INFO: Extracting Error Information from ADO in VC++ with #import
ID: Q169498
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The information in this article applies to:
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ActiveX Data Objects (ADO), versions 1.0, 1.5, 2.0, 2.1
SUMMARY
When ActiveX Data Objects (ADO) encounter an error, often the Errors
Collection is filled with detail on the cause of the error. This article
provides sample code for extracting the maximum possible information on any
errors raised by ADO within Visual C++ using #import as the mechanism to
get at ADO.
If ADO itself encounters an error, it does not populate the errors
collection, but instead you have to use the native error mechanism to get
the information. In this case, an exception raised with the _com_error
class. If the provider or underlying components generate error, then these
will be populated in the ADO Errors Collection.
MORE INFORMATION
Often the Errors Collection returns an HRESULT in either hexadecimal
format, for example, 0x80004005, or as a long value, for example, -2147467259. These HRESULTS can be raised by underlying components such as
OLE-DB or even OLE itself. When this is the case, it may be confusing since
these codes are not documented in the ADO online documentation. However,
frequently encountered HRESULTS can be found in the Microsoft Knowledge Base article listed in the REFERENCES section.
The documentation for the ADO Error object indicates that the Errors
Collection is populated if any error occurs within ADO or its underlying
provider. This is somewhat incorrect. Depending on the source of the error,
or even bugs in the underyling provider to ADO (OLE-DB) or within ADO
itself, the errors collection may not be populated. You need to track the
HRESULT returned by many ADO methods, as well as if the _com_error
exception has been raised by #import generated classes.
The Errors Collection is available only off the Connection object, so you
need to initialize ADO off of a Connection object. Following is sample code
that demonstrates how to open a connection and report any errors
encountered, as well as handling Exceptions, and cracking the returned
HRESULT:
// Obtain the error message for a given HRESULT
CString LogCrackHR( HRESULT hr )
{
LPVOID lpMsgBuf;
CString strTmp;
::FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM,
NULL,
hr,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR) &lpMsgBuf,
0,
NULL );
// STR_TMP is defined within LOG.CPP to provide safe format string
// for both ANSI and UNICODE
strTmp.Format( "%s", (char *) lpMsgBuf );
// Free the buffer.
::LocalFree( lpMsgBuf );
return strTmp;
}
// Obtain information from the Errors Collection.
HRESULT LogAdoErrorImport(_ConnectionPtr pConn)
{
ErrorsPtr pErrors = NULL;
ErrorPtr pError = NULL;
CString strTmp;
HRESULT hr = (HRESULT) 0L;
long nCount;
// Don't have an un-handled exception in the handler that
// handles exceptions!
try
{
pErrors = pConn->GetErrors();
nCount = pErrors->GetCount();
for( long i = 0; (!FAILED(hr)) && (i < nCount); i++ )
{
TRACE( "\t Dumping ADO Error %d of %d", i+1, nCount );
hr = pErrors->get_Item((_variant_t)((long)i), &pError );
_bstr_t bstrSource ( pError->GetSource() );
_bstr_t bstrDescription( pError->GetDescription() );
_bstr_t bstrHelpFile ( pError->GetHelpFile() );
_bstr_t bstrSQLState ( pError->GetSQLState() );
TRACE( "\t\t Number = %ld", pError->GetNumber() );
TRACE( "\t\t Source = %s", (LPCTSTR) bstrSource );
TRACE( "\t\t Description = %s", (LPCTSTR) bstrDescription );
TRACE( "\t\t HelpFile = %s", (LPCTSTR) bstrHelpFile );
TRACE( "\t\t HelpContext = %ld", pError->GetHelpContext() );
TRACE( "\t\t SQLState = %s", (LPCTSTR) bstrSQLState );
TRACE( "\t\t HelpContext = %ld", pError->GetHelpContext() );
TRACE( "\t\t NativeError = %ld", pError->GetNativeError() );
}
}
catch( CException *e )
{
TRACE( "*** UNABLE TO LOG EXCEPTION ***" );
e->Delete();
}
catch(...)
{
TRACE( "*** UNABLE TO LOG EXCEPTION ***" );
}
if( pErrors ) pErrors->Release();
if( pError ) pError->Release();
return hr;
}
void CAdoDemoDlg::OnAdoTest()
{
HRESULT hr = S_OK;
_ConnectionPtr pConn;
hr = ::CoInitialize( NULL );
if( !FAILED( hr ) )
hr = pConn.CreateInstance( __uuidof( Connection ) );
// The following exception handling assumes a valid Connection
// object, so drop out if we couldn't create one for any reason.
if ( FAILED(hr) )
return;
try
{
// ... Your code goes here.
pConn->Close();
// For any error condition, dump results to TRACE.
// You may get a failure that does not raise an exception.
// The ADO Errors collection will likely be empty, but
// check anyway.
if( FAILED( hr ) )
{
TRACE( "*** HRESULT ***" );
TRACE( LogCrackHR( hr ) );
LogAdoErrorImport( pConn );
}
}
catch( CException *e )
{
TRACE( "*** Unhandled MFC Exception ***" );
e->Delete();
}
catch( _com_error &e )
{
// Crack _com_error
_bstr_t bstrSource(e.Source());
_bstr_t bstrDescription(e.Description());
TRACE( "Exception thrown for classes generated by #import" );
TRACE( "\tCode = %08lx\n", e.Error());
TRACE( "\tCode meaning = %s\n", e.ErrorMessage());
TRACE( "\tSource = %s\n", (LPCTSTR) bstrSource);
TRACE( "\tDescription = %s\n", (LPCTSTR) bstrDescription);
// Errors Collection may not always be populated.
if( FAILED( hr ) )
{
TRACE( "*** HRESULT ***" );
TRACE( LogCrackHR( hr ) );
}
// Crack Errors Collection.
LogAdoErrorImport(pConn);
}
catch(...)
{
TRACE( "*** Unhandled Exception ***" );
}
}
REFERENCES
For additional information, please see the following articles in the
Microsoft Knowledge Base:
Q168354 INFO: Underlying OLE and OLEDB Provider Errors Exposed via ADO
Q167802 SAMPLE: EXCEPTEX Traps MFC and Win32 Structured Exceptions
Additional query words:
kbdse
Keywords : kbcode kbADO kbVC
Version : WINDOWS:1.0,1.5,2.0,2.1
Platform : WINDOWS
Issue type : kbinfo