友元实例

/*

 * 普通函数作为友元函数

 * Lzy      2011-8-4

 */

 

#include

using namespace std;

 

class Person

{

private:

    int id;

public:

    Person(int i):id(i){}

    friend int Display(Person &p);

};

 

int Display(Person &p)

{

    return p.id;

}

 

int main(void)

{

    Person p(3);

    cout<

    return 0;

}

 

 

 

/*

 * 成员函数作为友元函数

 * Lzy      2011-8-4

 */

 

#include

using namespace std;

 

class ClassA;

 

class ClassB

{

public:

    int Display(ClassA &a);

};

 

class ClassA

{

private:

    int num;

public:

    ClassA(int i):num(i){}

    friend int ClassB::Display(ClassA &a);

};

 

int ClassB::Display(ClassA &a)

{return a.num;}

 

int main(void)

{

    ClassA a(3);

    ClassB b;

    cout<

    return 0;

}

 

 

/*

 * 友元类

 * Lzy      2011-8-4

 */

 

#include

#include

using namespace std;

 

class Point;

 

class Point

{

private:

    float x, y;

public:

    Point(const float i,const float j):x(i),y(j){}

    friend class Distance;

};

 

class Distance

{

public:

    float distance(Point &p1, Point &p2){return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));}

};

 

int main(void)

{

    Point p1(3.0,4.0), p2(3.0,4.0);

    Distance d;

    cout<

    return 0;

}