#include <iostream>

using namespace std;

class Point{

public:

	Point(int _x = 0, int _y = 0, int _z = 0):x(_x), y(_y), z(_z){}

	Point(){}

	~Point(){}

	friend ostream& operator<<(ostream &os, const Point &pd);

private:

	int x;

	int y;

	int z;

};

ostream& operator<<(ostream &os, const Point &pd){

	os << pd.x<<" "<<pd.y<<" "<<pd.z;

	return os;

}

int main() {

	Point pd(1,2,3);

	cout<<pd;

	return 0;

}

基本的注意点就是。要把函数作为class Point的友元函数，在类的外面进行定义，此外要注意return os。达到链式的作用。