FIX: "Unhandled exception" in MFC DAO App After VC++ 5.0 SP1

• Microsoft Visual C++, 32-bit Editions, version 5.0sp1

SYMPTOMS

After installing the MFC42.dll (version 4.21.7160) that ships with Visual C++ 5.0 Service Pack 1, applications that were compiled with Visual C++ 4.2 and use MFC DAO may fail with an unhandled exception or MFC may display a "Command Failed" error message. Specifically, the exception will occur when creating index fields (CDaoTableDef::CreateIndex) or retrieving information about index fields (CDaoTableDef::GetIndexInfo). If you catch the exception to examine the error message you will see "No error message is available".

CAUSE

Apps compiled with Visual C++ 4.2 should use DAO 3.0. DAO 3.0 GUIDs were redefined (in DBDAOID.H) after DAO 3.5 was released and MFC DAO source was not modified to use the new definitions.

There are two places where MFC DAO uses the wrong GUIDs.In DaoCore.cpp:

1. Line 5527 inside AfxGetIndexFields(), IID_IDAOIndexFields is used instead of IID30_IDAOIndexFields.



2. Line 5580 inside AfxGetIndexFieldInfo(), IID_IDAOField is used instead of IID30_IDAOFields.


Any application that directly or indirectly calls these functions will fail.

RESOLUTION

There are three possible workarounds for this problem:

• Recompile your application with Visual C++ 4.2 and statically link to MFC.
  
  -or-



• Recompile your application with Visual C++ 5.0.
  
  -or-



• Place the MFC 4.2 dll (from Visual C++ 4.2) inside your application's directory so it will be used instead of the newer one.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been fixed in Visual Studio 97 Service Pack 3.

For more information, please see the following article in the Microsoft Knowledge Base:

Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

Following is an excerpt from DBDAOID.H included with Visual C++ 5.0:

   //   The pre-3.5 GUIDs have been redefined with "30" added to the ID.
   //      For example:
   //   IID_IDAOIndex becomes IID30_IDAOIndex
   //  

Steps to Reproduce Behavior

   CString strFilename = _T("c:\\db1.mdb");


   // Create a dao database

   CDaoDatabase database;
   database.Create(strFilename);

   // Create "DEFAULT" table

   CDaoTableDef tableDef(&database);
   tableDef.Create(_T("DEFAULT"));

   // Create a single field "IDENTIFIER"

   CDaoFieldInfo fieldInfo;
   fieldInfo.m_strName = _T("IDENTIFIER");
   fieldInfo.m_nType = dbText;
   fieldInfo.m_lSize = 255;
   fieldInfo.m_lAttributes = 0;
   fieldInfo.m_nOrdinalPosition = 0;
   fieldInfo.m_bRequired = FALSE;
   fieldInfo.m_bAllowZeroLength = FALSE;
   fieldInfo.m_lCollatingOrder = 0;
   tableDef.CreateField(fieldInfo);

   // Create the primary key

   CDaoIndexFieldInfo indexFieldInfo;
   indexFieldInfo.m_strName = _T("IDENTIFIER");
   indexFieldInfo.m_bDescending = FALSE;

   CDaoIndexInfo indexInfo;
   indexInfo.m_strName = _T("IDENTIFIER");
   indexInfo.m_pFieldInfos = &indexFieldInfo;
   indexInfo.m_nFields = 1;
   indexInfo.m_bPrimary = TRUE;
   indexInfo.m_bUnique = TRUE;
   indexInfo.m_bClustered = FALSE;
   indexInfo.m_bIgnoreNulls = FALSE;
   indexInfo.m_bRequired = TRUE;
   indexInfo.m_bForeign = TRUE;
   indexInfo.m_lDistinctCount = 0;
   tableDef.CreateIndex(indexInfo); // Generates exception 

Keywords : kbDAO kbDatabase kbMFC kbVC kbVS97sp2fix
Version : WINDOWS NT:5.0sp1
Platform : NT WINDOWS
Issue type : kbbug