linux 内核container_of

#include <stdio.h>#define offsetof(type, number) ((size_t) &((type *)0)->number)#define container_of(ptr,type,member) ({           \    const typeof(  ((type *)0)->member ) * _mptr = (ptr); \    (type *)((char *)_mptr - offsetof(type,member) );}) struct structtest {    int number;    char name;    float code;};int main(void){    struct structtest test = {99,'c',3.14};    char * temp = &test.name;    printf ("the pointer is %p\n",&test.number);    printf ("the pointer is %p\n",&test.name);    printf ("the pointer is %p\n",&test.code);    printf ("the pointer is %p\n",ttemp);    struct structtest * structtemp = container_of(temp,struct structtest,name);    printf ("the pointer is %p\n",structtemp);    return 0;}

container_of根据结构体成员指针，得到结构体首地址。

这里首先将结构体首地址指向0地址 ，之后根据typeof得到( ((type *)0)->member )指向的类型 定义类型指针，赋值
const typeof( ((type )0)->member ) _mptr = (ptr);

这里根据传入的结构体类型以及成员，得到相对应的偏移值 首先将结构体指向0地址，之后把指向number的指针转换为整数

#define offsetof(type, number) ((size_t) &((type *)0)->number)

先把成员指针值转换为char× 之后进行相减 就可以得到结构体首地址
(type )((char )_mptr - offsetof(type,member)