Article ID: 300683 - Last Review: June 5, 2003 - Revision: 2.0

FIX: ICallFrame::GetMarshalSizeMax() Clears IDispatch::Invoke Parameters

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This article was previously published under Q300683
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SYMPTOMS

VARIANT out parameters that are passed through the IDispatch::Invoke method may be cleared by the time they reach the method that is being called. This makes it impossible to update any out parameters.
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CAUSE

This problem occurs because a private, internal COM+ interface, ICallFrame, incorrectly handles VARIANT parameters.
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RESOLUTION

To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
260910  (http://support.microsoft.com/kb/260910/EN-US/ ) How to Obtain the Latest Windows 2000 Service Pack

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STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows 2000 Service Pack 2.
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MORE INFORMATION

Before the call to ICallFrame::Invoke, you have the following code: 
   // This is an [in, out] parameter.
   // Its value is updated to 14 by the method that is being called.
   pDispParams->rgvarg[0] = VT_I2 | VT_BYREF (value = 12)
   // [in] param
   pDispParams->rgvarg[1] = VT_I2 | VT_BYREF (value =  2)
After the call to ICallFrame::Invoke, you have the following code: 
   // Also, lVal is 840456 (not the expected 14).
   pDispParams->rgvarg[0] = VT_EMPTY
   pDispParams->rgvarg[1] = VT_EMPTY
All of the parameters in the DispParams have their type set to VT_EMPTY. This makes it impossible to update any out parameters.
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APPLIES TO
  • Microsoft COM+ 1.0, when used with:
    • Microsoft Windows 2000 Standard Edition
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Keywords: 
kbbug kbfix kbqfe kbwin2000presp2fix KB300683
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