HADLE CreateFile(PCTSTR lpFileName, //通信端口名，如"COM1"
WORD dwDesiredAccess, //对资源的访问类型
WORD dwShareMode, //指定共享模式，COM不能共享，该参数为0
PSECURITY_ATTRIBUTES lpSecurityAttributes,
//安全描述符指针，可为NULL
WORD dwCreationDisposition, //创建方式
WORD dwFlagsAndAttributes, //文件属性，可为NULL
HANDLE hTemplateFile //模板文件句柄，置为NULL
);

BOOL WINAPI GetCommState(
　HANDLE hFile, //标识通信端口的句柄
　LPDCB lpDCB //指向一个设备控制块(DCB结构)的指针
);

BOOL SetCommState(
　HANDLE hFile, //标识通信端口的句柄
　LPDCB lpDCB //指向一个设备控制块(DCB结构)的指针
);

typedef struct _DCB
{
　// dcb
　DWORD DCBlength; // sizeof(DCB)
　DWORD BaudRate; // current baud rate
　DWORD fBinary: 1; // binary mode, no EOF check
　DWORD fParity: 1; // enable parity checking
　DWORD fOutxCtsFlow: 1; // CTS output flow control
　DWORD fOutxDsrFlow: 1; // DSR output flow control
　DWORD fDtrControl: 2; // DTR flow control type
　DWORD fDsrSensitivity: 1; // DSR sensitivity
　DWORD fTXContinueOnXoff: 1; // XOFF continues Tx
　DWORD fOutX: 1; // XON/XOFF out flow control
　DWORD fInX: 1; // XON/XOFF in flow control
　DWORD fErrorChar: 1; // enable error replacement
　DWORD fNull: 1; // enable null stripping
　DWORD fRtsControl: 2; // RTS flow control
　DWORD fAbortOnError: 1; // abort reads/writes on error
　DWORD fDummy2: 17; // reserved
　WORD wReserved; // not currently used
　WORD XonLim; // transmit XON threshold
　WORD XoffLim; // transmit XOFF threshold
　BYTE ByteSize; // number of bits/byte, 4-8
　BYTE Parity; // 0-4=no,odd,even,mark,space
　BYTE StopBits; // 0,1,2 = 1, 1.5, 2
　char XonChar; // Tx and Rx XON character
　char XoffChar; // Tx and Rx XOFF character
　char ErrorChar; // error replacement character
　char EofChar; // end of input character
　char EvtChar; // received event character
　WORD wReserved1; // reserved; do not use
} DCB;

BOOL SetCommMask(
　HANDLE hFile, //标识通信端口的句柄
　DWORD dwEvtMask //能够使能的通信事件
);

值

事件描述

EV_BREAK

A break was detected on input.

EV_CTS

The CTS (clear-to-send) signal changed state.

EV_DSR

The DSR(data-set-ready) signal changed state.

EV_ERR

A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY.

EV_RING

A ring indicator was detected.

EV_RLSD

The RLSD (receive-line-signal-detect) signal changed state.

EV_RXCHAR

A character was received and placed in the input buffer.

EV_RXFLAG

The event character was received and placed in the input buffer. The event character is specified in the device's DCB structure, which is applied to a serial port by using the SetCommState function.

EV_TXEMPTY

The last character in the output buffer was sent.

BOOL WaitCommEvent(
　HANDLE hFile, //标识通信端口的句柄
　LPDWORD lpEvtMask, //指向存放事件标识变量的指针
　LPOVERLAPPED lpOverlapped, // 指向overlapped结构
);

BOOL ReadFile(HANDLE hFile, //标识通信端口的句柄
　LPVOID lpBuffer, //输入数据Buffer指针
　DWORD nNumberOfBytesToRead, // 需要读取的字节数
　LPDWORD lpNumberOfBytesRead, //实际读取的字节数指针
　LPOVERLAPPED lpOverlapped //指向overlapped结构
);
BOOL WriteFile(HANDLE hFile, //标识通信端口的句柄
　LPCVOID lpBuffer, //输出数据Buffer指针
　DWORD nNumberOfBytesToWrite, //需要写的字节数
　LPDWORD lpNumberOfBytesWritten, //实际写入的字节数指针
　LPOVERLAPPED lpOverlapped //指向overlapped结构
);

