Article: Q170979
Product(s): Microsoft C Compiler
Version(s): winnt:4.2
Operating System(s):
Keyword(s): kbole kbActiveDocs kbATL kbDLL kbMFC kbVC420bug kbVC500fix kbDSupport kbGrpDSMFCATL kbN
Last Modified: 17-JUL-2001
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The information in this article applies to:
- The Microsoft Foundation Classes (MFC), used with:
- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2
- Microsoft Visual C++, 32-bit Professional Edition, version 4.2
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SYMPTOMS
========
When using a class imported from an MFC extension DLL in an MFC application with
full server support for ActiveX documents, various problems may occur
including:
- Access violation
- Assert in dbgheap.c line 1011
- Incorrect values in data members
CAUSE
=====
The header file, afxdocob.h, which is only included for full server of ActiveX
documents, is missing the following near the end of the file:
#ifdef _AFX_PACKING
#pragma pack(pop)
#endif
RESOLUTION
==========
Add the above compiler directives after including afxdocob.h, or modify
afxdocob.h.
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 Microsoft Visual C++
5.0.
MORE INFORMATION
================
The default data member packing for structures and classes is 8 bytes. MFC
headers change this to 4 bytes to save memory. Because afxdocob.h is missing the
#pragma pack(pop), all user class declarations compiled after including this
file will be packed with 4-byte alignment. When sharing this class between an
application and an extension DLL, the structure will be packed differently since
the extension DLL doesn't include afxdocob.h. Subsequent use of this class may
result in invalid data or an access violation, especially when new and delete
are called.
The problem is more likely to occur when the class contains double or __int64
data members.
(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Adam Kim,
Microsoft Corporation
Additional query words: AFXDLL
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Keywords : kbole kbActiveDocs kbATL kbDLL kbMFC kbVC420bug kbVC500fix kbDSupport kbGrpDSMFCATL kbNoUpdate
Technology : kbAudDeveloper kbMFC
Version : winnt:4.2
Issue type : kbbug
Solution Type : kbfix
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