ERROR_DEV_NOT_EXIST when ::CreateFile in C++ MFC?

Question

Hi,

I am writing to open a port using this function:

HANDLE hFile = ::CreateFile(pszComName, GENERIC_READ|GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0,0);

// Check if we could open the device
if (hFile == INVALID_HANDLE_VALUE)
{
    DWORD hh=  ::GetLastError();

              error.Format(_T("test - [%d]"),hh); 

      AfxMessageBox(error,MB_ICONSTOP);
}

I cannot open the port and system error code I receive is 55: ERROR_DEV_NOT_EXIST 55 (0x37) from this list

what can i do to open the port? thanks

EDIT: I Enumerate Ports like this:

 for (UINT i=1; i<256; i++)
    {

      CString sPort;
      sPort.Format(_T("COM%d"), i);

      HANDLE hPort = ::CreateFile(sPort, GENERIC_READ | GENERIC_WRITE, 0, 0,OPEN_EXISTING,0, 0);
      if (hPort == INVALID_HANDLE_VALUE)
      {
        DWORD dwError = GetLastError();
      }
      else
      {
        AfxMessageBox(_T("1 open"));
        CloseHandle(hPort);
      }
    }

I also checked these formats:

sPort1.Format(_T("URT%d"), i);

sPort3.Format(_T("\.\COM%d"), i);

sPort4.Format(_T("\\.\COM%d"), i);

and sPort5.Format(_T("\COM%d"), i);

but I couldnt find any.

Answer 1

The obvious thing to check is whether you have the name correct. For a COM port, it'll normally be something like \\.\com1, but in C or C++ you need to escape all the back-slashes, so it'll look like "\\\\.\\com1" if you're using a string literal.

Answer 2

COM ports names in Windows CE/Mobile are in the format of COMX: - the difference is the colon - (for example COM1:).

Your code should look like this: CreateFile(L"COM1:",...)

You can also check the port name through the registry. If you have an ActiveSync connection, use a remote registry editor and go to [HKLM\Drivers\Active] - one of the subkeys will hold the information of the port you want (assuming it is loading properly).