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

Jonathan Mohr mohrj@Berio.Augustana.AB.CA
Wed Aug 5 17:30:00 GMT 1998

Subsequent to sending my previous message containing a simple example
illustrating what I take to be a bug in resolving the virtual overloading
of operator=, I found an even simpler example to illustrate the same bug.

When the following program is compiled on an i586 machine running Linux
with g++ version, it (correctly) invokes Derived::operator= and
reports that 'x' 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 'x' 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 ------------------------------------
//  An even simpler test of virtual overloading of operator= in  C++.
//  Under g++, this program properly shows that 'x' contains 2.
//  Under egcs-2.90.29 980515 (egcs-1.0.3 release) [and g++ 2.8.1],
//  the program shows 'x' 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
  Base() { value = 0; }
  virtual void operator= ( Base& b ) { value = 1; }
  int value;

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

void main()
  Derived x, d;

  x = d;
  cout << "x contains " << x.value << " (should be 2).\n";
----------------------- snip ------------------------------------

Sorry for the nuisance of sending the previous not-as-simple example.

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

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