How To Catch and Decipher DAO SDK-Based Exceptions

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This article was previously published under Q152695

SUMMARY

This article presents sample code for catching and deciphering exceptions that can be thrown by the DAO SDK class libraries.

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The following is a sample try/catch loop and helper functions that demonstrate how to decipher either a DAO SDK or MFC-based exceptions. The content of these exceptions is in part (or fully) dumped by using TRACE().

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Sample Code

The following code demonstrates a typical try/catch block using C++ Exception Handling for catching the DAO SDK CdbException, or one of the MFC exceptions that the DAO SDK can also throw.

    CdbDBEngine *pEng = NULL;

    try
    {
        // Call DAO SDK code here

        pEng = new CdbDBEngine();

        //... manipulate dbDao objects here ...

    }
    catch( CdbException e )
    {
        AfxDbDaoCatchException( e, pEng );
    }
    catch( CException *e )
    {
        AfxDbDaoCatchException( e );
    }
    catch( ... )
    {
        TRACE( "Caught Win32 Exception\n" );
    }

    if( pEng != NULL )
        delete pEng;

The implementation of the both over-loaded versions of AfxDbDaoCatchException() follows. You can easily expand the MFC implementation to extract more information from those MFC Exception classes which have additional data members and methods.

/////////////////////////////////////////////////////////////////// 
// 
// AfxDbDaoCatchException()
// 
// Purpose:     Deciphers dbDao (DAO SDK) based exception.
// 
// Parameters:  e    - Instance of CdbException class.
//              pEng - Pointer to DBEngine object (via the CdbDBEngine
//                     class).
// 
// Returns:     n/a
// 
////////////////////////////////////////////////////////////////////// 

    void AfxDbDaoCatchException( CdbException &e,
                                 CdbDBEngine  *pEng )
    {
        // Just in case exception handling code throws an exception
        try
        {
            // It's possible that the engine hasn't been instantiated yet
            if( pEng == NULL )
            {
                TRACE( _T("Caught CdbException attempting "
                          "to instantiate DBEngine.\n") );
                return;
            }

            // Log results of exception
            long nMax = pEng->Errors.GetCount();

            TRACE( _T("Caught CdbException, %ld Errors Reported:\n"),
                   nMax );

            // Traverse through contents of Errors Collection
            for( long l = 0; l < pEng->Errors.GetCount(); l++ )
            {
                TRACE( _T("\t #%ld -- %s\n"),
                       pEng->Errors[l].GetNumber(),
                       pEng->Errors[l].GetDescription() );
            }

            // Log results of Last OLE Error. This may or may not be
            // the same as results stored in the Errors collection.
            // Ignore CdbLastOLEError.GetHelpFile and
            // CdbLastOLEError.GetHelpContext
            CdbLastOLEError exError;

            TRACE( _T("\t CdbLastOLEError.Source:       %s\n"),
                   exError.GetSource()      );
            TRACE( _T("\t CdbLastOLEError.Description:  %s\n"),
                   exError.GetDescription() );
        }
        catch( CException *e2 )
        {
            TRACE( "AfxDbDaoCatchException() "
                   "caught an exception, but was unable to log it\n" );
            e2->Delete();
        }
        catch(...)
        {
            TRACE( "AfxDbDaoCatchException() "
                   "caught an exception, but was unable to log it\n" );
        }
    }

////////////////////////////////////////////////////////////////////// 
// 
// AfxDbDaoCatchException()
// 
// Purpose:     Catchs MFC-based exception.
// 
//              This code assumes AFXWIN.H and AFXOLE.H have been
//              included in STDAFX.H
// 
// Parameters:  e - Pointer to a class derived from MFC's
//                  CException class.
// 
////////////////////////////////////////////////////////////////////// 
   void AfxDbDaoCatchException( CException *e )
   {
// Just in case exception handling code throws an exception
       try
       {
            // Determine name of MFC Exception
            CString         strName;
            CRuntimeClass   *pClass;

            pClass = e->GetRuntimeClass();

            ASSERT( pClass != NULL );
            ASSERT( pClass->m_lpszClassName != NULL );

            TRACE( _T("Caught MFC Exception of Class: %s\n"),
                   pClass->m_lpszClassName );

            // Log additional information about error (if supported)
            // Only some derived classes from CException support
            // GetErrorMessage().

          if( e->IsKindOf(RUNTIME_CLASS(CFileException)
          || e->IsKindOf(RUNTIME_CLASS(COleException)
          || e->IsKindOf(RUNTIME_CLASS(COleDispatchException )
            {
                TCHAR   szBuf[256] = _T("");
                UINT    nHelpContextId;
                BOOL    bRetVal = TRUE;

                e->GetErrorMessage( szBuf, 256, &nHelpContextId );

                if( strlen( szBuf ) > 0 )
                {
                    TRACE( _T("\t Error Message = %s\n"), szBuf );
                }
            }
        }
        catch( CException *e2 )
        {
            TRACE( "AfxDbDaoCatchException() "
                   "caught an exception, but was unable to log it\n" );
            e2->Delete();
        }
        catch(...)
        {
            TRACE( "AfxDbDaoCatchException() "
                   "caught an exception, but was unable to log it\n" );
        }

        // Step 3: Delete Exception
        e->Delete();
    }

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