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

 Last reviewed: May 28, 1997
Article ID: Q105081
The information in this article applies to:
  • The Microsoft Foundation Classes (MFC) included with: 

        - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52
    - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0

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().

Keywords : MfcMisc kbfasttip kbprb
Technology : kbmfc
Version : 1.0 1.5 1.51 1.52 2.0
Platform : NT WINDOWS

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Last reviewed: May 28, 1997
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