PRB: Incorrect Function Signatures May Cause Problems in Release

ID: Q195032

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 4.2, 5.0, 6.0

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

Create a new Application Wizard MFC dialog project named Sample with default settings.

Add the following line of code to the dialog header file above the line class Sample:
```
      #define WM_MYMSG WM_USER+555 
```

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

Add the following line of code inside of the message handler:
```
      AfxMessageBox("Got WM_MYMSG"); 
```

Add a ON_MESSAGE entry in the message map in the dialog source file, for example:
```
      ON_MESSAGE(WM_MYMSG, OnMyMsg) 
```

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.

Additional query words: crash access violation release debug message map

Keywords : kbMFC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Version : WINNT:4.0,4.1,4.2,5.0,6.0
Platform : winnt
Issue type : kbprb