Storage Classes

Introduction

Storage classes — auto (local default), register (hint), static (persistent/block scope), extern (global linkage).

Understanding the topic

static local Retains value between function calls.

extern Declares symbol defined elsewhere.

• static local — Retains value between function calls.
• extern — Declares symbol defined elsewhere.

Step-by-step explanation

1. static local — Retains value between function calls.
2. extern — Declares symbol defined elsewhere.

Informative example

Example program:

#include <stdio.h>

void counter(void) {
    static int count = 0;
    count++;
    printf("%d\n", count);
}

int main(void) {
    counter(); counter(); counter();
    return 0;
}

1
2
3

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:

• static vs auto local
• extern variable in two files

Summary

Storage Classes in C — auto, register, static, extern — lifetime and visibility.