c++ - WIN API ReadFile() 返回 GetLastError() ERROR_INVALID_PARAMETER

Question

我在下面编写了这段代码，它在 code::blocks 下运行良好，使用 mingw gcc 4.7 进行编译。从那以后，我决定开始使用 Visual Studio 2013 Express。现在调用 ReadFile() 时出现错误。这似乎是一个无效参数。我看不到错误，希望这里有人能发现它。

这一切都包含在一个类 Serial 中。从我在 IDE 中看到的情况来看，与 CreateFile() 返回句柄的引用相比，m_hSerial 的内存引用是正确的。

m_hSerial = CreateFile(m_pchPort,
                       GENERIC_READ | GENERIC_WRITE,
                       0,
                       0,
                       OPEN_EXISTING,
                       FILE_FLAG_OVERLAPPED,
                       0);

我这样调用WorkThread

m_hThread = (HANDLE)_beginthreadex(0, 0, &WorkThread, (void*) this, 0, 0);

这是工作线程代码

unsigned int __stdcall Serial::WorkThread(void* pvParam)
{
// This is a pointer to the 'this' serial class.
// Needed to be able to set members of the class in a static class function
Serial * cThis = (Serial*) pvParam;
// Set up the overlapped event
OVERLAPPED ov;
memset(&ov, 0, sizeof(ov));
ov.hEvent = CreateEvent(0, true, 0, 0);
DWORD dwEventMask = 0;
DWORD dwWait;
HANDLE aHandles[2];
aHandles[0] = cThis->m_hThreadTerminator;
aHandles[1] = ov.hEvent;

SetEvent(cThis->m_hThreadRunning);
while (true)
{
    if (!WaitCommEvent(cThis->m_hSerial, &dwEventMask, &ov))
    {
        assert(GetLastError() == ERROR_IO_PENDING);

    }

    dwWait = WaitForMultipleObjects(2, aHandles, FALSE, INFINITE);
    switch(dwWait)
    {
        case WAIT_OBJECT_0:
        {
            _endthreadex(1);
        }
        case WAIT_OBJECT_0 + 1:
        {
            if (dwEventMask & EV_TXEMPTY)
            {
                ResetEvent(ov.hEvent);
            }
            else if (dwEventMask & EV_RXCHAR)
            {
                // read data here
                DWORD dwBytesRead = 0;
                DWORD dwErrors;
                COMSTAT cStat;
                OVERLAPPED ovRead;
                ovRead.hEvent = CreateEvent(0, true, 0, 0);

                // Get the Bytes in queue
                ClearCommError(cThis->m_hSerial, &dwErrors, &cStat);
                DWORD nSize = cStat.cbInQue;
                // EM_REPLACESEL needs a LPARAM null terminated string, make room and set the CString NULL
                char *szBuf = new char[nSize+1];
                memset(szBuf, 0x00, sizeof(szBuf));

                if (!ReadFile(cThis->m_hSerial, &szBuf, nSize, &dwBytesRead, &ovRead))
                    DWORD err = GetLastError();
                if (dwBytesRead == nSize)
                    SendMessage(cThis->m_hHwnd, WM_SERIAL, 0, LPARAM(&szBuf));

                CloseHandle(ovRead.hEvent); // clean up!!!
                delete[] szBuf;
            }
            // Reset the overlapped event
            ResetEvent(ov.hEvent);
        }
        break;
    }//switch
}

return 0;

Answer 1

ReadFile(cThis->m_hSerial, &szBuf, nSize, &dwBytesRead, &ovRead)

你要求一个异步操作，同时要求函数告诉你已经读取了多少字节。您传递了 &dwBytesRead 作为倒数第二个参数。当您执行重叠读取时，为此参数传递 NULL。 documentation说:

Use NULL for this parameter if this is an asynchronous operation to avoid potentially erroneous results.

在上面的代码中传递&szBuf也是错误的。你的意思是传递 szBuf。

您也无法初始化 OVERLAPPED 结构。这样做:

OVERLAPPED ovRead = {};

一个更大的问题是您请求异步访问，但随后编写的代码就像它是同步的一样。 ReadFile 返回后，您将尝试从 dwBytesRead 中获取有意义的信息，并关闭放置在重叠结构中的事件。

如果您真的打算异步编写代码，则需要重新编写异步代码。从表面上看，您似乎还没有完全理解重叠 I/O 的含义，您或许应该切换到非重叠、同步 I/O。