How to get pointer to IUnknown in C#

.NET interop wraps COM objects into .NET objects (runtime-callable wrappers, RCWs), which hide the usual interface querying. In order to register a COM object representing a filter graph with the Running Objects Table, I need the (native) address of its IUnknown interface (see How can I reverse engineer a DirectShow graph?).

So the question is: How can开发者_如何学运维 I get a COM object's IUnknown pointer in C#?

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Use Marshal.GetIUnknownForObject().