1.前言

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。

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。

#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》