Exit Sub
eh_other:
    Debug.Print "eh_other " & Err.Description
End Sub

To clear the error we use On Error GoTo -1. Think of it like setting a mouse trap. When the trap goes off you need to set it again.

In the code below we add this line and the second error will now cause the code to jump to the eh_other label

' https://excelmacromastery.com/
Sub TwoErrors()

    On Error Goto eh
        
    ' generate "Type mismatch" error
    Error (13)

Done:
    Exit Sub
eh:
    ' clear error
    On Error Goto -1
    
    On Error Goto eh_other
    ' generate "Application-defined" error
    Error (1034)
Exit Sub
eh_other:
    Debug.Print "eh_other " & Err.Description
End Sub

Note 1: There are probably rare cases where using On Error GoTo -1 is useful. In most cases using Resume Next is better as it clears the error and resumes the code at the next line after the error occurs.

Note 2: The Err Object has a member Clear. Using Clear clears the text and numbers in the Err object, but it does NOT reset the error.

Using On Error

As we have seen, VBA will do one of three things when an error occurs

• Stop and display the error.
• Ignore the error and continue on.
• Jump to a specific line.

VBA will always be set to one of these behaviors. When you use On Error, VBA will change to the behaviour you specify and forget about any previous behavior.

In the following Sub, VBA changes the error behaviour each time we use the On Error statement

' https://excelmacromastery.com/
Sub ErrorStates()

    Dim x As Long
    
    ' Go to eh label if error
    On Error Goto eh
    
    ' this will ignore the error on the following line
    On Error Resume Next
    x = 1 / 0
    
    ' this will display an error message on the following line
    On Error Goto 0
    x = 1 / 0
  
Done:  
   Exit Sub
eh:
    Debug.Print Err.Description
End Sub

Resume Next

The Resume Next statement is used to clear the error and then resume the code from the line after where the error occurred.

If your code can have multiple errors and you want to keep detecting them then this line is very useful.

For example, in the following code we want to resume the code after the error has been reported:

Private Sub Main()

    On Error Goto eh
    
    Dim i As Long
    For i = 1 To 3
        ' Generate type mismatch error
         Error 13
    Next i

done:
    Exit Sub
eh:
    Debug.Print i, Err.Description
End Sub

 
We could use On Error Goto -1 to clear the code and then use a goto statement to go back to the code like this:

Private Sub Main()

    On Error Goto eh
    
    Dim i As Long
    For i = 1 To 3
        ' Generate type mismatch error
         Error 13
continue:
    Next i

done:
    Exit Sub
eh:
    Debug.Print i, Err.Description
    On Error Goto -1 ' clear the error
    Goto continue ' return to the code
End Sub

 
The Resume Next provides a nicer way of doing it and it always means the code is much clearer and easier to understand:

Private Sub Main()

    On Error Goto eh
    
    Dim i As Long
    For i = 1 To 3
        ' Generate type mismatch error
         Error 13
continue:
    Next i

done:
    Exit Sub
eh:
    Debug.Print i, Err.Description
    ' clear the error and return to the code
    Resume Next  
End Sub

The Err Object

When an error occurs you can view details of the error using the Err object.

When an runtime error occurs, VBA automatically fills the Err object with details.

The code below will print “Error Number: 13 Type Mismatch” which occurs when we try to place a string value in the long integer total

' https://excelmacromastery.com/
Sub UsingErr()

    On Error Goto eh
    
    Dim total As Long
    total = "aa"

Done:
    Exit Sub
eh:
    Debug.Print "Error number: " & Err.Number _
            & " " & Err.Description
End Sub

The Err.Description provides details of the error that occurs. This is the text you normally see when an error occurs e.g. “Type Mismatch”

The Err.Number is the ID number of the error e.g. the error number for “Type Mismatch” is 13. The only time you really need this is if you are checking that a specific error occurred and this is only necessary on rare occasions.

The Err.Source property seems like a great idea but it does not work for a VBA error. The source will return the project name, which hardly narrows down where the error occurred. However, if you create an error using Err.Raise you can set the source yourself and this can be very useful.

Getting the Line Number

The Erl function is used to return the line number where the error occurs.

It often causes confusion. In the following code, Erl will return zero

' https://excelmacromastery.com/
Sub UsingErr()

    On Error Goto eh
    
    Dim val As Long
    val = "aa"

Done:
    Exit Sub
eh:
    Debug.Print Erl
End Sub

This is because there are no line numbers present. Most people don’t realise it but VBA allows you to have line numbers.

If we change the Sub above to have line number it will now print out 20

' https://excelmacromastery.com/
Sub UsingErr()

10        On Error Goto eh
          
          Dim val As Long
20        val = "aa"

Done:
30        Exit Sub
eh:
40        Debug.Print Erl
End Sub

Adding line numbers to your code manually is cumbersome. However there are tools available that will allow you to easily add and remove line numbers to a sub.

When you are finished working on a project and hand it over to the user it can be useful to add line numbers at this point. If you use the error handling strategy in the last section of this post, then VBA will report the line where the error occurred.

Using Err.Raise

Err.Raise allows us to create errors. We can use it to create custom errors for our application which is very useful. It is the equivalent of the Throw statement in JavaC#.

