C/c++:c++ Friend class

C + + friend class:

Under normal circumstances, a class is not accessible to private members of another class. Just like this:

#include <iostream>class a{private:    int a;public:    A () {        a = 1;    }}; Class B:public A{public:    B () {        std::cout << A << std::endl;    }}; int main () {    B p;    P ();    return 0;}

This is an error: main.cpp|6|error: ' int a::a ' is private| In other words, A is private and B is not accessible.

At this point, we are going to use the concept of the friend class.

<span style= "FONT-SIZE:18PX;" > #include <iostream>class a{    friend class b;//specifies a friend of B as a. Private:    int a;public:    A () {        a = 1;    }}; Class B:public A{public:    B () {        std::cout << A << std::endl;    }}; int main () {    B p;    return 0;} </span>

At this point, B will be able to access the private members of a. Even if B does not inherit to a, it can be accessed. Just like this:

<span style= "FONT-SIZE:18PX;" > #include <iostream>class a{    friend class b;//specifies a friend of B as a. Private:    int a;public:    A () {        a = 1;    }}; Class B{public:    B () {        a A;        Std::cout << a.a << std::endl;    }; int main () {    B p;    return 0;} </span>

In fact, however, in the development process, the programmer seldom uses the friend class, because it makes the two classes directly related to too close.

PS: Beginner C + +, there is nothing wrong place, be sure to tell me _ (: З"∠) _. I am good at correcting my studies, and I will not mislead others.

C/c++:c++ Friend class