I'm trying to get access to a COM Port using this code:

HANDLE hCom = CreateFile("COM1",
GENERIC_READ | GENERIC_WRITE,
0,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED,
NULL);

This works almost all the time...but on this one machine we have it keeps
failing (hCOM == -1).

Device Manager shows the com port looks fine. I've tried changing COM1 to
COM2 without success. Any ideas?

Is it relevant whether I use "COM1" or "\\\\.\\COM1" ?

Thanks,
Alain

Alain Dekker wrote:
> I'm trying to get access to a COM Port using this code:
>
> HANDLE hCom = CreateFile("COM1",
> GENERIC_READ | GENERIC_WRITE,
> 0,
> NULL,
> OPEN_EXISTING,
> FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED,
> NULL);
>
> This works almost all the time...but on this one machine we have it keeps
> failing (hCOM == -1).
>
> Device Manager shows the com port looks fine. I've tried changing COM1 to
> COM2 without success. Any ideas?
>
> Is it relevant whether I use "COM1" or "\\\\.\\COM1" ?
>
> Thanks,
> Alain
>
>

Throw your code into a search engine, and look for examples ?

http://vbnet.mvps.org/index.html?cod...comtestapi.htm

Paul