The format is as follows

Err.Raise [error number], [error source], [error description]

Let’s look at a simple example. Imagine we want to ensure that a cell has an entry that has a length of 5 characters. We could have a specific message for this

' https://excelmacromastery.com/
Public Const ERROR_INVALID_DATA As Long = vbObjectError + 513

Sub ReadWorksheet()

    On Error Goto eh
    
    If Len(Sheet1.Range("A1")) <> 5 Then
        Err.Raise ERROR_INVALID_DATA, "ReadWorksheet" _
            , "The value in the cell A1 must have exactly 5 characters."
    End If
    
    ' continue on if cell has valid data
    Dim id As String
    id = Sheet1.Range("A1")
    

Done:
    Exit Sub
eh:
    ' Err.Raise will send code to here
    MsgBox "Error found: " & Err.Description
End Sub

When we create an error using Err.Raise we need to give it a number. We can use any number from 513 to 65535 for our error. We must use vbObjectError with the number e.g.

Err.Raise vbObjectError + 513

Using Err.Clear

Err.Clear is used to clear the text and numbers from the Err.Object. In other words, it clears the description and number.If you want the clear the actual error you can use either On Error GoTo -1 or Resume Next

It is rare that you will need to use Err.Clear but let’s have a look at an example where you might.

In the code below we are counting the number of errors that will occur. To keep it simple we are generating an error for each odd number.

We check the error number each time we go through the loop. If the number does not equal zero then an error has occurred. Once we count the error we need to set the error number back to zero so it is ready to check for the next error.

' https://excelmacromastery.com/
Sub UsingErrClear()

    Dim count As Long, i As Long

    ' Continue if error as we will check the error number
    On Error Resume Next
    
    For i = 0 To 9
        ' generate error for every second one
        If i Mod 2 = 0 Then Error (13)
        
        ' Check for error
        If Err.Number <> 0 Then
            count = count + 1
            Err.Clear    ' Clear Err once it is counted
        End If
    Next

    Debug.Print "The number of errors was: " & count
End Sub

Note 1: Err.Clear resets the text and numbers in the error object but it does not clear the error – see Resume Next Or On Error GoTo -1 for more information about clearing the actual error.

Logging

Logging means writing information from your application when it is running. When an error occurs you can write the details to a text file so you have a record of the error.

The code below shows a very simple logging procedure

' https://excelmacromastery.com/
Sub Logger(sType As String, sSource As String, sDetails As String)
    
    Dim sFilename As String
    sFilename = "C:templogging.txt"
    
    ' Archive file at certain size
    If FileLen(sFilename) > 20000 Then
        FileCopy sFilename _
            , Replace(sFilename, ".txt", Format(Now, "ddmmyyyy hhmmss.txt"))
        Kill sFilename
    End If
    
    ' Open the file to write
    Dim filenumber As Variant
    filenumber = FreeFile 
    Open sFilename For Append As #filenumber
    
    Print #filenumber, CStr(Now) & "," & sType & "," & sSource _
                                & "," & sDetails & "," & Application.UserName
    
    Close #filenumber
    
End Sub

You can use it like this

' Create unique error number
' https://excelmacromastery.com/
Public Const ERROR_DATA_MISSING As Long = vbObjectError + 514

Sub CreateReport()

    On Error Goto eh
    
    If Sheet1.Range("A1") = "" Then
       Err.Raise ERROR_DATA_MISSING, "CreateReport", "Data is missing from Cell A1"
    End If

    ' other code here
Done:
    Exit Sub
eh:
    Logger "Error", Err.Source, Err.Description
End Sub

The log is not only for recording errors. You can record other information as the application runs. When an error occurs you can then check the sequence of events before an error occurred.

Below is an example of logging. How you implement logging really depends on the nature of the application and how useful it will be:

' https://excelmacromastery.com/
Sub ReadingData()
    
    Logger "Information", "ReadingData()", "Starting to read data."
       
    Dim coll As New Collection
    ' add data to the collection
    coll.Add "Apple"
    coll.Add "Pear"
    
    If coll.Count < 3 Then
        Logger "Warning", "ReadingData()", "Number of data items is low."
    End If
    Logger "Information", "ReadingData()", "Number of data items is " & coll.Count
    
    Logger "Information", "ReadingData()", "Finished reading data."

End Sub

Having a lot of information when dealing with an error can be very useful. Often the user may not give you accurate information about the error that occurred. By looking at the log you can get more accurate information about the information.

Other Error Related Items

This section covers some of the other Error Handling tools that VBA has. These items are considered obsolete but I have included them as they may exist in legacy code.

Error Function

The Error Function is used to print the error description from a given error number. It is included in VBA for backward compatibility and is not needed because you can use the Err.Description instead.

Below are some examples:

' Print the text "Division by zero"
Debug.Print Error(11)
' Print the text "Type mismatch"
Debug.Print Error(13)
' Print the text "File not found"
Debug.Print Error(53)

Error Statement

The Error statement allows you to simulate an error. It is included in VBA for backward compatibility. You should use Err.Raise instead.

In the following code we simulate a “Divide by zero” error.

