Chapter 6 – Data Section & Heap

Data Section

Core idea

Stores global and static variables.

Key properties

• Fixed size
• Exists for entire process lifetime
• Shared by all functions
• Can be read-only or read-write

Exam angle

• Globals ≠ stack variables
• Concurrency risks (shared data)

Heap

Core idea

The heap is for dynamic memory allocation.

Characteristics

• Allocated via malloc, free, new
• Grows low to high
• Accessible by all functions
• Persists until explicitly freed

Common problems

• Memory leaks – allocated but never freed
• Dangling pointers – pointer to freed memory
• Double free – freeing same memory twice

Performance notes

• Stack is faster (better cache locality)
• Heap is flexible but slower

Exam traps

• Losing a pointer ≠ freeing memory
• Freeing memory ≠ clearing pointers