CSerialPort多线程串口编程工具详解

1.前言

既然有了MSComm这种简单粗暴的控件，为什么还需要CSerialPort类？这是因为与前者相比，这个类在程序的发布上不需要加入其他的文件，而且CSerialPort提供给我们的函数都是开放透明的，允许我们进行二次改造。

CSerialPort类是一个非常好用的多线程串口编程工具，可以在很短的时间就可以完成一个串口通讯框架的搭建，所以有必要加以记载！

2.CSerialPort类的功能及成员函数介绍

2.1 CSerialPort工作流程

首先设置好串口参数，在开启串口监测工作线程，串口监测工作线程监测到串口接收到的数据、流控制事件或其他串口时间后，就以消息的方式通知主程序，激发消息处理函数来进行数据处理，这是对接收数据而言的！发送数据的话，可以直接向串口发送。

2.2 CSerialPort类定义的消息

消息名称
消息号
功能说明WM_COMM_BREAK_DETECTEDWM_USER+1检测到输入中断WM_COMM_CTS_DETECTEDWM_USER+2检测到CTS（清除发送）信号状态改变WM_COMM_DSR_DETECTEDWM_USER+3检测到DSR（数据准备就绪）状态改变WM_COMM_ERR_DETECTEDWM_USER+4发生线状态错误（包括CE_FRAME
，CE_OVERRUN，和CE_RXPARITY）WM_COMM_RING_DETECTEDWM_USER+5检测到响铃指示信号WM_COMM_RLSD_DETECTEDWM_USER+6检测到RLSD（接收线信号）状态改变WM_COMM_RXCHARWM_USER+7接收到一个字符并已放入接受缓冲区WM_COMM_RXFLAG_DETECTEDWM_USER+8检测到接受到字符（已放缓冲区）事件WM_COMM_TXEMPTY_DETECTEDWM_USER+9检测到发送缓冲区最后一字符已被发送

2.3 CSerialPort类定义的成员函数

1.串口初始化函数InitPort

BOOL CSerialPort::InitPort(CWnd *pPortOwner,    // the owner (CWnd) of the port (receives message)                            UINT  portnr,        // portnumber (1..4)                            UINT  baud,            // baudrate                            char  parity,        // parity                            UINT  databits,        // databits                            UINT  stopbits,        // stopbits                            DWORD dwCommEvents,    // EV_RXCHAR, EV_CTS etc                            UINT  writebuffersize)    // size to the writebuffer 

这个函数是用来初始化串口的，即设置串口的通信参数：需要打开的串口号、波特率、奇偶校验方式、数据位、停止位，这里还可 以用来进行事件的设定。

如果串口初始化成功，就返回TRUE，若串口被其他设备占用、不存在或存在其他股占，就返回FALSE，编程者可以在这儿提示串口操作是否成功。

如果在当前主串口调用这个函数，那么pPortOwner可用this指针表示，串口号在函数中做了限制，只能用1，2，3和4四个串口号，而事实上在编程时可能用到更多串口号，可以通过通过注释掉本函数中的“assert(portur>0&&portnr<5)”语句取消对串口号的限制。

2.启用串口通信检测线程函数StartMonitoring()

BOOL CSerialPort::StartMonitoring() { if (!(m_Thread = AfxBeginThread(CommThread, this))) return FALSE; TRACE("Thread started\n"); return TRUE; } 

串口初始化成功后，就可以调用BOOL StartMonitoring()来启动串口检测线程，线程启动成功，返回TRUE。

调用InitPort和StartMonitoring()以后，串口就被打开了，各种串口状态和事件就可以被监测到。

3.暂停或听着监测线程函数StopMonitoring()

BOOL CSerialPort::StopMonitoring() {      TRACE("Thread suspended\n");      m_Thread->SuspendThread();      return TRUE; } 

