Read a Text File with C++

In C++, you can read data from a text file using file handling features provided by the <fstream>header. This is useful when you want your program to read input stored in a file instead of typing it every time.

To do this, you use a special object called ifstream (input file stream), which helps your program open the file and read its contents line by line or word by word.

Reading a text file is helpful when:

• You want to process saved data (like scores, settings, or logs).
• You want to work with large inputs without typing them manually.

Reading a Text File Line by Line

You can read text from a file line by line using the getline() function. This function reads an entire line from the file and stores it in a string. It takes two parameters: the file stream object and a string variable where the line's content will be stored.

Algorithm

Here are the simple steps to read a text file line by line:

• Include the <fstream> and <string> headers.
• Create an ifstream object and open the file using it.
• Check if the file was opened successfully.
• Use a loop with the getline() function to read the file line by line.
• Print each line.
• Close the file.

C++ Program to Read a Text File Line by Line

This program opens a file named sample.txt and prints its content line by line to the screen.

#include<iostream>
#include<fstream>
#include<string>
using namespace std;
int main() {
   // Open the text file
   ifstream file("sample.txt");  
   // Check if the file was opened successfully
   if (!file) {
      cout<<"File cannot be opened!"<<endl;
      return 1;
   }
   string line;
   while (getline(file, line)) {
      // Print each line
      cout<<line<<endl;  
   }
   // Close the file
   file.close();  
   return 0;
}

Assume that "sample.text" files contains the content as "This is a notes text file" and "Come back file".

If the file exists, the output will be as:

This is a notes text file
Come back file

If the file doesn't exists, the output will be as:

File cannot be opened

Reading a Text File Word by Word

You can read text from a file word by word using the extraction operator (>>). This method reads one word at a time from the file and stores it in a string variable. It automatically skips any whitespace characters such as spaces, tabs, or newlines.

Algorithm

Here are the simple steps to read a text file word by word:

• Include the <fstream> and <string> headers.
• Create an ifstream object and open the file using it.
• Check if the file was opened successfully.
• Use a loop with the extraction operator (>>) to read the file word by word.
• Print each word.
• Close the file.

C++ Program to Read a Text File Word by Word

This program reads and prints each word from the file one at a time.

#include<iostream>
#include<fstream>
#include<string>
using namespace std;
int main() {
   // Open the text file
   ifstream file("sample.txt");  
   string word;
   while (file>>word) {
      // Print each word from the file
      cout<<word<<endl;     
   }
   // Close the file
   file.close();  
   return 0;
}

Assume that "sample.text" files contains the content as "This is a notes text file".

If the file exists, the output will be as:

This 
is
a
notes
text
file

If the file doesn't opens, the output will be as:

File cannot be opened