' https://excelmacromastery.com/
Sub SimDivError()

    On Error Goto eh
        
    ' This will create a division by zero error
    Error 11
    
    Exit Sub
eh:
    Debug.Print Err.Number, Err.Description
End Sub

This statement is included in VBA for backward compatibility. You should use Err.Raise instead.

A Simple Error Handling Strategy

With all the different options you may be confused about how to use error handling in VBA. In this section, I’m going to show you how to implement a simple error handling strategy that you can use in all your applications.

The Basic Implementation

This is a simple overview of our strategy

1. Place the On Error GoTo Label line at the start of our topmost sub.
2. Place the error handling Label at the end of our topmost sub.
3. If an expected error occurs then handle it and continue.
4. If the application cannot continue then use Err.Raise to jump to the error handling label.
5. If an unexpected error occurs the code will automatically jump to the error handling label.

The following image shows an overview of how this looks

The following code shows a simple implementation of this strategy:

' https://excelmacromastery.com/
Public Const ERROR_NO_ACCOUNTS As Long = vbObjectError + 514

Sub BuildReport()

    On Error Goto eh
    
    ' If error in ReadAccounts then jump to error
    ReadAccounts
    
    ' Do something with the code
    
Done:
    Exit Sub
eh:
    ' All errors will jump to here
    MsgBox Err.Source & ": The following error occured  " & Err.Description
End Sub

Sub ReadAccounts()
    
    ' EXPECTED ERROR - Can be handled by the code
    ' Application can handle A1 being zero
    If Sheet1.Range("A1") = 0 Then
        Sheet1.Range("A1") = 1
    End If
    
    ' EXPECTED  ERROR - cannot be handled by the code
    ' Application cannot continue if no accounts workbook
    If Dir("C:DocsAccount.xlsx") = "" Then
        Err.Raise ERROR_NO_ACCOUNTS, "UsingErr" _
                , "There are no accounts present for this month."
    End If

    ' UNEXPECTED ERROR - cannot be handled by the code
    ' If cell B3 contains text we will get a type mismatch error
    Dim total As Long
    total = Sheet1.Range("B3")
    
    
    ' continue on and read accounts
    
End Sub

This is a nice way of implementing error handling because

• We don’t need to add error handling code to every sub.
• If an error occurs then VBA exits the application gracefully.

A Complete Error Handling Strategy

The above strategy has one major drawback. It doesn’t provide any information about the error. It is better than having no strategy as it prevents the application crashing. But that is the only real benefit.

VBA doesn’t fill Err.Source with anything useful so we have to do this ourselves.

In this section, I am going to introduce a more complete error strategy. I have written two subs that perform all the heavy lifting so all you have to do is add them to your project.

The purpose of this strategy is to provide you with the Stack* and line number when an error exists.

*The Stack is the list of sub/functions that were currently in use when the error occurred.

This is our strategy

1. Place error handling in all the subs.
2. When an error occurs, the error handler adds details to the error and raises it again.
3. When the error reaches the topmost sub it is displayed.

We are simply “bubbling” the error to the top. The following diagram shows a simple visual of what happens when an error occurs in Sub3

The only messy part to this is formatting the strings correctly. I have written two subs that handle this, so it is taken care of for you.

There are the two helper subs, RaiseError and DisplayError. You can download the library below:

An Example of using this strategy

Here is a simple coding example that uses these subs. In this strategy, we don’t place any code in the topmost sub. We only call subs from it.

' https://excelmacromastery.com/
Sub Topmost()

    On Error Goto EH
    
    Level1

Done:
    Exit Sub
EH:
    DisplayError Err.source, Err.Description, "Module1.Topmost", Erl
End Sub

Sub Level1()

    On Error Goto EH
    
    Level2

Done:
    Exit Sub
EH:
   RaiseError Err.Number, Err.source, "Module1.Level1", Err.Description, Erl
End Sub

Sub Level2()

    On Error Goto EH
    
    ' Error here
    Dim a As Long
    a = "7 / 0"

Done:
    Exit Sub
EH:
    RaiseError Err.Number, Err.source, "Module1.Level2", Err.Description, Erl
End Sub

The result looks like this:

If your project has line numbers the result will include the line number of the error:

Error Handling in a Nutshell

• Error Handling is used to handle errors that occur when your application is running.
• You write specific code to handle expected errors. You use the VBA error handling statement On Error GoTo [label] to send VBA to a label when an unexpected error occurs.
• You can get details of the error from Err.Description.
• You can create your own error using Err.Raise.
• Using one On Error statement in the top most sub will catch all errors in subs that are called from here.
• If you want to record the name of the Sub with the error, you can update the error and rethrow it.
• You can use a log to record information about the application as it is running.

What’s Next?

Free VBA Tutorial If you are new to VBA or you want to sharpen your existing VBA skills then why not try out the The Ultimate VBA Tutorial.

Related Training: Get full access to the Excel VBA training webinars and all the tutorials.

(NOTE: Planning to build or manage a VBA Application? Learn how to build 10 Excel VBA applications from scratch.)

If VBA can’t execute a statement (command) then a run-time error occurs. By default Excel deals with these, so when a run-time error occurs, you’ll see a default error message like this:

But you can change this and instruct Excel to allow your code to deal with run-time errors.

