Memory Management

ABSTRACT

This chapter covers the transition from fixed, stack-allocated data to dynamic, heap-allocated memory. It explores the internal mechanics of how the C Standard Library manages memory, the importance of data alignment, and the architectural abstractions provided by Virtual Memory.

1. Fundamentals of Structs

How C groups variables and stores them in memory.

• Structs in C: Defining custom types and the “pass-by-value” behavior that necessitates pointers.
• Fixed-Sized Struct: Using array members and understanding the limitations of the Stack.
• Size of Struct: Exploring padding, alignment, and how the compiler organizes memory for CPU efficiency.

2. Pointer Mechanics

Deep-diving into how addresses are manipulated and measured.

• Memory and References: Using & and sizeof to locate and measure data on the stack.
• Pointer Operations: Pointer arithmetic, scaling based on type size, and the relationship between a[i] and *(a + i).
• Metadata and Pointer Operations: How allocators use “hidden” bitwise flags in pointers to track memory status.

3. The Heap & Dynamic Allocation

Managing memory that persists across function calls.

• Dynamic Struct: Using malloc to create flexible structures that outlive their scope.
• Heap and Strings: Handling variable-length text data safely using dynamic buffers.
• Memory Leak: The lifecycle of malloc and free, and the critical rules to avoid “orphaned” memory.

4. Allocator Implementation

Building a custom version of malloc from scratch.

• Implementation of Malloc: Using mmap and headers to partition raw memory into usable blocks.
• Coalescing Heap: Advanced techniques for merging adjacent free blocks to reduce memory fragmentation.

5. Quick Reference: Allocation Comparison