Microsoft KB Archive/145992

= PRB: Global MFC DAO Objects Cause Assertions =

Article ID: 145992

Article Last Modified on 11/21/2006

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APPLIES TO

 Microsoft Foundation Class Library 4.2, when used with:  Microsoft Visual C++ 4.0 Standard Edition

 Microsoft Visual C++ 4.1 Subscription 

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This article was previously published under Q145992



SYMPTOMS
An assertion can occur on line 729, 732, or 1314 of Daocore.cpp when you define an MFC DAO object that has its destructor called after the call to CWinApp::ExitInstance.

This will happen when an MFC DAO object is defined globally or as a member of a global object (like an MFC application's CWinApp-derived object).



CAUSE
CWinApp::ExitInstance closes all open DAO workspaces by calling AfxDaoTerm and removes them from the global workspace map. In the destructors for MFC DAO objects such as CDaoDatabase and CDaoRecordset, MFC tries to remove the workspace objects again.



RESOLUTION
Here are two workarounds:

 Instead of using a global DAO object, define a global pointer to a DAO object. Be sure to destroy the MFC object before CWinApp::ExitInstance. -or-

</li>  Explicitly assign the CDaoWorkspace object to the DAO object rather than allowing MFC to create a CDaoWorkspace object implicitly. You can do this by passing the workspace objects and database objects into the constructors of the CDaoDatabase and CDaoRecordset objects respectively. Or you can explicitly set the CDaoDatabase::m_pWorkspace and CDaoRecordset::m_pDatabase variables before opening the CDaoDatabase or CDaoRecordset. Here is an example: CDaoWorkspace  wsp; CDaoDatabase   db; CMyDaoRecordset rs;

BOOL InitializeDBStuff {     db.m_pWorkspace=&wsp; db.Open( _T("D:\\work\\assert.mdb") ); rs.m_pDatabase=&db; rs.Open(dbOpenDynaset, _T("Select * from table1")); rs.Close; db.Close; } </li></ul>

<div class="status_section">

STATUS
This behavior is by design.

Additional query words: recordset 4.00 4.10

Keywords: kbdatabase kbprb KB145992

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