c++组合类构造函数顺序

#include <iostream>
#include <cmath>
using namespace std;
 
class Point{
    private:
        int x, y;
    
    public:
        Point(int a = 0, int b = 0)
        {
            x = a; y = b;
            cout << "Point construction: " << x << ", "<< y << endl;
        }
        Point(Point &p) // copy constructor,其实数据成员是int类型，默认也是一样的 
        {
            x = p.x;
            y = p.y;
            cout << "Point copy construction: " << x << ", "<< y << endl; 
        }
        int getX()
        {
            return x;
        }
        int getY()
        {
            return y;
        }
}; 
 
class Line{
    private:
        Point start, end;
    
    public:
        Line(Point pstart, Point pend)
                    :start(pstart), end(pend) // 组合类的构造函数对内前对象成员的初始化必须采用初始化列表形式
        {
            cout << "Line constructior " << endl;
        }
        float getDistance()
        {
            double x = double(end.getX()-start.getX());
            double y = double(end.getY()-start.getY());
            return (float)（sqrt）(x*x+y*y);
        }
};
 
int main()
{
    Point p1(10,20),p2(100,200);
    Line line(p1,p2);
    cout << "The distance is: "<<line.getDistance()<<endl; return 0;
}

输出结果：

Point construction: 10, 20
Point construction: 100, 200
Point copy construction: 100, 200
Point copy construction: 10, 20
Point copy construction: 10, 20
Point copy construction: 100, 200
Line constructior
The distance is: 201.246

Line line(p1,p2);这一行代码在vs下面直接跳到point的复制构造函数，然后才进入line的构造函数的初始化列表，并再次进入point的复制构造函数