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Editorial Team
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Asked: 2026-05-24T09:30:56+00:00

I maintain an application that, amongst other things, provides a list to the user

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I maintain an application that, amongst other things, provides a list to the user of available serial port devices on the host computer. This application makes use of the GetDefaultCommConfig() function in order to verify that devices in its list of serial port names are valid. I have received notice that my application does not work with Bluetooth serial ports. While debugging this issue today, I found that the GetDefaultCommConfig() function does not return a successful value when called with the bluetooth serial port name. The GetLastError() function returns 29 (invalid parameter) in these circumstances. Is there a workaround for this problem?

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  1. Editorial Team

    I’ve had a look at the serial ports on my machines with Bluetooth and can confirm that GetDefaultCommConfig() fails for virtual Serial Ports created by the Microsoft Bluetooth stack. It seems to work ok for Widcomm ports however. (I haven’t tested BlueSoleil/Toshiba/etc.)

    So it seems the best plan is not to use GetDefaultCommConfig() for the MSFT ports. To identify which ports are which stack, check the values under HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM, which lists the COM port name as the value. If the value name is “\Device\BtModemNNN” then it’s the MSFT Bluetooth stack. (Widcomm has “\Device\BtPortNNN”).

    [HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM]
"\\Device\\BtPort3"="COM19"
"\\Device\\BthModem2"="COM25"

    Alan

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