Specified port, COMX, does not exist (Windows)

[anderwm]

Just an FYI. There seems to be some port number, beyond which the Serial constructor throws a IO Exception on Windows. When my device was enumerated at COM20 (with -e in test_serial), trying to connect to it throws. When I changed to COM2 it worked as expected. I have had this problem with Windows software before so I knew to try that...I can't remember the root cause.

C:\Users\AndersonM\Documents\Visual Studio 2013\Projects\wjwwood-serial-6e47bdd\
visual_studio\Debug>test_serial.exe -e
(COM20, USB Serial Port (COM20), FTDIBUS\COMPORT&VID_0403&PID_6001)

C:\Users\AndersonM\Documents\Visual Studio 2013\Projects\wjwwood-serial-6e47bdd\
visual_studio\Debug>test_serial.exe "COM20" 57600
Unhandled Exception: IO Exception: Specified port, COM20, does not exist., file
c:\users\andersonm\documents\visual studio 2013\projects\wjwwood-serial-6e47bdd\
src\impl\win.cc, line 71.

[wjwwood]

Thanks for the report, that is definitely strange. Can other serial programs (pyserial) open it when it is COM20?

If you have any more information about how this might be resolved please let me know.

[anderwm]

I had actually tried it in pyserial just before I changed the port number and it opened it without error. It works on port numbers below COM10 and fails for everything COM10 and above. This must be some common Microsoft problem because I have seen it from other vendors in the past.

Edit: For some reason for port number above 9 you must use this notation "\.\COM10". But this notation also works for ports below 9. So if you start having this problem possibly just change the constructor to append "\." to portname.

microsoft support

[bakercp]

Just a confirmation over here: bakercp/ofxSerial#5 (comment)

@wjwwood Seems like the solution would be to take @anderwm 's approach and append "." in the win impl.

[jmarsico]

what I used:
"string port = "";
port.append("\\.");
port.append("\");
port.append(devicesInfo[deviceIndx].getPort());
success = device.setup(port), 9600);"

learned that \ removes following char. thanks @bakercp

[wjwwood]

I reproduced this and fixed it in #84, thanks guys!