编写此代码的更有效方法是什么？

Question

所以，我是C ++的新手，我正在尝试学习继承。 我写了一个程序，仅打印出不同形状的周长，即正方形和三角形。 不幸的是，我这样做的方式最终得到了一些重复的代码。 这就是我的意思：

#include <iostream>

class Shape {
public:
  int sides;
  int sideLength;
};

class Square : public Shape {
public:
  int sides = 4;
  int sideLength = 6;
  void calculatePerimeter() {
    int perimeter = sideLength * sides;
    std::cout << "perimeter length: " << perimeter << std::endl;
  }
};

class Triangle : public Shape {
public:
  int sides = 3;
  int sideLength = 4;
  void calculatePerimeter() {
    int perimeter = sideLength * sides;
    std::cout << "perimeter length: " << perimeter << std::endl;
  }
};

int main() {
  Square s;
  std::cout << "number of sides a square has: " << s.sides << std::endl;

  Triangle t;
  std::cout << "number of sides a triangle has: " << t.sides << std::endl;

  s.calculatePerimeter();
  t.calculatePerimeter();
}

如您所见，Square和Triangle类中使用了calculatePerimeter函数。 将其放在Shape类中并调用它会导致输出0。如何提高此效率，所以不必为我制作的每个Shape类都复制/粘贴它？

Answer 1

使用继承时，可以在基类中考虑常见的行为和状态，并使派生类通过其特定功能扩展此状态和行为。

1. 从Shape中删除side和sideLength成员。 而是在Shape类中提供返回这些值的虚拟函数，并使派生类覆盖它们。

2. Move方法将周长计算为Shape类，并使用getSides（）和getSideLength（）实现

    #include <iostream> class Shape { public: virtual int getSides() = 0; virtual int getSideLength() = 0; void calculatePerimeter() { int perimeter = getSideLength() * getSides(); std::cout << "perimeter length: " << perimeter << std::endl; } }; class Square : public Shape { public: virtual int getSides() { return 4; } virtual int getSideLength() { return 6; } }; class Triangle : public Shape { public: virtual int getSides() { return 3; } virtual int getSideLength() { return 4; } }; 

这就是所谓的模板方法设计模式（不要与C ++的模板函数概念混淆，C ++是与该语言完全无关的概念）。

Answer 2

您需要Shape的构造函数，并从派生的构造函数传递变量。 然后，您可以将calculatePerimiter移到父类中。

class Shape {
public:
  Shape(int n_sides, int side_length) : sides(n_sides), sideLength(side_length) {}

  void calculatePerimeter() {
    int perimeter = sideLength * sides;
    std::cout << "perimeter length: " << perimeter << std::endl;
  }

  int sides;
  int sideLength;
};

class Square : public Shape {
public:
  Square() : Shape(4,6) {}     
};

class Triangle : public Shape {
public:
  Triangle() : Shape(3, 4) {}
};

Answer 3

这段代码：

int sides = 3; int sideLength = 4;

正在使用本地范围视图创建新变量。 如果不运行代码，我想如果您只是摆脱两行前面的“ int”，就可以解决您的问题。

编辑：当然将它们放入构造函数中。

编辑：好的，结合代码...

    class Triangle : public Shape {
public:

  Triangle ()
  {
    sides = 3;
    sideLength = 4;
  }

  void calculatePerimeter() {
    int perimeter = sideLength * sides;
    std::cout << "perimeter length: " << perimeter << std::endl;
  }
};

根据您要理解的内容，其他答案可以更好地解决问题。 这很简单，只需将参数放入calcualatePerimeter（）方法即可，但是当然，这不会测试您对范围内变量的理解，这似乎是您的绊脚石。

