linux中非常有趣的函数container_of实验

最新推荐文章于 2025-04-16 00:15:00 发布

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本文介绍了Linux内核中container_of宏的功能与实现原理，并通过一个简单的C语言实验演示了如何从结构体成员指针获取指向整个结构体的指针。

今天看linux代码，看到container_of函数，可以从结构体的成员指针，加上结构体类型，得到指向结构体头的指针，非常有趣。

这一段是container_of的宏定义

/Users/foursking/Documents/linux/linux-2.6.24/include/linux/kernel.h:
  350  
  351  /**
  352:  * container_of - cast a member of a structure out to the containing structure
  353   * @ptr:	the pointer to the member.
  354   * @type:	the type of the container struct this is embedded in.
  ...
  356   *
  357   */
  358: #define container_of(ptr, type, member) ({			\
  359  	const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
  360  	(type *)( (char *)__mptr - offsetof(type,member) );})

看这段函数不大明白，于是我做了如下的实验，代码如下

#include <stdio.h>

struct list_head{
	struct list_head *next,*prev;
};

struct test{
	int a;
	int b;
	struct list_head *f_list;
	int c;
};
//this code indicate the engine of container_of
int main(void)
{
	
	struct list_head* ptr;
	struct test* test1;
	 
	
	long offset=(long)&((struct test*)0)->f_list;
	printf("offset: %ld\n",offset);
	//we caculate the ptr offset in struct test
	
	const struct test* __mptr=ptr;
	(struct test*)((char *)__mptr-offset);
	return 0;
	//first, we point __mptr to ptr
	//next, we minus offset in __mptr so we point to the first element 
	//of struct test
}