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message map macro?

Posted on 2002-06-07
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What is the macro exactly? How is it different how a normal method/function/procedure? What C++ do with message map macro? Is it gonna be compiled to machine code or something?
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Question by:quanghoc
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jkr earned 150 total points
ID: 7063352
A message map macro is just a MFC construct to make it easier to connect windows messages to methods of a class - it basically is

#define DECLARE_MESSAGE_MAP() \
private: \
    static const AFX_MSGMAP_ENTRY _messageEntries[]; \
protected: \
    static AFX_DATA const AFX_MSGMAP messageMap; \
    static const AFX_MSGMAP* PASCAL _GetBaseMessageMap(); \
    virtual const AFX_MSGMAP* GetMessageMap() const; \

#define BEGIN_MESSAGE_MAP(theClass, baseClass) \
    const AFX_MSGMAP* PASCAL theClass::_GetBaseMessageMap() \
        { return &baseClass::messageMap; } \
    const AFX_MSGMAP* theClass::GetMessageMap() const \
        { return &theClass::messageMap; } \
    AFX_COMDAT AFX_DATADEF const AFX_MSGMAP theClass::messageMap = \
    { &theClass::_GetBaseMessageMap, &theClass::_messageEntries[0] }; \
    AFX_COMDAT const AFX_MSGMAP_ENTRY theClass::_messageEntries[] = \
    { \

#define END_MESSAGE_MAP() \
        {0, 0, 0, 0, AfxSig_end, (AFX_PMSG)0 } \
    }; \

So, what it does is declaring an array of message entries and accessor methods for both the classe's map and the the map of the base class, which are evaluated when a message is routed through the framework...
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by:quanghoc
ID: 7063415
Don't get it!!?? So message map just create an array?
What about macro? What is that? Can I have my own macro? is message map macro is MFC's stuffs or C++'s stuffs?
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Expert Comment

by:jkr
ID: 7063428
>>So message map just create an array?

Basically, yes - but this array is pretty complex :o)

>>Can I have my own macro?

Sure - a macro in general is an expression that is expanded by the precompiler, e.g. like

#define ADD(a,b) a + b

int a = 1;
int b = 2;

int c = ADD(a,b);

will result in

int c = a + b;

>>is message map macro is MFC's stuffs or C++'s stuffs?

A message map is a MFC construct and certainly isn't included in any C++ standard.
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by:DanRollins
ID: 7064161
>>Can I have my own macro?
You can add message-map entries to the map.  For instance:

  ON_MESSAGE( 123456, MyFn )


This means if a message comes in and MSG.message value is 123456, then the function maned MyFn will be executed.
 
-- Dan
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by:quanghoc
ID: 7064203
So, in what .h file I can find all the source that message map does? And to jkr: var c will be a global variable?
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by:jkr
ID: 7064609
All the message map macros can be found in afxwin.h
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by:quanghoc
ID: 7064637
Why this has to done with macro? Why Microsoft doesn't just use a method to this? What is the advantage to use macro?
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Expert Comment

by:DanRollins
ID: 7064643
quanghoc,
Is this question about C++ macros in general?  Or is it about how MFC uses its message mapping system?  

Please describe what you need to know.  So far you are thrashing about without direction.

-- Dan
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by:quanghoc
ID: 7064754
Well, as the begin questions:
-------------------
What is the macro exactly? How is it different how a normal method/function/procedure? What C++ do with
message map macro? Is it gonna be compiled to machine code
or something?
-------------------
So far, I already understand about message map and how macro construct. But as the last couple questions:
-------------------
Why this has to done with macro? Why Microsoft doesn't just use a method to this? What is the advantage
to use macro?
-------------------
I would like to know why they created macro for! That's it. The whole thing is just the relationship between macro and message map.
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by:DanRollins
ID: 7064816
I think you want to know this:
Why did Microsoft use a set of macros to implement the message-handling table.

The reason is that the table is complicated and they wanted to provide an easy way for programmers and automated tools such as the the ClassWizard to add and remove items from the table.  

For instance, which would you rather type.  This...

BEGIN_MESSAGE_MAP(CD01Dlg, CDialog)
     ON_BN_CLICKED(IDC_BUTTON1, OnButton1)
     ON_NOTIFY(LVN_BEGINDRAG, IDC_LIST1, OnBegindragList1)
END_MESSAGE_MAP()

... or this ...

const AFX_MSGMAP* PASCAL theClass::_GetBaseMessageMap()
{ return &baseClass::messageMap; }
const AFX_MSGMAP* theClass::GetMessageMap() const
{ return &theClass::messageMap; }
AFX_COMDAT AFX_DATADEF const AFX_MSGMAP theClass::messageMap =
 &theClass::_GetBaseMessageMap, &theClass::_messageEntries[0] };
AFX_COMDAT const AFX_MSGMAP_ENTRY theClass::_messageEntries[] =
{
     { WM_LBUTTONDOWN, 0, 0, 0, AfxSig_vwp,
          (AFX_PMSG)(AFX_PMSGW)(void (AFX_MSG_CALL CWnd::*)(UINT, CPoint))&OnLButtonDown
     },
     { WM_NOTIFY, (WORD)(int)wNotifyCode, (WORD)id,
          (WORD)id, AfxSig_vNMHDRpl,
          (AFX_PMSG)(void (AFX_MSG_CALL CCmdTarget::*)(NMHDR*, LRESULT*))&memberFxn
     },
     {0, 0, 0, 0, AfxSig_end, (AFX_PMSG)0 }
};

-- Dan
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