Re: g++ and aliasing bools

[Joe Buck <jbuck at synopsys dot COM>]

On Sat, 26 Jan 2002, Mark Mitchell wrote:
> > > The argument can be extended to handle non-virtual single or multiple
> > > inheritance: from the C point of view,

Daniel Berlin writes:
> > This isn't obvious yet.
> > 
> > You have to at least discuss zero-sized base classes and whether or not
> > GNU C handles them in the same way -- including cases like this:
> > 
> >   struct A {};
> >   struct B : public A {};
> >   struct C : public A {};
> >   struct D : public B, C {};
> > 
> > Here, D has size two to avoid having two A's at the same address.
> > If C did not derive from A, D would have size one.  In GNU C, does:
> > 
> >   struct A {};
> >   struct B { struct A __base1; };
> >   struct C { struct A __base1; };
> >   struct D {
> >      struct B __base1;
> >      struct C __base2;
> >   };
> > 
> > have size two?
> > 
> No, it has size 0.
> > Does the variant where C is empty have size 1?
> Nope.

But the C aliasing rules completely ignore the question of size, so you're
bringing up a red herring.  The rules have *nothing* to do with whether we
think that two objects have the same address!  It doesn't even come up.
For that reason, you don't have to waste any time thinking about class
layout.