C++：虚方法和抽象方法的问题

[redstoneleo]

#include <iostream>
using namespace std;

class Shape{
 	protected:
 		virtual double getArea() =0;
 		virtual double getCircumference()=0;
 		
 		virtual void print(){
		cout<<"Circumference = "<<getArea()<<"\n";
		cout<<"Area = " <<getCircumference()<<"\n\n";
		}
 };
 

class Circle:public Shape	{
public:
	Circle(double radius = 0){
		this->radius = radius;
	} 
	double getArea(){
		return Pi* radius* radius;
	}
	double getCircumference(){
		return 2*Pi* radius;
	}

private:
	const static double Pi =3.14;
	double radius ;
	
};

class Triangle:public Shape{
public:
	Triangle(double width ,double height){
		this->width = width;
		this->height=height;
	}
	double getArea(){
		return width * height;
	}
	double getCircumference(){
		return 2*width + 2*height;
	}

private:
 double width , height;
};


int main(int argc, char *argv[])
{
cout << "Let's create a Circle .\nEnter a radius: ";
double Radius = 0;
cin >> Radius;
Circle MyCircle(Radius);
MyCircle.print();


cout << "Let's create a Triangle .\nEnter the width and height : ";
double width ,height;
cin >> width >>height;
Triangle MyTriangle(width ,height);
MyTriangle.print();
	return 0;
}

代码有误，求解释出错的原因

[jinjianxinxh]

print()成员函数是protected保护类型的

[恨天低]

编译的错误信息会提示的吧?


class Shape{
protected:
virtual double getArea() =0;
virtual double getCircumference()=0;

virtual void print(){
cout<<"Circumference = "<<getArea()<<"\n";
cout<<"Area = " <<getCircumference()<<"\n\n";
}
};

protected --> public 至于为什么这么改，你自己再去看看C++语法基础吧！

[Coder_Y_Jao]

1、protected:要么改为 public，要么在子类中包装一下
2、const static(static const) 类内初始化的时候必须为整形，否则需要类外初始化，如果是较老的编译器一律类外初始化

[redstoneleo]

不是说protected允许其子类来访问的吗？

[Coder_Y_Jao]

[Quote=引用 4 楼 的回复:]

不是说protected允许其子类来访问的吗？
[/Quote]

是这个意思:

class A
{

protected:
	void fun()
	{
	}
};

class B:public A
{
public:
	void callfun()
	{
		A::fun();
	}
};

int main(int argc, char *argv[])
{
	B b;
	b.callfun();
	return 0;
}

[cuilll]

引用 4 楼 redstoneleo 的回复:

不是说protected允许其子类来访问的吗？

允许子类的 方法内 访问， 而LZ放在了main（）方法内了