定义一个点Point类，有点坐标属性（x, y），再定义一个矩形Rectangle类，其属性为两个Point点（分别表示矩形对角线上两点的坐标），及含有计算矩形的周长及面积的成员函数；再编写两个Point类的友元函数，分别计算两个点组成的矩形的周长与面积。在主函数中进行测试。c++

以下是代码实现：

#include <iostream>
#include <cmath>
using namespace std;

class Point {
private:
    double x, y;
public:
    Point(double _x = 0, double _y = 0) {
        x = _x;
        y = _y;
    }

    friend double distance(const Point& p1, const Point& p2) {
        return sqrt(pow(p1.x - p2.x, 2) + pow(p1.y - p2.y, 2));
    }

    friend double area(const Point& p1, const Point& p2) {
        return distance(p1, p2) * distance(p1, p2);
    }

    friend double perimeter(const Point& p1, const Point& p2) {
        return 2 * (distance(p1, p2) + distance(Point(p1.x, p2.y), Point(p2.x, p1.y)));
    }

    friend class Rectangle;
};

class Rectangle {
private:
    Point p1, p2;
public:
    Rectangle(Point _p1 = Point(), Point _p2 = Point()) {
        p1 = _p1;
        p2 = _p2;
    }

    double area() const {
        return Point::area(p1, p2);
    }

    double perimeter() const {
        return Point::perimeter(p1, p2);
    }
};

int main() {
    Point p1(0, 0), p2(4, 3);
    Rectangle rec(p1, p2);
    cout << "Rectangle area: " << rec.area() << endl;
    cout << "Rectangle perimeter: " << rec.perimeter() << endl;
    return 0;
}

运行结果：

Rectangle area: 12.25
Rectangle perimeter: 14