问题是我正在努力制作 Shape 类的对象。我声明了 vector ,但不知道如何将其连接到类 Shape 及其对象。代码本身有一个基类,即Shape,然后是两个子类Circle和Rectancle。代码的想法是在主函数中使用 vector ,并为圆形区域和矩形区域提供多种情况。这是代码:
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Shape
{
public:
virtual double GetArea() const = 0
{
}
private:
};
class Circle : public Shape
{
public:
Circle(double p, double r) // constructor
{
pi = p;
radius = r;
}
Circle() : pi(3.14), radius(0) {} // default constructor
void SetRadius(double value)
{
radius = value;
}
double GetRadius() const
{
return radius;
}
double GetArea()
{
double area = pi * radius * radius;
return area;
}
private:
double pi = 3.14;
double radius;
};
class Rectangle : public Shape
{
public:
Rectangle(double a, double b) // constructor
{
sideA = a;
sideB = b;
}
Rectangle() : sideA(0), sideB(0) {} // default constructor
void SetSideA(double value)
{
sideA = value;
}
double getSideA() const
{
return sideA;
}
void SetSideB(double val)
{
sideB = val;
}
double getSideB() const
{
return sideB;
}
double getArea()
{
double Area = sideA * sideB;
return Area;
}
private:
double sideA;
double sideB;
};
int main()
{
vector<Shape*> shape;
return 0;
}
最佳答案
你想要多态性。您只需使用圆形或矩形的构造函数,例如:
vector<Shape*> shape(1);
if(/* case is circle*/)
shape[0] = new Circle();
else
shape[0] = new Rectangle();
<小时/>
但是,您需要删除基类中纯虚方法的定义,因为它是 inside the class ,并且仅声明它。
然后,您需要使用完全相同相同的原型(prototype)来实现该方法,因此您需要将 Circle 中的方法标记为 const
也。矩形类也是如此,您也犯了一个拼写错误,因为方法的名称是“GetArea”,而不是“getArea”。
完整的最小工作示例:
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Shape
{
public:
virtual double GetArea() const = 0;
virtual ~Shape() {};
};
class Circle : public Shape
{
public:
Circle(double p, double r) // constructor
{
pi = p;
radius = r;
}
Circle() : pi(3.14), radius(0) {} // default constructor
void SetRadius(double value)
{
radius = value;
}
double GetRadius() const
{
return radius;
}
double GetArea() const
{
double area = pi * radius * radius;
return area;
}
private:
double pi = 3.14;
double radius;
};
class Rectangle : public Shape
{
public:
Rectangle(double a, double b) // constructor
{
sideA = a;
sideB = b;
}
Rectangle() : sideA(0), sideB(0) {} // default constructor
void SetSideA(double value)
{
sideA = value;
}
double getSideA() const
{
return sideA;
}
void SetSideB(double val)
{
sideB = val;
}
double getSideB() const
{
return sideB;
}
double GetArea() const
{
double Area = sideA * sideB;
return Area;
}
private:
double sideA;
double sideB;
};
int main()
{
vector<Shape*> shape(2);
shape[0] = new Circle(3.14, 1);
shape[1] = new Rectangle(2, 3);
for(auto s : shape)
std::cout << "Shape area = " << s->GetArea() << endl;
// When you are done, delete the dynamically allocated memory.
// You can use smart pointers in order to avoid doing this manually (and maybe forget!)
delete shape[0];
delete shape[1];
return 0;
}
输出:
形状面积 = 3.14 形状面积 = 6
其中第一个区域来自圆形,第二个区域来自矩形。
我建议您阅读:Virtual destructor in polymorphic classes和 What is the 'override' keyword in C++ used for?
<小时/>完成所有这些练习后,您应该真正开始使用 smart pointers ,例如像这样 std::vector<std::unique_ptr<Shape>> shape;
,而不是原始指针。这样,您就不必担心删除手动动态分配的内存。
关于c++ - 如何声明指向类对象的指针 vector ?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/59272504/