友元函数

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstdlib>
#include<cmath>
using namespace std;
class MyPointer {
public:
  MyPointer(double x, double y)
  {
    p_x = x;
    p_y = y;
  }
  double get_x() { return p_x; }
  double get_y() { return p_y; }
  friend void f_distance(MyPointer, MyPointer);
private:
  double p_x, p_y;
};
void f_distance(MyPointer a, MyPointer b)
{
  double result = sqrt(pow(abs(a.p_x-b.p_x),2),pow(abs(a.p_y-b.p_y),2));
  cout << "distance:" << result << endl;
}
void mydistance(MyPointer a, MyPointer b)
{
  double result = sqrt(pow(abs(a.get_x-b.get_x), 2), pow(abs(b.get_y - b.get_y), 2));
  cout << "distance:" << result << endl;
}
int main()
{
  MyPointer p1(0, 0), p2(5,0);
  mydistance(p1, p2);
  f_distance(p1, p2);
  system("pause");
  return 0;
}