container_of 例子说明

很早前之前看的linux内核，一直想把container_of记录一下，趁今天想起就记录一下：

内核中的描述

/**
 * container_of - cast a member of a structure out to the containing structure
 * @ptr: the pointer to the member.
 * @type: the type of the container struct this is embedded in.
 * @member: the name of the member within the struct.
 *
 */
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr);\
(type *)( (char *)__mptr - offsetof(type,member) );})


作用：返回member成员对应的所在的父结构体指针。下面的例子就通过child变量的一个成员地址获取到child变量的地址，以便访问child变量的其他成员

#include <stdio.h>#include <stdlib.h>#include <unistd.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 parentStruct{int a;        int b;};struct childStruct{struct parentStruct parent;int a;        int b;};void main(void){struct childStruct * child =(struct childStruct*) malloc(sizeof(struct childStruct));child->a =100;child->b =1000;child->parent.a =200;child->parent.b =2000;struct parentStruct *parent = &child->parent;struct childStruct * child1 = container_of(parent,struct childStruct,parent);printf("%d,%d\n",child->a,child1->a);printf("%d,%d\n",child->b,child1->b);printf("%d,%d\n",child->parent.a,child1->parent.a);printf("%d,%d\n",child->parent.b,child1->parent.b);printf("%#x,%#x\n",child,child1);free(child);}