Microsoft KB Archive/141661

= FIX: Access Violation Firing an Error Event in OLE Control =

Article ID: 141661

Article Last Modified on 10/24/2003

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APPLIES TO


 * Microsoft Visual C++ 2.0 Professional Edition
 * Microsoft Visual C++ 2.1
 * Microsoft Visual C++ 2.2

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This article was previously published under Q141661



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: kbbug kbfix kbctrl KB141661

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