Re: Inheritance question

From:
"Alex Blekhman" <tkfx.REMOVE@yahoo.com>
Newsgroups:
microsoft.public.vc.language
Date:
Fri, 14 Mar 2008 10:56:52 +0200
Message-ID:
<u5rJVFbhIHA.6092@TK2MSFTNGP06.phx.gbl>
"Jack" wrote:

I have the following scenario:

/////////////////////////////////////////
class B : public D3DXMATRIX
{
};
[...]
when I cast D3DXMATRIX to B, the following error occurs

Error 8 error C2440: 'type cast' : cannot convert from
'D3DXMATRIX' to 'B' c:\documents and
settings\luckie\projectA\cmesh.cpp 118

Sorry for the above code may be inaccurate cos I have furnished
it a bit


Because `D3DXMATRIX' class is not `B'. What would you expect to
happen? How compiler can know what to do with `D3DXMATRIX' in
order to make it `B'? You, as a developer, should provide this
info:

1. Make additional constructor in the `B' class that takes `const
D3DXMATRIX&' or `LPCD3DXMATRIX' parameter.

2. If and only if the `B' class has the same binary layout as
`D3DXMATRIX' struct (i.e., no data members, no virtual functions,
no other base classes), then you could downcast `D3DXMATRIX' to
reference to `B':

aPointer->m_pArray[i] =
    static_cast<B&>(*GetBoneOffsetMatrix());

HTH
Alex

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