Re: Address of two different objects of the same type

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 12 Feb 2008 20:38:25 -0500

Message-ID:

<Ol2yhEebIHA.4712@TK2MSFTNGP05.phx.gbl>

"Ben Voigt [C++ MVP]" <rbv@nospam.nospam> wrote in message
news:ur9wiidbIHA.4180@TK2MSFTNGP06.phx.gbl

Igor Tandetnik wrote:

Matthias Hofmann <hofmann@anvil-soft.com> wrote:

As far as I understand the C++ standard, pointers to two different
objects of the same type cannot appear at the same address. Now
please take a look at the following code:

#include <iostream>

struct A {};
struct B : public A { A a; };

int main()
{
   B b;
   A* p = &b;

   std::cout << p << std::endl;
   std::cout << &b.a << std::endl;

   return 0;
}

The output I am getting on Visual C++ 2005 Express Edition is:

0012F3D8
0012F3D8

The bottom line is, the example appears conformant under DR73 (which
is incorporated into TC1 and thus is normative), but also seems to go
against the intent of the authors, as embodied in the non-normative
10/5 note.

In any case, the behavior observed certainly would seem to be "A Bad
Thing"TM, agreed?

Quite. Empty base optimization should probably be suppressed here, just
in case.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925