This document discusses Microsoft Foundation Class (MFC) message handling in C++ applications. It explains that MFC provides an application framework for Windows programming that makes it easy to override basic functionality. It describes how message maps are used to map messages to handler functions in classes derived from CCmdTarget. It provides an example of a simple MFC application with a MyApp class derived from CWinApp and a MyWnd class derived from CFrameWnd, along with message map macros to handle the WM_LBUTTONDOWN message.

1. MFC(Microsoft Foundation Class
Library) Message Handling
Janani A
10 Oct 2011

2. Agenda
• Win32 application
• MFC
• Macros
• Message mapping

3. A Windows program
InitApplication()

4. Windows Program (contd…)
InitInstance()
Run()
Message Handler

5. MFC - Overview
• An "application framework" for programming in Microsoft
Windows.
• It's easy to extend or override the basic functionality that MFC
provides.
• Object Linking and Embedding (OLE), Data Access Objects
(DAO) and Open Database Connectivity (ODBC) etc

6. Execution begins here…
int AFXAPI AfxWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow)
{
ASSERT(hPrevInstance == NULL);
int nReturnCode = -1;
CWinApp* pApp = AfxGetApp();
// AFX internal initialization
if (!AfxWinInit(hInstance, hPrevInstance, lpCmdLine, nCmdShow))
goto InitFailure;
// App global initializations (rare)
ASSERT_VALID(pApp);
if (pApp != NULL && !pApp->InitApplication())
goto InitFailure;
ASSERT_VALID(pApp);
// Perform specific initializations
if (!pApp->InitInstance())
{
if (pApp->m_pMainWnd != NULL)
{
TRACE(traceAppMsg, 0, "Warning: Destroying non-NULL m_pMainWndn");
pApp->m_pMainWnd->DestroyWindow();
}
nReturnCode = pApp->ExitInstance();
goto InitFailure;
}
ASSERT_VALID(pApp);
nReturnCode = pApp->Run();
ASSERT_VALID(pApp);
InitFailure:
AfxWinTerm();
return nReturnCode;
}

7. The Windows program using MFC
class MyApp : public CWinApp
{
public:
virtual BOOL InitInstance();
};
class MyWnd : public CFrameWnd
{
public:
MyWnd()
{
Create (NULL, "My Application");
}
afx_msg void OnLButtonDown(UINT nFlags, CPoint point);
DECLARE_MESSAGE_MAP()
};
BEGIN_MESSAGE_MAP(MyWnd, CFrameWnd)
ON_WM_LBUTTONDOWN()
END_MESSAGE_MAP()
void MyWnd:: OnLButtonDown(UINT nFlags, CPoint point)
{
MessageBox(TEXT("Left mouse button pressed..."),NULL,MB_OK);
}
BOOL MyApp:: InitInstance()
{
m_pMainWnd = new MyWnd();
m_pMainWnd -> ShowWindow(m_nCmdShow);
m_pMainWnd -> UpdateWindow();
return TRUE;
}
MyApp intApp;

8. Macros
//DECLARE_MESSAGE_MAP()
#define DECLARE_MESSAGE_MAP()
private :
static const AFX_MSGMAP_ENTRY _messageEntries[];
protected:
static const AFX_MSGMAP messageMap;
virtual const AFX_MSGMAP* GetMessageMap() const;
//BEGIN_MESSAGE_MAP()
#define BEGIN_MESSAGE_MAP(theClass, baseClass)
const AFX_MSGMAP* theClass::GetMessageMap() const
{ return &theClass::messageMap; }
AFX_DATADEF const AFX_MSGMAP theClass::messageMap =
{ &baseClass::messageMap, &theClass::_messageEntries[0] };
const AFX_MSGMAP_ENTRY theClass::_messageEntries[] =
{
#define END_MESSAGE_MAP()
{0, 0, 0, 0, AfxSig_end, (AFX_PMSG)0 }
};
#define ON_WM_LBUTTONDOWN()
{ WM_LBUTTONDOWN, 0, 0, 0, AfxSig_vwp,
(AFX_PMSG)(AFX_PMSGW)(void (AFX_MSG_CALL CWnd::*)(UINT, CPoint))&OnLButtonDown },

9. After Pre-processing
class MyApp : public CWinApp
{
public:
virtual BOOL InitInstance();
};
class MyWnd : public CFrameWnd
{
public:
MyWnd()
{
Create (NULL, "My Application");
}
afx_msg void snFlags, CPoint point);
private :
static const AFX_MSGMAP_ENTRY
_messageEntries[];
protected:
static const AFX_MSGMAP messageMap;
virtual const AFX_MSGMAP* GetMessageMap()
const;
};
const AFX_MSGMAP* MyWnd::GetMessageMap() const
{ return & MyWnd::messageMap; }
AFX_DATADEF const AFX_MSGMAP MyWnd::messageMap =
{ &CFrameWnd::messageMap, & MyWnd::_messageEntries[0] };
const AFX_MSGMAP_ENTRY MyWnd::_messageEntries[] =
{
{ WM_LBUTTONDOWN, 0, 0, 0, AfxSig_vwp,
(AFX_PMSG)(AFX_PMSGW)(void (AFX_MSG_CALL
CWnd::*)(UINT, CPoint))&OnLButtonDown },
{0, 0, 0, 0, AfxSig_end, (AFX_PMSG)0 }
};
void MyWnd:: OnLButtonDown(UINT nFlags, CPoint point)
{
MessageBox(TEXT("Left mouse button pressed..."),
NULL,MB_OK);
}
BOOL MyApp:: InitInstance()
{
m_pMainWnd = new MyWnd();
m_pMainWnd -> ShowWindow(m_nCmdShow);
m_pMainWnd -> UpdateWindow();
return TRUE;
}
MyApp intApp;

10. Message map structures

11. Message Handling
• The CCmdTarget class: Base class for CFrameWnd,
CView, CWinApp, CDocument, CWnd with functions/
handlers for polymorphism. Override base functions
for custom behavior.
• Message Maps: Map the message codes to handlers
(CCmdTarget). Declare with
DECLARE_MESSAGE_MAP

12. References
• http://msdn.microsoft.com/en-us/library/d06h2x6e(v=vs.80).aspx
• http://www.functionx.com/visualc/
• MFC Internals- Inside The Microsoft Foundation Class, George Shepherd
and Scot Wingo
• http://home.arcor.de/it-
solution/cpp/books/Professional%20MFC/CH03_7.HTM
• afxmsg_.h

13. THANK YOU