C++看程序写结果:调用一次Line类构造函数,执行几次Point类复制构造函数?
#include <iostream> #include <cmath> using namespace std; class Point { //Point类定义 public: Point(int xx = 0, int yy = 0) { x = xx; y = yy; } Point(Point &p); int getX() { return x; } int getY() { return y; } private: int x, y; }; Point::Point(Point &p) { //复制构造函数的实现 x = p.x; y = p.y; cout << "Calling the copy constructor of Point" << "x=" << x<< ",y=" <<y <<endl; } //类的组合 class Line { //Line类的定义 public: //外部接口 Line(Point xp1, Point xp2, Point xp3); Line(Line &l); double getLen() { return len; } private: //私有数据成员 Point p2, p1,p3; //Point类的对象p1,p2 double len; }; //组合类的构造函数 Line::Line(Point xp1, Point xp2,Point xp3) : p1(xp1), p2(xp2), p3(xp3) { cout << "Calling 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); } Line::Line (Line &l): p1(l.p1), p2(l.p2) , p3(l.p3) {//组合类的复制构造函数 cout << "Calling the copy constructor of Line" << endl; len = l.len; } //主函数 int main() { Point myp1(1, 2), myp2(3, 4),myp3(5,6); //建立Point类的对象 Line line(myp1, myp2,myp3); //建立Line类的对象 return 0; }
一共执行6次point类复制构造函数。前三次是把point类的值传入line类构造函数,后三次是根据line类声明的先后顺序,通过初始化列表执行point类复制构造函数。
特别反直觉的是,虽然是 line(myp1,myp2,myp3) ,但是最先执行复制构造函数的是myp3,传值进去的构造顺序是反过来的。
Calling the copy constructor of Pointx=5,y=6 Calling the copy constructor of Pointx=3,y=4 Calling the copy constructor of Pointx=1,y=2 Calling the copy constructor of Pointx=3,y=4 Calling the copy constructor of Pointx=1,y=2 Calling the copy constructor of Pointx=5,y=6 Calling constructor of Line
标签:Point,C++,Calling,constructor,Pointx,Line,构造函数 From: https://www.cnblogs.com/uacs2024/p/18081434