Q195032: PRB: Incorrect Function Signatures May Cause Problems in Release
Article: Q195032
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.1,4.2,5.0,6.0
Operating System(s):
Keyword(s): kbMFC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL
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 Editions, versions 4.0, 4.1
- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2
- Microsoft Visual C++, 32-bit Professional Edition, version 4.2
- Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0
- Microsoft Visual C++, 32-bit Professional Edition, version 5.0
- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
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SYMPTOMS
========
When developing applications in Visual C++ with MFC, you may receive an invalid
page fault in Mfc42.dll in release builds due to an incorrect function signature
for any of the following MFC macros:
ON_MESSAGE()
ON_REGISTERED_MESSAGE()
ON_THREAD_MESSAGE()
ON_REGISTERED_THREAD_MESSAGE()
CAUSE
=====
The message handlers for ON_MESSAGE(), ON_REGISTERED_MESSAGE(),
ON_THREAD_MESSAGE(), and ON_REGISTERED_THREAD_MESSAGE() require the programmer
to have the correct function signatures. By not having a correct function
signature for the handler, an invalid page fault in Mfc42.dll results after the
handler executes in release builds. A crash in debug builds does not occur
because the stack frame is set up differently for debug builds than it is for
release builds.
RESOLUTION
==========
Make sure your message handlers for ON_MESSAGE(), ON_REGISTERED_MESSAGE(),
ON_THREAD_MESSAGE(), and ON_REGISTERED_THREAD_MESSAGE() have the correct
signatures.
The correct signature for ON_MESSAGE() is:
afx_msg LRESULT OnMyMsg(WPARAM, LPARAM)
The correct signature for ON_REGISTERED_MESSAGE is:
afx_msg LRESULT OnMyRegisteredMsg(WPARAM, LPARAM)
The correct signature for ON_THREAD_MESSAGE is:
afx_msg void OnMyThreadMsg(WPARAM, LPARAM)
The correct signature for ON_REGISTERED_THREAD_MESSAGE is:
afx_msg void OnMyRegisteredThreadMsg(WPARAM, LPARAM)
For signatures for other versions of Visual C++, please consult help for
ON_MESSAGE(), ON_REGISTERED_MESSAGE(), ON_THREAD_MESSAGE() and
ON_REGISTERED_THREAD_MESSAGE().
To get a compile-time error when using these macros, you can re-define the macros
after the "#include <afxwin.h>" line in your Stdafx.h file. The code below
uses the static_cast<> operator to aid the compiler and developer by doing
strict type conversion on the function pointer:
#undef ON_MESSAGE
#define ON_MESSAGE(message, memberFxn) \
{ message, 0, 0, 0, AfxSig_lwl, \
(AFX_PMSG) (AFX_PMSGW) (static_cast< LRESULT (AFX_MSG_CALL
CWnd::*)(WPARAM, LPARAM) > (&memberFxn)) },
#undef ON_REGISTERED_MESSAGE
#define ON_REGISTERED_MESSAGE(nMessageVariable, memberFxn) \
{ 0xC000, 0, 0, 0, (UINT)(UINT*)(&nMessageVariable), \
(AFX_PMSG)(AFX_PMSGW)(static_cast<LRESULT (AFX_MSG_CALL
CWnd::*)(WPARAM, LPARAM)>(&memberFxn)) },
#undef ON_THREAD_MESSAGE
#define ON_THREAD_MESSAGE(message, memberFxn) \
{ message, 0, 0, 0, AfxSig_vwl, \
(AFX_PMSG)(AFX_PMSGT)(static_cast<void (AFX_MSG_CALL
CWinThread::*)(WPARAM, LPARAM)>(&memberFxn)) },
#undef ON_REGISTERED_THREAD_MESSAGE
#define ON_REGISTERED_THREAD_MESSAGE(nMessageVariable, memberFxn) \
{ 0xC000, 0, 0, 0, (UINT)(UINT*)(&nMessageVariable), \
(AFX_PMSG)(AFX_PMSGT)(static_cast<void (AFX_MSG_CALL
WinThread::*)(WPARAM, LPARAM)>(&memberFxn)) },
The ON_MESSAGE(), ON_REGISTERED_MESSAGE(), ON_THREAD_MESSAGE() and
ON_REGISTERED_THREAD_MESSAGE() macros are defined in \mfc\include\afxmsg_.h.
STATUS
======
Microsoft has confirmed this to be a problem in the Microsoft products listed at
the beginning of this article.
MORE INFORMATION
================
Steps to Reproduce Behavior
---------------------------
1. Create a new Application Wizard MFC dialog project named Sample with default
settings.
2. Add the following line of code to the dialog header file above the line class
Sample:
#define WM_MYMSG WM_USER+555
3. Add a custom message handler to the dialog class with incorrect function
signature, for example:
afx_msg void OnMyMsg(void); //in header file
void CSampleDlg::OnMyMsg(void) {} //in source file
4. Add the following line of code inside of the message handler:
AfxMessageBox("Got WM_MYMSG");
5. Add a ON_MESSAGE entry in the message map in the dialog source file, for
example:
ON_MESSAGE(WM_MYMSG, OnMyMsg)
6. Add the following line of code inside of the OnInitDialog of the class after
CDialog::OnInitDialog();:
SendMessage(WM_MYMSG);
In debug builds, the message box appears and no invalid page fault occurs. In
release builds, the message box appears and an invalid page fault in Mfc42.dll
occurs after you dismiss the message box.
REFERENCES
==========
ON_MESSAGE() in the Visual C++ Product Documentation.
ON_REGISTERED_MESSAGE() in the Visual C++ Product Documentation.
ON_THREAD_MESSAGE() in the Visual C++ Product Documentation.
ON_REGISTERED_THREAD_MESSAGE() in the Visual C++ Product Documentation.
(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Nathan
Manis, Microsoft Corporation.
(c) Microsoft Corporation 1998, All Rights Reserved.
Contributions by Nathan Manis, Microsoft Corporation
Additional query words: crash access violation release debug message map
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Keywords : kbMFC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 kbGrpDSMFCATL
Technology : kbAudDeveloper kbMFC
Version : winnt:4.0,4.1,4.2,5.0,6.0
Issue type : kbprb
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