FIX: Access Violation When Connecting in MFC ODBC Application (167731)
The information in this article applies to:
- Microsoft Visual C++, 32-bit Enterprise Edition 4.2
- Microsoft Visual C++, 32-bit Enterprise Edition 4.2b
- Microsoft Visual C++, 32-bit Enterprise Edition 5.0
- Microsoft Visual C++, 32-bit Professional Edition 4.2
- Microsoft Visual C++, 32-bit Professional Edition 4.2b
- Microsoft Visual C++, 32-bit Professional Edition 5.0
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
| Modification Type: | Major | Last Reviewed: | 12/2/2003 |
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| Keywords: | kbBug kbDatabase kbfix kbMDACNoSweep kbProgramming KB167731 |
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