虚纯函数

Question

我知道类中的纯虚函数使该类抽象。这意味着我无法使用该类创建对象，并且必须在所有派生类中覆盖该虚函数。

我有以下代码：

class Forma{
    protected:
        double x,y;
    public:
        Forma(double h=0, double v=0);
        virtual double Arie() const;
        virtual double Perimetru() const=0;
};

class Dreptunghi: public Forma{
    public:
        Dreptunghi(double h=0, double v=0);
        virtual double Arie() const;
        virtual double Perimetru() const;
};

class Cerc:public Forma{
    protected:
        double raza;
    public:
        Cerc(double h=0, double v=0, double r=0);
        virtual double Arie() const;
        virtual double Perimetru() const;
 };

 Forma::Forma(double h,double v){x=h; y=v;}
 double Forma::Arie() const{return x*y;}
 double Forma::Perimetru() const{return x+y;}

 Dreptunghi::Dreptunghi(double h,double v){Forma(h,v);}
 double Dreptunghi::Arie() const{return x*y;}
 double Dreptunghi::Perimetru() const{return 2*x+2*y;}

我的错误如下：

33 53 [Error] cannot allocate an object of abstract type 'Forma'
4 7   [Note] because the following virtual functions are pure within 'Forma':
31 9  [Note] virtual double Forma::Perimetru() const

我该如何解决这个问题？谢谢。

Answer 1

将参数传递给基类的语法如下：

Dreptunghi::Dreptunghi(double h, double v) : Forma(h, v) {}

按照您的编写方式，它会尝试创建Forma 的实例，这当然是不允许的。