Listing serial (COM) ports on Windows?

Question

Hello,

I'm looking for a robust way to list the available serial (COM) ports on a Windows machine. There's this post about using WMI, but I would like something less .NET specific - I want to get the list of ports in a Python or a C++ program, without .NET.

I currently know of two other approaches:

1. Reading the information in the HARDWARE\\DEVICEMAP\\SERIALCOMM registry key. This looks like a great option, but is it robust? I can't find a guarantee online or in MSDN that this registry cell indeed always holds the full list of available ports.

2. Tryint to call CreateFile on COMN with N a number from 1 to something. This isn't good enough, because some COM ports aren't named COMN. For example, some virtual COM ports created are named CSNA0, CSNB0, and so on, so I wouldn't rely on this method.

Any other methods/ideas/experience to share?

Edit: by the way, here's a simple Python implementation of reading the port names from registry:

import _winreg as winreg
import itertools


def enumerate_serial_ports():
    """ Uses the Win32 registry to return a iterator of serial 
        (COM) ports existing on this computer.


    """
    path = 'HARDWARE\\DEVICEMAP\\SERIALCOMM'
    try:
        key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, path)
    except WindowsError:
        raise IterationError

    for i in itertools.count():
        try:
            val = winreg.EnumValue(key, i)
            yield (str(val[1]), str(val[0]))
        except EnvironmentError:
            break

Answer 1

Several options are available:

1. Call QueryDosDevice with a NULL lpDeviceName to list all DOS devices. Then use CreateFile and GetCommConfig with each device name in turn to figure out whether it's a serial port.

2. Call SetupDiGetClassDevs with a ClassGuid of GUID_DEVINTERFACE_COMPORT.

3. WMI is also available to C/C++ programs.

There's some conversation on the win32 newsgroup and a CodeProject, er, project.

Answer 2

I just created the following, based on reading through the C++ source to EnumSerialPorts and seeing the function GetDefaultCommConfig(). It looked like the simplest method using simple ANSI C and a single API call for each possible COM port.

#include <stdio.h>
#include <windows.h>
#include <winbase.h>

BOOL COM_exists( int port)
{
    char buffer[7];
    COMMCONFIG CommConfig;
    DWORD size;

    if (! (1 <= port && port <= 255))
    {
        return FALSE;
    }

    snprintf( buffer, sizeof buffer, "COM%d", port);
    size = sizeof CommConfig;

    // COM port exists if GetDefaultCommConfig returns TRUE
    // or changes <size> to indicate COMMCONFIG buffer too small.
    return (GetDefaultCommConfig( buffer, &CommConfig, &size)
                                                    || size > sizeof CommConfig);
}

int main()
{
    int i;

    for (i = 1; i < 256; ++i)
    {
        if (COM_exists( i))
        {
            printf( "COM%d exists\n", i);
        }
    }

    return 0;
}

Answer 3

The PySerial project provides a couple of solutions.