Member function pointer of C ++ class

//************************************** *******************
// Member function pointer variables of Clause 1 can be strongly converted to each other.
//************************************** *******************

Class A {}; Class B {}; Class C {}; typedef void (A: * afun) (void); typedef int (B: * bfun) (INT, INT); typedef void (C: * cfun) (double); afun pafun; bfun pbfun; cfun pcfun; // No relationship exists between Class A, Class B, and class C, although the following conversions are OK, there is basically no significance for pafun = (afun) pbfun; // okpafun = (afun) pcfun; // okpbfun = (bfun) pafun; // okpbfun = (bfun) pcfun; // okpcfun = (cfun) pafun; // okpcfun = (cfun) pbfun; // OK

 

 

//************************************** *******************
// Use of member function pointers in Clause 2
//************************************** *******************

// Definitions of Class A and Class B Class A {public: void test () {cout <"A: Test ()" <Endl ;}}; Class B: public A {public: void test () {cout <"B: Test ()" <Endl ;}}; // define the class member function pointer typedef void (A: * a_mfun) (void); typedef void (B: * B _mfun) (void); // codea; b; a_mfun pafun = & (A: Test); // Note: The test member function must be public; otherwise, the B _mfun pbfun = & (B: Test) error is returned ); // Note: The test member function must be public. Otherwise, an error is returned (. * pafun) (); // Output A: Test () (B. * pbfun) (); // output B: Test ()
(B. * pafun) (); // Output A: Test ()

A * pA = & A; B * pb = & B; (Pa-> * pafun) (); // Output A: Test () (Pb-> * pbfun) (); // output B: Test () (Pb-> * pafun) (); // Output A: Test (), B * variables can be assigned to a * variables.

// ******* Error ******
(Pa-> * pbfun) (); // error: cannot convert from 'A * 'to' B *'
// Error: cannot dereference a 'B _ mfun' on a 'a *'
//*****************

// ******* OK ******
B * pb_new = (B *) Pa; // strong conversion, but essentially missing
(Pb_new-> * pbfun) (); // output B: Test (). Although OK, remember not to use it like this. This is only used as an experiment demonstration.
// Essentially, a member function of a class is a function with the this pointer, but some restrictions will be added to the compiler during use,
// For example, a member function pointer of a class cannot be forced to convert to a common variable pointer or a common function pointer variable. This is mentioned in the previous article.
//**************

// The following is truly meaningful. It is used in the Framework mechanism of MFC. // The base class variable pointer + base class member function pointer is used to call the sub-class function a_mfun pafun_ B = (a_mfun) & (B: Test); A * pa_ B = & B; (pa_ B-> * pafun_ B) (); // output B: Test () // example: // The message ing in the dialog box includes on_bn_clicked (idc_btn_new_dlg, & ctestdlg: onbnclickedbtnnewdlg) // map the RESPONSE event of the button with ID as response to the onbnclickedbtnnewdlg member function of ctestdlg // we will study on_bn_clicked # define on_bn_clicked (ID, memberfxn) \ on_control (bn_clicked, ID, memberfxn) # define on_control (wnotifycode, ID, memberfxn) \ {wm_command, (Word) wnotifycode, (Word) ID, (Word) ID, afxsigcmd_v, \ (static_cast <afx_pmsg> (memberfxn)}, typedef void (afx_msg_call c1_target: * afx_pmsg) (void ); // you can see that the address of the subclass member function is assigned to the variable of the pointer type of the base class member function.