NOTE : I’m going to use the terms sub, function and procedure interchangeably. For the purposes of this article they all mean the same thing – a chunk of code written to do a particular thing.

The On Error Statement

To instruct Excel what to do when an error occurs, you use the On Error statement. You can use On Error in four ways:

On Error GoTo 0
On Error Resume Next
On Error GoTo [label]
On Error GoTo -1 

On Error GoTo 0

This is the default mode and is already turned on when you start writing your code. You don’t need to use an On Error GoTo 0 statement at the start of your VBA.

In this mode VBA displays the standard style error message box, and gives you the choice to Debug the code (enter VBA editor and use debugging tools) or End code execution.

You would use On Error GoTo 0 to turn default error handling back on if you have previously told VBA to deal with errors in some other way e.g. by using On Error Resume Next.

On Error Resume Next

On Error Resume Next tells VBA to continue executing statements immediately after the statement that generated the error.

On Error Resume Next allows your code to continue running even if an error occurs. Resume Next does not fix an error, it just ignores it. This can be good and bad.

The Good?

If you know that your code could generate an error, then using Resume Next can prevent an interruption in code execution.

For example, we want to create a file, but I want to make sure a file with the same name doesn’t already exist. To do this, I will attempt to delete the file, and of course if it doesn’t already exist, an error will occur.

I don’t care if an error occurs. If it does, the file doesn’t exist and that’s fine for what I want to do. So before I attempt to delete the file, I instruct VBA to ignore the error.

Sub DeleteFile()
    
    Dim FilePath As String
    
    FilePath = "d:tempsomefile.csv"
    
    On Error Resume Next
    
    'Delete the file
    Kill FilePath
    
    'If the file doesn't exist the Kill statement
    'generates an error.
    'But I have assumed that is ok as it indicates that
    'I am ok to create a new file with the same filename
    'This is a bad assumption - see the next sub 
    'UnhandledError()

End Sub

The Bad

But hang on. What if the file I am trying to delete is read only? If it is I will get an error when I try to delete it. I’ve assumed that I will only get an error if the file isn’t there. So an error caused by trying to delete a read only file will get missed.

And If I then try to create a new file with the same name, or open it for writing data to it, I will generate more errors and they will be missed too.

Sub UnhandledError()

    Dim FilePath As String
    
    FilePath = "d:tempsomefile.csv"
    
    On Error Resume Next
    
    'Delete the file
    Kill FilePath
    
    'But if the file is read-only I can't delete it
    'and the Kill statement generates an error
    'I can't now create a new file with the same name
    
    'Trying to Open the file for writing data to it will
    'also generate an error but it will be missed as
    'we've told VBA to continue executing code if an
    'error occurs
    Open FilePath For Output As #1
    Write #1, "Some data"
    Close #1

End Sub

If you do use On Error Resume Next you should immediately turn default error handling back on (or turn on your custom error handler – see below)

Be careful when using On Error Resume Next. You are better off seeing if an error occurred by checking the Err object (see below). Doing this can tell you the error number and help you figure out exactly what happened.

On Error GoTo [LABEL]

If an error occurs, this transfers code execution to the line following the label. This is typically used to specify your own error handling code.

None of the code between the line generating the error and the label is executed.

Error Handlers

So you write your own error handling code and use On Error GoTo [LABEL] to instruct VBA to use your code to deal with errors.

You can place your error-handling code anywhere in a procedure, but typically it is placed at the end.

Your error handler should either fix the error and resume code execution, or terminate the routine gracefully.

Sub ErrorHandler()

    Dim num As Integer

    On Error GoTo ErrHandler

    num = 1 / 0
    
    MsgBox "This line is not executed"

Exit sub


ErrHandler:

    MsgBox "Oops, an error has occured." & vbCrLf & vbCrLf & "Error Code : " & Err.Number & " , " & Err.Description

End Sub

As VBA will execute each line of code in turn going from top to bottom, if no error is generated then it will execute your error handling code when it gets to that point in your sub.

To prevent this happening, use an Exit Sub, Exit Function, or Exit Property statement before your error handling routine.

In the example above, if the value assigned to num was valid e.g. num = 1/1, then we don’t want the code beneath ErrHandler: executed. So just before the ErrHandler: label, I’ve used an Exit Sub statement.

Multiple Error Handlers

You can have more than one error handler in a routine, but only one of them can be active at any time.

You could have something like:

Sub MultipleErrorHandlers()
	On Error GoTo ErrHandler1
	[some code]

	On Error GoTo ErrHandler2
	[some code]

	Exit Sub

ErrHandler1:
	[ErrHandler1 Code]
	Exit Sub

ErrHandler2:
	[ErrHandler1 Code]
	Exit Sub
End Sub

If an error occurs between On Error GoTo ErrHandler1 and On Error GoTo ErrHandler2 then the ErrHandler1 code is executed.

If an error occurs after On Error GoTo ErrHandler2 then the ErrHandler2 code is executed.

NOTE: Notice that at the end of each error handling routine is an Exit Sub statement. If I didn’t use these, when the ErrHandler1 code is finished executing, VBA could just continue on down to the next line and execute the ErrHandler2 code as well.