BOOL CMultiThreadComApp::InitInstance()
{
　AfxEnableControlContainer();
　//打开并设置COM1
　hComm1=CreateFile("COM1", GENERIC_READ|GENERIC_WRITE, 0, NULL ,OPEN_EXISTING, 0,NULL);
　if (hComm1==(HANDLE)-1)
　{
　　AfxMessageBox("打开COM1失败");
　　return false;
　}
　else
　{
　　DCB wdcb;
　　GetCommState (hComm1,&wdcb);
　　wdcb.BaudRate=9600;
　　SetCommState (hComm1,&wdcb);
　　PurgeComm(hComm1,PURGE_TXCLEAR);
　}
　//打开并设置COM2
　hComm2=CreateFile("COM2", GENERIC_READ|GENERIC_WRITE, 0, NULL ,OPEN_EXISTING, 0,NULL);
　if (hComm2==(HANDLE)-1)
　{
　　AfxMessageBox("打开COM2失败");
　　return false;
　}
　else
　{
　　DCB wdcb;
　　GetCommState (hComm2,&wdcb);
　　wdcb.BaudRate=9600;
　　SetCommState (hComm2,&wdcb);
　　PurgeComm(hComm2,PURGE_TXCLEAR);
　}

　CMultiThreadComDlg dlg;
　m_pMainWnd = &dlg;
　int nResponse = dlg.DoModal();
　if (nResponse == IDOK)
　{
　　// TODO: Place code here to handle when the dialog is
　　// dismissed with OK
　}
　else if (nResponse == IDCANCEL)
　{
　　// TODO: Place code here to handle when the dialog is
　　// dismissed with Cancel
　}
　return FALSE;
}

BOOL CMultiThreadComDlg::OnInitDialog()
{
　CDialog::OnInitDialog();
　// Add "About..." menu item to system menu.

　// IDM_ABOUTBOX must be in the system command range.
　ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
　ASSERT(IDM_ABOUTBOX < 0xF000);

　CMenu* pSysMenu = GetSystemMenu(FALSE);
　if (pSysMenu != NULL)
　{
　　CString strAboutMenu;
　　strAboutMenu.LoadString(IDS_ABOUTBOX);
　　if (!strAboutMenu.IsEmpty())
　　{
　　　pSysMenu->AppendMenu(MF_SEPARATOR);
　　　pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
　　}
　}

　// Set the icon for this dialog. The framework does this automatically
　// when the application's main window is not a dialog
　SetIcon(m_hIcon, TRUE); // Set big icon
　SetIcon(m_hIcon, FALSE); // Set small icon

　// TODO: Add extra initialization here
　//启动串口1处理线程
　DWORD nThreadId1;
　hCommThread1 = ::CreateThread((LPSECURITY_ATTRIBUTES)NULL, 0,
(LPTHREAD_START_ROUTINE)Com1ThreadProcess, AfxGetMainWnd()->m_hWnd, 0, &nThreadId1);
　if (hCommThread1 == NULL)
　{
　　AfxMessageBox("创建串口1处理线程失败");
　　return false;
　}
　//启动串口2处理线程
　DWORD nThreadId2;
　hCommThread2 = ::CreateThread((LPSECURITY_ATTRIBUTES)NULL, 0,
(LPTHREAD_START_ROUTINE)Com2ThreadProcess, AfxGetMainWnd()->m_hWnd, 0, &nThreadId2);
　if (hCommThread2 == NULL)
　{
　　AfxMessageBox("创建串口2处理线程失败");
　　return false;
　}

　return TRUE; // return TRUE unless you set the focus to a control
}

DWORD WINAPI Com1ThreadProcess(HWND hWnd//主窗口句柄)
{
　DWORD wEven;
　char str[10]; //读入数据
　SetCommMask(hComm1, EV_RXCHAR | EV_TXEMPTY);
　while (TRUE)
　{
　　WaitCommEvent(hComm1, &wEven, NULL);
　　if(wEven = 0)
　　{
　　　CloseHandle(hCommThread1);
　　　hCommThread1 = NULL;
　　　ExitThread(0);
　　}
　　else
　　{
　　　switch (wEven)
　　　{
　　　　case EV_TXEMPTY:
　　　　　if (wTxPos < wTxLen)
　　　　　{
　　　　　　//在串口1写入数据
　　　　　　DWORD wCount; //写入的字节数
　　　　　　WriteFile(hComm1, com1Data.TxBuf[wTxPos], 1, &wCount, NULL);
　　　　　　com1Data.wTxPos++;
　　　　　}
　　　　　break;
　　　　case EV_RXCHAR:
　　　　　if (com1Data.wRxPos < com1Data.wRxLen)
　　　　　{
　　　　　　//读取串口数据, 处理收到的数据
　　　　　　DWORD wCount; //读取的字节数
　　　　　　ReadFile(hComm1, com1Data.RxBuf[wRxPos], 1, &wCount, NULL);
　　　　　　com1Data.wRxPos++;
　　　　　　if(com1Data.wRxPos== com1Data.wRxLen);
　　　　　　　::PostMessage(hWnd, COM_SENDCHAR, 0, 1);
　　　　　}
　　　　　break;
　　　　}
　　　}
　　}
　}
　return TRUE;
}

