Reading a text file in c word by word

1. Use std::ifstream to Read File Word by Word in C++
2. Use std::ispunct and std::string::erase Functions to Parse Punctuation Symbols in C++

This article will demonstrate multiple methods about how to read a file word by word in C++.

Use std::ifstream to Read File Word by Word in C++

The std::ifstream class can be utilized to conduct input operations file-based streams. Namely, the std::ifstream type is used to interface with file buffer and operate on it using the extraction operator. Note that, std::fstream type is also provided in the I/O library that’s compatible with both extraction (>>) and insertion operators (<<).

At first, we need to create an object of type ifstream by calling one of its constructors; in this case, only filename string is passed to the constructor function. Once the ifstream object is created, one of its methods — is_open should be called to verify that the call was successful and then proceed to read the file contents.

To read the file word by word, we call the extraction operator on ifstream object. We redirect it to the string variable, which automatically reads in the first word before the first space character is encountered. Since we need to read each word until the end of the file, we insert the extraction statement into a while loop expression. Additionally, we declared a vector of strings to store each word on every iteration and print later with a separate loop block.

#include <iostream>
#include <fstream>
#include <vector>

using std::cout; using std::cerr;
using std::endl; using std::string;
using std::ifstream; using std::vector;

int main()
{
    string filename("input.txt");
    vector<string> words;
    string word;
    
    ifstream input_file(filename);
    if (!input_file.is_open()) {
        cerr << "Could not open the file - '"
             << filename << "'" << endl;
        return EXIT_FAILURE;
    }

    while (input_file >> word) {
        words.push_back(word);
    }
    
    for (const auto &i : words) {
        cout << i << endl;
    }
    input_file.close();

    return EXIT_SUCCESS;
}

Use std::ispunct and std::string::erase Functions to Parse Punctuation Symbols in C++

The only downside of the previous method is that it stores the punctuation characters close to words in the destination vector. It would be better to parse each word and then store them into a vector container. We are using the ispunct function that takes a single character as int parameter and returns a non-zero integer value if the character is punctuation; otherwise — zero is returned.

Note that the behavior of ispunct function is undefined if the given argument is not representable as unsigned char; thus, it is recommended to cast the character to the corresponding type. In the following example, we implemented the two simple if conditions to check the first and last characters of each word. If the punctuation is found, we call a built-in string function — erase to remove the found characters.

#include <iostream>
#include <fstream>
#include <vector>

using std::cout; using std::cerr;
using std::endl; using std::string;
using std::ifstream; using std::vector;

int main()
{
    string filename("input.txt");
    vector<string> words;
    string word;
    
    ifstream input_file(filename);
    if (!input_file.is_open()) {
        cerr << "Could not open the file - '"
             << filename << "'" << endl;
        return EXIT_FAILURE;
    }

    while (input_file >> word) {
        if (ispunct(static_cast<unsigned char>(word.back())))
            word.erase(word.end()-1);
        else if (ispunct(static_cast<unsigned char>(word.front())))
            word.erase(word.begin());
        
        words.push_back(word);
    }
    
    for (const auto &i : words) {
        cout << i << endl;
    }
    input_file.close();

    return EXIT_SUCCESS;
}

In this section we will see how we can read file content word by word using C++. The task is very simple. we have to use the file input stream to read file contents. The file stream will open the file by using file name, then using FileStream, load each word and store it into a variable called word. Then print each word one by one.

Algorithm

read_word_by_word(filename)

begin
   file = open file using filename
   while file has new word, do
      print the word into the console
   done
end

File Content (test_file.txt)

This is a test file. There are many words. The program will read this file word by word

Example

#include<iostream>
#include<fstream>
using namespace std;
void read_word_by_word(string filename) {
   fstream file;
   string word;
   file.open(filename.c_str());
   while(file > word) { //take word and print
      cout << word << endl;
   }
   file.close();
}
main() {
   string name;
   cout << "Enter filename: ";
   cin >> name;
   read_word_by_word(name);
}

Output

Enter filename: test_file.txt
This
is
a
test
file.
There
are
many
words.
The
program
will
read
this
file
word
by
word

There are several ways to do this. Here’s one.

Below is a class I use pretty often called NTuple. It is the same idea as the Tuple<T>, Tuple<T1, T2>, etc classes that come with the .NET framework. However, the NTuple class is designed to hold a variable number of items. Two NTuple instances are equal if they contain the same number of values and those values are equal.

