CreateFile COM port error 2

Question

I'm trying to open and write to a COM serial port on Windows 7, using below code in Visual Studio 2012 (C++)

printf("argv[2]= '%s'\n", argv[2]);

m_hCommPortSend= ::CreateFile(argv[2] ,GENERIC_READ|GENERIC_WRITE,0,0,OPEN_EXISTING,0,0);

if(m_hCommPortSend == INVALID_HANDLE_VALUE) 
{
    printf("%s error: %d\n", argv[2], GetLastError());
    return -1;
}

This Code works well with argv[2] as COM1 or COM7

I have another com port COM39, When I pass COM39 as argv[2] it is not openeded GetLastError() returning 2.

Not sure why ?

Answer 1

The MSDN page for CreateFile says the following under Communications Resources:

To specify a COM port number greater than 9, use the following syntax: \\\\.\\COM10 . This syntax works for all port numbers and hardware that allows COM port numbers to be specified.