c++ - 链表项的类型转换问题

Question

这是我的 PER_IO_CONTEXT 结构(我将它们存储在单链表中):

 typedef struct _PER_IO_CONTEXT 
 {

    SLIST_ENTRY       ItemEntry;
    WSAOVERLAPPED     Overlapped;
    WSABUF                 wsabuf; 
    /* some other data*/

 } PER_IO_CONTEXT, *PPER_IO_CONTEXT;

下面是 WSAsend ，它使用列表来获取 WSAOVERLAPPED 结构:

...
PSLIST_HEADER pListHead;
...

PSLIST_ENTRY  pListEntry = InterlockedPopEntrySList(pListHead);
PPER_IO_CONTEXT ovl = (PPER_IO_CONTEXT)pListEntry;
WSASend(pTmp1->Socket,..., &(ovl->Overlapped), NULL);

GQCS收到通知的最后部分:

 LPWSAOVERLAPPED lpOverlapped = NULL;
 PPER_IO_CONTEXT lpIOContext = NULL; 
 ....
 GetQueuedCompletionStatus(..... (LPOVERLAPPED *)&lpOverlapped,  INFINITE);
 lpIOContext = (PPER_IO_CONTEXT)lpOverlapped;
 lpIOContext->wsabuf       // this fail

如您所见，下面的转换 lpIOContext =(PPER_IO_CONTEXT)lpOverlapped 不起作用，因为 WSAsend 提供了 wsaoverlapped - PER_IO_CONTEXT 结构的第二个成员，因此取消引用如 lpIOContext-> 不能在这种情况下使用。

有办法处理这种情况吗？

Answer 1

要获取相应的 PER_IO_CONTEXT 结构的地址，您可以使用:

lpIOContext = CONTAINING_RECORD(lpOverlapped, PER_IO_CONTEXT, Overlapped);

CONTAINING_RECORD 是在 VC\crt\src\collections.h 中这样定义的一个宏:

#define CONTAINING_RECORD(address, type, field) \
    ((type *)((char *)(address) - (ULONG_PTR)(&((type *)0)->field)))

更多信息:http://msdn.microsoft.com/en-us/library/windows/hardware/ff542043%28v=vs.85%29.aspx