File Read/Write Program in C, C++, Java & Python – Code with Explanation & Examples in Short and Simple

   

C Program

#include <stdio.h>
void file_rw() {
    FILE *f = fopen("data.txt", "w");
    fprintf(f, "Hello File!");
    fclose(f);
    f = fopen("data.txt", "r");
    char c;
    while ((c = fgetc(f)) != EOF)
        putchar(c);
    fclose(f);
}

C Output

Hello File!

C++ Program

#include <fstream>
#include <iostream>
using namespace std;
void file_rw() {
    ofstream out("data.txt");
    out << "Hello File!";
    out.close();
    ifstream in("data.txt");
    string s;
    while (getline(in, s)) cout << s;
}

C++ Output

Hello File!

JAVA Program

import java.io.*;
void fileRW() throws Exception {
    FileWriter fw = new FileWriter("data.txt");
    fw.write("Hello File!");
    fw.close();
    BufferedReader br = new BufferedReader(new FileReader("data.txt"));
    System.out.println(br.readLine());
    br.close();
}

JAVA Output

Hello File!

Python Program

def file_rw():

    with open("data.txt", "w") as f:

        f.write("Hello File!")

    with open("data.txt", "r") as f:

        print(f.read())

Python Output

Hello File!

In-Depth Explanation

Example

We do the following in this example:

Open a file named data.txt in write mode and write "Hello File!".

Close the file so that the content is saved.

Open the file in read mode again.

Read and print the content — which prints Hello File!.

This repeated writing and reading illustrates the fundamental idea of file handling in programming.

Real-Life Analogy

Imagine a file as a notebook. When you write into it, you're employing write() or fprintf() in programming. When you read out of it, you're opening the notebook to see what you wrote before using read() or fgetc(). Similar to actual notebooks, when you don't close the book (file), pages could be missing or not saved!

Files enable you to persist data long-term — as opposed to variables, which are lost once the program terminates.

Why It Matters

File handling is critical because:

It enables data persistence across a program's lifespan.

It enables reading and writing settings, logs, reports, or any stored data.

It emulates real-world systems such as database storage, document editors, and others.

Mastering file handling introduces you to:

Log management

Data serialization

Database-like file structures

It also demonstrates how one can communicate with the external system in the real world beyond the console.

What You Learn from This

You learn to:

Open, write to, and read files

Manipulate file streams and buffers

Employ file modes: w (write), r (read), a (append), etc.

Close files without corrupting data safely

This develops skills that can be applied to:

Developing file-based applications

Saving game data, user input, or reports

Learning file I/O basics, which lies at the foundation of database access, CSV/JSON processing, and beyond

Interview Relevance and Real Projects

In interviews, file read/write is a common test of your:

Knowledge of file handling functions

Logic organization

Resource management (opening/closing files)

In real projects, file I/O is ubiquitous:

Saving user data in applications

Reading configuration files (e.g., .ini, .conf, .json)

Logging activities and performance metrics

Exporting reports or results of analysis

SEO-Optimized Explanation

A C, C++, Java, and Python file read/write application instructs saving and loading data through file handling functions. By saving data to a file and loading it, novices learn how to save information, handle file streams, and apply real-world data saving techniques in applications. Such knowledge is pivotal in developing applications that deal with external files, like logs, reports, or user content. Knowing how to use file I/O is essential for interviews, data analysis scripts, and applications that need permanent storage of data. This understanding fills the gap between in-memory temporary variables and actual physical persistent storage devices.