C++ File handling: Append data to existing text file

Last update on April 14 2025 12:41:49 (UTC/GMT +8 hours)

7. Append New Data to an Existing Text File

Write a C++ program to append new data to an existing text file.

Sample Solution:

C Code:

#include <iostream>   // Including the input/output stream library
#include <fstream>    // Including the file stream library
#include <string>     // Including the string handling library

// Function to display the content of a file
void displayFileContent(const std::string & filename) {
  std::ifstream file(filename); // Open file with given filename for reading
  std::string line; // Declare a string to store each line of text

  if (file.is_open()) { // Check if the file was successfully opened
    std::cout << "File content:" << std::endl; // Displaying a message indicating file content
    while (std::getline(file, line)) { // Read each line from the file
      std::cout << line << std::endl; // Display each line of the file
    }
    file.close(); // Close the file
  } else {
    std::cout << "Failed to open the file." << std::endl; // Display an error message if file opening failed
  }
}

int main() {
  displayFileContent("new_test.txt"); // Display content of "new_test.txt" before any modification
  std::cout << std::endl;

  std::ofstream outputFile; // Declare an output file stream object
  // Open the file in append mode
  outputFile.open("new_test.txt", std::ios::app); // Open "new_test.txt" in append mode

  displayFileContent("new_test.txt"); // Display content of "new_test.txt" after opening in append mode
  std::cout << std::endl;

  if (outputFile.is_open()) { // Check if the file was successfully opened
    std::string newData; // Declare a string to store new data entered by the user

    std::cout << "Enter the data to append: "; // Prompt the user to enter data
    // Read the new data from the user
    std::getline(std::cin, newData); // Get user input for new data

    // Append the new data to the file
    outputFile << newData << std::endl; // Write the new data to the file
    outputFile.close(); // Close the file

    std::cout << "Data appended successfully." << std::endl; // Display a success message
    displayFileContent("new_test.txt"); // Display content of "new_test.txt" after appending data
    std::cout << std::endl;
  } else {
    std::cout << "Failed to open the file." << std::endl; // Display an error message if file opening failed
  }

  return 0; // Return 0 to indicate successful execution
}

Sample Output:

File content:
CPP is a high-level, general-purpose programming language created by Danish computer scientist Bjarne Stroustrup.
First released in 1985 as an extension of the C programming language, it has since expanded significantly over time.
Modern CPP currently has object-oriented, generic, and functional features, in addition to facilities for low-level memory manipulation.
It is almost always implemented in a compiled language.
Many vendors provide CPP compilers, including the Free Software Foundation, LLVM, Microsoft, Intel, Embarcadero, Oracle, and IBM.

Enter the data to append: Here are some exercies of C++.
Data appended successfully.
File content:
CPP is a high-level, general-purpose programming language created by Danish computer scientist Bjarne Stroustrup.
First released in 1985 as an extension of the C programming language, it has since expanded significantly over time.
Modern CPP currently has object-oriented, generic, and functional features, in addition to facilities for low-level memory manipulation.
It is almost always implemented in a compiled language.
Many vendors provide CPP compilers, including the Free Software Foundation, LLVM, Microsoft, Intel, Embarcadero, Oracle, and IBM.
Here are some exercies of C++.

Explanation:

In the above exercise -

Use the std::ofstream class to open the file in append mode.
The std::ios::app flag is passed as the second argument to the open() function, which ensures that new data is appended to the existing file content.
Check if the file was successfully opened using the is_open() function.
If the file is open, prompt the user to input the data they want to append to the file. The std::getline() function reads new data from the user.
Next use the output stream operator << to append the new data to the file.
The std::endl inserts a new line character after the new data.
After appending the data, close the file using outputFile.close(), and display a message.

Note: Content of a file is displayed using displayFileContent("filename.txt").

Flowchart:

For more Practice: Solve these Related Problems:

Write a C++ program to open a text file in append mode and add a new line of text at the end.
Write a C++ program that appends user-inputted data to an existing file, preserving its original content.
Write a C++ program to dynamically append multiple lines to a text file and then display the updated content.
Write a C++ program that opens a file in append mode, writes additional data, and verifies that the data was appended by reopening the file.

CPP Code Editor:

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