Dynamic Memory Allocation

Introduction

Dynamic memory allocation reserves memory at runtime on the heap using malloc, calloc, realloc, and releases it with free.

Understanding the topic

malloc Allocate uninitialized bytes — check for NULL.

calloc Allocate and zero-initialize.

free Release memory — avoid double-free and use-after-free.

• malloc — Allocate uninitialized bytes — check for NULL.
• calloc — Allocate and zero-initialize.
• free — Release memory — avoid double-free and use-after-free.

Step-by-step explanation

1. malloc — Allocate uninitialized bytes — check for NULL.
2. calloc — Allocate and zero-initialize.
3. free — Release memory — avoid double-free and use-after-free.

Syntax reference

Syntax reference:

ptr = malloc(n * sizeof(type));
free(ptr);

Informative example

Example program:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    int *arr = malloc(5 * sizeof(int));
    if (!arr) return 1;
    for (int i = 0; i < 5; i++) arr[i] = i * 2;
    printf("%d\n", arr[4]);
    free(arr);
    return 0;
}

8

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:

• Dynamic array of n integers
• Resize with realloc

Summary

Dynamic Memory Allocation in C — Heap APIs: malloc, calloc, realloc, free.