Dynamic Memory Allocation in C (malloc, calloc, realloc, free)

About this page

This page focuses on dynamic (heap) memory — malloc, calloc, realloc and free with code examples. For the broader picture including static and stack memory, see Memory management In C.

Introduction

Stack memory is automatic and limited. Dynamic memory is allocated from the heap at runtime using malloc, calloc, and realloc. You must release it with free to avoid memory leaks.

Key Functions

All are declared in <stdlib.h>.

Example — malloc and free

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

int main(void) {
    int n = 5, i;
    int *arr = (int *)malloc(n * sizeof(int));

    if (arr == NULL) {
        printf("Memory allocation failed\n");
        return 1;
    }

    for (i = 0; i < n; i++)
        arr[i] = (i + 1) * 10;

    for (i = 0; i < n; i++)
        printf("%d ", arr[i]);

    free(arr);
    arr = NULL;
    return 0;
}

Sample Output

10 20 30 40 50

calloc Example

int *zeros = (int *)calloc(10, sizeof(int));  /* all bytes set to 0 */

realloc Example

arr = (int *)realloc(arr, 10 * sizeof(int));  /* grow array */
if (arr == NULL) { /* handle failure — original block may still exist */ }

Best Practices

Common Mistakes

Related Pages

Continue learning with these related tutorials and programs:

• C Tutorials — Browse all C Tutorials.
• Memory management In C — Concept — static, stack and heap memory.
• File Management — More in c advance.
• Storage Classes In C — More in c advance.