#include <stdio.h>

#include <stdlib.h>

#define CONTAINER_OF(ptr, type, member)((type *)((char *)ptr - (char *)&((type*)0)->member))

#define ARRAY_SIZE(a)(sizeof(a) / sizeof((a)[0]))

struct user_data

{

     char a;

     char b;

     int c;

};

int main(int argc, char *argv[])

{

      struct user_data *tmp;

      char *h;

      struct user_data = (struct user_data *)malloc (sizeof(struct user_data));

if(p_data ==NULL)

{

      printf("no memory!\n");

      return -1;

}

     h = &p_data->b;

     printf("p_data's address is 0x%p\n", p_data);

     printf("h's           address is 0x%p\n", h);

     tmp = CONTAINER_OF(h, struct user_data, b);

     printf("tmp's address is 0x%p\n", tmp);

     return 0;

}