How to append text to a text file in C++?

Appending text means adding new content to an existing file without removing its current content. In C++, this can be done by opening the file in append mode and writing the specified content to it.

Steps to Append Text to a Text File

You need to follow the below steps to open a file in append mode and append the content to it:

• First of all, you need to include the <fstream> header file.
• Them, create an ofstream object to write to the file.
• Open the file in append mode using the ios::app flag.
• Use the << operator to append text to the file, text can be input through the user, store it into a variable and then use the variable instead of text to append in the file.
• Close the file using the file.close() function.

Algorithm

Following is the algorithm to append Text to a Text File in C++:

Begin
   Open that file data.txt as output file stream class object to perform
   output operation in append mode using fout file reference.
   If the file exists then
      Appending text to that file.
   Close fout.
   Open the file "data.txt" for reading the content of the file.
   Extracting the text from file and printing the text.
End.

Example 1: Basic Program to Append Text to a File

This program opens a file in append mode and adds a new line of text to the end without deleting existing content. If the file doesn't exist, it creates one (the text):

#include<iostream>
#include<fstream>  // For file handling
using namespace std;
int main() {
   ofstream file;
   // Open file in append mode
   file.open("data.txt", ios::app);
   if (!file) {
      cout << "Error opening file!" << endl;
      return 1;
   }
   // Append text to the file
   file << "This is a new line added to the file.\n";
   cout << "Text appended successfully!" << endl;
   // Close the file
   file.close();  
   return 0;
}

Assume these as the text files(data.txt) as:

Hello World
C++ File Handling

Output

If the "data.txt" file exists with text the output will be:

Hello World
C++ File Handling
This is a new line added to the file.

If it doesn't exists, the output will be

This is a new line added to the file.

The console output will be generated as:

Text appended successfully!

Example 2: Taking Input from User and Appending to File

This program takes a line of text from the user and appends it to a file named data.txt. If the file exists, the ,new text is added at the end and if the file doesn't exists it is automatically created and the text itself is written into it:

#include<iostream>
#include<fstream>
using namespace std;
int main() {
   ofstream file;
   string userInput;
   // Open in append mode
   file.open("data.txt", ios::app);
   if (!file) {
       cout<<"Cannot open file!"<<endl;
       return 1;
   }
   cout<<"Enter text to append to the file: ";
   // Get full line including spaces
   getline(cin, userInput);  
   file<<userInput<<endl;
   // Append user input	
   cout<<"Text added to file successfully!"<<endl;
   // Close file
   file.close();
   return 0;
}

Output

Following is the output is as follows:

Enter text to append to the file: C++ is very interesting!

If data.txt exists, the output is :

Hello World
C++ File Handling
C++ is very interesting!

If data.txt doesnot exist, the output is:

C++ is very interesting!

The console output will be generated as:

Enter text to append to the file: C++ is very interesting!
Text added to file successfully!