C++的友元类和友元函数实例

#include <math.h>
#include<iostream>
using namespace std; class Point
{
public:
Point(double xx, double yy)
{
x=xx;
y=yy;
}
void Getxy();
friend double Distance(Point &a, Point &b); //类Point的友元函数
friend class You; //类Point的友元类
private:
double x, y;
}; class You
{
public:
double Multi(Point &a)
{
return a.x * a.y + ;
}
}; void Point::Getxy()
{
cout<<"("<<x<<","<<y<<")"<<endl;
}
double Distance(Point &a, Point &b) //类Point的友元函数
{
double dx = a.x - b.x;
double dy = a.y - b.y;
return sqrt(dx*dx+dy*dy);
}
int main(void)
{
Point p1(3.0, 4.0), p2(6.0, 8.0);
p1.Getxy();
p2.Getxy();
double d = Distance(p1, p2); //Distance是类Point的友元函数，不是成员函数
cout<<"Distance is "<<d<<endl;
You you;
d = you.Multi(p1);
cout<<"Math.Multi is "<<d<<endl;
return true;
}