Given a set of columns

// as per OP, the list of columns to group by will be generated at runtime
IEnumerable<string> columnsToGroupBy = ...; 

you can use the NTuple class to group by those columns like this:

var groups = dt.AsEnumerable()
    .GroupBy(r => new NTuple<object>(from column in columnsToGroupBy select r[column]));

Here’s the beef:

public class NTuple<T> : IEquatable<NTuple<T>>
{
    public NTuple(IEnumerable<T> values)
    {
        Values = values.ToArray();
    }

    public readonly T[] Values;

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(this, obj))
            return true;
        if (obj == null)
            return false;
        return Equals(obj as NTuple<T>);
    }

    public bool Equals(NTuple<T> other)
    {
        if (ReferenceEquals(this, other))
            return true;
        if (other == null)
            return false;
        var length = Values.Length;
        if (length != other.Values.Length)
            return false;
        for (var i = 0; i < length; ++i)
            if (!Equals(Values[i], other.Values[i]))
                return false;
        return true;
    }

    public override int GetHashCode()
    {
        var hc = 17;
        foreach (var value in Values)
            hc = hc*37 + (!ReferenceEquals(value, null) ? value.GetHashCode() : 0);
        return hc;
    }
}

Here’s a test case:

static void Main(string[] args)
{
    // some sample data
    var dt = new DataTable();
    dt.Columns.Add("NAME", typeof(string));
    dt.Columns.Add("CITY", typeof(string));
    dt.Columns.Add("STATE", typeof(string));
    dt.Columns.Add("VALUE", typeof(double));
    dt.Rows.Add("Mike", "Tallahassee", "FL", 3);
    dt.Rows.Add("Mike", "Tallahassee", "FL", 6);
    dt.Rows.Add("Steve", "Tallahassee", "FL", 5);
    dt.Rows.Add("Steve", "Tallahassee", "FL", 10);
    dt.Rows.Add("Steve", "Orlando", "FL", 7);
    dt.Rows.Add("Steve", "Orlando", "FL", 14);
    dt.Rows.Add("Mike", "Orlando", "NY", 11);
    dt.Rows.Add("Mike", "Orlando", "NY", 22);

    // some "configuration" data
    IEnumerable<string> columnsToGroupBy = new[] {"CITY", "STATE"};
    string columnToAggregate = "VALUE";

    // the test routine
    foreach (var group in dt.AsEnumerable().GroupBy(r => new NTuple<object>(from column in columnsToGroupBy select r[column])))
    {
        foreach (var keyValue in group.Key.Values)
        {
            Debug.Write(keyValue);
            Debug.Write(':');
        }
        Debug.WriteLine(group.Sum(r => Convert.ToDouble(r[columnToAggregate])));
    }
}

1. 06-10-2003

   
   

   #1

   

   
   Registered User
   

   ---

   Reading in a file word by word
   

   I am trying to write a program that reads a file name from the
   command line, reads the contents of that file, and output a list of words, one word per line, to a second file, whose name is also on the command line.

   For this program a word is a sequence of alphabetic characters. Any character which is not alphabetic is a separator character.

   I know how to open files and create files but I am not sure what to do so that I can read in just one word at a time. I also want to know of any tips on how to write to the new file. Thank you in advance for any help!

   Example

   input file:
   Hello%$this is just a test!

   output file:
   Hello
   this
   is
   just
   a
   test

   ---

2. 06-10-2003

   
   

   #2

   

   
   ATH0
   

   

   ---

   Just continue in whatever book showed you how to open files a page or two, and they’ll show you how to read.

   Basicly there are may ways to do it.
   fgets would work.
   fgetc would also work.
   fscanf would also work…

   Basicly, there are a whole lot of f-ing functions that would do the job.

   Quzah.

   Hope is the first step on the road to disappointment.

   ---

3. 06-10-2003

   
   

   #3

   

   
   Registered User
   

   ---

   Open files
   

   Cool thank you I got it work… I kept forgetting to point to the right spot. Thank you for your help! The only last thing I need to figure out is how to make a new word after a «non letter».

   Example:

   If you use this code:

   Code:

   FILE *fp = fopen(argv[1],"r");
   
   	char buf[10];
   
   		while( fscanf(fp, "%s", buf) != EOF )
   		{
   			printf("%sn", &buf);
   		}

   On an input file that contains:

   This@#$is just a test!

   Your out put will be
   This@#$is
   just
   a
   test!

   What I need the output to be is:
   This
   is
   just
   a
   test

   Last edited by Bumblebee11; 06-10-2003 at 09:15 PM.

   ---

4. 06-10-2003

   
   

   #4

   

   
   ATH0
   

   

   ---

   What you would want to do then, is either modify how your fscanf call works, or, use a loop to run through the string you read in, and check for non-alpha characters.

   To do that, something like this would work.

   Quzah.

   Hope is the first step on the road to disappointment.

   ---

5. 06-10-2003

   
   

   #5

   

   
   Registered User
   

   ---

   Got it to work
   

   I was just able to get my program to work. Thank you for your help!!!

   ---