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Q174891: FIX: CComQIPtr operator= Causes an Access Violation

Article: Q174891
Product(s): Microsoft C Compiler
Version(s): WINDOWS:2.0,2.1
Operating System(s): 
Keyword(s): kbATL200bug kbATL210bug kbCOMt kbVS97sp2fix kbATL300fix kbGrpDSMFCATL kbArchitecture
Last Modified: 26-JUN-2001

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The information in this article applies to:

- The Microsoft Active Template Library (ATL), versions 2.0, 2.1 
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SYMPTOMS
========

When a CComQIPtr is assigned a NULL pointer, an access violation occurs.

CAUSE
=====

When a CComQIPtr is assigned a NULL pointer, no check is done, and a
QueryInterface is attempted with the NULL pointer. This behavior causes the
access violation.

RESOLUTION
==========

Do not assign NULL pointer to a CComQIPtr object.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug has been fixed in Visual Studio 97 Service
Pack 3.

For more information, please see the following article in the Microsoft Knowledge
Base:

  Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

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

Steps to Reproduce Behavior
---------------------------

     CComQIPtr<IMyInterface, IID_IMyInterface> ptr;
     IUnknown* pUnk = NULL;
     ptr = pUnk;

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Chuck Bell,
Microsoft Corporation

Additional query words:

======================================================================
Keywords          : kbATL200bug kbATL210bug kbCOMt kbVS97sp2fix kbATL300fix kbGrpDSMFCATL kbArchitecture 
Technology        : kbAudDeveloper kbATLsearch kbATL200 kbATL210
Version           : WINDOWS:2.0,2.1
Issue type        : kbbug
Solution Type     : kbfix

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