KB195032 - PRB: Incorrect Function Signatures May Cause Problems in Release

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.

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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);

PRB: Incorrect Function Signatures May Cause Problems in Release

SYMPTOMS

CAUSE

RESOLUTION

STATUS

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Steps to Reproduce Behavior

REFERENCES