GetOverlappedResult 返回成功，但传输字节数总为0

下面时打开的代码 
        m_hCom=CreateFile(m_sPort, GENERIC_READ | GENERIC_WRITE, 0, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED, 
NULL); // 重叠方式 if(m_hCom==INVALID_HANDLE_VALUE)
return FALSE; SetupComm(m_hCom,MAXBLOCK,MAXBLOCK);
SetCommMask(m_hCom, EV_RXCHAR); TimeOuts.ReadIntervalTimeout=MAXDWORD; 
TimeOuts.ReadTotalTimeoutMultiplier=0; 
TimeOuts.ReadTotalTimeoutConstant=0;  /* 设置写超时以指定WriteComm成员函数中的GetOverlappedResult函数的等待时间*/
TimeOuts.WriteTotalTimeoutMultiplier=50;
TimeOuts.WriteTotalTimeoutConstant=2000; SetCommTimeouts(m_hCom, &TimeOuts);