Basic C memory arena implementation

Overview

va_c_arena is a stb-style, single-header arena allocator. Include va_arena.h, define VA_ARENA_IMPLEMENTATION once, and you get fast bump-pointer allocations with optional alignment and expansion.

Features

• C99 core; C11+ adds aligned allocation helpers.
• Single-header API; drop-in and cross-platform (uses malloc/realloc/free only).
• Arena expansion via arena_expand when you need more space.
• Optional aligned allocations (arena_alloc_aligned) for stricter alignment needs.
• Unit tests and examples included.

Usage sketch

• Create an arena with a starting size (e.g., 4 KB).
• Allocate with arena_alloc(...); optionally use arena_alloc_aligned(...) on C11+.
• Optionally call arena_expand(...) to grow the arena (note: existing pointers may become invalid after expansion).
• Destroy the arena to free memory.

Example (Aligned Allocation, C11+)

#include <stdio.h>
#include <stdalign.h>

#define VA_ARENA_IMPLEMENTATION
#include "va_arena.h"

typedef struct {
    VA_ALIGNAS(32) int id;
    VA_ALIGNAS(32) double position[3];
    VA_ALIGNAS(32) char name[32];
} Entity;

int main(void) {
    Arena *arena = arena_create(4096);
    Entity *entities = (Entity *)arena_alloc_aligned(arena, sizeof(Entity) * 10, 32);
    if (!entities) {
        fprintf(stderr, "Failed to allocate aligned entities\n");
        arena_destroy(&arena);
        return 1;
    }
    // Use entities...
    arena_destroy(&arena);
    return 0;
}

Notes

• Not thread-safe; add your own synchronization if sharing across threads.
• Expansion can move the underlying block; do not use old pointers after arena_expand.
• Aligned helpers require C11 or newer.