Re: Problem with VB -> C++ interface pointer

Hi,

Thanks for the reply but I'm afraid I still don't see why it doesn't
work. I understand what you are saying about the cast and totally
agree that if they were completely separate objects then pSpot would be
garbage. But (and this is where I might have things muddled) they are
not sepeare objects...are they? Doesn't CSpot derive from ISpot via
IDispatchImpl?

I'm very new to COM so maybe it isn't as simple as I think. I see it
like this:
class ClassA : public ClassB
{
  public:
  void foo();
};

ClassB* myClass = new ClassA();
Bar(myClass);

void Bar (ClassB* pMyClass)
{
  ClassA* pClassA = reinterpret_cast<ClassA*>(pMyClass);
  pClassA->foo();
}

This should work fine (not the best code, but it would work). My
understanding is that I am doing this in COM (maybe the QueryInterface
should be replaced with a dynamic_cast) - so maybe there is something
COM related that I am not understanding that stops it from being a
valid thing to do?

What I am ultimately trying to achieve here is that I want to call a
function of CSpot from within the C code. I thought I could retrieve
the CSpot* from the ISpot* so that I could do this.

I hope that all makes sense!

Thanks for any help.

Cheers,
Steve

Igor Tandetnik wrote: