Question regarding guidInstance in DirectInput library; also deals with enumeration of devices.

Question

Regarding guidInstance in DIDEVICEINSTANCE

Microsoft says:

Unique identifier for the instance of the device. An application can save the instance globally unique identifier (GUID) into a configuration file and use it at a later time. Instance GUIDs are specific to a particular computer. An instance GUID obtained from one computer is unrelated to instance GUIDs on another.

So, if I connect my device to the computer and my program does enumeration and finds the guid, do I ever have to enumerate again? Even if the user plugs and unplugs the device. If another device of the same type is plugged in, does it still recognize that the second device is not the same as the first and therefore requires a different guid? Should I just renumerate all the interfaces all the time my program runs to find my device or is once enough for a given pc?

Thanks.

Answer 1

The InstanceGuid will always be a unique identifier for every device plugged in - but if you remove the installation information (e.g. uninstalling a usb device) you also lose that InstanceGuid. The device will get some new unpredictable Guid when plugged in again.

The ProductGuid will always be the same for one device, since it's stored in the devices USB HID chip. It may happen though that two devices of the exact same type have the same ProductGuid. If they do, you can only identify them by their InstanceGuid (which may become invalid in some cases, as written above...).