DOCUMENT:Q105081  07-MAY-2001  [visualc]
TITLE   :PRB: "Warning: Calling DestroyWindow in CWnd::~CWnd" Message
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:
OPER/SYS:
KEYWORDS:kbMFC kbVC kbWndw kbGrpDSMFCATL

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-------------------------------------------------------------------------------
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:

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

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