Microsoft KB Archive/167731

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

Article ID: 167731

Article Last Modified on 12/2/2003

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APPLIES TO


 * Microsoft Visual C++ 4.2 Enterprise Edition
 * Microsoft Visual C++ 4.2 Enterprise Edition
 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 4.2 Professional Edition
 * Microsoft Visual C++ 4.2 Professional Edition
 * Microsoft Visual C++ 5.0 Professional Edition

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This article was previously published under Q167731



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:

170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

Keywords: kbbug kbfix kbdatabase kbprogramming kbmdacnosweep KB167731

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