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);
    
}

​