Q168123: FIX: CWindow::GetTopLevelWindow() Returns NULL

Article: Q168123
Product(s): Microsoft C Compiler
Version(s): 2.1,3.0
Operating System(s): 
Keyword(s): kbATL210bug kbATLWC kbInprocSvr kbServer kbVC500bug kbVC600fix kbATL300fix kbGrpDSMFCAT
Last Modified: 26-JUN-2001

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

- The Microsoft Active Template Library (ATL), versions 2.1, 3.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

A call to CWindow::GetTopLevelWindow() always returns NULL.

CAUSE
=====

This is due to a bug in the function.

RESOLUTION
==========

Change the function in AtlWin.cpp from:

     HWND CWindow::GetTopLevelWindow() const
     {
        ...
        while(hWndTmp != NULL)
        {
           hWndTmp = (::GetWindowLong(hWndParent, GWL_STYLE) & WS_CHILD) ?
              ::GetParent(hWndParent) :
              ::GetWindow(hWndParent, GW_OWNER);

           hWndParent = hWndTmp;
        }

        return hWndParent;
     }

to the following:

     HWND CWindow::GetTopLevelWindow() const
     {
        ...
        while(hWndTmp != NULL)
        {
           // Modification
           hWndParent = hWndTmp;

           hWndTmp = (::GetWindowLong(hWndParent, GWL_STYLE) & WS_CHILD) ?
              ::GetParent(hWndParent) :
              ::GetWindow(hWndParent, GW_OWNER);

        }

        return hWndParent;
     }

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem was corrected in Visual C++ version 6.0
for Windows.

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Sridhar
Madhugiri, Microsoft Corporation


Additional query words: GetTopLevelWindow NULL kbatl210bug kbctrl kbvc600fix kbserver kbinternet

======================================================================
Keywords          : kbATL210bug kbATLWC kbInprocSvr kbServer kbVC500bug kbVC600fix kbATL300fix kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbATLsearch kbATL300 kbATL210
Version           : :2.1,3.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.