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Q149137: FIX: ODBC Long Binary Functions Use SQL_NO_TOTAL Incorrectly

Article: Q149137
Product(s): Microsoft C Compiler
Version(s): 4.0,4.1
Operating System(s): 
Keyword(s): kbDatabase kbMDAC kbMFC kbODBC kbVC kbVC400bug kbVC420fix kbGrpDSVCDB kbDSupport kbMDAC
Last Modified: 25-FEB-2002

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

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
-------------------------------------------------------------------------------

SYMPTOMS
========

Running an application built using the MFC ODBC classes from Visual C++ 4.0 or
4.1 to retrieve CLongBinary data from a database may result in data truncation.
If you're using Visual C++ 4.1, the truncation is only evident in release
builds; debug builds work as expected.

CAUSE
=====

There is a programming error in the MFC code that can lead to this behavior. MFC
expects SQL_NO_TOTAL to be the return code of the ::SQLGetData() ODBC API.
SQL_NO_TOTAL is used by some drivers when retrieving long binary data. In
reality, SQL_NO_TOTAL will be returned as a value of one of the parameters of
::SQLGetData().

As a consequence of the bug, a datasource that uses a driver that returns
SQL_NO_TOTAL may experience truncation of long binary data. MFC will only call
SQLGetData once rather than in a loop until all data is retrieved as is expected
by ODBC.

Refer to the MFC source code (Dbrfx.cpp in Mfc\Src), and look at the do while
loop in the function CFieldExchange::GetLongBinaryData() for more details.

In MFC 4.1, a fix was implemented, but it was enclosed in conditional compilation
directives that only compile the code in debug builds.

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 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++ 32- bit Edition
version 4.2.

Additional query words: 4.00 4.10 4.20

======================================================================
Keywords          : kbDatabase kbMDAC kbMFC kbODBC kbVC kbVC400bug kbVC420fix kbGrpDSVCDB kbDSupport kbMDACNoSweep 
Technology        : kbAudDeveloper kbMFC
Version           : :4.0,4.1
Issue type        : kbbug
Solution Type     : kbfix

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