Linux kernel - contain_of

This marco is mostly used in kernel .
The figure is illustrated to descible how the marco "contain_of" work.

The following is the  source code using the marco "contain_of".

#include <stdio.h>

#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#define container_of(ptr, type, member) ({            \
     const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
     (type *)( (char *)__mptr - offsetof(type,member) );})

struct  St_Inner{
    int         dw_a;
};

struct St_Outer {
    int         dw_a;
    struct St_Inner    St_b;
    int         dw_c;
};

     
int main ()
{
    struct St_Outer  src;
    struct St_Outer  *p_dest;
    struct  St_Inner *p_Inner;
    p_Inner = &src.St_b;
    
    
    p_dest = container_of (p_Inner,struct St_Outer, St_b);
    
    printf ("p_dest %x == src %x\n",p_dest,&src);
    return 0;
}