You could just open and close ports until you get an error. Something like this:
int nComPort;
int nOpenComError;
int bPrevBreak;
// ...
// ignore library errors trying to open com port
bPrevBreak = SetBreakOnLibraryErrors (0);
nComPort = 1;
do
{
nOpenComError = OpenCom (nComPort, "");
if (nOpenComError == 0)
// Close Com port and increment nComPort
CloseCom (nComPort++);
else
// return to the last successful port
// (0 if no ports opened)
nComPort--;
} while (nOpenComError == 0);
// restore previous break condition
SetBreakOnLibraryErrors (bPrevBreak);
// nComPort now contains the highest port number found
// (0 if none were found)
You could also be more selective in which OpenCom errors you allow. For example, if another application
has COM1 open, you'll get error -7 (Cannot open port), but not error -2 (invalid port number). (See the CVI help for the return value of ComOpen). If COM2 opens with no error, you could allow the user to select COM2 but not COM1.
