container_of()宏

在学习Linux驱动的过程中，遇到一个宏叫做container_of。
该宏定义在include/linux/kernel.h中，首先来贴出它的代码：

/** * 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) );})

<pre name="code" class="cpp">再看上述代码的第3行，其中需要说明的是offsetof，它定义在include/linux/stddef.h中，其定义如下：#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)