具有纯虚函数和指针数组对象类型的父类的指针数组

Question

在这里，我要在主函数中创建一个指针数组。对象类型应每次更改。这样的事情。形状* a [10] =新矩形；但是我想做一个[0]矩形类型。 a [1]圆圈类型，依此类推。

class shape
{
    public:
        virtual float boundary_length()=0;
};
class rectangle: public shape
{
    public:
        float boundary_length()
        {
            cout<<"Boundary length of rectangle"<<endl;
            return 2*(length+width);
        }
};
class circle: public shape
{

    public:
        float boundary_length()
        {
            return 2*(3.14*radius);
        }   
};
class triangle: public shape
{
        float boundary_length()
        {
            return (base+perp+hyp);
        }
};
int main()
{
    shape* a=new rectangle;
    return 0;
}

Answer 1

如果我对您的理解正确，则需要类似以下的内容

#include <iostream>

class shape
{
    public:
        virtual float boundary_length() const = 0;
        virtual ~shape() = default;
};

class rectangle: public shape
{
    public:
        rectangle( float length, float width ) : length( length ), width( width )
        {
        }
        float boundary_length() const override
        {
            return 2*(length+width);
        }
    protected:
        float length, width;
};

class circle: public shape
{
    public:
        circle( float radius ) : radius( radius )
        {
        }
        float boundary_length() const override
        {
            return 2*(3.14*radius);
        }

    private:
        float radius;
};

//...

int main(void) 
{
    const size_t N = 10;    
    shape * a[N] =
    {
        new rectangle( 10.0f, 10.0f ), new circle( 5.0f )
    };

    for ( auto s = a; *s != nullptr; ++s )
    {
        std::cout << ( *s )->boundary_length() << '\n';
    }        

    for ( auto s = a; *s != nullptr; ++s )
    {
        delete *s;
    }        
}

程序输出为

40
31.4