c++ - 不调用父类(super class)构造函数的多级继承

Question

我创建了三个类:方形、矩形和多边形。 Square 继承自 Rectangle，Rectangle 继承自 Polygon。

问题是，每当我调用 Square 构造函数时，都会调用 Rectangle 构造函数，并且出现错误。我该如何解决这个问题？

#include <iostream>
using namespace std;

// Multilevel Inheritance

class Polygon
{
protected:
    int sides;
};

class Rectangle: public Polygon
{
protected:
    int length, breadth;
public:
    Rectangle(int l, int b)
    {
        length = l;
        breadth = b;
        sides = 2;
    }
    void getDimensions()
    {
        cout << "Length = " << length << endl;
        cout << "Breadth = " << breadth << endl;
    }

};

class Square: public Rectangle
{
public:
    Square(int side)
    {
        length = side;
        breadth = length;
        sides = 1;
    }
};

int main(void)
{
    Square s(10);
    s.getDimensions();
}

如果我注释掉 Rectangle 构造函数，一切正常。但我想要两个构造函数。有什么我可以做的吗？

Answer 1

您不应在派生类构造函数中设置基类的成员。相反，显式调用基类构造函数:

class Polygon
{
protected:
    int sides;
public:
    Polygon(int _sides): sides(_sides) {} // constructor initializer list!
};

class Rectangle: public Polygon
{
protected:
    int length, breadth;
public:
    Rectangle(int l, int b) :
         Polygon(2), // base class constructor
         length(l),
         breadth(b)
    {}
};

class Square: public Rectangle
{
public:
    Square(int side) : Rectangle(side, side)
    {
        // maybe you need to do this, but this is a sign of a bad design:
        sides = 1;
    }
};