Re: Implementation of abstract classes

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Sun, 21 Sep 2008 10:54:33 -0700 (PDT)
Message-ID:
<43b1d011-b387-4c52-a63e-9488a091c06b@f63g2000hsf.googlegroups.com>
On Sep 21, 4:55 pm, Rune Allnor <all...@tele.ntnu.no> wrote:

On 20 Sep, 19:12, Erik Wikstr=F6m <Erik-wikst...@telia.com> wrote:

Just because a function is pure virtual does not mean it
cannot be implemented:

#include <iostream>

struct Base
{
  virtual ~Base() = 0
  {
    std::cout << "~Base\n";
  }
};


Can this be correct? The way I understand

virtual void foo() = 0;

is that the statement inituializes a NULL pointer in the
virtaul function table.


It might. All the standard says is that if a virtual function
call resolves to a pure virtual function, the behavior is
undefined.

It this is correct your code above will result in undefined
behaviour.


Only if you manage to have a virtual function call resolve to
Base::~Base. And I don't see any way of doing that that
wouldn't create undefined behavior anyway. (Basically, the only
way you could have it would be with an explicit destructor call
from a constructor or the destructor of Base.)

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