该函数暂停或停止串口检测，要注意的是，调用该函数后，串口资源仍然被占用

4.关闭串口函数ClosePort()

void CSerial::ClosePort(){SetEvent(m_hShutdownEvent);}

该函数功能是关闭串口，释放串口资源，调用该函数后，如果要继续使用串口，还需要调用InitPort()函数

5.通过串口发送字符/写串口函数WriteToPort()

void CSerialPort::WriteToPort(char *string) {assert(m_hComm != 0); memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer)); strcpy(m_szWriteBuffer, string);  // set event for write SetEvent(m_hWriteEvent); } 

该函数完成写串口功能，即向串口发送字符。

以上是常用的函数介绍，熟悉该类的使用后，可以仔细看看其他函数，对上面介绍的函数，在对串口资源的使用上要记住一下三点：

l 打开串口用调用InitPort()和StartMonitoring()；关闭串口用StopMonitoring()和ClosePort(),而且以上函数的调用顺序不能乱

l 通过串口发送字符调用函数WriteToPort（）

l 接受串口收到的字符需要自己编写WM_COMM_RXCHAR消息处理函数，需要手工添加。

3.CSerialPort.h和CSerialPort.cpp文件细节

#ifndef __SERIALPORT_H__   #define __SERIALPORT_H__      #define WM_COMM_BREAK_DETECTED        WM_USER+1    // A break was detected on input.   #define WM_COMM_CTS_DETECTED        WM_USER+2    // The CTS (clear-to-send) signal changed state.    #define WM_COMM_DSR_DETECTED        WM_USER+3    // The DSR (data-set-ready) signal changed state.    #define WM_COMM_ERR_DETECTED        WM_USER+4    // A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY.    #define WM_COMM_RING_DETECTED        WM_USER+5    // A ring indicator was detected.    #define WM_COMM_RLSD_DETECTED        WM_USER+6    // The RLSD (receive-line-signal-detect) signal changed state.    #define WM_COMM_RXCHAR                WM_USER+7   // A character was received and placed in the input buffer.    #define WM_COMM_RXFLAG_DETECTED  WM_USER+8 // The event character was received and placed in the input buffer.     #define WM_COMM_TXEMPTY_DETECTED    WM_USER+9    // The last character in the output buffer was sent.           class CSerialPort   {   public:       void ClosePort();       void WriteToPort(LPCTSTR string, int n);       void WriteToPort(LPCTSTR string);       void WriteToPort(char *string, int n);       CSerialPort();       virtual        ~CSerialPort();       BOOL        InitPort(CWnd *pPortOwner,    // the owner (CWnd) of the port (receives message)                            UINT  portnr,        // portnumber (1..4)                            UINT  baud,            // baudrate                            char  parity,        // parity                            UINT  databits,        // databits                            UINT  stopbits,        // stopbits                            DWORD dwCommEvents,    // EV_RXCHAR, EV_CTS etc                            UINT  writebuffersize);    // size to the writebuffer          BOOL        StartMonitoring();       BOOL        RestartMonitoring();       BOOL        StopMonitoring();       DWORD       GetWriteBufferSize();       DWORD       GetCommEvents();       DCB         GetDCB();          void        WriteToPort(char *string);       int m_nWriteSize;      protected:       // protected memberfunctions       void        ProcessErrorMessage(char *ErrorText);       static UINT    CommThread(LPVOID pParam);       static void    ReceiveChar(CSerialPort *port, COMSTAT comstat);       static void    WriteChar(CSerialPort *port);          // thread       CWinThread            *m_Thread;          // synchronisation objects       CRITICAL_SECTION    m_csCommunicationSync;       BOOL                m_bThreadAlive;          // handles       HANDLE                m_hShutdownEvent;       HANDLE                m_hComm;       HANDLE                m_hWriteEvent;          // Event array.       // One element is used for each event. There are two event handles for each port.       // A Write event and a receive character event which is located in the overlapped structure (m_ov.hEvent).       // There is a general shutdown when the port is closed.       HANDLE                m_hEventArray[3];          // structures       OVERLAPPED          m_ov;       COMMTIMEOUTS        m_CommTimeouts;       DCB                 m_dcb;          // owner window       CWnd                *m_pOwner;          // misc       UINT                m_nPortNr;       char                *m_szWriteBuffer;       DWORD                m_dwCommEvents;       DWORD                m_nWriteBufferSize;   };      #endif __SERIALPORT_H__   

