得出结构体某成员的大小

from http://topic.csdn.net/u/20100416/09/7ff66ea2-dbb6-4515-885d-39498a49eb14.html

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

typedef struct book {
    char   name[50];    
    char   author[20];
    char   publish[30];
    char   isbn[20];
    char   local[20];
    int    amount;    
    float  price;

    struct book *next;
} BOOK;

#define PR_SIZEOF(_t, _m)       \
        (void)printf("sizeof(%s)=%d\n", #_t "." #_m, (int)sizeof(((_t *)0)->_m))

#define PR_OFFSET(_t, _m)       \
        (void)printf("offset(%s)=%d\n", #_t "." #_m, (int)offsetof(_t, _m))
        
int main(void)
{

        PR_SIZEOF(BOOK, name);
        PR_SIZEOF(BOOK, author);
        PR_SIZEOF(BOOK, publish);
        PR_SIZEOF(BOOK, isbn);
        PR_SIZEOF(BOOK, local);
        PR_SIZEOF(BOOK, amount);
        PR_SIZEOF(BOOK, price);
        PR_SIZEOF(BOOK, next);

        PR_OFFSET(BOOK, name);
        PR_OFFSET(BOOK, author);
        PR_OFFSET(BOOK, publish);
        PR_OFFSET(BOOK, isbn);
        PR_OFFSET(BOOK, local);
        PR_OFFSET(BOOK, amount);
        PR_OFFSET(BOOK, price);
        PR_OFFSET(BOOK, next);

        return (0);
}

/* output */
/*
sizeof(BOOK.name)=50
sizeof(BOOK.author)=20
sizeof(BOOK.publish)=30
sizeof(BOOK.isbn)=20
sizeof(BOOK.local)=20
sizeof(BOOK.amount)=4
sizeof(BOOK.price)=4
sizeof(BOOK.next)=4
offset(BOOK.name)=0
offset(BOOK.author)=50
offset(BOOK.publish)=70
offset(BOOK.isbn)=100
offset(BOOK.local)=120
offset(BOOK.amount)=140
offset(BOOK.price)=144
offset(BOOK.next)=148
*/