Answer 4

您可以访问直接基类成员，也可以对其进行初始化。

class Shape {
public:
  int sides;
  int sideLength;
  Shape(int m,int n)
  {
      sides =m;
     sideLength = n;
  }
};

class Square : public Shape {
public:
  Square(int j,int k);

  int calculatePerimeter() {
    int perimeter = sides * sideLength ;
    std::cout << "perimeter length: " << perimeter << std::endl;
    return perimeter;
  }
};

Square::Square(int j,int k):Shape(j,k)
{


}

Answer 5

对于支持C ++ 11的编译器，这将是我的方法。

#include <iostream>
#include <string>
#include <vector>

using namespace std;

template<class Seq>
void purge(Seq& s) {
    for (auto x: s) {
        delete x;
        x = nullptr;
    }
}

class Shape {
public: 
    virtual void calculatePerimeter() = 0; // to avoid object slicing
    virtual ~Shape() {};
};

class Square : public Shape {
    int m_sides{0};
    int m_sideLength{0};
public: 
    Square() = delete; // suppress default constructor
    Square(int sides, int sideLength): m_sides(sides), m_sideLength(sideLength) {}
    ~Square() {}
    void calculatePerimeter() {
        int perimeter = m_sideLength * m_sides;
        cout << "Square perimeter length: " << perimeter << endl;
    }
};

class Triangle : public Shape {
    int m_sides{0};
    int m_sideLength{0};
public: 
    Triangle() = delete; // suppress default constructor
    Triangle(int sides, int sideLength): m_sides(sides), m_sideLength(sideLength) {}
    ~Triangle() {}
    void calculatePerimeter() {
        int perimeter = m_sideLength * m_sides;
        cout << "Triangle perimeter length: " << perimeter << endl;
    }
};

int main() {
    vector<Shape*> vec;

    vec.push_back(new Square(4, 7));
    vec.push_back(new Triangle(3, 13));

    for (auto x: vec) {
        x->calculatePerimeter();
    }

    // clean up
    purge(vec);

    system("pause");
    return 0;
}

Answer 6

模板方式：

template <std::size_t SideCount, typename T>
class EquilateralPolygon
{
public:
    explicit EquilateralPolygon(T sideLength) : sideLength(sideLength) {}
    std::size_t GetSideCount() const { return SideCount; }
    T GetSideLength() const { return sideLength; }

    T calculatePerimeter() const { return SideCount * sideLength; }
private:
    T sideLength;
};

template <std::size_t SideCount, typename T>
void displayPerimeter(const EquilateralPolygon<SideCount, T>& p) {
    std::cout << "perimeter length: " << p.calculatePerimeter() << std::endl;
}

using EquilateralTriangle = EquilateralPolygon<3, std::size_t>;
using Square = EquilateralPolygon<4, std::size_t>;

和用法：

int main() {
    Square s(5);
    std::cout << "number of sides a square has: " << s.GetSideCount() << std::endl;

    EquilateralTrianglet(5);
    std::cout << "number of sides a triangle has: " << t.GetSideCount() << std::endl;

    displayPerimeter(s);
    displayPerimeter(t);
}

现场演示

Answer 7

这应该可以回答您的问题。 另外，我建议将sides和sideLength的值作为参数传递给函数调用以启用通用用法。

#include <iostream>

class Shape {
    protected void calculatePerimeter(int sides, int sideLength) {
    int perimeter = sideLength * sides;
    std::cout << "perimeter length: " << perimeter << std::endl;
  }
};

class Square : public Shape {
  int sides = 4;
  int sideLength = 6;
  public void calculatePerimeter()
  {
      Shape::calculatePerimeter(sides, sideLength);
  }
};

class Triangle : public Shape {
  int sides = 3;
  int sideLength = 4;
  public void calculatePerimeter()
  {
      Shape::calculatePerimeter(sides, sideLength);
  }
};

int main() {
  Square s;
  std::cout << "number of sides a square has: " << s.sides << std::endl;

  Triangle t;
  std::cout << "number of sides a triangle has: " << t.sides << std::endl;

  s.calculatePerimeter();
  t.calculatePerimeter();
}