Microsoft KB Archive/105081
Article ID: 105081
Article Last Modified on 11/21/2006
- Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 6.1
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 5.0 Learning Edition
This article was previously published under Q105081
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
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.
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: kbprb kbwndw KB105081