c++用类中的成员函数做友元函数

//计算两点之间距离
#include<iostream>
#include<MATH.H>
using namespace std;
class Point;
class test
{
public:
	double dist(Point &p1,Point &p2);
};
class Point
{

private:
	int x,y;
public:
	Point(int xx=0,int yy=0)
	{
		x=xx;
		y=yy;
	}
	void display()
	{
		cout<<"("<<x<<","<<y<<")";
	}
	friend double test::dist(Point &p1,Point &p2);

};
double test::dist(Point &p1,Point &p2)
{
		return sqrt(double((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)));
}
int main()
{
	Point p1(3,4),p2(4,5);
	p1.display();
	cout<<"----->";
	p2.display();
	test a;
	cout<<"距离："<<a.dist(p1,p2)<<endl;
	return 0;
}