FIX: Problems Occur After Destroying Dockable CControlBar

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++, 32-bit Editions, version 2.0

SYMPTOMS

Destroying a dockable CControlBar object may cause unexpected behavior. For example, an exception may be thrown that if not caught will generate a message box containing something similar to this:

  Unhandled Exception in myapp.exe (MFC30D.DLL):
  0xC0000005: Access Violation. 

CAUSE

This problem occurs because of the way toolbars are handled by the framework. MFC implements a CDockBar object for use as the parent of dockable control bars. To arrange the control bars docked at the location it manages, this CDockBar object maintains a list of the CControlBar objects that it has as children.

The CControlBar destructor does not remove the control bar from the CDockBar's list of control bars. Subsequent attempts by the CDockBar object to manipulate the pointer maintained in its list will cause unpredictable behavior such as an Access Violation.

RESOLUTION

To work around the problem, make sure that dockable toolbars are removed from their parent CDockBar objects before destroying them.

To do this, call CDockBar::RemoveControlBar before destroying the ControlBar object. You will need to include the header file <afxpriv.h> to be able to call this function. For example:

Change this:

   #include "stdafx.h"
   ...
   ...
   void SomeFunction()
   {
     delete pToolBar;
   } 

   #include "stdafx.h"
   #include <afxpriv.h>
   ...
   ...
   void SomeFunction()
   {
     if(pToolBar->m_pBar!=NULL)
       pToolBar->m_pBar->RemoveControlBar(pToolBar);
     delete pToolBar;
   } 

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ version 2.1 (MFC 3.1).

Additional query words: 3.00 toolbar CToolBar

Keywords : kbprg kbui kbMFC KbUIDesign kbVC
Version : 2.0
Platform : NT WINDOWS
Issue type : kbbug