转换问题与链接列表项 [英] casting issue with linked list item

问题描述

这是我的PER_IO_CONTEXT结构（我将它们存储在单独链接的列表中）：

This is my PER_IO_CONTEXT structure (i stored them in singly linked list):

 typedef struct _PER_IO_CONTEXT 
 {

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

 } PER_IO_CONTEXT, *PPER_IO_CONTEXT;

以下是WSAsend，它们使用列表获取WSAOVERLAPPED结构：

and below is WSAsend , that use the list for getting WSAOVERLAPPED structure:

...
PSLIST_HEADER pListHead;
...

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

和GQCS获得通知的最后一部分：

and the last part when GQCS gets notification:

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

> lpIOContext =（PPER_IO_CONTEXT）lpOverlapped 不工作，因为WSAsend提供了wsaoverlapped - PER_IO_CONTEXT结构的第二个成员，因此在这种情况下不能使用诸如lpIOContext->之类的解引用。

As you can see following cast lpIOContext =(PPER_IO_CONTEXT)lpOverlapped doesn't work because WSAsend was provided with wsaoverlapped - the second member of PER_IO_CONTEXT structure, so dereferences such as lpIOContext-> can't be used in this case.

有办法处理这种情况吗？

There is a way to deal with this situation?

推荐答案

相应的PER_IO_CONTEXT结构可以使用这个：

To get the address of the corresponding PER_IO_CONTEXT struct you can use this:

lpIOContext = CONTAINING_RECORD(lpOverlapped, PER_IO_CONTEXT, Overlapped);

CONTAINING_RECORD是 VC\crt\src\ collections.h ：

CONTAINING_RECORD is a macro defined in VC\crt\src\collections.h in such a way:

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

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

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