C++类的组合

照着教材敲了一遍，采用单步跟踪的方式，查看程序的运行过程

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


class Point {
public:
    Point(int xx = 0, int yy = 0) {//构造函数
        x = xx;
        y = yy;
    }
    Point(Point& p);//复制构造函数

    int getx() {
        return x;
    }
    int gety() {
        return y;
    }

private:
    int x, y;
};


Point::Point(Point& p) {
    x = p.x;
    y = p.y;
    cout << "Callinbg the copy constructor of Point" << endl;
}

//类的组合
class Line {
public:
    Line(Point xp1, Point xp2);
    Line(Line &L);
    double getLen() { return len; }

private:
    Point p1, p2;
    int len;
};

//组合类的构造函数
Line::Line(Point xp1, Point xp2) :p1(xp1), p2(xp2) {
    cout << "Caling the constructor of Line" << endl;
    double x = static_cast<double>(p1.getx() - p2.getx());
    double y = static_cast<double>(p1.gety() - p2.gety());
    len = sqrt(x * x + y * y);
}

//组合类的复制构造函数
Line::Line(Line& L) :p1(L.p1), p2(L.p2) {
    cout << "Calling the copy constructor of Line" << endl;
    len = L.len;
}

int main()
{
    Point myp1(1,1),myp2(4, 5);
    Line line(myp1, myp2);
    Line line2(line);
    cout << "The length of the line is :";
    cout << line.getLen() << endl;
    cout << "The length of the line2 is :";
    cout << line2.getLen() << endl;
	return 0;
}

  

运行结果如下