如何将 ReadDirectoryChangesW() 方法与完成例程一起使用？

Question

我想在异步模式下使用函数 ReadDirectoryChangesW() 并提供 I/O 完成例程。

问题是我不知道如何检索有关完成例程（CALLBACK 函数）中更改的确切信息。 完成例程的定义如下：

VOID CALLBACK FileIOCompletionRoutine(
  [in]                 DWORD dwErrorCode,
  [in]                 DWORD dwNumberOfBytesTransfered,
  [in]                 LPOVERLAPPED lpOverlapped
);

我想知道这些信息是否包含在 LPOVERLAPPED 结构中。 但我不知道如何得到它。

Answer 1

很好的问题！ 虽然晚了 7 年，但这里有一些答案，或者更重要的是，如何找到它。 因此，ReadDirectoryChangesW 的文档：

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365465%28v=vs.85%29.aspx

提供了 FileIOCompletionRoutine 的链接：

https://msdn.microsoft.com/ en-us/library/windows/desktop/aa364052%28v=vs.85%29.aspx

在示例部分中提供了使用完成例程的命名管道服务器的链接：

https://msdn.microsoft.com/en-us/library /windows/desktop/aa365601%28v=vs.85%29.aspx

信不信由你，它甚至没有使用 ReadDirectoryChangesW，但实际上给出了一个使用 ReadFileEx 的示例，其中还使用 FileIOCompletionRoutine ：

https://msdn .microsoft.com/en-us/library/windows/desktop/aa365468%28v=vs.85%29.aspx

，您可以看到使用这两个函数（ReadFileEx 和 CompletedReadRoutine）的示例（这是一个这段代码中应用程序定义的回调函数 FileIOCompletionRoutine 的实现））：

// CompletedWriteRoutine(DWORD, DWORD, LPOVERLAPPED) 
// This routine is called as a completion routine after writing to 
// the pipe, or when a new client has connected to a pipe instance.
// It starts another read operation. 
    
VOID WINAPI CompletedWriteRoutine(DWORD dwErr, DWORD cbWritten, 
    LPOVERLAPPED lpOverLap) 
{ 
    LPPIPEINST lpPipeInst; 
    BOOL fRead = FALSE; 
    
// lpOverlap points to storage for this instance. 
    
    lpPipeInst = (LPPIPEINST) lpOverLap; 
    
// The write operation has finished, so read the next request (if 
// there is no error). 
    
    if ((dwErr == 0) && (cbWritten == lpPipeInst->cbToWrite)) 
        fRead = ReadFileEx( 
            lpPipeInst->hPipeInst, 
            lpPipeInst->chRequest, 
            BUFSIZE*sizeof(TCHAR), 
            (LPOVERLAPPED) lpPipeInst, 
            (LPOVERLAPPED_COMPLETION_ROUTINE) CompletedReadRoutine); 
    
// Disconnect if an error occurred. 
    
    if (! fRead) 
        DisconnectAndClose(lpPipeInst); 
} 
    
// CompletedReadRoutine(DWORD, DWORD, LPOVERLAPPED) 
// This routine is called as an I/O completion routine after reading 
// a request from the client. It gets data and writes it to the pipe. 
    
VOID WINAPI CompletedReadRoutine(DWORD dwErr, DWORD cbBytesRead, 
    LPOVERLAPPED lpOverLap) 
{ 
    LPPIPEINST lpPipeInst; 
    BOOL fWrite = FALSE; 
    
// lpOverlap points to storage for this instance. 
    
    lpPipeInst = (LPPIPEINST) lpOverLap; 
    
// The read operation has finished, so write a response (if no 
// error occurred). 
    
    if ((dwErr == 0) && (cbBytesRead != 0)) 
    { 
        GetAnswerToRequest(lpPipeInst); 
    
        fWrite = WriteFileEx( 
            lpPipeInst->hPipeInst, 
            lpPipeInst->chReply, 
            lpPipeInst->cbToWrite, 
            (LPOVERLAPPED) lpPipeInst, 
            (LPOVERLAPPED_COMPLETION_ROUTINE) CompletedWriteRoutine); 
    } 
    
// Disconnect if an error occurred. 
    
    if (! fWrite) 
        DisconnectAndClose(lpPipeInst); 
}

这不是一个很好的答案（我只是在探索我自己是否想使用这些函数），但它应该可以帮助人们入门。

另请参阅：

https:// /msdn.microsoft.com/en-us/library/windows/desktop/aa365261%28v=vs.85%29.aspx