Determine if slot 0 of the vtbl[] is reserved for something else. For class objects, yes, this is where the classinfo ptr goes. For COM interfaces, no. For non-COM interfaces, yes, this is where the Interface ptr goes.
0 vtbl[0] is first virtual function pointer 1 vtbl[0] is classinfo/interfaceinfo pointer
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Determine if slot 0 of the vtbl[] is reserved for something else. For class objects, yes, this is where the classinfo ptr goes. For COM interfaces, no. For non-COM interfaces, yes, this is where the Interface ptr goes.