友元声明无效。。

yiguo

<span style="background-color: rgb(255, 255, 255);">运行下列代码时，提示友元声明无效，请问是为什么。。？</span>

[img]file:///C:\Users\lenovo\Documents\Tencent Files\346411967\Image\C2C\6DS9EY3VARSVYAW@3[_0F_1.jpg[/img]

yiguo

// Class.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
using namespace std;


class Point
{
public:
        Point(float x=0,float y=0);
        void setPoint(float,float);
        float getX(){return x;}
        float getY(){return y;}
        friend ostream & operater << (ostream &,const Point &);
protected:
        float x,y;
};

Point::Point(float a, float b)
{
x=a;y=b;
}

void Point::setPoint(float a,float b)
{
x=a;y=b;
}

ostream &operater<<(ostream & output,Point &p) 
{
        output<<"["<<p.x<<","<<p.y<<"]";
        return output;
}


int main()
{
        Point p(4.3,5.2);
        cout<<"x="<<p.getX()<<"y="<<p.getY()<<endl;
        p.setPoint(5.6,7.6);
        cout<<"p(new)"<<p<<endl;
        return 0;
}