CSerialPort.cpp   /*    ** FILENAME CSerialPort.cpp    **    ** PURPOSE This class can read, write and watch one serial port.    ** It sends messages to its owner when something happends on the port    ** The class creates a thread for reading and writing so the main    ** program is not blocked.    **    ** CREATION DATE 15-09-1997    ** LAST MODIFICATION 12-11-1997    **    ** AUTHOR Remon Spekreijse    **    **    */         #include "stdafx.h"      #include "CSerialPort.h"      #include <assert.h>         //      // Constructor      //      CSerialPort::CSerialPort()      {          m_hComm = NULL;             // initialize overlapped structure members to zero          m_ov.Offset = 0;          m_ov.OffsetHigh = 0;             // create events          m_ov.hEvent = NULL;          m_hWriteEvent = NULL;          m_hShutdownEvent = NULL;             m_szWriteBuffer = NULL;             m_bThreadAlive = FALSE;             m_nWriteSize = 0;      }         //      // Delete dynamic memory      //      CSerialPort::~CSerialPort()      {          do          {              SetEvent(m_hShutdownEvent);          }       while (m_bThreadAlive);             TRACE("Thread ended\n");             delete [] m_szWriteBuffer;      }         //      // Initialize the port. This can be port 1 to 4.      //      BOOL CSerialPort::InitPort(CWnd *pPortOwner, // the owner (CWnd) of the port (receives message)                                 UINT  portnr, // portnumber (1..4)                                 UINT  baud, // baudrate                                 char  parity, // parity                                 UINT  databits, // databits                                 UINT  stopbits, // stopbits                                 DWORD dwCommEvents, // EV_RXCHAR, EV_CTS etc                                 UINT  writebuffersize) // size to the writebuffer      {          assert(portnr > 0 && portnr < 5);          assert(pPortOwner != NULL);             // if the thread is alive: Kill          if (m_bThreadAlive)          {              do              {                  SetEvent(m_hShutdownEvent);              }           while (m_bThreadAlive);              TRACE("Thread ended\n");          }             // create events          if (m_ov.hEvent != NULL)              ResetEvent(m_ov.hEvent);          else              m_ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);             if (m_hWriteEvent != NULL)              ResetEvent(m_hWriteEvent);          else              m_hWriteEvent = CreateEvent(NULL, TRUE, FALSE, NULL);             if (m_hShutdownEvent != NULL)              ResetEvent(m_hShutdownEvent);          else              m_hShutdownEvent = CreateEvent(NULL, TRUE, FALSE, NULL);             // initialize the event objects          m_hEventArray[0] = m_hShutdownEvent; // highest priority          m_hEventArray[1] = m_ov.hEvent;          m_hEventArray[2] = m_hWriteEvent;             // initialize critical section          InitializeCriticalSection(&m_csCommunicationSync);             // set buffersize for writing and save the owner          m_pOwner = pPortOwner;             if (m_szWriteBuffer != NULL)              delete [] m_szWriteBuffer;          m_szWriteBuffer = new char[writebuffersize];             m_nPortNr = portnr;             m_nWriteBufferSize = writebuffersize;          m_dwCommEvents = dwCommEvents;             BOOL bResult = FALSE;          char *szPort = new char[50];          char *szBaud = new char[50];             // now it critical!          EnterCriticalSection(&m_csCommunicationSync);             // if the port is already opened: close it          if (m_hComm != NULL)          {              CloseHandle(m_hComm);              m_hComm = NULL;          }             // prepare port strings          sprintf(szPort, "COM%d", portnr);          sprintf(szBaud, "baud=%d parity=%c data=%d stop=%d", baud, parity, databits, stopbits);             // get a handle to the port          m_hComm = CreateFile(szPort, // communication port string (COMX)                               GENERIC_READ | GENERIC_WRITE, // read/write types                               0, // comm devices must be opened with exclusive access                               NULL, // no security attributes                               OPEN_EXISTING, // comm devices must use OPEN_EXISTING                               FILE_FLAG_OVERLAPPED, // Async I/O                               0); // template must be 0 for comm devices             if (m_hComm == INVALID_HANDLE_VALUE)          {              // port not found              delete [] szPort;              delete [] szBaud;                 return FALSE;          }             // set the timeout values          m_CommTimeouts.ReadIntervalTimeout = 1000;          m_CommTimeouts.ReadTotalTimeoutMultiplier = 1000;          m_CommTimeouts.ReadTotalTimeoutConstant = 1000;          m_CommTimeouts.WriteTotalTimeoutMultiplier = 1000;          