DOCUMENT:Q173645  17-JUL-2001  [visualc]
TITLE   :FIX: Access Violation in MSDAER.DLL with _com_error Exceptions
PRODUCT :Microsoft C Compiler
PROD/VER:WINDOWS:5.0
OPER/SYS:
KEYWORDS:kbATM kbVC500bug kbVC600fix kbVS97sp2fix

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-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
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SYMPTOMS
========

When using the compiler #import feature, ADO, the OLE DB 1.1 ODBC Provider, and
trapping _com_error exceptions, an access violation occurs in MSDAER.DLL when
closing an application.

CAUSE
=====

A method created with #import can throw a _com_error exception. When it throws
the exception, Release() is not called on the IErrorInfo pointer which is
returned from GetErrorInfo(). This leaves the internal error object in the OLEDB
ODBC Provider stranded which causes the access violation to occur as the
application shuts down.

RESOLUTION
==========

Create a macro which can be used to Release() the IErrorInfo interface at the
end of the "catch" block. For example:

      #define BUGFIX_RELEASE_IERRORINFO(error) \ 
              IErrorInfo * pErr = error.ErrorInfo();  \ 
              pErr->Release();                        \ 
              pErr->Release();

Here is an example of how you would use it:

      try
      {
        //.... call a #import generated method
        if ( m_connection == NULL )   {
         if(S_OK == m_connection.CreateInstance("ADODB.Connection.1", NULL,
      CLSCTX_INPROC_SERVER))
            m_connection->Open(varDataSource, varUserId, varPwd);
         }
      }
      catch(_com_error & err)
      {
        // Error handling code...
        ::MessageBox(NULL, (LPCSTR)err.Description(), _T("ADO Error"), MB_OK);

        BUGFIX_RELEASE_IERRORINFO(err);
      }

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 and Visual C++ version 6.0.

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

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

Additional query words: unhandled exception AV

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Keywords          : kbATM kbVC500bug kbVC600fix kbVS97sp2fix 
Technology        : kbVCsearch kbAudDeveloper kbVC500 kbVC32bitSearch kbVC500Search
Version           : WINDOWS:5.0
Issue type        : kbbug
Solution Type     : kbfix

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