dyn_array.c

#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>

#define INITIAL_CAP 64

typedef struct ArrayHeader {
    // honestly storing the type size is kinda weird
    size_t size, capacity;
    char data[];
} ArrayHeader;

void* __array_create(size_t type_size) {
    ArrayHeader* header = malloc(sizeof(ArrayHeader) + (type_size * INITIAL_CAP));
    *header = (ArrayHeader){
        .size = 0, 
        .capacity = INITIAL_CAP
    };
    return &header->data[0];
}

void __array_destroy(void* ptr) {
    ArrayHeader* header = ((ArrayHeader*) ptr) - 1;
    free(header);
}

void* __array_reserve(void* ptr, size_t type_size, size_t extra) {
    ArrayHeader* header = ((ArrayHeader*) ptr) - 1;

    // I mean you can make a better expansion pattern if you care idk tho
    if (header->size + extra >= header->capacity) {
        header->capacity = (header->size + extra) * 2;
        ArrayHeader* new_ptr = realloc(header, sizeof(ArrayHeader) + (type_size * header->capacity));
        if (!new_ptr) abort();
        
        return &new_ptr->data[0];
    }

    return ptr;
}

#define array_create(T) __array_create(sizeof(T))
#define array_destroy(arr) __array_destroy(&arr)
#define array_put(arr, new_data) do {                     \
        arr = __array_reserve(arr, sizeof(*arr), 1);      \
        ArrayHeader* header = ((ArrayHeader*) arr) - 1;   \
        arr[header->size++] = (new_data);                 \
    } while (0)
#define array_length(arr) ((((ArrayHeader*) (arr)) - 1)->size)

int main() {
    int* arr = array_create(int);
    printf("%p\n\n", arr);

    for (size_t i = 0; i < 100; i++) {
        array_put(arr, 16);
        array_put(arr, 24);
    }

    size_t l = array_length(arr);
    for (size_t i = 0; i < l; i++) {
        printf("%d\n", arr[i]);
    }
    return 0;
}