Re: Virtual Destructor - Implication & Specification

"Le Chaud Lapin" <>
Tue, 3 Apr 2007 10:38:52 CST
On Apr 3, 4:02 am, "Le Chaud Lapin" <> wrote:

There are three ways to solve the heap mismatch problem. You have
pointed out ways #1 and #2. I am going to say what #3 is in a second,
but first #1 and #2:

1. Microsoft KB article Q122675
2. Class-specific new/delete

and now the most important one in context of current dicussion..

3. Simply make the destructor virtual.

In my haste, I made an error. #2 Does _not_ solve the new/delete
mismatch problem. This is actually what my colleagues keey saying,
which I keep refuting. This just goes to show that, if you hear
incorrect information often enough, you start repeating it.

What solves the heap-mismatch problem is the virtual destructor, and
the virtual destructor alone. So #2 should be elminated as a

Just in case anyone is interested in exploring this issue further, I
have cut-and-pasted some sample code here.

[Note to Mods: I realize this code is platform-specific, but to
illustrate the underlying principle inherently requires platform-
specific code.]

***** FOO.HPP:

struct Abstract
    virtual ~Abstract (); // Add definition for this in DLL.CPP please.
} ;

struct Concrete
    ~Concrete () {}
} ;

_declspec (dllexport) Abstract * gimme_abstract ();
_declspec (dllexport) Concrete * gimme_concrete ();
_declspec (dllimport) Abstract * gimme_abstract ();
_declspec (dllimport) Concrete * gimme_concrete ();

***** EXE.CPP

// EXE.cpp : Defines the entry point for the console application.

#include "stdafx.h"

#include "..\Foo.hpp"

int _tmain(int argc, _TCHAR* argv[])

    Abstract *pAbstract = gimme_abstract();
    Concrete *pConcrete = gimme_concrete();

    delete pAbstract;
    delete pConcrete;

    return 0;

***** DLL.CPP

// DLL.cpp : Defines the entry point for the DLL application.

#include "stdafx.h"


#include "..\Foo.hpp"

Abstract * gimme_abstract ()
    return new Abstract;

Concrete * gimme_concrete ()
    return new Concrete;

                       DWORD ul_reason_for_call,
                       LPVOID lpReserved
    return TRUE;

      [ See for info about ]
      [ comp.lang.c++.moderated. First time posters: Do this! ]

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