[cfe-dev] Microsoft vtordisp field support for clang.

[John McCall]

On Feb 14, 2012, at 3:40 AM, r4start wrote:
> On 14/02/2012 15:34, r4start wrote:
>> On 14/02/2012 05:06, John McCall wrote:
>>> class A { virtual void foo(); } class B : public A { }; class C : public virtual B { C(); virtual void foo(); }; 
>> For this test we will get next result:
>>  class C    size(12):
>>        +---
>>  0    | {vbptr}
>>        +---
>>  4    | (vtordisp for vbase B)
>>        +--- (virtual base B)
>>        | +--- (base class A)
>>  8    | | {vfptr}
>>        | +---
>>        +---
>> If somewhere in inheritance path class has declare ctor or dtor and overload virtual method from virtual base,
>> then before virtual base Microsoft compiler push vtordisp in layout.
>> 
> Also for this test case:
> 
> class A { virtual void foo(){} };
> class B : public A { };
> class C : public virtual B { C(){} virtual void foo(){} };
> class D : public C { int qqq; };
> 
>  class D    size(16):
>         +---
>         | +--- (base class C)
>   0    | | {vbptr}
>         | +---
>   4    | qqq
>         +---
>   8    | (vtordisp for vbase B)
>         +--- (virtual base B)
>         | +--- (base class A)
>  12   | | {vfptr}
>         | +---
>         +---
> As you can see D also has vtordisp for B.

Okay.  I don't think this fundamentally changes the algorithm.  I did think of
a case that might matter, though:  a superclass might override a method
from a non-virtual base that is *also* a virtual base in some derived class.
That is to say, is there a vtordisp in 'C' in the following code?

class A { virtual void foo(); };
class B: public A { virtual void foo(); B(); };
class C : public B, public virtual A { C(); };

John.