Program's Memory Layout

Introduction

A C program's memory layout includes text (code), data (globals), BSS (uninitialized globals), heap (dynamic), and stack (locals, calls).

Understanding the topic

Stack Local variables, function frames — grows downward.

Heap malloc/calloc allocations — manual free required.

Data/BSS Global and static variables.

Text Read-only machine code.

• Stack — Local variables, function frames — grows downward.
• Heap — malloc/calloc allocations — manual free required.
• Data/BSS — Global and static variables.
• Text — Read-only machine code.

Step-by-step explanation

1. Stack — Local variables, function frames — grows downward.
2. Heap — malloc/calloc allocations — manual free required.
3. Data/BSS — Global and static variables.
4. Text — Read-only machine code.

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:

• Print address of local vs global
• Diagram stack on recursive calls

Summary

Program's Memory Layout in C — Text, data, BSS, stack, and heap regions.