buf.c

buf.c

#include "buf.h"
#include "die.h"

void buf_do_realloc_(void **a, size_t nr, size_t sz)
{
	struct buf *b;

	b = realloc(buf_get_(*a), offsetof(struct buf, data) + nr * sz);
	if (!b)
		die_errno("realloc");

	b->cap = nr;
	if (!*a)
		b->len = 0;
	*a = &b->data;
}

buf.h

#ifndef BUF_H_
#define BUF_H_

#include <stdlib.h>

#define offsetof(TYPE, MEMBER)	((size_t)&((TYPE *)0)->MEMBER)

#define container_of(ptr, type, member)					\
	((type *)((void *)(ptr) - offsetof(type, member)))

/* Based on Sean Barrett's stretchy buffer at http://www.nothings.org/stb/stretchy_buffer.txt
 * init: NULL, free: buf_free(), push_back: buf_push(), size: buf_len()
 */
struct buf {
	size_t len, cap;
	char data[];
};

#define buf_len(a)		((a) ? buf_get_(a)->len : 0)
#define buf_cap(a)		((a) ? buf_get_(a)->cap : 0)
#define buf_free(a)		free(buf_get_(a))

#define buf_for_each(it, a)						\
	for ((it) = (a); (it) < (a) + buf_len(a); (it)++)

#define buf_push(a, v) ({						\
	if (buf_len(a) == buf_cap(a)) {					\
		size_t cap = buf_new_cap_(buf_cap(a));			\
		buf_reserve(a, cap);					\
	}								\
	(a)[buf_get_(a)->len++] = (v);					\
})

#define buf_resize(a, n) ({						\
	buf_reserve(a, n);						\
	if (a)								\
		buf_get_(a)->len = (n);					\
})

#define buf_reserve(a, n) ({						\
	if ((n) > buf_cap(a))						\
		buf_do_realloc_((void **) &(a), n, sizeof(*(a)));	\
})

/* Private */
#define buf_get_(a)							\
	((a) ? (struct buf *)(container_of(a, struct buf, data)) : NULL)

static inline size_t buf_new_cap_(size_t old_cap)
{
	size_t cap = 3 * old_cap / 2;

	if (cap < 16)
		cap = 16;
	return cap;
}

void buf_do_realloc_(void **a, size_t nr, size_t sz);

#endif // BUF_H_

buf_test.c

#include <math.h>
#include <stdio.h>

#include "buf.h"

#define my_buf_push(a, v)	({					\
	size_t cap, old_cap = buf_cap(a);				\
	buf_push(a, v);							\
	cap = buf_cap(a);						\
	if (old_cap != cap)						\
		printf("realloc: %ld old: %ld\n", cap, old_cap);	\
})

int main(int argc, char **argv)
{
	float *a = NULL, *it;
	int i;

	for (i = 0; i < 10000000000; i++) {
		float f = i * i;
		my_buf_push(a, f);
		my_buf_push(a, pow(f, 1.0 / 3.0));
		my_buf_push(a, i);
	}

	buf_for_each(it, a)
		printf("a[%ld] = %f\n", it - a, *it);

	return 0;
}

die.h

#ifndef DIE_H_
#define DIE_H_

#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static void die(const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vfprintf(stderr, fmt, ap);
	fprintf(stderr, "\n");
	va_end(ap);
	exit(-1);
}

#define die_errno(msg)		die("%s: %s", msg, strerror(errno))

#endif // DIE_H_