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Reputation: 1060

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

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.

Upvotes: 0

Views: 862

Answers (2)

obermeister
obermeister

Reputation: 89

I'm actually trying to solve a similar problem. According to the MSDN here, it looks like InstanceGUID is supposed to always be the same on the same computer. I've verified that if I unplug my USB device and plug it into a different port, it does indeed keep the same Instance GUID. However, if a different user logs into the same PC, DirectInput shows the same device having a different InstanceGUID!! I can't find any acknowledgement from Microsoft that this is a known problem.

So, I can partially answer your question. If you have two identical devices, you will get different InstanceGUIDs, and identical ProductGUIDs. Those InstanceGUIDs will stay consistent if you unplug your devices and move them to different USB ports. HOWEVER you will get different InstanceGUIDs if a different user logs in. At least I can verify that this is an issue on Windows 7 64bit.

Upvotes: 1

Martin Hennings
Martin Hennings

Reputation: 16856

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...).

Upvotes: 0

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