Question

#include <iomanip>
#include <iostream>
#include <string>
using namespace std;

class Box
{
protected:
    double length;
    double width;
    double height;
public:
    // Constructors
    Box(double lv, double wv, double hv) : length {lv}, width {wv}, height {hv}
    { std::cout << "Box(double, double, double) called.\n"; }

    Box(double side) : Box {side, side, side}
    { std::cout << "Box(double) called.\n"; }

    Box() { std::cout << "Box() called.\n"; }

    double volume() const
    { return length * width * height; }

    double getLength() const { return length; }
    double getWidth() const { return width; }
    double getHeight() const { return height; }
    ~Box()
    { cout << "box destructor" << endl; }
};


class Carton : public Box
{
private:
    string material {"Cardboard"};
public:
    Carton(double lv, double wv, double hv, const string desc) : Box {lv, wv, hv}, material {desc}
    { std::cout << "Carton(double,double,double,string) called.\n"; }

    Carton(const string desc) : material {desc}
    { std::cout << "Carton(string) called.\n"; }

    Carton(double side, const string desc) : Box {side},material {desc}
    { std::cout << "Carton(double,string) called.\n"; }

    Carton() { std::cout << "Carton() called.\n"; }

    ~Carton()
    { cout << "carton destructor" << endl; }
};

int main()
{
      Carton carton3 {4.0, "Plastic"};
}

在此代码中，我期望作为输出

Box(double) called.
Carton(double,string) called.
cartoon destructor
box destructor

但它显示为输出

Box(double, double, double) called.
Box(double) called.
Carton(double,string) called.
cartoon destructor
box destructor

我不明白屏幕上是如何显示Box(double, double, double) called.的。我已经逐步跟踪代码，但它不能在输出上。有人可以解释这个问题吗？感谢。

Answer 1

这一行

Carton(double side, const string desc) : Box {side},material {desc}

表示将调用构造函数Box::Box(double side)。但是，该构造函数定义为：

Box(double side) : Box {side, side, side} // HERE is the call to second constructor
{ std::cout << "Box(double) called.\n"; }

这意味着它将依次调用构造函数Box::Box(double lv, double wv, double hv)。您正在描述的行为是预期的。在线上设一个断点：

{ std::cout << "Carton(double,double,double,string) called.\n"; }

你将看到它在运行程序时会被点击。

继承构造函数输出

1 个答案: