Memory leak concepts

Introduction

A memory leak happens when a program keeps using memory but never gives it back. This can make the program slow or crash.

When writing programs that use dynamic memory (like with malloc).

When you want your program to run smoothly without running out of memory.

When debugging why a program gets slower or crashes after running for a while.

When learning how to manage memory properly in C.

When working on long-running programs like servers or games.

Syntax

C

/* Memory leak example in C */
#include <stdlib.h>
int *ptr = malloc(sizeof(int));
*ptr = 10;
// Forgot to free(ptr);

malloc() reserves memory but does not give it back automatically.

You must use free() to release memory when done.

Examples

This code allocates memory but never frees it, causing a memory leak.

C

#include <stdlib.h>
int *ptr = malloc(sizeof(int));
*ptr = 5;
// No free called here, memory leak occurs

This code correctly frees the memory after use, preventing a leak.

C

#include <stdlib.h>
int *ptr = malloc(sizeof(int));
*ptr = 5;
free(ptr);

Allocating memory for a string but forgetting to free it causes a leak.

C

#include <stdlib.h>
#include <string.h>
char *str = malloc(20 * sizeof(char));
strcpy(str, "hello");
// Missing free(str); causes leak

Sample Program

This program allocates memory for 3 integers, uses them, then frees the memory to avoid a leak.

C

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

int main() {
    int *numbers = malloc(3 * sizeof(int));
    if (numbers == NULL) {
        printf("Memory allocation failed\n");
        return 1;
    }
    numbers[0] = 10;
    numbers[1] = 20;
    numbers[2] = 30;

    printf("Numbers: %d, %d, %d\n", numbers[0], numbers[1], numbers[2]);

    // Forgetting to free here would cause a memory leak
    free(numbers);

    return 0;
}

Important Notes

Always pair each malloc() with a free() to avoid leaks.

Memory leaks can cause your program to use more and more memory over time.

Tools like Valgrind can help find memory leaks in your programs.

Summary

Memory leaks happen when allocated memory is not freed.

Use free() to release memory after use.

Preventing leaks keeps programs fast and stable.