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Q132116: FIX: CheckAutoCenter May Return TRUE with DS_ABSALIGN

Article: Q132116
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbMFC KbUIDesign kbVC200bug kbVC210bug kbVC400bug kbVC410bug kbVC420bug kbVC500fix kbGr
Last Modified: 06-MAY-2001

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

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++ 32-bit Edition, versions 2.0, 2.1 
-------------------------------------------------------------------------------

SYMPTOMS
========

Positioning a dialog box, using DS_ABSALIGN and the Y axis screen coordinate of
zero causes the dialog box to be centered within the application's main window.

CAUSE
=====

The function Dialog::CheckAutoCenter() is called to determine whether the dialog
should be centered. In the case of y == 0, CheckAutoCenter() will always return
TRUE. This happens because of the following code from CheckAutoCenter() in
WINCORE.CPP:

     BOOL bResult = !(lpTemplate->style & DS_ABSALIGN) &&
         lpTemplate->x == 0 || lpTemplate->y == 0;

Note that because of the way C/C++ handles logical expressions, if
lpTemplate->style == DS_ABSALIGN, then lpTemplate->x == 0 will not be
evaluated. However, lpTemplate->y == 0 is evaluated and therefore is capable
of returning TRUE to CheckAutoCenter().

RESOLUTION
==========

Do not use a Y coordinate of zero with DS_ABSALIGN.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem has been fixed in Visual C++ 5.0 for
Windows.

MORE INFORMATION
================

To reproduce this problem set the DS_ABSALIGN style and a y position of zero for
the about box of a standard Appwizard-generated application.

Additional query words: center

======================================================================
Keywords          : kbMFC KbUIDesign kbVC200bug kbVC210bug kbVC400bug kbVC410bug kbVC420bug kbVC500fix kbGrpDSMFCATL kbNoUpdate kbbuglist kbfixlist
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Issue type        : kbbug
Solution Type     : kbfix

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