Q151030: PRB: Data Corruption with LBS_SORT and CCheckListBox on Win32s

Article: Q151030
Product(s): Microsoft C Compiler
Version(s): winnt:2.0,2.1,2.2,4.0,4.1
Operating System(s): 
Keyword(s): kbnokeyword kbCtrl kbListBox kbMFC kbVC200 kbVC400 kbVC410 kbOSWin32s kbHWx86 kbGrpDSMF
Last Modified: 30-JUL-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 4.1, on platform(s):
      - the hardware: Intel x86 
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SYMPTOMS
========

A CCheckListBox with the LBS_SORT style incorrectly copies the item data.
Different strings in the listbox point to the same item data object. In debug
mode using Visual C++ 4.0 and 4.1, this behavior will ASSERT in DBGHEAP.C as
_free_dbg() is called on the same memory block multiple times.

This is only a problem in Win32s.

CAUSE
=====

This is a problem in Win32s with owner-draw listboxes that have the
LBS_HASSTRINGS and LBS_SORT listbox styles. CCheckListBox is an owner-draw
listbox that uses LBS_OWNERDRAWFIXED or LBS_OWNERDRAWVARIABLE with
LBS_HASSTRINGS. CCheckListBox uses the item data to maintain the check state
information for each item.


RESOLUTION
==========

To work around this behavior, avoid the LBS_SORT style or use InsertString()
instead of AddString(). InsertString() does not cause a LBS_SORT list to be
sorted.

If the listbox needs to be sorted, the strings should be sorted before being
added to the listbox or the strings should be inserted in order.

STATUS
======

This behavior is by design.

Additional query words: 2.00 2.10 2.20 4.00 4.10 CListBox list box

======================================================================
Keywords          : kbnokeyword kbCtrl kbListBox kbMFC kbVC200 kbVC400 kbVC410 kbOSWin32s kbHWx86 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:2.0,2.1,2.2,4.0,4.1
Issue type        : kbprb

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