Re: Multiple Inheritance and vptr

From:

James Kanze <kanze.james@neuf.fr>

Newsgroups:

comp.lang.c++.moderated

Date:

9 May 2006 08:18:50 -0400

Message-ID:

<e3obth$vdb$1@emma.aioe.org>

Venkat wrote:

  > Considering the following class hierarchy,

  > class Base1
  > {
  > public:
  > Base1(){}
  > virtual void MyFun()
  > {
  > }
  > };

  > class Base2
  > {
  > public:
  > virtual void MyFun1()
  > {
  > }
  > };

  > class Derived1 : public Base1, public Base2
  > {
  > public:
  > virtual void MyFun2()
  > {
  > }
  > };

  > I know that Derived1 has 2 vptrs and 2 vtables. I want to
  > know to which vtable MyFun2() gets added? To vtable from
  > Base1 or vtable from Base2?

First, of course, it's all implementation defined; an
implementation doesn't even have to use vtables. Typically,
however, there will be at least five different vtables in the
above hierarchy: Base1_vtbl (used during the construction of
Base1 -- doesn't know about any derived class), Base2_vtbl (as
above, but for Base2), and Base1_in_Derived1_vtbl and
Base2_in_Derived1_vtbl, used in the complete object, and
Derived1_vtbl. In practice, in the absence of virtual
inheritance, all implementations I know of will merge
Base1_in_Derived1_vtbl (in fact, whichever base class is
mentioned first) and Derived1_vtbl. In the absence of virtual
inheritance only, however.

--
James Kanze kanze.james@neuf.fr
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