Bug in invoking virtual functions in g++ 2.8.1/egcs 1.0.3 release

[Jonathan Mohr]

Here is a simple example illustrating what I take to be a bug in
resolving which virtual function should be invoked.  (This is a simpler
example than the one I previously announced on the 'egcs-bugs' mailing
list on 1998 July 30).

When the following program is compiled on an i586 machine running Linux
with g++ version 2.7.2.3, it (correctly) invokes Derived::operator= and
reports that A[0] contains 2.  However, when compiled on a Cyrix 6x86
machine running Linux with egcs-2.90.29 980515 (egcs-1.0.3 release),
it invokes Base::operator= and reports that A[0] contains 1.

Can anyone else duplicate this result?  Is this actually a compiler bug,
or was there some change in standard C++ that makes this program illegal?

----------------------- snip ------------------------------------
//
//  A simple test of virtual overloading of operator= in  C++.
//
//  Under g++ 2.7.2.3, this program properly shows that A[0] contains 2.
//  Under egcs-2.90.29 980515 (egcs-1.0.3 release) [and g++ 2.8.1],
//  the program shows A[0] as containing 1 (i.e., it executes virtual
//  function Base::op= instead of Derived::op=).
//
//  J. Mohr  1998 August 5
//

#include <iostream.h>


class Base
{
public:
  Base( int val = 0 ) { value = new int( val ); }
  virtual ~Base() {}
  virtual void operator= ( Base& b ) { *value = 1; }
  int Value() { return *value; }
protected:
  int* value;
};


class Derived : public Base
{
public:
  Derived( int val = 0 ) : Base( val ) {}
  virtual void operator= ( Base& b ) { *value = 2; }
};


class Array
{
public:
  Array() { data = new Derived[ 1 ]; }
  Derived & operator[] ( int i ) { return data[i]; }
protected:
  Derived * data;
};


void main()
{
  Derived d(0);
  Array A;

  A[0] = d;
  cout << "A[0] contains " << A[0].Value() << " (should be 2)\n"; 
}
----------------------- snip ------------------------------------

Thanks in advance for any light you can shed.

Regards,
Jonathan Mohr

---
Jonathan Mohr, Associate Professor of Computing Science
Augustana University College, 4901-46 Ave., Camrose, AB, Canada  T4V 2R3
E-mail: mohrj@augustana.ab.ca  Phone: (403) 679-1514  Fax: (403) 679-1129