win32 ReadFile 读文件到最后 （异步方式）

参考网页 :

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365690(v=vs.85).aspx

VS2010 建立一个console 工程，设置编码格式为：

代码如下：

#include "stdafx.h"
#include 
#include 
#include 

#define BUF_SIZE (61)

LPCTSTR ErrorMessage( DWORD error ) 

// Routine Description:
//      Retrieve the system error message for the last-error code
{ 

    LPVOID lpMsgBuf;

    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | 
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        error,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPTSTR) &lpMsgBuf,
        0, NULL );

    return((LPCTSTR)lpMsgBuf);
}

void GoDoSomethingElse(void)

// Routine Description:
//     Placeholder to demo when async I/O might want to do
//     other processing.
{
    printf("Inside GoDoSomethingElse()\n");
}

DWORD AsyncTestForEnd( HANDLE hEvent, HANDLE hFile )

// Routine Description:
//      Demonstrate async ReadFile operations that can catch
//      End-of-file conditions. Unless the operation completes
//      synchronously or the file size happens to be an exact
//      multiple of BUF_SIZE, this routine will eventually force
//      an EOF condition on any file.

// Parameters:
//      hEvent - pre-made manual-reset event.
//
//      hFile - pre-opened file handle, overlapped.
//
//      inBuffer - the buffer to read in the data to.
//
//      nBytesToRead - how much to read (usually the buffer size).

// Return Value:
//      Number of bytes read.
{
    char inBuffer[BUF_SIZE];
    DWORD nBytesToRead      = BUF_SIZE;
    DWORD dwBytesRead       = 0;
    DWORD dwFileSize        = GetFileSize(hFile, NULL);
    OVERLAPPED stOverlapped = {0};

    DWORD dwError  = 0;
    LPCTSTR errMsg = NULL;

    BOOL bResult   = FALSE;
    BOOL bContinue = TRUE;

    // Set up overlapped structure event. Other members are already 
    // initialized to zero.
    stOverlapped.hEvent = hEvent; 

    // This is an intentionally brute-force loop to force the EOF trigger.
    // A properly designed loop for this simple file read would use the
    // GetFileSize API to regulate execution. However, the purpose here
    // is to demonstrate how to trigger the EOF error and handle it.

    while(bContinue)
    {
        // Default to ending the loop.
        bContinue = FALSE;

        // Attempt an asynchronous read operation.
        bResult = ReadFile(hFile,
                           inBuffer,
                           nBytesToRead,
                           &dwBytesRead,
                           &stOverlapped); 

        dwError = GetLastError();

        // Check for a problem or pending operation. 
        if (!bResult) 
        { 
            switch (dwError) 
            { 

                case ERROR_HANDLE_EOF:
                {
                    printf("\nReadFile returned FALSE and EOF condition, async EOF not triggered.\n");
                    break;
                }
                case ERROR_IO_PENDING: 
                { 
                    BOOL bPending=TRUE;

                    // Loop until the I/O is complete, that is: the overlapped 
                    // event is signaled.

                    while( bPending )
                    {
                        bPending = FALSE;

                        // Pending asynchronous I/O, do something else
                        // and re-check overlapped structure.
                        printf("\nReadFile operation is pending\n");

                        // Do something else then come back to check. 
                        GoDoSomethingElse(); 

                        // Check the result of the asynchronous read
                        // without waiting (forth parameter FALSE). 
                        bResult = GetOverlappedResult(hFile,
                                                      &stOverlapped,
                                                      &dwBytesRead,
                                                      FALSE) ; 

                        if (!bResult) 
                        { 
                            switch (dwError = GetLastError()) 
                            { 
                                case ERROR_HANDLE_EOF: 
                                { 
                                    // Handle an end of file
                                    printf("GetOverlappedResult found EOF\n");
                                    break;
                                } 

                                case ERROR_IO_INCOMPLETE:
                                {
                                    // Operation is still pending, allow while loop
                                    // to loop again after printing a little progress.
                                    printf("GetOverlappedResult I/O Incomplete\n");
                                    bPending = TRUE;
                                    bContinue = TRUE;
                                    break;
                                }

