Memory Leaks

Introduction

A memory leak occurs when heap memory is allocated but never freed — program loses access while memory stays reserved.

Understanding the topic

Cause Missing free, lost last pointer to block.

Detection valgrind --leak-check=full ./program

Prevention Every malloc has exactly one free; use clear ownership.

• Cause — Missing free, lost last pointer to block.
• Detection — valgrind --leak-check=full .
• Prevention — Every malloc has exactly one free; use clear ownership.

Step-by-step explanation

1. Cause — Missing free, lost last pointer to block.
2. Detection — valgrind --leak-check=full .
3. Prevention — Every malloc has exactly one free; use clear ownership.

Informative example

Example program:

#include <stdlib.h>

void leak(void) {
    int *p = malloc(100 * sizeof(int));
    (void)p; /* never free(p) — leak */
}

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:

• Fix a program with valgrind report
• Free in error paths

Summary

Memory Leaks in C — Orphaned allocations and how to detect them.