宏确定域在结构中的偏移量

#include <stdio.h>

#define FIND(type, f)    (size_t)&(((type *)0)->f)

#define OFFSET(type, f)    ((size_t)((char *)&((type *)0)->f - (char *)(type *)0))

struct _st
{
    int a;
    char c;
    int b;
};

int
main(void)
{
    printf("%d\n", FIND(struct _st, a));
    printf("%d\n", OFFSET(struct _st, a));

    printf("%d\n", FIND(struct _st, c));
    printf("%d\n", OFFSET(struct _st, c));

    printf("%d\n", FIND(struct _st, b));
    printf("%d\n", OFFSET(struct _st, b));

    return (0);
}