C++ 面向对象程序设计：基于 Point 类和 Plane 类设计圆类 Circle，并实现运算符重载和文件读写操作

#include <iostream>
#include <fstream>
using namespace std;
//点类Point
class Point
{
private:
    double x;
    double y;
public:
    Point(double xv=0,double yv=0);/*构造函数*/
    void setX(double xv);          /*设置X坐标*/
    void setY(double yv);          /*设置Y坐标*/
    double getX() const;           /*获取X坐标*/
    double getY() const;           /*获取Y坐标*/
    friend ostream & operator << (ostream &out, const Point &p); //运算符<<重载
    friend istream & operator >> (istream &in, Point &p); //运算符>>重载
};
class Plane /*平面图形基类*/
{
public:
    virtual double length()const=0;/*周长*/
    virtual double area()const=0;  /*面积*/
};
//圆类Circle
class Circle:public Point,public Plane
{
private:
    double radius;
protected:
    static const double PI;
public:
    Circle(double xv=0,double yv=0,double r=0);/*构造函数*/
    void setR(double r);                       /*设置半径*/
    double getR() const;                       /*获取半径*/
    double area()const;                        /*面积*/
    double length()const;                      /*周长*/
    friend ostream & operator << (ostream &out, const Circle &c); //运算符<<重载
    friend istream & operator >> (istream &in, Circle &c); //运算符>>重载
};

/*请在这里填写第一部分答案*/
const double Circle::PI = 3.14159;

Point::Point(double xv, double yv) : x(xv), y(yv) {}
void Point::setX(double xv) { x = xv; }
void Point::setY(double yv) { y = yv; }
double Point::getX() const { return x; }
double Point::getY() const { return y; }
ostream & operator << (ostream &out, const Point &p) {
    out << '(' << p.x << ',' << p.y << ')';
    return out;
}
istream & operator >> (istream &in, Point &p) {
    in >> p.x >> p.y;
    return in;
}

Circle::Circle(double xv, double yv, double r) : Point(xv, yv), radius(r) {}
void Circle::setR(double r) { radius = r; }
double Circle::getR() const { return radius; }
double Circle::area() const { return PI * radius * radius; }
double Circle::length() const { return 2 * PI * radius; }
ostream & operator << (ostream &out, const Circle &c) {
    out << '(' << c.getX() << ',' << c.getY() << ')' << ',' << c.radius; 
    return out;
}
istream & operator >> (istream &in, Circle &c) {
    in >> c.x >> c.y >> c.radius;
    return in;
}

void f(Plane  const &p) {
    cout << p.area() << endl;
    cout << p.length() << endl;
}
//主函数
int main(void) {
    double d1, d2;
    cin >> d1 >> d2;
    Point p(d1, d2);
    Circle c;
    
/*请在这里填写第二部分答案*/
    ofstream ofs("s3.txt");
    ofs << p;
    ofs.close();

    ifstream ifs("s3.txt");
    ifs >> p;
    ifs.close();

    c.setX(p.getY());
    c.setY(p.getX());
    c.setR(p.getX() + p.getY());
    ofstream bofs("b3.dat", ios::binary);
    bofs << c;
    bofs.close();

    ifstream bifs("b3.dat", ios::binary);
    bifs >> c;
    bifs.close();

    f(c);
    return 0;
}