Re: dynamic_cast does not work across modules with multiple inheritance (VC2005)

"" <>
10 Jul 2006 01:25:45 -0700
Ulrich Eckhardt wrote:

Where is the declaration of this function? Could it be that it doesn't
return an ITVUnknown? The reason I ask is that you say:

ITVClassFactoryPtr ptrCF = fnGCO();
ITVUnknown* theUnk = ptrCF->CreateInstance(TVCLSID_TestTwo,
ITestOne* theTest = dynamic_cast<ITestOne*>(theUnk);


The important bit I have discovered is that when I run this in the
debugger and hover over theUnk when it has been initialised, I see:
- __vfptr 0x0050c4f0 const tvcomp::CTVComObject<class
CTestImpl>::`vftable'{for `ITestOne'} *

I.e. the debugger thinks it is an ITestOne object, and not a ITVUnknown. It
should however either be an ITVUnknown (because the pointer really points
to such an object, even if it is a subobject of another) or to a CTestImpl,
because that is what it really is.

Just in case you were wondering, otherwise your code seems fine.


Thank you Uli,

I was just creating a more complete test program to send here (so you
could see all bits and pieces) when I discovered what was wrong. Some
time in the past I apparently had a problem with inheritance and I
chose the sledgehammer bug-fix: When I return the ITVUnknown* I
actually do a reinterpret_cast<ITVUnknown*> which obviously should not
be needed. What I should really have done is inherit ITVUnknown
_virtually_ in one more interface and the cast would not have been
needed needed.

So I guess it's on to find the next bug now :)

/ Daniel

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