定义一个Point类，派生出Rectangle和Circle类，计算个派生类对象的面积Area()。 要求：①Point类，Rectangle和Circle类都有成员变量、成员函数； ②分别写出他们的构造函数和析构函数； ③在main函数中实现输出。 ④力争做到数据输入输出的直观性。

以下是一个可能的实现，其中Point类包含了x和y坐标，Rectangle类包含了左上角和右下角两个点的坐标，Circle类包含了圆心和半径：

#include <iostream>
#include <cmath>

using namespace std;

class Point {
public:
    Point(double x = 0, double y = 0);
    ~Point();
    double getX() const;
    double getY() const;
    void setX(double x);
    void setY(double y);
private:
    double m_x;
    double m_y;
};

class Rectangle : public Point {
public:
    Rectangle(double x1 = 0, double y1 = 0, double x2 = 0, double y2 = 0);
    ~Rectangle();
    double getWidth() const;
    double getHeight() const;
    double getArea() const;
private:
    double m_width;
    double m_height;
};

class Circle : public Point {
public:
    Circle(double x = 0, double y = 0, double r = 0);
    ~Circle();
    double getRadius() const;
    double getArea() const;
private:
    double m_radius;
};

Point::Point(double x, double y) : m_x(x), m_y(y) {
    cout << "Constructing Point (" << m_x << ", " << m_y << ")" << endl;
}

Point::~Point() {
    cout << "Destructing Point (" << m_x << ", " << m_y << ")" << endl;
}

double Point::getX() const {
    return m_x;
}

double Point::getY() const {
    return m_y;
}

void Point::setX(double x) {
    m_x = x;
}

void Point::setY(double y) {
    m_y = y;
}

Rectangle::Rectangle(double x1, double y1, double x2, double y2) :
        Point(x1, y1), m_width(fabs(x2 - x1)), m_height(fabs(y2 - y1)) {
    cout << "Constructing Rectangle (" << getX() << ", " << getY() << "), width = " << m_width << ", height = " << m_height << endl;
}

Rectangle::~Rectangle() {
    cout << "Destructing Rectangle (" << getX() << ", " << getY() << "), width = " << m_width << ", height = " << m_height << endl;
}

double Rectangle::getWidth() const {
    return m_width;
}

double Rectangle::getHeight() const {
    return m_height;
}

double Rectangle::getArea() const {
    return m_width * m_height;
}

Circle::Circle(double x, double y, double r) : Point(x, y), m_radius(r) {
    cout << "Constructing Circle (" << getX() << ", " << getY() << "), radius = " << m_radius << endl;
}

Circle::~Circle() {
    cout << "Destructing Circle (" << getX() << ", " << getY() << "), radius = " << m_radius << endl;
}

double Circle::getRadius() const {
    return m_radius;
}

double Circle::getArea() const {
    return M_PI * m_radius * m_radius;
}

int main() {
    Rectangle r(1, 1, 4, 3);
    Circle c(2, 2, 2);
    cout << "Rectangle area: " << r.getArea() << endl;
    cout << "Circle area: " << c.getArea() << endl;
    return 0;
}

在main函数中，我们创建了一个Rectangle对象和一个Circle对象，并且分别调用它们的getArea()函数计算面积并输出。程序输出如下：

Constructing Point (1, 1)
Constructing Rectangle (1, 1), width = 3, height = 2
Constructing Point (2, 2)
Constructing Circle (2, 2), radius = 2
Rectangle area: 6
Circle area: 12.5664
Destructing Circle (2, 2), radius = 2
Destructing Point (2, 2)
Destructing Rectangle (1, 1), width = 3, height = 2
Destructing Point (1, 1)