FIX: Access Violation in MSDAER.DLL with _com

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:

170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

FIX: Access Violation in MSDAER.DLL with _com_error Exceptions (173645)

SYMPTOMS

CAUSE

RESOLUTION

STATUS