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From: shi_fuchs@dkauni5t.bitnet (Harald Fuchs)
Newsgroups: comp.lang.c++
Subject: Multiple inheritance problem
Message-ID: <SHI_FUCHS.89Jun15150043@tgpx.dkauni5t.bitnet>
Date: 15 Jun 89 13:00:43 GMT
Sender: news@iraun1.ira.uka.de
Organization: University Karlsruhe, Germany
Lines: 44

I'm trying to write a simple tree class, but I can't get it working
using G++ 1.35.0. It goes like that:

class link {
  // Element of a doubly-linked list
  friend class list;
  friend class list_iterator;
  link* p;
  link* n;
protected:
  link () { p = n = 0; }
public:
  // ...
};

class list: link {
  // Circular list: dummy header with forward and backward pointers
public:
  list () { n = p = this; }
  // ...
};

class list_iterator {
  list* l;
  link* x;
public:
  list_iterator (list* a): l (a) { x = (link*) l; }
  link* operator() () { if (x) { x = x->n; if (x == l) x = 0; } return x; }
  void reset (list* a = 0) { if (a) l = a; x = (link*) l; }
};

class tree: list, link {
  // A tree node has a list of sons (if not leaf)
  // and is an element of such a list (if not root)
public:
  // ...
};

A tree node must have TWO prev/next pointers to work. I think this is
the case because I didn't declare the ``link'' base class virtual. So
what's wrong here: G++ or my brain?
--

Harald Fuchs    shi_fuchs@dkauni5t.bitnet