串口ReadFile返回实际读取大小始终为0？解决思路

串口ReadFile返回实际读取大小始终为0？
VC6，异步，串口设备半双工
现在的一个应用就是向串口设备发送字符串命令，然后串口设备会返回一串结果，该结果长度可能在20~260之间，需要解析
可遇到一个问题，ReadFile的第三个参数（需要读取多长字节）小于串口设备实际返回长度的话，ReadFile函数返回的实际读取长度将是正确的（等于第三个参数的大小），若填260，则返回的实际读取长度始终为0，似乎是没完成260的额度ReadFile就无法读取串口返回数据了
串口读写上花费太多时间了，急死了，协议都没解析，已经耽误了事情
请大家帮我看看问题在哪里，顺便看看我的串口函数写得是不是有不合理的情况，我只能发56分的帖子倾囊发帖，非常感谢！！！

C/C++ code


// ***************************************打开串口
HANDLE OpenComm( LPCTSTR lpCommPort, UINT nBaudRate, UINT nParity, UINT nDataBits, UINT nStopBits)
{
    HANDLE hComm = CreateFile(
        lpCommPort,
        GENERIC_READ | GENERIC_WRITE,
        0,
        NULL,
        OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED,
        NULL
        );
    if (hComm == INVALID_HANDLE_VALUE)
        return NULL;

    DCB dcb = {0};
    dcb.DCBlength = sizeof(DCB);
    if (!GetCommState(hComm, &dcb))
    {
        CloseComm(hComm);
        return NULL;
    }
    dcb.BaudRate = nBaudRate;
    dcb.fBinary  = TRUE;
    dcb.fParity  = nParity ? TRUE : FALSE;
    dcb.Parity   = nParity;
    dcb.ByteSize = nDataBits;
    dcb.StopBits = nStopBits;
    if (!SetCommState(hComm, &dcb))
    {
        CloseComm(hComm);
        return NULL;
    }
    
    return hComm;
}

// ***************************************读串口
BOOL ReadComm(HANDLE hComm, LPVOID lpBuf, DWORD nBufSize, LPDWORD lpReadSize)
{
    if (hComm == NULL || hComm == INVALID_HANDLE_VALUE || lpBuf == NULL || nBufSize == 0) return FALSE;

    COMSTAT ComStat;
    DWORD dwErrorFlags;
    OVERLAPPED m_osRead;
    memset(&m_osRead,0,sizeof(OVERLAPPED));
    // ******************WaitForSingleObject方式
    m_osRead.hEvent=CreateEvent(NULL,TRUE,FALSE,NULL);
    
    ClearCommError(hComm,&dwErrorFlags,&ComStat);
    if((DWORD)ComStat.cbInQue)
        return FALSE;
    BOOL bReadStatus;
    bReadStatus = ReadFile(hComm, lpBuf, nBufSize, lpReadSize, &m_osRead);
    
    if(!bReadStatus)
    {
        DWORD LASTERROR = GetLastError();
        if(LASTERROR == ERROR_IO_PENDING)
        {
            // ******************WaitForSingleObject方式
            DWORD dwWaitObj = WaitForSingleObject(m_osRead.hEvent, 3000);
            if(dwWaitObj == WAIT_OBJECT_0)
            {
                //问题就是：
                // ReadComm倒数第二个参数nBufSize为15（等比较小的数）时，可以进到这里，*lpReadSize将等于15
                // 若填260，则dwWaitObj总是超时，此时即使不判断dwWaitObj依然查看m_osRead.InternalHigh值的话，
                // 该值始终始终为0
                *lpReadSize = m_osRead.InternalHigh;
                if(*lpReadSize > 0)
                {
                    int b = *lpReadSize;
                }
                bReadStatus = TRUE;
            }
            else
            {
                bReadStatus = FALSE;
            }

            // ******************GetOverlappedResult方式
            //::GetOverlappedResult(hComm, &m_osRead, lpReadSize, TRUE);
        }
        else if(LASTERROR == NO_ERROR)
        {
            bReadStatus = TRUE;
        }
        else
        {
            bReadStatus = FALSE;
        }
    }
    PurgeComm(hComm, PURGE_TXABORT | PURGE_RXABORT | PURGE_TXCLEAR | PURGE_RXCLEAR);
    return bReadStatus;
}

// ***************************************写串口
BOOL WriteComm(HANDLE hComm, LPCVOID lpBuf, DWORD nDataSize, LPDWORD lpWriteSize)
{
    if (hComm == NULL || hComm == INVALID_HANDLE_VALUE || lpBuf == NULL || nDataSize == 0) return FALSE;

    DWORD dwErrorFlags;
    COMSTAT ComStat;
    OVERLAPPED m_osWrite;
    BOOL bWriteStat;
    memset(&m_osWrite,0,sizeof(OVERLAPPED));
    // ******************WaitForSingleObject方式
    m_osWrite.hEvent=CreateEvent(NULL,TRUE,FALSE,NULL);
    
    ClearCommError(hComm, &dwErrorFlags, &ComStat);
    bWriteStat = WriteFile(hComm, lpBuf, nDataSize, lpWriteSize, &m_osWrite);
    if(!bWriteStat)
    {
        DWORD LASTERROR = GetLastError();
        if(LASTERROR == ERROR_IO_PENDING)
        {
            // ******************WaitForSingleObject方式
            DWORD dwWaitObj = WaitForSingleObject(m_osWrite.hEvent, 500);
            if(dwWaitObj == WAIT_OBJECT_0)
            {
                *lpWriteSize = m_osWrite.InternalHigh;
                bWriteStat = TRUE;
            }
            else
            {
                bWriteStat = FALSE;
            }

            // ******************GetOverlappedResult方式
            //::GetOverlappedResult(hComm, &m_osWrite, lpWriteSize, TRUE);
        }
        else if(LASTERROR == NO_ERROR)
        {
            bWriteStat = TRUE;
        }
        else
        {
            bWriteStat = FALSE;
        }
    }
    PurgeComm(hComm, PURGE_TXABORT | PURGE_RXABORT | PURGE_TXCLEAR | PURGE_RXCLEAR);
    return bWriteStat;
}

// ***************************************向串口写入命令并等待回复
BOOL SendGetComm(HANDLE hComm,LPBYTE lpByteCommand,DWORD dwCommandSize,BOOL bWantReturn,LPBYTE lpByteReturn,
DWORD dwByteToRead,LPDWORD lpReturnSize)
{
    DWORD dwSendCommandSize = 0;
    
    if (!WriteComm(hComm, lpByteCommand, dwCommandSize, (LPDWORD)&dwSendCommandSize))
    {
        return FALSE;
    }
    
    if( dwSendCommandSize == dwCommandSize )
    {
        if(bWantReturn)
        {
            if(!lpReturnSize || !lpByteReturn || dwByteToRead < 0)
                return FALSE;
            *lpReturnSize = 0;
            if (!ReadComm(hComm, lpByteReturn, dwByteToRead, lpReturnSize))
            {
                return FALSE;
            }
            else
            {
                return TRUE;
            }
        }
        else
        {
            return TRUE;
        }
    }
    else
    {
        return FALSE;
    }
}

// 倒数第二个参数填15（等比较小的数）时，dwReadSize将大于0，
// 若填260，dwReadSize始终为0，
BYTE szReturn[260];
DWORD dwReadSize;
return SendGetRWComm(m_hComm, lpCommandInfo, nCommandSize, TRUE, szReturn, 15, &dwReadSize);

串口ReadFile返回实际读取大小始终为0？解决思路

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