Append Text to Existing File in C, C++, Java & Python – Code with Explanation & Examples in Short and Simple

   

C Program

#include <stdio.h>
void appendFile() {
    FILE *f = fopen("data.txt", "a");
    fprintf(f, "\nAppended from C.");
    fclose(f);
}

C Output

Input:  
Hello World!  

Output:  
Hello World!
Appended from C.

C++ Program

#include <fstream>
using namespace std;
void appendFile() {
    ofstream f("data.txt", ios::app);
    f << "\nAppended from C++.";
    f.close();
}

C++ Output

Input:  
Hello World!  

Output:  
Hello World!
Appended from C++.

JAVA Program

import java.io.*;
void appendFile() throws Exception {
    FileWriter fw = new FileWriter("data.txt", true);
    fw.write("\nAppended from Java.");
    fw.close();
}

JAVA Output

Input:  
Hello World!  

Output:  
Hello World!
Appended from Java.

Python Program

def append_file():
    with open("data.txt", "a") as f:
        f.write("\nAppended from Python.")

Python Output

Input:  
Hello World!  

Output:  
Hello World!
Appended from Python.

In-Depth Explanation

Example

Assume that your file initially has:

Hello, this is line one.

Once you run the append program, it will be:

Hello, this is line one.

Appended from Python.

The previous content remains unchanged, and the new line is inserted at the end — this is what append mode does.

Real-Life Analogy

Consider a file as a notebook or diary. Appending is similar to adding a new journal entry — you do not destroy the past, you merely add to it. It's beneficial in situations such as logging, where you need to have a running record.

Similarly, we add pages to a notebook, appending in programming allows you to add onto existing files — without destroying the previous data.

Why It Matters

Adding to files is important when:

Constructing log files that increase over time

Writing messages to a chat transcript

Logging sensor or user activity data

Keeping historical records

It also covers file modes:

"write" = overwrite

"append" = add to end

"read"

"read + append"

Being familiar with these modes is a must in real-world programming.

What You Learn from This

You learn:

Skill with file stream management

Knowledge of how files act in the various modes

Practical experience for activities like logging, updating configs, or constructing audit trails

Appending is the starting point towards interactive file manipulation in applications such as:

Notepads or editors

Data loggers

Command-line tools that save session history

Interview Relevance and Real Projects

This subject is a common beginner-level interview question in:

College exams

Interview questions on file handling

System scripts or automation tests

Real-world applications include:

Logging system events, transactions, or errors

Chat applications writing every message to a log file

Real-time input data recorders

SEO-Optimized Explanation

Adding text to a pre-existing file in C, C++, Java, and Python is a basic file operation in which new information is appended to the end of the file without erasing earlier data. This is done with the use of append mode ("a" or true in file functions). It's typically utilized in writing logs, storing messages, or monitoring activities across time. Knowing how to append to a file assists learners in comprehending file modes, permanent data storage, and the way actual programs create history without data loss. The idea is fundamental in file-based development, automation scripts, and system tools that involve cumulative data writing.