Re: Virtual Destructor - Implication & Specification

"Alf P. Steinbach" <>
Mon, 2 Apr 2007 17:04:27 CST
* Le Chaud Lapin:

On Apr 2, 8:09 am, "Martin Bonner" <> wrote:

On Apr 2, 8:36 am, "Le Chaud Lapin" <> wrote:
What "new/delete heap mismatch problem"?


... a problem can arise when a
static library has been used in particular situation - an EXE decides
to interact with a DLL that was built by a programmer who decided to
use the static library for memory allocation to build his/her DLL.

OK, so that's what you mean by "heap mismatch problem": that the object
is allocated on one heap (e.g. in the main program), and an attempt is
made to deallocate it from another heap (e.g. in a Windows DLL).

Well, whether a virtual destructor helps or not depends on the C++
compiler: the C++ standard is silent on the issue of dynamic libraries.

The in-practice: the Visual C++ compiler has supported a workaround for
the problem since and including version 5.0. It relies on using a
non-standard extension ("declspec"), plus a virtual destructor, as
you've noted; see Microsoft KB article Q122675. You can't assume that
that workaround will be implemented by other compilers.

You can instead /take control over allocation and deallocation/ via
standard C++ means.

Namely, by defining operator new and operator delete for the class in
question (you will still need a virtual destructor when destroying an
object polymorphically).


- Alf

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