DOCUMENT:Q141661  30-JUL-2001  [visualc]
TITLE   :FIX: Access Violation Firing an Error Event in OLE Control
PRODUCT :Microsoft C Compiler
PROD/VER:2.00 2.10 2.20
OPER/SYS:
KEYWORDS:kbole kbCtrlkbbuglist kbfixlist

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

 - Microsoft Visual C++, versions 2.0, 2.1, 2.2 
-------------------------------------------------------------------------------

SYMPTOMS
========

An access violation occurs when the error event is fired in an OLE Control. This
occurs on the first firing of an error event in Release builds and only after
several firings in Debug builds.

CAUSE
=====

An invalid "this" pointer is being loaded off the stack on a call to
ExternalRelease() at the end of COleControl::FireEvent().

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 Microsoft Visual C++,
32-bit Edition, version 4.0.

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

To reproduce this problem, add the stock Error event to an OLE Control using
ClassWizard's OLE Events tab. The name given the member function to fire the
event will be FireError. In the OnLButtonDown handler of the OLE Control, call
FireError() and pass the following parameters:

   FireError(CTL_E_OUTOFMEMORY, " ");

This causes the SCODE of the error to be 0x800A0007 (CTL_E_OUTOFMEMORY), and the
description string to be " ", a single space followed by a NULL byte. The rest
of the parameters will be defaults.

Now, run the test container, insert your control, and click the control's client
area. In Release builds, this causes an access violation on the first occurrence
of the event. In Debug, it takes several occurrences before the access violation
is seen.

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

Below is the OnLButtonDown handler for the Circ3 tutorial sample, modified to
call the error event.

   /* Compile options needed:
   */ 
   void CCirc3Ctrl::OnLButtonDown(UINT nFlags, CPoint point)
   {
      /*  Comment the tutorial.
           CDC* pdc;
      // Flash the color of the control if within the
              ellipse.
      if (InCircle(point))
      {
         pdc = GetDC();
         FlashColor(pdc);
         ReleaseDC(pdc);
         // Fire the ClickIn event
         FireClickIn(point.x, point.y);
      }
      else
         // Fire the ClickOut event
         FireClickOut();
           */ 
           // Here's the call.
      FireError(CTL_E_OUTOFMEMORY, " ");
      COleControl::OnLButtonDown(nFlags, point);
   }

Additional query words: 2.00 2.10 2.20 3.00 3.10 3.20

======================================================================
Keywords          : kbole kbCtrl kbbuglist kbfixlist
Technology        : kbVCsearch kbAudDeveloper kbVC220 kbVC200 kbVC210
Version           : 2.00 2.10 2.20
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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