如何获得可使用的COM口

//HKEY_LOCAL_MACHINE//HARDWARE//DEVICEMAP//SERIALCOMM//
HKEY hKey;
int rtn;
m_cmbComm.ResetContent();
rtn = RegOpenKeyEx( HKEY_LOCAL_MACHINE, "Hardware//DeviceMap//SerialComm", NULL, KEY_READ, &hKey);
if( rtn == ERROR_SUCCESS) // 打开串口注册表
{
int i=0;
char portName[256],	commName[256];
DWORD dwLong,dwSize;
while(1)
{
dwSize = sizeof(portName);
dwLong = dwSize;
rtn = RegEnumValue( hKey, i, portName, &dwLong, NULL, NULL, (PUCHAR)commName, &dwSize );
if( rtn == ERROR_NO_MORE_ITEMS ) // 枚举串口
break; // commName就是串口名字
i++;
}
RegCloseKey(hKey);
}