構造体メンバのオフセット取得

#include <stdio.h>
#include <stddef.h>   // offsetof()

struct x
{
  int a;
  char b;
};

size_t sz;

sz = 
/* offsetof(Data, Member) */
offsetof(struct x, a);

printf("%zu\n", sz);

sz = offsetof(struct x, b);
printf("%zu\n", sz);

#include <stdio.h>
 
struct Test
{
  char c;
  int n;
  double d;
};
 
int main(void)
{
  size_t sc = (size_t) &((struct Test*)0)-> c;
  size_t sn = (size_t) &((struct Test*)0)-> n;
  size_t sd = (size_t) &((struct Test*)0)-> d;
 
  printf("%d %d %d\n", sc, sn, sd);
	
  return 0;
}