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Q105081: PRB: "Warning: Calling DestroyWindow in CWnd::~CWnd" Message

Article: Q105081
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbMFC kbVC kbWndw kbGrpDSMFCATL
Last Modified: 07-MAY-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++ for Windows 
   - Microsoft Visual C++ 32-bit Edition 
-------------------------------------------------------------------------------

SYMPTOMS
========

The following warnings are displayed when a debug version of a program is
executed and TRACE() diagnostics are enabled:

  Warning: calling DestroyWindow in CWnd::~CWnd
  OnDestroy or PostNcDestroy in derived class will not be called

CAUSE
=====

The above warnings are displayed by the CWnd::~CWnd() destructor. The warnings
indicate the following:

- The programmer has most likely called "delete" on a CWnd object rather than
  DestroyWindow().

- An object derived from CWnd is not performing a DestroyWindow() call in its
  destructor.

- Because the DestroyWindow() call is executed in the destructor for CWnd, only
  the CWnd portion of the CWnd-derived object is remaining when the
  DestroyWindow() is called. Thus, if you have a CWnd-derived object and
  receive this warning, the derived object's virtual functions will not exist
  and the CWnd functions will be called instead.

RESOLUTION
==========

MFC Technote #17 contains more information on how to properly destroy a Window
object and states the following cardinal rule:

  To destroy a C++ Windows object, use DestroyWindow, not "delete".

Also, examining CWnd::~CWnd() will reveal that the foremost task of the
destructor is to ensure that the associated Windows window object has been
destroyed. If a program calls DestroyWindow() before the CWnd destructor is
called, the m_hWnd data member will be NULL, the TRACE0() messages will not
occur, and DestroyWindow() will not be called in CWnd::~CWnd().

Additional query words:

======================================================================
Keywords          : kbMFC kbVC kbWndw kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Issue type        : kbprb

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