Basics of File Handling

Introduction

File handling in C uses FILE pointers — fopen to open, fclose to close, and fprintf/fscanf or fread/fwrite for data.

Understanding the topic

Open modes r read, w write, a append, rb/wb binary.

Always check fopen returns NULL on failure.

Close files fclose flushes buffers and releases handle.

• Open modes — r read, w write, a append, rb/wb binary.
• Always check — fopen returns NULL on failure.
• Close files — fclose flushes buffers and releases handle.

Step-by-step explanation

1. Open modes — r read, w write, a append, rb/wb binary.
2. Always check — fopen returns NULL on failure.
3. Close files — fclose flushes buffers and releases handle.

Syntax reference

Syntax reference:

FILE *f = fopen("path", "mode");

Informative example

Example program:

#include <stdio.h>

int main(void) {
    FILE *f = fopen("demo.txt", "w");
    if (!f) return 1;
    fprintf(f, "Hello file\n");
    fclose(f);
    return 0;
}

Execution workflow

Best practices

• Enable warnings: gcc -Wall -Wextra -std=c11 source.c -o app
• Give every variable a defined value before it is read.
• Stay inside array bounds — C will not stop you from over-running a buffer.

Common mistakes

• Reading uninitialized storage — behavior is undefined.
• Dismissing compiler warnings instead of fixing root causes.
• Ignoring NULL returns from malloc, fopen, and similar APIs.

Hands-on exercise

Practice problems:

• Write integers to a file
• Read them back

Summary

Basics of File Handling in C — FILE streams, open modes, and fclose discipline.