Re: memory leak detection techniques

From:
David Wilkinson <no-reply@effisols.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Wed, 10 Oct 2007 19:25:04 -0400
Message-ID:
<uGN8JT5CIHA.1056@TK2MSFTNGP03.phx.gbl>
David Webber wrote:

Thank you! I have never needed that before. I now know where the
leak is, but not why.

But the plot thickens:

In my non-MFC DLL I have a global instance of an object of the form

CMyCollection : public std::vector<CMyThing>;

Its normal constructor is called on startup, which just creates and
empty collection.
It is only called once.
It is filled in (also once) with a method of CMyColllection
schematically of the form

CMyCollection::FillIn()
{

   CMyThing thing;

   for( allthings )
   {
       thing = .... // fill in the thing
       push_back( thing ); //*********
   }
}

It is usually not changed, and lasts until the program shuts down.
It is never copied. (It has a copy constructor, because I feel nervous
without them, but it is never called.)
The destructor is called once, and just calls clear() (because I feel
it is neat to do so).

I am being told that the memory leak is associated with the CMyThing's
copy constructor invoked by push_back() above.

How can that be?

Even stranger, I have had all of this present in the code for years and
a memory leak has only been reported recently.

Any ideas gratefully received.


Dace:

What happens if you call clear() on your vector from somewhere else
(like ExitInstance()) rather than waiting for your derived destructor to
do it.

Actually, I don't think calling clear() from the destructor is
necessary, because the destructors of the contained objects are
automatically called by the std::vector destructor. I think the problem
is that your derived constructor is getting called too late relative to
the leak reporting mechanism.

--
David Wilkinson
Visual C++ MVP

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