DWORD WINAPI Com2ThreadProcess(HWND hWnd //主窗口句柄)
{
　DWORD wEven;
　char str[10]; //读入数据
　SetCommMask(hComm2, EV_RXCHAR | EV_TXEMPTY);
　while (TRUE)
　{
　　WaitCommEvent(hComm2, &wEven, NULL);
　　if (wEven = 0)
　　{
　　　CloseHandle(hCommThread2);
　　　hCommThread2 = NULL;
　　　ExitThread(0);
　　}
　　else
　　{
　　　switch (wEven)
　　　{
　　　　case EV_TXEMPTY:
　　　　　if (wTxPos < wTxLen)
　　　　　{
　　　　　　//在串口2写入数据
　　　　　　DWORD wCount; //写入的字节数
　　　　　　WriteFile(hComm2, com2Data.TxBuf[wTxPos], 1, &wCount, NULL);
　　　　　　com2Data.wTxPos++;
　　　　　}
　　　　　break;
　　　　case EV_RXCHAR:
　　　　　if (com2Data.wRxPos < com2Data.wRxLen)
　　　　　{
　　　　　　//读取串口数据, 处理收到的数据
　　　　　　DWORD wCount; //读取的字节数
　　　　　　ReadFile(hComm2, com2Data.RxBuf[wRxPos], 1, &wCount, NULL);
　　　　　　com2Data.wRxPos++;
　　　　　　if(com2Data.wRxPos== com2Data.wRxLen);
　　　　　　　::PostMessage(hWnd, COM_SENDCHAR, 0, 1);
　　　　　}
　　　　　break;
　　　　}
　　　}
　　}
　　return TRUE;
　}

typedef struct tagSerialPort
{
　BYTE RxBuf[SPRX_BUFLEN];//接收Buffer
　WORD wRxPos; //当前接收字节位置
　WORD wRxLen; //要接收的字节数
　BYTE TxBuf[SPTX_BUFLEN];//发送Buffer
　WORD wTxPos; //当前发送字节位置
　WORD wTxLen; //要发送的字节数
}SerialPort, * LPSerialPort;

#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:
　　// contruction and destruction
　　CSerialPort();
　　virtual ~CSerialPort();

　　// port initialisation
　　BOOL InitPort(CWnd* pPortOwner, UINT portnr = 1, UINT baud = 19200, char parity = 'N', UINT databits = 8, UINT stopsbits = 1, DWORD dwCommEvents = EV_RXCHAR | EV_CTS, UINT nBufferSize = 512);

　　// start/stop comm watching
　　BOOL StartMonitoring();
　　BOOL RestartMonitoring();
　　BOOL StopMonitoring();

　　DWORD GetWriteBufferSize();
　　DWORD GetCommEvents();
　　DCB GetDCB();

　　void WriteToPort(char* string);

　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::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;
}

//
// Delete dynamic memory
//
CSerialPort::~CSerialPort()
{
　do
　{
　　SetEvent(m_hShutdownEvent);
　}
　while (m_bThreadAlive);

　TRACE("Thread ended"n");

　delete []m_szWriteBuffer;
}

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);
　　m_ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

　if (m_hWriteEvent != NULL)
　　ResetEvent(m_hWriteEvent);
　　m_hWriteEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

　if (m_hShutdownEvent != NULL)
　　ResetEvent(m_hShutdownEvent);
　　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;
}

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;
}

//
// 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
　　　　strlen((char*)port->m_szWriteBuffer), // 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
　if (BytesSent != strlen((char*)port->m_szWriteBuffer))
　{
　　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.

　　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);

　// set event for write
　SetEvent(m_hWriteEvent);
}

//
// Return the output buffer size
//
DWORD CSerialPort::GetWriteBufferSize()
{
　return m_nWriteBufferSize;
}

//
// Return the device control block
//
DCB CSerialPort::GetDCB()
{
　return m_dcb;
}

//
// Return the communication event masks
//
DWORD CSerialPort::GetCommEvents()
{
　return m_dwCommEvents;
}

//
// 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;
}