Detecting two interface pointers are the same object

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C++

I've got a class hierarchy of multiple interface inheritance

e.g.

IBase
IInterface1: public IBase
IInterface2: public IBase

CClass: public IInterface1, IInterface2

(all these interfaces are pure virtual)

Now, if I have a function that takes objects of both types:

void MyFunc( IInterface1* pObj1, IInterface2* pObj2 );

how can I detect if pObj1 and pObj2 are the same object? I can't simply cast down to IBase*, because of the multiple inheritance.

So far, the best answer I've found is to have a GetUID() method in IBase, and make each object generate a UID at creation time. Is there a better solution?

[update] Simply comparing the pointers won't work - even if cast down to base, since pObj1 has Interface1's implementation of IBase, and pObj2 has Interface2's implementation of IBase (due to the way c++ vtables work)