#include <iostream>

#include <cmath>

using namespace std;

//友元函数举例

class Point {

public:

    Point(int xx = , int yy = )

    {

        X = xx; Y = yy;

    }

    int GetX() { return X; }

    int GetY() { return Y; }

    friend float fDist(Point &a, Point &b);

private:

    int X, Y;

};

//友元函数的实现

float fDist(Point &p1, Point &p2)

{

    //通过对象访问私有数据成员

    double x = double(p1.X - p2.X);

    double y = double(p1.Y - p2.Y);

    return float(sqrt(x*x + y*y));

}

void main()

{

    Point myp1(, ), myp2(, );

    cout << "The distance is: ";

    cout << fDist(myp1, myp2) << endl;

    system("pause");

}

#include <iostream>

using namespace std;

class A {

public:

    friend class B;//在 B类中可以访问 A类 的私有成员、私有函数。

    // 友元类声明的位置和 public/private 没有关系。

    friend void modifyA(A *pA, int _a); //该函数是 类A 的好朋友

    A(int a=, int b=)

    {

        this->a = a;

        this->b = b;

    }

    int getA()

    {

        return this->a;

    }

private:

    int a, b;

};

void modifyA(A *pA, int _a)

{

    pA->a = _a;

}

//友元类使用场景较少

class B

{

public:

    void Set(int a)

    {

        Aobject.a = a;

    }

    void printB()

    {

        cout << Aobject.a << endl;

    }

private:

    A Aobject;

};

void main()

{

    A a1(, );

    cout << a1.getA() << endl;

    modifyA(&a1, );

    cout << a1.getA() << endl;

    B b1;

    b1.Set();

    b1.printB();

    system("pause");

}