Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!NSS.CS.UCL.AC.UK!Graeme.Dixon%newcastle.ac.uk
From: Graeme.Dixon%newcastle.ac.uk@NSS.CS.UCL.AC.UK (Graeme Dixon)
Newsgroups: gnu.g++.bug
Subject: Overloaded delete operator bug
Message-ID: <AA26080.8904101226.snipe@uk.ac.newcastle>
Date: 10 Apr 89 12:26:40 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
Organization: GNUs Not Usenet
Lines: 73

There is a bug in the code generated by g++ when the delete operator
is overloaded that results in the delete operator being called once for
each derived class in a hierarchy. The following program illustrates
the bug:

#include <stream.h>

class A
{
public:
    A()  { cout << "A::A\n"; }
    ~A() { cout << "A::~A\n"; }

    void* operator new(long size)  { cout << "A::new\n"; return malloc(size); }
    void operator delete(A* todel) { cout << "A::delete\n"; free(todel); }
};

class B: public A
{
public:
    B()  { cout << "B::B\n"; }
    ~B() { cout << "B::~B\n"; }
};

class C: public B
{
public:
    C()  { cout << "C::C\n"; }
    ~C() { cout << "C::~C\n"; }
};

main()
{
    B *b = new B;
    delete b;      // OK

    C *c = new C;
    delete c;      // not OK - delete called twice
}

and produces the following when compiled with g++ (version 1.34.0) and
linked with /usr/lib/debug/malloc.o (using
g++ -o bug bug.cc /usr/lib/debug/malloc.o):

A::new
A::A
B::B
B::~B
A::~A
A::delete
A::new
A::A
B::B
C::C
C::~C
B::~B
A::~A
A::delete
A::delete
free: block 0x21804 was already free

Abort (core dumped)

Each successively derived class results in an additional invocation of
the delete operator when an instance of that class is deleted.

Graeme Dixon -
  Computing Laboratory, University of Newcastle upon Tyne, UK

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