C code starting point for getting most of what std::vector offers

buf.c

static void _buf_init(void **buf, int *cap, int elsize, const char *file, const int line)
{
        fprintf(stderr, "_buf_init(%p, %s, %d)\n", buf, file, line);
        *buf = NULL;
        *cap = 0;
}

static void _buf_reserve(void **buf, int *cap, int cnt, int elsize, const char *file, const int line)
{
        fprintf(stderr, "_buf_reserve(%p, %s, %d)\n", buf, file, line);
        void *ptr;
        if (*cap >= cnt)
                return;
        cnt = 2*cnt - 1; while (cnt & (cnt-1)) cnt = cnt & (cnt-1);
        ptr = realloc(*buf, cnt * elsize);
        if (!ptr)
                fatal("OOM!");
        *buf = ptr;
}

static void _buf_exit(void **buf, int *cap, int elsize, const char *file, const int line)
{
        fprintf(stderr, "_buf_exit(%p, %s, %d)\n", buf, file, line);
        free(*buf);
        *buf = NULL;
        *cap = 0;
}


#define BUF_INIT(buf, cap) _buf_init((void**)&(buf), &(cap), sizeof(*(buf)), __FILE__, __LINE__);
#define BUF_RESERVE(buf, cap, cnt) _buf_reserve((void**)&(buf), &(cap), (cnt), sizeof(*(buf)), __FILE__, __LINE__);
#define BUF_EXIT(buf, cap) _buf_exit((void**)&(buf), &(cap), sizeof(*(buf)), __FILE__, __LINE__);