Strictly speaking I don’t need the Exit Sub at the end of the ErrHandler2 code, as it is the last line in the sub, but it is a good habit to get into.

Err object

When an error occurs the Err object contains information about the error like the error number and a description of the error.

As any given line of code can generate multiple errors it’s a good idea to examine the Err object to determine what you want to do in your code.

Err.Number gives you the error number, and Err.Description gives you a description of the error.

Sub CheckErrObject()
    
    Dim FilePath As String
    
    FilePath = "d:tempsomefile.csv"
    
    On Error GoTo ErrHandler
    
    'Delete the file
    Kill FilePath
    
    Open FilePath For Output As #1
    Write #1, "Some data"
    Close #1

    
    Exit Sub
    

ErrHandler:
    
    Select Case Err.Number
      
        Case 53   ' File doesn't exist
            Err.Clear ' Clear the error
      
        Case 75   ' File is Read Only
            MsgBox "Error Number : " & Err.Number & vbCrLf & vbCrLf & Err.Description
            Exit Sub
      
      Case Else
         ' Code to handle other errors
         
   End Select
   
   Resume Next ' Continue executing code after line that generated error
   
End Sub

Resume

The Resume statement tells VBA to resume executing code at a specified point. Resume can only be used in an error handling routine, any other use will generate an error.

Resume takes three forms:

Resume
Resume Next
Resume [label]

Using just Resume causes execution to resume at the same line of code that caused the error. If you haven’t fixed the error, your code will begin an infinite loop as it switches between the line of code generating the error and the error handling routine.

If you look at the example sub Resume_Next() which is below, num = 1 / 0 causes a Divide by 0 error. I’ve instructed VBA to use my error handler, called ErrHandler.

In ErrHandler I’ve attempted to fix the error by assigning num the value 1. If I then used only Resume, all that would happen is that VBA would go back to num = 1 / 0 and another Divide by 0 error would be generated.

Instead, I use Resume Next to carry on executing code at the line after the one causing the error.

In doing so I have handled the error by assigning the value 1 to num, and execution will continue without another error at the line result = num / 1

Sub Resume_Next()

    Dim num As Integer
    Dim result As Integer

    On Error GoTo ErrHandler

    num = 1 / 0
    result = num  / 1
    
    Exit Sub

ErrHandler:   
    num = 1
    Resume Next
   
End Sub

Resume [label] passes code execution to the line with that label.

Sub Resume_Next()

    Dim num As Integer
    Dim result As Integer

    On Error GoTo ErrHandler

    num = 1 / 0
    result = num  / 1

MyLabel:

‘Code execution starts again from here
result = num * 1

    Exit Sub

ErrHandler:   
    num = 1
    Resume MyLabel
   
End Sub

Whenever you use Resume it clears the Err object.

Error Handling With Multiple Procedures

Every sub/function doesn’t have to have an error handler. If an error occurs, VBA will use the last On Error statement to determine what happens.

If an On Error statement has been used in a procedure and an error occurs in that procedure, then that error is handled as I’ve just described.

But if an error occurs in a sub that hasn’t used an On Error statement, VBA goes back through procedure calls until it finds an On Error directive.

Let’s look at an example with three subs.

SubOne() calls SubTwo(). SubTwo calls SubThree(), and has some code of its own to execute. SubThree() carries out a calculation.

Sub SubOne()

    On Error GoTo ErrHandler
    
    SubTwo

    Exit Sub
    
ErrHandler:
    
    MsgBox "Error caught in SubOne"
    
End Sub

Sub SubTwo()

    SubThree
    
    MsgBox "No errors here"
    
End Sub

Sub SubThree()

    Dim num As Integer
    
    num = 1 / 0
    
End Sub

SubOne() has an error handler routine, ErrHandler, and has instructed VBA to use it.

SubTwo() will display a message on screen after it’s call to SubThree() has finished.

However SubThree() generates a Divide by 0 error.

SubThree() hasn’t used an On Error statement to tell VBA what to do if an error occurs, so VBA goes back to SubTwo(). That also doesn’t have an On Error statement so VBA goes back to SubOne().

Here we have our error handler and the code in it is executed.

Note that the message «No errors here» in SubTwo() is not displayed because that line of code is not executed.

When SubThree() generated an error, code execution went back to the error handler in SubOne() and any code in SubTwo() after the call to SubThree() is missed out.

On Error GoTo -1

This resets the current error. It’s the equivalent of using Err.Clear.

You can see that in this sub, after the Divide By 0 error is generated, after On Error GoTo -1 is used, Err.Number is 0 (no error) and Err.Description is empty.

Sub GoToMinus1()

    Dim num As Integer

    On Error Resume Next

    num = 1 / 0

    'If error is Divide by Zero
    If Err.Number = 11 Then

        MsgBox "Error Code : " & Err.Number & " , " & Err.Description
        On Error GoTo -1
        MsgBox "Error Code : " & Err.Number & " , " & Err.Description
    
    End If

End Sub

Sample Code

Поискав по рунету материал на тему обработки ошибок в VBA, не увидал на первых двух страницах результатов поиска чего-то, что мне понравилось. Может плохо смотрел, но решил написать на эту тему свою статью.

