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Q140590: FIX: Error in COleDispatchException Constructor

Article: Q140590
Product(s): Microsoft C Compiler
Version(s): WINDOWS:1.5,1.51,1.52,4.0; winnt:2.0,2.1,2.2,4.0
Operating System(s): 
Keyword(s): kbole kbActiveX kbAutomation kbCOMt kbMFC kbVC150bug kbVC151bug kbVC152bug kbVC200bug k
Last Modified: 06-MAY-2001

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The information in this article applies to:

- Microsoft Visual Basic Standard Edition for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition for Windows, version 4.0 
- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.5, 1.51, 1.52 
   - Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0 
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SYMPTOMS
========

In an MFC application, AfxThrowOleDispatchException is used to throw an
exception from within an OLE Automation function. When Microsoft Visual Basic is
used as the automation client application, it will not be able to correctly
interpret the error code passed to AfxThrowOleDispatchException.

CAUSE
=====

AfxThrowOleDispatchException constructs and throws a COleDispatchException
object, which is used to handle exceptions specific to the OLE IDispatch
interface. The constructor of COleDispatchException incorrectly initializes the
COleDispatchException object, resulting in the Visual Basic client being unable
to interpret the error code of the exception.

RESOLUTION
==========

To implement the proper behavior for throwing an OLE dispatch exception from an
MFC server, do not use AfxThrowOleDispatchException. Instead, construct your own
COleDispatchException, set m_scError = 0, and throw the exception yourself as
illustrated in the sample code in this article.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in Visual C++ 4.1.

MORE INFORMATION
================

COleDispatchException has two public members (m_wCode and m_scError) which are
mapped by COleDispatchException::Process() to the wCode and scode members of an
EXCEPINFO structure. An EXCEPTINFO structure is used by an automation object to
describe an exception that occurred during IDispatch::Invoke. When an automation
object raises an exception, it should store an error code inside either wCode or
scode but not both. If an error code is passed to the constructor of the
COleDispatchException object, the values of both wCode and scode in the
EXCEPINFO structure will be set.

Sample Code
-----------

  // Insert the following code instead of AfxThrowOleDispatchException
  COleDispatchException* pException;
  pException = new COleDispatchException(
                   _T("Some Exception"), 200, 425);
  pException->m_scError = 0;
  THROW(pException);

REFERENCES
==========

"Inside OLE" second edition by Kraig Brockschmidt, published by Microsoft Press,
Chapter 14, pages 658 - 660.

Additional query words: kbVC400bug 1.50 1.51 1.52 2.00 2.10 2.20 2.50 2.51 2.52 3.00 3.10 3.20 4.00 2.0 2.1 2.2 4.10

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Keywords          : kbole kbActiveX kbAutomation kbCOMt kbMFC kbVC150bug kbVC151bug kbVC152bug kbVC200bug kbVC210bug kbVC220bug kbVC400bug kbVC410fix kbGrpDSMFCATL kbNoUpdate 
Technology        : kbVBSearch kbAudDeveloper kbPTNotAssigned kbMFC kbZNotKeyword2
Version           : WINDOWS:1.5,1.51,1.52,4.0; winnt:2.0,2.1,2.2,4.0
Issue type        : kbbug
Solution Type     : kbfix

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