m_CommTimeouts.WriteTotalTimeoutConstant = 1000;             // configure          if (SetCommTimeouts(m_hComm, &m_CommTimeouts))          {              if (SetCommMask(m_hComm, dwCommEvents))              {                  if (GetCommState(m_hComm, &m_dcb))                  {                      m_dcb.fRtsControl = RTS_CONTROL_ENABLE; // set RTS bit high!                      if (BuildCommDCB(szBaud, &m_dcb))                      {                          if (SetCommState(m_hComm, &m_dcb))                              ; // normal operation... continue                          else                              ProcessErrorMessage("SetCommState()");                      }                      else                          ProcessErrorMessage("BuildCommDCB()");                  }                  else                      ProcessErrorMessage("GetCommState()");              }              else                  ProcessErrorMessage("SetCommMask()");          }          else              ProcessErrorMessage("SetCommTimeouts()");             delete [] szPort;          delete [] szBaud;             // flush the port          PurgeComm(m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);             // release critical section          LeaveCriticalSection(&m_csCommunicationSync);             TRACE("Initialisation for communicationport %d completed.\nUse Startmonitor to communicate.\n", portnr);             return TRUE;      }         //      //  The CommThread Function.      //      UINT CSerialPort::CommThread(LPVOID pParam)      {          // Cast the void pointer passed to the thread back to          // a pointer of CSerialPort class          CSerialPort *port = (CSerialPort *)pParam;             // Set the status variable in the dialog class to          // TRUE to indicate the thread is running.          port->m_bThreadAlive = TRUE;             // Misc. variables          DWORD BytesTransfered = 0;          DWORD Event = 0;          DWORD CommEvent = 0;          DWORD dwError = 0;          COMSTAT comstat;          BOOL  bResult = TRUE;             // Clear comm buffers at startup          if (port->m_hComm) // check if the port is opened              PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);             // begin forever loop.  This loop will run as long as the thread is alive.          for (;;)          {                 // Make a call to WaitCommEvent().  This call will return immediatly              // because our port was created as an async port (FILE_FLAG_OVERLAPPED              // and an m_OverlappedStructerlapped structure specified).  This call will cause the              // m_OverlappedStructerlapped element m_OverlappedStruct.hEvent, which is part of the m_hEventArray to              // be placed in a non-signeled state if there are no bytes available to be read,              // or to a signeled state if there are bytes available.  If this event handle              // is set to the non-signeled state, it will be set to signeled when a              // character arrives at the port.                 // we do this for each port!                 bResult = WaitCommEvent(port->m_hComm, &Event, &port->m_ov);                 if (!bResult)              {                  // If WaitCommEvent() returns FALSE, process the last error to determin                  // the reason..                  switch (dwError = GetLastError())                  {                  case ERROR_IO_PENDING:                  {                      // This is a normal return value if there are no bytes                      // to read at the port.                      // Do nothing and continue                      break;                  }                  case 87:                  {                      // Under Windows NT, this value is returned for some reason.                      // I have not investigated why, but it is also a valid reply                      // Also do nothing and continue.                      break;                  }                  default:                  {                      // All other error codes indicate a serious error has                      // occured.  Process this error.                      port->ProcessErrorMessage("WaitCommEvent()");                      break;                  }                  }              }              else              {                  // If WaitCommEvent() returns TRUE, check to be sure there are                  // actually bytes in the buffer to read.                  //                  // If you are reading more than one byte at a time from the buffer                  // (which this program does not do) you will have the situation occur                  // where the first byte to arrive will cause the WaitForMultipleObjects()                  // function to stop waiting.  The WaitForMultipleObjects() function                  // resets the event handle in m_OverlappedStruct.hEvent to the non-signelead state                  // as it returns.                  //                  // If in the time between the reset of this event and the call to                  // ReadFile() more bytes arrive, the m_OverlappedStruct.hEvent handle will be set again                  // to the signeled state. When the call to ReadFile() occurs, it will                  // read all of the bytes from the buffer, and the program will                  // loop back around to WaitCommEvent().                  //                  // At this point you will be in the situation where m_OverlappedStruct.hEvent is set,                  // but there are no bytes available to read.  If you proceed and call                  // ReadFile(), it will return immediatly due to the async port setup, but                  // GetOverlappedResults() will not return until the next character arrives.                  //                  // It is not desirable for the GetOverlappedResults() function to be in                  // this state.  The thread shutdown event (event 0) and the WriteFile()                  // event (Event2) will not work if the thread is blocked by GetOverlappedResults().                  //                  // The solution to this is to check the buffer with a call to ClearCommError().                  // This call will reset the event handle, and if there are no bytes to read                  // we can loop back through WaitCommEvent() again, then proceed.                  // If there are really bytes to read, do nothing and proceed.                     bResult = ClearCommError(port->m_hComm, &dwError, &comstat);                     if (comstat.cbInQue == 0)                      continue;              } // end if bResult                 // Main wait function.  This function will normally block the thread              // until one of nine events occur that require action.              Event = WaitForMultipleObjects(3, port->m_hEventArray, FALSE, INFINITE);                 switch (Event)              {              case 0:              {                  // Shutdown event.  This is event zero so it will be                  // the higest priority and be serviced first.                     port->m_bThreadAlive = FALSE;                     // Kill this thread.  break is not needed, but makes me feel better.                  AfxEndThread(100);                  break;              }              case 1: // read event              {                  GetCommMask(port->m_hComm, &CommEvent);                  if (CommEvent & EV_CTS)                      ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_CTS_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);                  if (CommEvent & EV_RXFLAG)                      ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RXFLAG_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);                  if (CommEvent & EV_BREAK)                      ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_BREAK_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);                  if (CommEvent & EV_ERR)                      ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_ERR_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);                  if (CommEvent & EV_RING)                      ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RING_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);                     if (CommEvent & EV_RXCHAR)                      // Receive character event from port.                      ReceiveChar(port, comstat);                     break;              }              case 2: // write event              {                  // Write character event from port                  WriteChar(port);                  break;              }                 } // end switch             } // close forever loop             return 0;      }         //      // start comm watching      //      BOOL CSerialPort::StartMonitoring()      {          if (!(m_Thread = AfxBeginThread(CommThread, this)))              return FALSE;          TRACE("Thread started\n");          return TRUE;      }         //      // Restart the comm thread      //      BOOL CSerialPort::RestartMonitoring()      {          TRACE("Thread resumed\n");          m_Thread->ResumeThread();          return TRUE;      }            //      // Suspend the comm thread      //      BOOL CSerialPort::StopMonitoring()      {          TRACE("Thread suspended\n");          m_Thread->SuspendThread();          return TRUE;      }            //      // If there is a error, give the right message      //      void CSerialPort::ProcessErrorMessage(char *ErrorText)      {          char *Temp = new char[200];             LPVOID lpMsgBuf;             FormatMessage(              FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,              NULL,              GetLastError(),              MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language              (LPTSTR) &lpMsgBuf,              0,              NULL          );             sprintf(Temp, "WARNING:  %s Failed with the following error: \n%s\nPort: %d\n", (char *)ErrorText, lpMsgBuf, m_nPortNr);          MessageBox(NULL, Temp, "Application Error", MB_ICONSTOP);             LocalFree(lpMsgBuf);          delete[] Temp;      }         //      // Write a character.      //      void CSerialPort::WriteChar(CSerialPort *port)      {          BOOL bWrite = TRUE;          BOOL bResult = TRUE;             DWORD BytesSent = 0;             ResetEvent(port->m_hWriteEvent);             // Gain ownership of the critical section          EnterCriticalSection(&port->m_csCommunicationSync);             if (bWrite)          {              // Initailize variables              port->m_ov.Offset = 0;              port->m_ov.OffsetHigh = 0;                 // Clear buffer              PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);                 bResult = WriteFile(port->m_hComm, // Handle to COMM Port                                  port->m_szWriteBuffer, // Pointer to message buffer in calling finction                                  //原句 strlen((char*)port->m_szWriteBuffer), // Length of message to send                                  port->m_nWriteSize,//更改后，Length of message to send                                  &BytesSent, // Where to store the number of bytes sent                                  &port->m_ov); // Overlapped structure                 // deal with any error codes              if (!bResult)              {                  DWORD dwError = GetLastError();                  switch (dwError)                  {                  case ERROR_IO_PENDING:                  {                      // continue to GetOverlappedResults()                      BytesSent = 0;                      bWrite = FALSE;                      break;                  }                  default:                  {                      // all other error codes                      port->ProcessErrorMessage("WriteFile()");                  }                  }              }              else              {                  LeaveCriticalSection(&port->m_csCommunicationSync);              }          } // end if(bWrite)             if (!bWrite)          {              bWrite = TRUE;                 bResult = GetOverlappedResult(port->m_hComm, // Handle to COMM port                                            &port->m_ov, // Overlapped structure                                            &BytesSent, // Stores number of bytes sent                                            TRUE);  // Wait flag                 LeaveCriticalSection(&port->m_csCommunicationSync);                 // deal with the error code              if (!bResult)              {                  port->ProcessErrorMessage("GetOverlappedResults() in WriteFile()");              }          } // end if (!bWrite)             // Verify that the data size send equals what we tried to send          //原句 if (BytesSent != strlen((char*)port->m_szWriteBuffer))          if(BytesSent |= port->m_nWriteSize) //修改后，Length of message to send          {              TRACE("WARNING: WriteFile() error.. Bytes Sent: %d; Message Length: %d\n", BytesSent, strlen((char *)port->m_szWriteBuffer));          }      }         //      // Character received. Inform the owner      //      void CSerialPort::ReceiveChar(CSerialPort *port, COMSTAT comstat)      {          BOOL  bRead = TRUE;          BOOL  bResult = TRUE;          DWORD dwError = 0;          DWORD BytesRead = 0;          unsigned char RXBuff;             for (;;)          {              // Gain ownership of the comm port critical section.              // This process guarantees no other part of this program              // is using the port object.                    //添加信息 防止死锁              if(WaitForSingleObject(port->m_hShutdownEvent, 0) == WAIT_OBJECT_0)                  return ;                    EnterCriticalSection(&port->m_csCommunicationSync);                 // ClearCommError() will update the COMSTAT structure and              // clear any other errors.                 bResult = ClearCommError(port->m_hComm, &dwError, &comstat);                 LeaveCriticalSection(&port->m_csCommunicationSync);                 // start forever loop.  I use this type of loop because I              // do not know at runtime how many loops this will have to              // run. My solution is to start a forever loop and to              // break out of it when I have processed all of the              // data available.  Be careful with this approach and              // be sure your loop will exit.              // My reasons for this are not as clear in this sample              // as it is in my production code, but I have found this              // solutiion to be the most efficient way to do this.                 if (comstat.cbInQue == 0)              {                  // break out when all bytes have been read                  break;              }                 EnterCriticalSection(&port->m_csCommunicationSync);                 if (bRead)              {                  bResult = ReadFile(port->m_hComm, // Handle to COMM port                                     &RXBuff, // RX Buffer Pointer                                     1, // Read one byte                                     &BytesRead, // Stores number of bytes read                                     &port->m_ov); // pointer to the m_ov structure                  // deal with the error code                  if (!bResult)                  {                      switch (dwError = GetLastError())                      {                      case ERROR_IO_PENDING:                      {                          // asynchronous i/o is still in progress                          // Proceed on to GetOverlappedResults();                          bRead = FALSE;                          break;                      }                      default:                      {                          // Another error has occured.  Process this error.                          port->ProcessErrorMessage("ReadFile()");                          break;                      }                      }                  }                  else                  {                      // ReadFile() returned complete. It is not necessary to call GetOverlappedResults()                      bRead = TRUE;                  }              }  // close if (bRead)                 if (!bRead)              {                  bRead = TRUE;                  bResult = GetOverlappedResult(port->m_hComm, // Handle to COMM port                                                &port->m_ov, // Overlapped structure                                                &BytesRead, // Stores number of bytes read                                                TRUE);  // Wait flag                     // deal with the error code                  if (!bResult)                  {                      port->ProcessErrorMessage("GetOverlappedResults() in ReadFile()");                  }              }  // close if (!bRead)                 LeaveCriticalSection(&port->m_csCommunicationSync);                 // notify parent that a byte was received              ::SendMessage((port->m_pOwner)->m_hWnd, WM_COMM_RXCHAR, (WPARAM) RXBuff, (LPARAM) port->m_nPortNr);          } // end forever loop         }         //      // Write a string to the port      //      void CSerialPort::WriteToPort(char *string)      {          assert(m_hComm != 0);             memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));          strcpy(m_szWriteBuffer, string);          m_nWriteSize = strlen(string);             // set event for write          SetEvent(m_hWriteEvent);      }         //      // Return the device control block      //      DCB CSerialPort::GetDCB()      {          return m_dcb;      }         //      // Return the communication event masks      //      DWORD CSerialPort::GetCommEvents()      {          return m_dwCommEvents;      }         //      // Return the output buffer size      //      DWORD CSerialPort::GetWriteBufferSize()      {          return m_nWriteBufferSize;      }            void CSerialPort::WriteToPort(char *string, int n)      {          assert(m_hComm != 0);          memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));          memcpy(m_szWriteBuffer, string, n);          m_nWriteSize = n;          //set event for write          SetEvent(m_hWriteEvent);      }         void CSerialPort::WriteToPort(LPCTSTR string)      {          assert(m_hComm != 0);          memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));          strcpy(m_szWriteBuffer, string);          m_nWriteSize = strlen(string);          //set event for write          SetEvent(m_hWriteEvent);      }         void CSerialPort::WriteToPort(LPCTSTR string, int n)      {          assert(m_hComm != 0);          memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));          memcpy(m_szWriteBuffer, string, n);          m_nWriteSize = n;          //set event for write          SetEvent(m_hWriteEvent);      }         void CSerialPort::ClosePort()      {          if (m_bThreadAlive)          {              MSG message;              while (m_bThreadAlive)              {                  if(::PeekMessage(&message, m_pOwner->m_hWnd, 0, 0, PM_REMOVE))                  {                      ::TranslateMessage(&message);                      ::DispatchMessage(&message);                  }                  SetEvent(m_hShutdownEvent);              }              TRACE("Thread ended\n");             }          if(m_szWriteBuffer != NULL)          {              delete [] m_szWriteBuffer;              m_szWriteBuffer = NULL;          }             if(m_hComm)          {              CloseHandle(m_hComm);              m_hComm = NULL;       }   }   

参考资料：龚建伟等，《VisualC++串口通讯编程实践》