friend keyword

There is a friend keyword in c++, which allows the modified object to break through the encapsulation feature of the class, so that it can access the private object of the class.

Simply put, it is:

• If you declare func() as your friend in class A, func() can use all the member variables of class A, regardless of where it is defined.

• If you declare that Class B is your friend in Class A, then the method in Class B can access all the member variables of Class A.

#include<iostream>
using namespace std;

class A {
public:
    A() {
        password = 1111;
        birthday = 808;
    }

    ~A() { }

    friend int func(A a); // To c++, int func (A) is my friend, so it can use everything I have.
    friend class B;       // To c++, class B is my friend, so it can use everything I have.

private:
    int password;
    int birthday;
};

int func(A a) {
    cout << a.password << " and " << a.birthday << endl; //Can access
    a.password = 1;                                      //It can even be modified.
    cout << a.password << endl;
    return 0;
}

class B {
public:
    B() { }

    ~B() { }
    // Because Class B has been declared as its friend in Class A, methods in Class B can access private variables in Class A.
    void show(A a) {
        cout << "your account is " << a.account << " and with pass: " << a.password << endl;
    }

private:
};

int main() {

    A a;

    func(a);

    B b;

    b.show(a);

    system("pause");
}

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Using friend Overload or > Operation

With this, we can overload the operation of or

#include<iostream>
using namespace std;

class A {
public:
    A() {
        password = 1111;
        account = 808;
    }

    ~A() { }

    friend ostream& operator << (ostream &os , A a);

private:
    int password;
    int account;
};

ostream& operator << (ostream &os , A a) {
    os << "your account is " << a.account << " and with pass: " << a.password << endl;
    return os;
}

int main() {

    A a;

    cout << a;

    system("pause");
}

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