我尝试使用其中2种方法创建一个基本虚拟类"形状"。下面我创建了3个从基类继承的子类。在主要函数中,我创建了3个实例,每个子类,我想拥有从我的基类创建的所有子类的列表,该列表应通过基类中定义的任何一种虚拟方法来排序。
我试图根据互联网的一些示例来实现列表库,但我不太了解它以使其正常工作。
#include <iostream>
#include <cmath>
#include <conio.h>
#include <list>
using namespace std;
class Shape
{
protected:
int value_;
public:
/*static list<Shape*> instances_;
Shape(int val);
static void showList();*/
virtual void surface()=0;
virtual void circuit()=0;
};
/*Shape::Shape(int val) {
instances_.push_back(this);
value_ = val;}
list<Shape*> Shape::instances_;
void Shape::showList() {
for (list<Shape*>::iterator p = instances_.begin();
p != instances_.end(); ++p)
cout << (*p)->value_ << endl;}*/
//////////////////////////////////
class Circle :public Shape
{
float r;
public:
Circle(float x)
{
r=x;
}
virtual void surface()
{
cout<<"Circle surface: "<<3.14*r*r<<endl;
}
virtual void circuit(){
cout<<"Circle circuit: "<<3.14*2*r<<endl;
}
};
////////////////////////////////////////
class Square:public Shape
{
float a;
public:
Square:public (float x)
{
a=x;
}
virtual void surface()
{
cout<<"Square surface: "<<a*a<<endl;
}
virtual void circuit(){
cout<<"Square circuit : "<<4*a<<endl;
}
};
int main()
{
Circle k(8);
Square kw(2);
return 0;
};
此代码中有几件事可以改进。但是,您必须了解继承,多态性和在C 中实施多态性背后的粗略细节的概念。
。例如:默认的基类破坏者不是自动虚拟的。当您打算实现多态性结构时,您需要指定虚拟基类驱动器。派生的类自动设置为虚拟iff(仅以及仅当(基类带有虚拟驱动器。
要排序您首先需要创建Shape*
列表的形状列表。然后,您需要编写一个比较功能,该功能将采用2种形状,并使用其成员之一比较它们。在您的示例中,没有什么可用的。两个成员函数均为void
,成员变量均为私有。
请参阅下面的代码,希望它将有意义。
#include <iostream>
#include <cmath>
#include <list>
struct Shape
{
Shape() = default;
virtual float surface() const = 0;
virtual void circuit() = 0;
virtual ~Shape() noexcept = default;
};
class Circle final : public Shape
{
private:
float r;
public:
Circle(float r_) : r(r_)
{;}
float surface() const override
{
return M_PI*pow(r,2);
}
void circuit() override
{
std::cout<<"Circle circuit: " << 2.f*M_PI*r <<std::endl;
}
~Circle() noexcept = default;
};
class Square final : public Shape
{
private:
float a;
public:
Square(float a_) : a(a_)
{;}
float surface() const override
{
return pow(a,2);
}
void circuit() override
{
std::cout<<"Square circuit: " << 4.f*a <<std::endl;
}
~Square() noexcept = default;
};
bool compare_shape(const Shape *const s1, const Shape *const s2)
{
return (s1->surface() < s2->surface());
}
int main()
{
// no polymorphism
Circle c(8);
std::cout<< "Circle surface: " << c.surface() <<std::endl;
c.circuit();
Square s(2);
std::cout<< "Square surface: " << s.surface() <<std::endl;
s.circuit();
std::cout<< "____________________" <<std::endl<<std::endl;
// polymorphism
Shape *c_ptr = new Circle(8);
std::cout<< "Circle surface: " << c_ptr->surface() <<std::endl;
c_ptr->circuit();
delete c_ptr;
Shape *s_ptr = new Square(2);
std::cout<< "Square surface: " << s_ptr->surface() <<std::endl;
s_ptr->circuit();
delete s_ptr;
std::cout<< "____________________" <<std::endl<<std::endl;
// list of Shapes
std::list<Shape*> shapes;
shapes.push_back( new Circle(8) );
shapes.push_back( new Square(2) );
for (auto &&i : shapes)
{
std::cout<< "Shapes' surface: " << i->surface() <<std::endl;
i->circuit();
}
std::cout<< "n-- sorting the list based on the shapes' surface.n" <<std::endl;
shapes.sort(compare_shape);
for (auto &&i : shapes)
{
std::cout<< "Shapes' surface: " << i->surface() <<std::endl;
i->circuit();
}
};
在线代码示例:https://rextester.com/ebkih52610
如果要以多态性的方式进行排序,请搜索对``bool Operator&lt;(('方法的搜索文档。要比较类型,您可以使用'typeID'operator。