C + +, const:

??? ??

Problem:

• Can the const member function and the ordinary member function be the same with the same parameter? Yes, this is an overload of a function.
• Can the const member function modify the value of a member variable of an object? Cannot be modified. Error C3490: cannot be modified because "year" is being accessed through a const object
• Does the non-const member function have access to const object members? cannot be accessed. Error C2662: "Time::show_time": Cannot convert "This" pointer from "Const time" to "Time &"
• Can the const member function invoke a non-const member function? No.
• Can the const member function access non-const member variables? Yes.

??

? 1.? The const member function and the ordinary member function can be the same with the same parameter, which is an overload of a function.

#include "stdafx.h"

#include <iostream>

using namespace Std;

?? ??

Class time

{

Public

Time (): Year (2015)

{

?}

??

? void Show_time (void) const

{

cout<< "Year:" <<year<<endl;

}

? ??

void print (int i)

{

cout<< "Fun i:" <<i<<endl;

}

? ??

void print (int i) const

{

cout<< "Const fun i:" <<i<<endl;

}

? ??

Private

const int year;

};

? ?? ??

int _tmain (int argc, _tchar* argv[])

{

Time time;

Time.show_time ();

Time.print (1);

? ??

Time const CTime;

Ctime.show_time ();

Ctime.print (1);

? ??

System ("pause");

return 0;

}

? ??

/*

year:2015

year:2015

Please press any key to continue ...

*/

??? 2.? The const member function cannot modify the value of a member variable of an object.

Class time

{

Public

void Show_time (void) const

{

cout<< "Year:" <<year<<endl;

Year = 11;//error C3490: cannot be modified because "year" is being accessed through a const object

}

? ??

? ??

Private

int year;

};

??? 3.? Non-const member functions do not have access to const object Members:

??

? 4.? A const member function cannot call a non-const member function;

Class time

{

Public

???? Time (): Year (2015)

???? {

???????? ?

????}

??

???? void Show_time (void) const

???? {

???????? cout<< "Year:" <<year<<endl;

???????? print (one);//error C2662: "time::p rint": "This" cannot be The pointer is converted from "constTime" to "time&"

????}

??

???? void print (int i)

???? {

???????? cout<< "Fun i:" <<i<<endl;

????}

??

Private

???? int year;

};

??

? 5.? The const member function can access non-const member variables. But cannot be modified.

Class time

{

...

void Show_time (void) const

{

cout<< "Year:" <<year<<endl;

}

...

??

Private

const int year;

};

??

Reference:

1. constant object and constant member function ? http://blog.chinaunix.net/uid-21411227-id-1826906.html

   ??

C + +, const: