纯虚类编程中的问题

[dinghing]

#include<iostream>
using namespace std;
class Shape
{
public:
virtual void area() const;
virtual void volume() const;
virtual void print ()=0;
virtual void printShapeName() const=0;
};
class TwoDimensionalShape:public Shape
{
public:
virtual void area()const;
virtual void printShapeName()const=0;
};
class Circle:public TwoDimensionalShape
{
public:
Circle(float=0.0,float=0.0,float=0.0);
void setPoint(float,float);
float getX() const{return x;}
float getY() const{return y;}
void setRadius(float);
float getRadius() const;
virtual void area() const;
virtual void print()const{cout<<"is TwoDimensionalShape";}
virtual void printShapeName() const{cout<<"Circle:";}
private:
float x,y;
float radius;
};
Circle::Circle(float r,float a,float b)
{
radius=r;
x=a;
y=b;
}
void Circle::setPoint(float a,float b)
{
x=a;
y=b;
}
void Circle::setRadius(float r)
{
radius=r;
}
float Circle::getRadius() const{return radius;}
void Circle::area() const{cout<<"S="<<3.14159*radius*radius<<endl;}
void main()
{
Circle circle(1.2,2,3);
circle.area();
}
为什么一直报
error C2259: 'Circle' : cannot instantiate abstract class due to following members:
谢谢啊。。。。
疯了。。

[冻结]

在你的Circle类中把
virtual void volume() const;
也重载了，不然你的Circle也是一个抽象类。

[pengzhixi]

#include<iostream>
using namespace std;
class Shape  
{
public:
virtual void area() const{}
virtual void volume() const{}
virtual void print ()const=0;
virtual void printShapeName() const=0;
};
class TwoDimensionalShape:public Shape
{
public:   
  virtual void area()const{}   
  virtual void printShapeName()const=0;
};
class Circle:public TwoDimensionalShape
{
public:   
Circle(float=0.0,float=0.0,float=0.0);   
void setPoint(float,float);   
float getX() const{return x;}   
float getY() const{return y;}   
void setRadius(float);   
float getRadius() const;   
virtual void area() const;   
virtual void print()const{cout<<"is TwoDimensionalShape";}   
virtual void printShapeName() const{cout<<"Circle:";}   
private:   
  float x,y;   
  float radius;
};  
Circle::Circle(float r,float a,float b) 
{   
radius=r;   
x=a;   
y=b;   
}   
void Circle::setPoint(float a,float b)   
{   
x=a;
y=b;   
}
void Circle::setRadius(float r)   
{   
  radius=r;  
}
float Circle::getRadius() const{return radius;}   
void Circle::area() const{cout<<"S="<<3.14159*radius*radius<<endl;}   
int main()
{
Circle circle(1.2,2,3);
circle.area();
    system("pause");
    return 0;
}

[pengzhixi]

搞这么多抽象类，你很多函数都未在最后的那个类里面实现的。还有些函数你没有加const进行修饰。

[冻结]

class Shape
{
public:
virtual void area() const;
virtual void volume() const;
virtual void print () const = 0;
virtual void printShapeName() const = 0;
};

非const 不可重载 const 函数。

[冻结]

[Quote=引用 1 楼 freezezdj 的回复:]
在你的Circle类中把
virtual void volume() const;
也重载了，不然你的Circle也是一个抽象类。
[/Quote]

作废！

[cattycat]

area和volumn虚函数没有实现，Circle仍然会被视为抽象类。

[cattycat]

virtual void print ()const=0;
加个const吧，Circle和父类的函数类型不一样。

[wesleyluo]

是只要有 虚函数的类 都视为抽象类，不能创建一个实例？