Re: Is void* as key a bad idea?

From:

DeMarcus <use_my_alias_here@hotmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 19 Feb 2010 00:18:04 +0100

Message-ID:

<4b7dcaae$0$277$14726298@news.sunsite.dk>

Alf P. Steinbach wrote:

* Leigh Johnston:

All that's needed is inheritance.

Example? And don't say virtual inheritance.

Please quote enough of the article you're responding to to establish the
necessary context for your response. Not all readers have easy access to
the thread history.

Anyway, you're asking for and doubting the existence of this problem:

  #include <assert.h>

  struct A
  {
      int blah;
  };

  struct B: A
  {
      virtual ~B() {}
      int doh;
  };

  int main()
  {
      B* p1 = new B;
      A* p2 = p1;
      void* pv1 = p1;
      void* pv2 = p2;

      assert( pv1 == pv2 ); // Uh oh, not guaranteed.
  }

To some C++ programmers it comes as a surprise.

I had no idea this was the case! I've spent a while trying to find more
to read about this, both in Stroustrup's book and on C++-faq-lite
without luck.

I would appreciate if you could direct me to more information.

Thanks!