Q131102: FIX: Enumerating Connection Points Causes GP Fault

Article: Q131102
Product(s): Microsoft C Compiler
Version(s): 1.0
Operating System(s): 
Keyword(s): kbole kbActiveX kbCOMt kbCtrl kbLocalSvr kbMFC kbVC500fix kbGrpDSMFCATL kbNoUpdatekbbug
Last Modified: 08-NOV-2001

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The information in this article applies to:

- Microsoft ActiveX SDK, version 1.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Attempting to enumerate connection points with the IEnumConnectionPoints
interface results in a general protection (GP) fault. Specifically, attempting
to call the IEnumConnectionPoints::Next() method cause a GP Fault.

CAUSE
=====

The problem occurs in the CEnumConnPoints::OnNext() function located in the CDK
source file CTLCONN.CPP.

     BOOL CEnumConnPoints::OnNext(void FAR* pv)
     {
        if (!CEnumArray::OnNext(pv))
           return FALSE;

        // outgoing connection point needs to be AddRef'ed
        //  (the caller has responsibility to release it)

        ((LPCONNECTIONPOINT)pv)->AddRef();
        return TRUE;
     }

AddRef() is called through an improperly dereferenced pointer. The line of code
should be this:

     (*(LPCONNECTIONPOINT*)pv)->AddRef();

RESOLUTION
==========

Currently, there is no workaround for this problem. Avoid enumerating connection
points. You can also retrieve connection points with the
IConnectionPointContainer::FindConnectionPointFromIID() function.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem has been fixed in Visual C++ version
5.0.

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

Visual C++ Version 2.x Sample Code to Demonstrate Problem
---------------------------------------------------------

     void CControlContainerView::OnEnumCtrlConnPoints()
     {
        if (!m_pSelection) // pointer to a COleClientItem derived object
                           // that supports additional OLE Control interfaces

        {
           AfxMessageBox(_T("No Control selected!"));
           return;
        }

        LPCONNECTIONPOINTCONTAINER lpCPC;
        LPENUMCONNECTIONPOINTS lpEnumCPTS;
        LPCONNECTIONPOINT lpCPT;

        if (SUCCEEDED(m_lpSelection->m_lpObject->QueryInterface(
           IID_IConnectionPointContainer,(LPVOID FAR*)&lpCPC)))
        {
           if (SUCCEEDED(lpCPC->EnumConnectionPoints(&lpEnumCPTS)))
           {
              HRESULT hr = lpEnumCPTS->Next(1,&lpCPT,NULL); //GPF occurs here

              if (NOERROR == hr)
              {
                 AfxMessageBox(_T("Connection Point retrieved!"));
                 lpCPT->Release();
              }
              lpEnumCPTS->Release();
           }
           else
              AfxMessageBox(_T("EnumConnectionPoints failed!"));

           lpCPC->Release
        }
        else
           AfxMessageBox(_T("QI for IConnectionPointContainer failed!"));
     }

Additional query words: GPF

======================================================================
Keywords          : kbole kbActiveX kbCOMt kbCtrl kbLocalSvr kbMFC kbVC500fix kbGrpDSMFCATL kbNoUpdate kbbuglist kbfixlist
Technology        : kbAudDeveloper kbZNotKeyword kbSDKSearch kbSDKActiveXsearch kbSDKActiveX
Version           : :1.0
Issue type        : kbbug
Solution Type     : kbfix

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