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Q167731: FIX: Access Violation When Connecting in MFC ODBC Application

Article: Q167731
Product(s): Microsoft C Compiler
Version(s): 4.2,4.2b,5.0
Operating System(s): 
Keyword(s): kbProgramming kbDatabase kbMFC kbODBC kbVC kbVC420bug kbVC500bug kbGrpDSMDAC kbDSupport
Last Modified: 07-MAY-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 4.2b, 5.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 4.2b, 5.0 
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SYMPTOMS
========

If MFC42.DLL version 4.21.7002 is installed and ODBC 3.0 is not installed, MFC
ODBC applications hit an access violation when they try to call
SQLSetConnectOption() in DBCORE.CPP.

CAUSE
=====

MFC was changed in version 4.21.7002 (the version which is distributed with
Visual C++ 5.0) to call SQLxxxA versions of the ODBC APIs. For example, the MFC
DLL now calls 'SQLSetConnectOptionA' instead of 'SQLSetConnectOption'. These new
function names are only exposed by the ODBC 3.0 Driver Manager. They are not
available under the ODBC 2.x Driver Manager.

To prevent implicitly loading ODBC32.DLL every time the MFC DLL is loaded, the
MFC DLL loads the Driver Manager, and performs GetProcAddress calls to get the
address of the various ODBC API functions. It then calls through these pointers
into the ODBC32.DLL. In the case where the ODBC 3.0 Driver Manager is not
installed, the call to GetProcAddress for any of the SQLxxxA functions fails and
returns a null pointer. This causes the access violation to occur when the
pointer is dereferenced. MFC does not properly handle checking for the null
pointer.

RESOLUTION
==========

It is likely that Visual C++ 4.2x applications will see this problem because
these applications don't ship with ODBC 3.0. To prevent an application from
being exposed to this problem, ship the ODBC 3.0 components rather than the ODBC
2.x components, even if the application is a Visual C++ 4.2x application.

Installing ODBC 3.0 on the system fixes the problem. Redistributing the Visual
C++ 4.2 application using a static build of MFC also corrects the problem.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug has been corrected in Visual Studio 97
Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see
the following article in the Microsoft Knowledge Base:

  Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

Additional query words:

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Keywords          : kbProgramming kbDatabase kbMFC kbODBC kbVC kbVC420bug kbVC500bug kbGrpDSMDAC kbDSupport kbMDACNoSweep 
Technology        : kbVCsearch kbAudDeveloper kbVC420 kbVC500 kbVC32bitSearch kbVC420b kbVC500Search
Version           : :4.2,4.2b,5.0
Issue type        : kbbug
Solution Type     : kbfix

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