                                default:
                                {
                                    // Decode any other errors codes.
                                    errMsg = ErrorMessage(dwError);
                                    _tprintf(TEXT("GetOverlappedResult failed (%d): %s\n"), 
                                        dwError, errMsg);
                                    LocalFree((LPVOID)errMsg);
                                }
                            }
                        } 
                        else
                        {
                            printf("ReadFile operation completed\n");

                            // Manual-reset event should be reset since it is now signaled.
                            ResetEvent(stOverlapped.hEvent);
                        }
                    }
                    break;
                }

                default:
                {
                    // Decode any other errors codes.
                    errMsg = ErrorMessage(dwError);
                    printf("ReadFile GLE unhandled (%d): %s\n", dwError, errMsg); 
                    LocalFree((LPVOID)errMsg);
                    break;
                }
            }
        }
        else
        {
            // EOF demo did not trigger for the given file.
            // Note that system caching may cause this condition on most files
            // after the first read. CreateFile can be called using the
            // FILE_FLAG_NOBUFFERING parameter but it would require reads are
            // always aligned to the volume's sector boundary. This is beyond
            // the scope of this example. See comments in the main() function.

            printf("ReadFile completed synchronously\n");
        }

        // The following operation assumes the file is not extremely large, otherwise 
        // logic would need to be included to adequately account for very large
        // files and manipulate the OffsetHigh member of the OVERLAPPED structure.

        stOverlapped.Offset += dwBytesRead;
        if ( stOverlapped.Offset < dwFileSize )             
            bContinue = TRUE;
    }

    return stOverlapped.Offset;
}

#define   FILE_NAME    TEXT("126.txt")

void __cdecl _tmain(int argc, TCHAR *argv[])

// To force an EOF condition, execute this application specifying a
// zero-length file. This is because the offset (file pointer) must be
// at or beyond the end-of-file marker when ReadFile is called. For
// more information, see the comments for the AsyncTestForEnd routine.

{
    HANDLE hEvent;
    HANDLE hFile;
    DWORD dwReturnValue;

    printf("\n");


    hFile = CreateFile(FILE_NAME,                // file to open
                       GENERIC_READ,           // open for reading
                       FILE_SHARE_READ,        // share for reading
                       NULL,                   // default security
                       OPEN_EXISTING,          // existing file only
                       FILE_FLAG_OVERLAPPED,   // overlapped operation
                       NULL);                  // no attr. template

    if (hFile == INVALID_HANDLE_VALUE) 
    { 
        DWORD dwError = GetLastError();
        LPCTSTR errMsg = ErrorMessage(dwError);
        printf("Could not open file (%d): %s\n", dwError, errMsg); 
        LocalFree((LPVOID)errMsg);
        return; 
    }

    hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

    if (hEvent == NULL) 
    { 
        DWORD dwError = GetLastError();
        LPCTSTR errMsg = ErrorMessage(dwError);
        printf("Could not CreateEvent: %d %s\n", dwError, errMsg); 
        LocalFree((LPVOID)errMsg);
        return; 
    }

    dwReturnValue = AsyncTestForEnd(hEvent, hFile);

    printf( "\nRead complete. Bytes read: %d\n", dwReturnValue);

    CloseHandle(hFile);
    CloseHandle(hEvent);
}

读的文件内容如下：

This is some test data to write to the file.
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
cccccccccccccccccccccccccccccccccccccccccc
dddddddddddddddddddddddddddddddddddddddddd
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

运行结果如下：

ReadFile operation is pending
Inside GoDoSomethingElse()
ReadFile operation completed

ReadFile operation is pending
Inside GoDoSomethingElse()
ReadFile operation completed

ReadFile operation is pending
Inside GoDoSomethingElse()
ReadFile operation completed

ReadFile operation is pending
Inside GoDoSomethingElse()
ReadFile operation completed

ReadFile operation is pending
Inside GoDoSomethingElse()
ReadFile operation completed

Read complete. Bytes read: 266
请按任意键继续. . .