FIX: ATL Control May Cause an Access Violation (167526)
The information in this article applies to:
- The Microsoft Active Template Library (ATL) 2.0
- The Microsoft Active Template Library (ATL) 2.1
- The Microsoft Active Template Library (ATL) 3.0
This article was previously published under Q167526 SYMPTOMS
An ATL control that superclasses a Windows control and runs on Windows NT can cause
an access violation.
CAUSE
When ATL registers the Window Class for the control, it copies the
WNDCLASSEX structure from the control it is superclassing. Because Windows
controls are a global class, that attribute is given to the ATL control.
The problem occurs when the control[ASCII 146]s DLL is unloaded and then reloaded in
the same process. ATL tries to register the Window Class with the current
WndProcAddress, but Windows NT does not allow a Global Class to be
overwritten. If the DLL was reloaded at another address, the next call to
the WndProc causes an access violation.
RESOLUTION
In the file Atlwin.cpp, insert the following line (on line 610)) in the
function CContainedWindow::RegisterWndSuperclass() just before the call to
RegisterClassEx :
wc.style &= ~CS_GLOBALCLASS; // don't register as global class
atom = ::RegisterClassEx(&wc);
STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed
at the beginning of this article. This bug has been corrected in Visual
Studio 97 Service Pack 1.
For additional information about the Visual Studio 97 Service Pack 1,
please see the following article in the Microsoft Knowledge Base:
170365
INFO: Visual Studio 97 Service Packs - What, Where, and Why
MORE INFORMATION
This bug is hard to reproduce because it will only appear if the client
application unloads and then reloads the DLL and then the DLL is loaded at
another address. But any superclassed control built without the above
resolution may fail under the right conditions.
(c) Microsoft Corporation 1997, All Rights Reserved.
Contributions by Chuck Bell, Microsoft Corporation
| Modification Type: | Major | Last Reviewed: | 10/24/2003 |
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| Keywords: | kbBug kbCtrlCreate kbfix kbVS97sp1fix kbWndwClass KB167526 |
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