Простите, но — немного словоблудия

Ошибки в программе

Ошибки времени исполнения программы возникают, когда среда программирования не может выполнить то, что вы хотите. Таких ситуаций может быть много. Например:

1. Вы обращаетесь к объекту по имени, а объекта с таким именем в коллекции нет

2. Вы хотите выделить ячеку на одном листе, а этот лист в данный момент не является активным (типичнейшая ошибка новичков в Excel VBA)

3. Вы хотите удалить отфильтрованные автофильтром строки, а фильтр вообще не вернул записей и удалять нечего

4. Вы ссылаетесь на элемент массива, который находится за пределами его границ.

5. Вы пытаетесь присвоить переменной значение, которое оно не может хранить. Например, переменной типа Long нельзя присвоить строковую константу или переменной типа Integer присвоить знанчение превышающее число 32767.

На любую из этих и сотни других ситуаций среда выполнения реагирует стандартно — прерывает ход выполнения программы на том операторе, где возникла ошибка или, как ещё принято говорить, исключение. На экран выводится информация о возникшей ошибке и предлагаются стандартные варианты для продолжения работы:

• Continue (продолжить) — этот пункт во время возникновения ошибки всегда не активен. Он активен, когда по ходу выполнения программы вы использовали оператор Stop. Кстати это очень полезный оператор для отладки программы.

• End (завершить) — завершение исполнения программы

• Debug (отладка) — переход в режим отладки, в котором можно посмотреть, на каком операторе возникла ошибка, что содержат переменные, можно даже перетащить жёлтую полоску, подсвечивающую текущий оператор, назад, и модифицировать знанчение переменных через окно Immediate window (впрочем это экзотика). В общем случае кнопка Debug позволяет посмотреть, где случилась ошибка и попытаться понять почему так случилось.

Если вы — автор программы, в которой случилась ошибка, то вы, должно быть, в начале будете рады увидеть подобное окно, ибо только так вы сможете отловить основные ошибки, скрытые в вашем коде. Однако, если эту ошибку видит пользователь, то для него это, мягко говоря, безрадостное и малопонятное зрелище. Ещё хуже, если за эту программу вам заплатили деньги. Поэтому в среде худо-бедно профессиональных программистов принято предусматривать обработку ошибок в своих программах.

Почему вообще в коде возникают ошибки?

1. Много ошибок во время написания кода возникает по невнимательности или не совсем адекватного понимания того, что делаешь. Таких ошибок, как правило, очень много, особенно у начинающих программистов, но эти ошибки довольно легко отловить и исправить, так как, пока вы их не исправите, ничего не работает. Ну, например, вы должны извлечь данные из 5-го столбца, а вы извлекаете из 6-го, а их там банально нет. Ясно, что вы это очень быстро заметите.

2. Вторая группа ошибок — это ошибки оптимиста. Когда программа написана в целом правильно, но алгоритм не готов к ударам судьбы в виде неожиданных действий со стороны пользователя, ошибок ввода-вывода (вы рассчитывали считать данные из файла, а файла с таким именем не оказалось, либо он заблокирован другим приложением), особенностей конфигурации компьютера (разные версии ОС или офиса, которые в некоторых мелочах отличаются).

3. Тонкие логические ошибки. Чем сложнее программа, тем больше шансов, что модель задачи в вашей голове, ваша программа и реальность не совсем согласованы между собой. Пока вы не достигните достаточного погружения в задачу вы такие ошибки не найдёте и не исправите. Порой на это уходит много времени. Но это характерно для сложных задач.

4. Ошибки на стыке вашего приложения и сервисов ОС, приводящие к неожиданным крахам приложения. Такого вообще возникать не должно, но как мы понимаем, и ОС и офис содержат ошибки, да и вы (что более вероятно) можете пользоваться системными вызовами не правильно. Подобные ошибки — сущий кошмар, особенно когда они проявляются лишь на некоторых конфигурациях, при определенных условиях, их трудно поймать и надёжно воспроизвести.

Задачи механизмов обработки ошибок

1. Обеспечить стабильную работу программы. Возникновение ошибки, появление которой вы не предусмотрели, приведёт в большинстве случаев к аварийному завершению всей программы или её части. При определенном уровне подобных ситуаций это ведёт к тому, что программой пользоваться становится невозможно.

2. Информирование. Мало обработать ошибку и предотвратить завершение программы. Надо ещё и адекватно проинформировать пользователя о причинах нестандартного поведения программы. Частно причиной ошибок в программе являются некорректные действия пользователя, поэтому важно сообщать ему о них.

3. Защита данных от повреждения. Программа обязана защищать от непреднамеренных повреждений результаты своей или пользовательской работы. Деструктивные действия должны быть снабжены соответствующими предупредительными диалоговыми окнами. Часто ошибка, не обработанная должным образом может повредить нужные данные.

Файл примера

Скачать

Код без обработки ошибок

Вот простой пример с потолка. Если вызвать Example_00, то она прекрасно отработает без ошибок и вернёт это:

В функцию GetCalories передаётся строка с блюдом, а она должна вернуть его калорийность, сверившись с таблицей в A1:B7.

