Q152695: HOWTO: Catch and Decipher DAO SDK-Based Exceptions
Article: Q152695
Product(s): Microsoft C Compiler
Version(s): 4.0 4.1 4.2 4.2b 5.0 6.0
Operating System(s):
Keyword(s): kbcode kbProgramming kbtshoot kbDAOsearch kbDatabase kbMFC kbVC kbVC400 kbVC410 kbVC420
Last Modified: 04-AUG-2001
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The information in this article applies to:
- The DAO SDK, included with:
- Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1
- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2
- Microsoft Visual C++, 32-bit Professional Edition, version 4.2
- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2b
- Microsoft Visual C++, 32-bit Professional Edition, version 4.2b
- Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0
- Microsoft Visual C++, 32-bit Professional Edition, version 5.0
- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
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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 kbProgramming kbtshoot kbDAOsearch kbDatabase kbMFC kbVC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Technology : kbAudDeveloper kbDAOsearch kbSDKDAOSearch kbSDKSearch
Version : 4.0 4.1 4.2 4.2b 5.0 6.0
Issue type : kbhowto
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