怎么让CSerialPort这个串口类支持com1-com4以外的串口（如com5）

如何让CSerialPort这个串口类支持com1-com4以外的串口（如com5）
按龚建伟的方法编串口通讯，可是只支持com1-com4，我是新手，不怎么会改。看他的介绍，应该是需要修改CSerialPort里的InitPort函数。谁知道怎么改啊？谢谢。（我自己只找到一处应该修改的，可好像还不够）
// 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); //这里的5应该改大一些，这个我知道 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.EvtChar = 'q';
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