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Q149139: FIX: Visual C++ Breaks ODBC CLongBinary w/ GlobalReAll Misuse

Article: Q149139
Product(s): Microsoft C Compiler
Version(s): 4.0
Operating System(s): 
Keyword(s): kbfile kbDatabase kbMFC kbODBC kbVC kbVC400bug kbVC410fix kbGrpDSVCDB kbGrpDSMDAC kbDSu
Last Modified: 19-FEB-2002

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Running an application built using the MFC ODBC classes from Visual C++ 4.0 to
retrieve CLongBinary data from a database may result in one or both of the
following behaviors when performing a recordset move or requery:

- Access violations.

- Out of memory exceptions.

CAUSE
=====

There is a programming error in the MFC code that can lead to this behavior
where GlobalReAlloc is used incorrectly. The return value of GlobalReAlloc is
not used, so the global handle embedded in the CLongBinary recordset member
variable becomes invalid if GlobalReAlloc moves the virtual memory block. Refer
to the MFC source code, Dbrfx.cpp in Mfc\Src, and look at the use of
GlobalReAlloc in the CFieldExchange::ReallocLongBinary() function.

RESOLUTION
==========

A new implementation of RFX_LongBinary that avoids this defect in the MFC code
is available to assist you in correcting this problem. Simply download the file
as described below, run the .exe file to expand the source files, and then
incorporate them into your project. Replace all occurrences of RFX_LongBinary
with the new RFX_LongBinary_Alloc and rebuild.

The following file is available for download from the Microsoft Software
Library:

  Alloc.exe (http://support.microsoft.com/download/support/mslfiles/Alloc.exe)

For more information about downloading files from the Microsoft Software Library,
please see the following article in the Microsoft Knowledge Base:

  Q119591 How to Obtain Microsoft Support Files from Online Services


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 4.1.

Additional query words:

======================================================================
Keywords          : kbfile kbDatabase kbMFC kbODBC kbVC kbVC400bug kbVC410fix kbGrpDSVCDB kbGrpDSMDAC kbDSupport kbMDACNoSweep 
Technology        : kbAudDeveloper kbMFC
Version           : :4.0
Issue type        : kbbug
Solution Type     : kbfix

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