最近在阅读linux
kernel的代码，发现很多地方都使用了一个名container_of的宏，根据上下文可以看出，它的功能是得到包含某个结构成员的结构的指针，看了一下宏的定义，原来并没有用什么高深的技巧，只是C语言中常识而已，其实现如下：
(kernel.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) );})
想起以前学习COM时，看过< COM本质论>，里面提到了类似的方法：
(COM本质论：inttable.h)
#define BASE_OFFSET(ClassName, BaseName)
(DWORD(static_cast<BaseName*>(reinterpret_cast<ClassName*>(0x10000000)))
- 0x10000000)
#define COMPOSITE_OFFSET(ClassName,
BaseName, MemberType, MemberName)
(DWORD(static_cast<BaseName*>(reinterpret_cast<MemberType*>(0x10000000
+ offsetof(ClassName, MemberName)))) - 0x10000000)
#define BEGIN_INTERFACE_TABLE(ClassName)
typedef ClassName
_InterfaceTableClassName;
static const INTERFACE_ENTRY
*GetInterfaceTable(void)
{
static const INTERFACE_ENTRY table[] = {
#define INTERFACE_TABLE_ENTRY(piid, pfn,
dwData)
{ piid, pfn, dwData },
#define IMPLEMENTS_INTERFACE(ItfName)
{ &IID_##ItfName, ENTRY_IS_OFFSET,
BASE_OFFSET(_InterfaceTableClassName, ItfName) },
#define
IMPLEMENTS_INTERFACE_AS(RequestedItfName, BaseClassName)
{ &IID_##RequestedItfName,
ENTRY_IS_OFFSET ,
BASE_OFFSET(_InterfaceTableClassName, BaseClassName)},
#define
IMPLEMENTS_INTERFACE_WITH_COMPOSITE(RequestedItfName, DataMemberType,
DataMemberName)
{ &IID_##RequestedItfName, ENTRY_IS_OFFSET , COMPOSITE_OFFSET(_InterfaceTableClassName,
RequestedItfName, DataMemberType, DataMemberName) },
#define END_INTERFACE_TABLE()
{ 0, 0, 0 }
};
return table;
}
呵，把这些代码摘录到这里和大家分享。