c++示例代码-友元

一、友元函数

#include <iostream.h>
#include <math.h>
class Point	//Point类声明
{ public:	//外部接口
	Point(int xx=0, int yy=0) {X=xx;Y=yy;}
	int GetX() {return X;}
	int GetY() {return Y;}
	friend float Distance(Point &a, Point &b); 
  private:	//私有数据成员
	int X,Y;
};

double Distance( Point& a, Point& b)
{
  double dx=a.X-b.X;
  double dy=a.Y-b.Y;
  return sqrt(dx*dx+dy*dy);
}
int main()
{ Point p1(3.0, 5.0), p2(4.0, 6.0);
  double d=Distance(p1, p2);
  cout<<"The distance is "<<d<<endl;
  return 0;
}

 

 

二、友元类

//友元类

class A
{   friend class B;
    public:
      void Display()
       {cout<<x<<endl;}
    private:
      int x;
}
class B
{   public:
      void Set(int i);
      void Display();
    private:
      A a;
};



void B::Set(int i)
{
   a.x=i;
}
void B::Display()
{
   a.Display();
}