Question

我创建了三个类：Square，Rectangle和Polygon。 Square继承自Rectangle，Rectangle继承自Polygon。

问题在于每当我调用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。但我想拥有两个构造函数。我有什么可以做的吗？

Answer 1

构造函数应该是

Square(int side) : Rectangle(side, side) { sides = 1; }

因为Rectangle没有默认构造函数。

Answer 2

您不应在派生类构造函数中设置基类的成员。相反，请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;
    }
};

多级继承而不调用超类构造函数

2 个答案: