Using WMI to Query for Currently Attached USB Device

[pcpro178]

I am writing an application wherein I need to scan the computer to see if either of two different USB devices are attached. The first device appears as a HID, and the second device appears as a virtual COM port. Which WMI classes should I be checking to see if each device is attached?

I am using this for the HID:

    m_bstrScope = SysAllocString( _T("root\\CIMV2") );
    m_bstrQuery = SysAllocString( _T("SELECT PNPDeviceID FROM Win32_PnPEntity") );

...and this for the virtual COM port device:

    m_bstrScope = SysAllocString( _T("root\\CIMV2") );
    m_bstrQuery = SysAllocString( _T("SELECT DeviceID,PNPDeviceID FROM Win32_SerialPort") );

This pseudo code shows how my scanning algorithm works:

    if ( ScanForDevice1() ) // HID attached
    {
        /* Success */
    }
    else if ( ScanForDevice2() ) // Virtual COM port device attached
    {
        /* Success */
    }
    else
    {
        /* Fail */
    }

This seems to work, except when I change which device is connected between running the application. If device 1 is found, the scan for device 2 is aborted; the scan for device 2 only occurs if device 1 is not found. What happens is this:

1. The application is run with both devices attached to the system. Device 1 is found, as expected. The application exits.
2. Device 1 is unplugged from the system.
3. The application is run with only device 2 attached to the system. Oddly, device 1 is found, even though it is not attached. The application exits.
4. Both devices are unplugged from the system.
5. The application is run with no devices attached. No devices are found, as expected. The application exits.
6. Only device 2 is plugged back into the system.
7. The application is run with only device 2 attached. The application finds device 2, as expected.

My best guess is that I am querying the wrong class(es). Which classes should my application be checking? Or, is there something else that I should be doing? Thanks.