3.设计并测试一个矩形类(Rectangle)，属性为矩形的左下角与右上角的坐标，矩形水平放置。操作为计算矩形的周长和面积，、构造函数、析构函数复制构造函数，并完成测试，并在主函数中对应的语句中注释调用了哪个函数。

没问题，我可以回答这个问题。以下是矩形类(Rectangle)的设计和测试：

#include <iostream>
using namespace std;

class Rectangle {
private:
    int x1, y1, x2, y2;

public:
    Rectangle(int x1=0, int y1=0, int x2=0, int y2=0) {
        this->x1 = x1;
        this->y1 = y1;
        this->x2 = x2;
        this->y2 = y2;
    }

    Rectangle(const Rectangle& r) {
        x1 = r.x1;
        y1 = r.y1;
        x2 = r.x2;
        y2 = r.y2;
    }

    ~Rectangle() {}

    int getWidth() const {
        return abs(x2-x1);
    }

    int getHeight() const {
        return abs(y2-y1);
    }

    int getPerimeter() const {
        return 2 * (getWidth() + getHeight());
    }

    int getArea() const {
        return getWidth() * getHeight();
    }
};

int main() {
    Rectangle r1(0, 0, 2, 2);
    cout << "width: " << r1.getWidth() << endl;
    cout << "height: " << r1.getHeight() << endl;
    cout << "perimeter: " << r1.getPerimeter() << endl;
    cout << "area: " << r1.getArea() << endl;
    Rectangle r2(r1);
    cout << "width: " << r2.getWidth() << endl;
    cout << "height: " << r2.getHeight() << endl;
    cout << "perimeter: " << r2.getPerimeter() << endl;
    cout << "area: " << r2.getArea() << endl;
    return 0;
}

注释调用的函数如下：

* 第7行：默认构造函数
* 第13行：复制构造函数
* 第15行：析构函数