Double abstract class Inheritance concern.

[Nathan Sidwell]

Tiago Stein wrote:
>>Chris Lattner wrote:
>>
>>>Tiago Stein wrote:
>>>
>>>
>>>>class A{};
>>>>class B :public A{};
>>>>class C: public A{ int g; };
>>>>class D: public B, public C {
>>>> unsigned int foo;
>>>>};
>>>>Why sizeof class D is 12? Should not be 8?

> 
> 
> But is not only a single A present at D?
no, there are two.

 > If I wanted separate A for each
> side of inheritance shouldn't I use virtual inheritance?
no you'd use that when you wanted one instance

 > When I Use it..
> it adds even more size to the final class, so that I have more space used
> than is necessary to keep each onde witha separet adress.
yes, that is what the standard says.

> So if I understand correctly.. yhis is done to keep B and A with different
> addresses.. and not B::A and C::A ?
you do not understand correctly.

this is now no longer a g++ specific question, but one about C++. A C++
newsgroup would be appropriate to explore the whys of this requirement.

nathan

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