DOCUMENT:Q167731 07-MAY-2001 [visualc] TITLE :FIX: Access Violation When Connecting in MFC ODBC Application PRODUCT :Microsoft C Compiler PROD/VER::4.2,4.2b,5.0 OPER/SYS: KEYWORDS:kbProgramming kbDatabase kbMFC kbODBC kbVC kbVC420bug kbVC500bug kbGrpDSMDAC kbDSupport ====================================================================== ------------------------------------------------------------------------------- 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 ------------------------------------------------------------------------------- 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: ====================================================================== 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 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.