求助！！！！在这个头文件中为啥提示我ostream没有定义

[xxx_Mrjie_xxx]

class point
{
float x;
float y;
public:
point(float xx=0,float yy=0);
void set_point(float,float);
float get_x() const;
float get_y() const;
friend ostream & operator<<(ostream &,const point &p);
};

[ipqtjmqj]

你要声明一下class ostream;

[幻夢之葉]

//#include <iostream> //或者 class ostream; class point { float x; float y; public: point(float xx=0,float yy=0); void set_point(float,float); float get_x() const; float get_y() const; friend std::ostream & operator<<(std::ostream &,const point &p); };