Давайте поищем слабые места в этом коде. Первое, что должно прийти в голову — если мы ищем, то, что произойдёт, если мы не найдём? А произойдёт, конечно же, ошибка. Её инициирует метод Match.

Ещё одно слабое место этой подпрограммы: функция возвращает вещественный тип Double, и даже, если поиск оказался удачным, то в Cells(intRow, 2) может случайно находиться текстовая строка, а потому, когда вы числовому типу попытаетесь присвоить строковый тип, также произойдёт ошибка. И, если вы второй ошибки сможете избежать за счёт дополнительного оператора if с проверкой через IsNumber(), то избежать первой ошибки таким способом нельзя. Что же делать? А вот тут на сцену выходят операторы обработки ошибок.

Есть 2 подхода к обработке ошибок: автономный подход и выносной. Эти термины я придумал только что, чтобы проще было их обсуждать.

Автономный подход

Смысл автономного подхода в том, чтобы не выносить сор из избы. Если в подпрограмме возникла ошибка, то мы должны предположить, на каком месте она возникнет и поджидать её там с дубиной. С ошибкой, в этом случае, разбираются обычно в операторе, идущем сразу после потенциально опасного места. Давайте смотреть, как это может выглядеть:

Итак, что тут сделано:

1. Сразу после объявления функции GetCalories_v1 идёт оператор on error resume next, который в случае возникновения в каком-либо месте ошибки, предписывает VBA просто передавать управление на следующий оператор, идущий после ошибочного.

2. Мы объявили переменные. Необъявленные переменные получают тип Variant и значение по умолчанию Empty. Объявленные переменные числовых типов инициируются нулём, строковые — пустой строкой, то есть я наперёд знаю, что они содержат, а это хорошо для обработки ошибок.

3. На вызове метода WorksheetFunction.Match у нас возникает ошибка, так как искомого значения в таблице нет. А это, между прочим, был оператор присваивания ( = ). Прежде, чем левой части оператора присваивания (intRow) что-то будет присвоено, необходимо вычислить правую часть оператора присваивания (WorksheetFunction.Match…), а поскольку в процессе этого вычисления возникает ошибка, то переменная intRow остаётся такой, какой была! А, как я уже сказал, VBA автоматически её инициализирует нулём до начала исполнения подпрограммы. Получается, что, если в этом операторе возникнет ошибка, то в intRow будет ноль. Если ошибки во время поиска не возникнет, то ноля там не будет ни при каких раскладах, так как строки на листе нумеруются с единицы.

4. И вот этот ноль мы и контролируем, добавляя оператор If. Если intRow больше нуля, то WorksheetFunction.Match отработала штатно, а если нет — то работу подпрограммы надо прерывать, но об этом чуть позже.

5. Далее мы помним, что Cells(intRow, 2) может теоретически вернуть строковое значение, которое вызовет ошибку Type missmatch при присвоении переменной типа Double (GetCalories_v1), поэтому мы вставляем дополнительную проверку промежуточной переменной varTemp тому, что она числовая. И если это так, то присваиваем GetCalories_v1 значение из varTemp.

6. В случае возникновения любой ошибки внутри GetCalories_v1 она просто вернёт ноль. Почему ноль? Потому что переменная GetCalories_v1 тоже инициализируется нулём и об этом не надо заботиться, а в случае ошибки она останется в неприкосновенности.

7. Соответственно родительский код (в нашем случае его роль играет процедура Example_01) должен проверить, а не вернёт ли GetCalories_v1 ноль, и быть готовым к этой ситуации.

8. А вот теперь тонкий момент, который не все понимают. Почему я использовал промежуточные переменные intRow и varTemp? Вроде бы есть очевидный ответ — чтобы не вычислять значение выражений с Match и Cells 2 раза. Отчасти это, конечно, так. Но это, в данном случае, не главная причина. Главная причина в том, что такой код

   вызовет неправильное поведение программы. Если у нас Match вызовет исключение, то VBA передаст управление на СЛЕДУЮЩИЙ оператор, а следующий оператор в данном случае это то, что идёт после Then — присваивание переменной varTemp значения. Таким образом наша проверка на наличие ошибки сработает с точностью до наоборот, передав управление в ту часть кода, которая должна быть защищена от ситуации, когда Match не нашла строку в таблице. Вот почему важно в операторе If не иметь ничего такого, что могло бы вызвать ошибку.

9. Как видите, в этом подходе мне зачастую даже нет необходимости проверять объект Err, чтобы понять, что произошла ошибка, так как я ориентируюсь на то, что промежуточные переменные остаются неинициализированными, что является показателем наличия ошибки.

Выносной подход

Данный метод основан на том, что, когда возникает ошибка, то VBA передаёт управление на специальный участок кода — обработчик ошибок, который обычно размещают в конце подпрограммы. Это может выглядеть так:

Обратите внимание, что:

1. Оператор on error теперь в случае ошибки предписывает передавать управление на метку ErrorHandler, которая объявлена в конце кода процедуры GetCalories_v2

2. В коде мы никак не заботимся о каких-либо проверках. Возникла ошибка? Иди на метку — там разберутся.

