why use SetupDiGetDeviceRegistryProperty get SPDRP_CLASSGUID always return the same id

Question

I use the following demo to simultaneously obtain the instanceId and guid of the device, but on my computer, all devices obtain the same SPDRP_CLASSGUID value. Why is this?

int main()
{
    HDEVINFO hDeviceInfoSet = SetupDiGetClassDevs(&GUID_DEVCLASS_MEDIA, NULL, NULL, DIGCF_PRESENT);
    if (hDeviceInfoSet == INVALID_HANDLE_VALUE)
    {
        printf("Failed to get device information set.\n");
        return 1;
    }

    SP_DEVINFO_DATA deviceInfoData;
    deviceInfoData.cbSize = sizeof(SP_DEVINFO_DATA);
    for (DWORD i = 0; SetupDiEnumDeviceInfo(hDeviceInfoSet, i, &deviceInfoData); i++)
    {
        WCHAR deviceId[MAX_DEVICE_ID_LEN];
        if (CM_Get_Device_ID(deviceInfoData.DevInst, deviceId, MAX_DEVICE_ID_LEN, 0) != CR_SUCCESS)
        {
            printf("Failed to get device ID.\n");
        }
        else
        {
            printf("Device Instance ID: %ws\n", deviceId);
        }

        WCHAR deviceGuidString[MAX_GUID_STRING_LEN];
        DWORD bufferSize = sizeof(deviceGuidString);
        if (SetupDiGetDeviceRegistryProperty(hDeviceInfoSet, &deviceInfoData, SPDRP_CLASSGUID, NULL, (PBYTE)deviceGuidString, bufferSize, &bufferSize))
        {
            printf("Device GUID: %ws\n", deviceGuidString);
        }
        else
        {
            printf("Failed to get device GUID.\n");
        }
    }

    SetupDiDestroyDeviceInfoList(hDeviceInfoSet);
    return 0;
}

the code result like this:

Answer 1

If you enumerate them from GUID_DEVCLASS_MEDIA, it is normal that they have the GUID_DEVCLASS_MEDIA Class Guid (their parent)...

Answer 2

Hi

Welcome to Microsoft Q&A!

why use SetupDiGetDeviceRegistryProperty get SPDRP_CLASSGUID always return the same id

SPDRP_CLASSGUID:contains the GUID that represents the device setup class of a device.

According to the Doc:Overview of device setup classes

There is a GUID associated with each device setup class. System-defined setup class GUIDs are defined in Devguid.h and typically have symbolic names of the form GUID_DEVCLASS_Xxx.

According to your code, you are using GUID_DEVCLASS_MEDIA.

DEFINE_GUID( GUID_DEVCLASS_MEDIA,               0x4d36e96cL, 0xe325, 0x11ce, 0xbf, 0xc1, 0x08, 0x00, 0x2b, 0xe1, 0x03, 0x18 );

Refer to the link:

https://github.com/tpn/winsdk-10/blob/master/Include/10.0.14393.0/shared/devguid.h#L47C1-L47C127

So SPDRP_CLASSGUID always return the same id is correct.

whether they are the same audio device

A device instance ID is a system-supplied device identification string that uniquely identifies a device in the system.

If you want to determine whether two audio devices are the same audio device. You could compare their device instance IDs. If the instance IDs are the same, the devices are the same.

Jeanine

Thank you