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

#define offset_of(t, m) ((size_t) & (((t*)0)->m))

struct test
{
	int a;
	char b;
	uint32_t c;
};

struct test2
{
	int a;
	char b;
	uint32_t c;
} __attribute__((packed));

int main(void)
{
	printf("offset_of a: %zu / b: %zu / c: %zu\n", offset_of(struct test, a),
		   offset_of(struct test, b), offset_of(struct test, c));

	printf("Packed: offset_of a: %zu / b: %zu / c: %zu\n", offset_of(struct test2, a),
		   offset_of(struct test2, b), offset_of(struct test2, c));
}