3. Если ошибки не случилось, то, чтобы программа не стала исполнять строчки, предназначенные для обработки ошибок, перед меткой ErrorHandler обычно ставят оператор Exit Sub или Exit Function (в зависимости от типа подпрограммы).

4. Принципиальный момент — наличие оператора On Error Resume Next сразу после метки ErrorHandler. Дело в том, что после того, как вы перешли на метку ErrorHandler, очень опасно иметь действующим оператор On Error GoTo ErrorHandler, так как, если у вас в обработчике ошибки случится любая ошибка, то управление будет передано опять на метку и, как нетрудно понять, образуется бесконечный цикл. Поэтому сразу после метки мы возможность возникновения цикла ликвидируем оператором On Error Resume Next.

Что лучше?

Какой метод лучше применять зависит от ваших предпочтений и конкретных ситуаций. Грамотную обработку ошибок можно сделать и так и эдак. Вот несколько соображений по преимуществам и недостакам данных подходов:

Автономный подход

Преимущества	Недостатки
Есть возможность точно идентифицировать каждую конкретную проблему (если вы её предусмотрели), возникающую во время исполнения, что позволит вам дать самые точные инстркции пользователю для предотвращения появления исключения в будущем.	Достаточно трудоёмок, так как подразумевает наличие большого количества проверок в коде. Каждое потенциально опасное действие должно быть снабжено соответствующим оператором If, в котором контролируется значение переменной или код ошибки.
	Надо хорошо представлять себе ситуации, где могут возникнуть ошибки, в противном случае ряд ошибок вы просто не заметите на этапе отладки.
	Необходимо больше кода, а также требуется опыт и фантазия.
	Необходимо больше промежуточных переменных

Выносной подход

Преимущества	Недостатки
Ни одна ошибка не проскочит незамеченной.	Не смотря на то, что вы перехватите все ошибки, отреагировать на них правильно затруднительно, так как вы, по большому счёту, не знаете, на каком операторе произошла ошибка и почему.
Удобнее организовывать централизованный сбор логов по ошибкам в приложении. Однозначно, фаворит для больших проектов.

Кратко пробежимся по операторам, функциям и объектам VBA, которые предназначены для обработки ошибок времени исполнения программы.

Операторы

On Error { GoTo label | Resume Next | GoTo 0 }

Оператор on error управляет тем, на какой участок вашего кода будет передано управление в случае возникновения ошибки. Данный оператор можно вставить в любое место вашей программы или подпрограммы. Есть 3 варианта:

1. On error goto label — после того, как этот оператор выполнен, ошибка, возникшая на других операторах программы приведёт к переходу на метку label.

2. On error resume next — после такого оператора, VBA будет игнорировать возникшую ошибку и передавать управление на следующий оператор, стоящий за тем, в котором возникла ошибка.

3. On error goto 0 — это режим по-умолчанию. В случае возникновения ошибки данный режим приведёт к появлению на экране стандартного обработчик ошибок VBA с кнопками End и Debug.

Resume { label | Next | [0] }

Данный оператор возобновляет выполнение программы. Применяется в выносном методе обработки ошибок.

1. resume label— возобновление с метки label

2. resume next — возобновление со следующего оператора

3. resume или resume 0 — возобновление с оператора, вызвавшего ошибку. Это имеет смысл, если вы устранили ошибку в своём обработчике. На мой взгляд, на практике такое применяется крайне редко.

Goto label

Переход на метку. Может пригодиться, однако, использование меток в коде для чего-то большего, чем обработка ошибок, считается страшным моветоном.

Exit { Do | For | Function | Sub }

Досрочный выход из циклов (Do или For) и досрочный выход из подпрограмм (функции или процедуры). Могут пригодиться при обработке ошибок, но вообще это операторы и без того чрезвычайно полезны.

Объект Err

1. Err — глобальный объект (его не надо объявлять, а можно сразу пользоваться), который содержит информацию о последней ошибке, случившейся в вашей программе. Проверяя Err сразу после возникновения исключения или после ситуации, которая могла привести к исключению, вы можете понять, что имело место на самом деле.

2. Свойство Err.Number — содержит числовой код ошибки, по которому их различают в программе. Поскольку Number — свойство по умолчанию, то вы можете его опускать, то есть Err и Err.Number — это эквиваленты. Значение ноль говорит о том, что ошибки не произошло.

3. Err.Description — содержит англоязычное краткое описание ошибки

4. Err.Source — возвращает имя модуля, в котором возникла ошибка

5. Err.Clear — сбрасывает последнюю ошибку. Err сбрасывается также при выполнении оператором Resume, Exit (любого типа кроме Do и For) и On Error.

6. Err.Raise — искусственно вызывает исключение указанного в переданном параметре типа. Можно использовать для тестирования вашей подсистемы обработки ошибок.

P.S.

Лично я привык в своих программах использовать автономный подход и, возможно, поэтому я не совсем осознаю все преимущества выносного подхода. Буду рад прочесть в комментариях ваше мнение на этот счёт. Тема обработки ошибок данной статьёй, конечно, быть исчерпана не может, но она послужит вам хорошей стартовой точкой в этом важном деле.

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