HOWTO: Catch and Decipher DAO SDK-Based Exceptions

ID: Q152695

The information in this article applies to:

The DAO SDK, included with:
- Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 4.2, 4.2b, 5.0, 6.0

SUMMARY

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

MORE INFORMATION

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().

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();
    }

Additional query words:

Keywords : kbcode kbprg kbtshoot kbDAO kbDatabase kbMFC kbVC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Version : 4.0 4.1 4.2 4.2b 5.0 6.0
Platform : NT WINDOWS
Issue type : kbhowto