Merge Contents of Two Files in C, C++, Java & Python – Code with Explanation & Examples in Short and Simple

   

C Program

#include <stdio.h>
void mergeFiles() {
    FILE *f1 = fopen("file1.txt", "r"), *f2 = fopen("file2.txt", "r"), *f3 = fopen("merged.txt", "w");
    char c;
    while ((c = fgetc(f1)) != EOF) fputc(c, f3);
    while ((c = fgetc(f2)) != EOF) fputc(c, f3);
    fclose(f1); fclose(f2); fclose(f3);
}

C Output

Input 1: Hello  
Input 2: World! 
Output:  
Hello World!

C++ Program

#include <fstream>
using namespace std;
void mergeFiles() {
    ifstream f1("file1.txt"), f2("file2.txt");
    ofstream f3("merged.txt");
    f3 << f1.rdbuf() << f2.rdbuf();
    f1.close(); f2.close(); f3.close();
}

C++ Output

Input 1: Hello  
Input 2: World! 
Output:  
Hello World!

JAVA Program

import java.io.*;
void mergeFiles() throws Exception {
    FileInputStream f1 = new FileInputStream("file1.txt");
    FileInputStream f2 = new FileInputStream("file2.txt");
    FileOutputStream f3 = new FileOutputStream("merged.txt");
    int b;
    while ((b = f1.read()) != -1) f3.write(b);
    while ((b = f2.read()) != -1) f3.write(b);
    f1.close(); f2.close(); f3.close();
}

JAVA Output

Input 1: Hello  
Input 2: World! 
Output:  
Hello World!

Python Program

def merge_files():
    with open("file1.txt") as f1, open("file2.txt") as f2, open("merged.txt", "w") as f3:
        f3.write(f1.read() + f2.read())

Python Output

Input 1: Hello  
Input 2: World! 
Output:  
Hello World!

In-Depth Explanation

Example

Suppose:

file1.txt has: Good

file2.txt has: Morning

Upon merging, merged.txt shall contain: Good Morning

This illustrates file reading and writing from different sources.

Real-Life Analogy

Consider two notebooks — your notebook and your friend's notebook. You now wish to have one notebook that integrates both. Merging files in code is just like that — duplicating the pages of two books into a new integrated notebook.

This method proves helpful in concatenating data logs, messages, or even document parts.

Why It Matters

File content merging is heavily utilized in:

Log merging (merging logs of other systems)

Report creation

Merging chunks of data in distributed systems

Text handling in NLP and automation scripts

It learns you:

Reading and writing a file

Using several file streams

Resource management efficiently (opening/closing files)

What You Learn from This

You learn:

Working with multiple file pointers or streams

Appending or merging text programmatically

Working with files line-by-line or entire streams

Combining data in automation pipelines

This principle ranges from simple tasks to big-scale ETL (Extract, Transform, Load) processes in data engineering.

Relevance and Actual Projects

This question is usually asked to check:

Knowledge of handling files

Multi-stream processing

Pure usage of I/O logic

In actual projects:

Combining user logs, error logs, or system diagnostics

Producing combined configuration or result files

Merging contents from multiple inputs into a single report

SEO-Optimized Explanation

Combining the contents of two files in C, C++, Java, or Python is a ubiquitous operation applied in real-life programming when several sources of data or text have to be merged. Reading from each file and writing the combined content to another file is the way it's performed. It is crucial for file processing, log handling, reporting, and workflow automation. Knowing how to combine files programmatically educates you on file stream management, effective text processing, and multi-source input handling. It is an important skill for beginners and professional programmers handling data, text files, and I/O operations in system-level and high-level programming environments.