C++ 预定义实例

Question

我正在设计一个 Vector3D 类，并希望能够轻松访问一些常用的 vector ，例如笛卡尔基 vector 和原点。下面是一种使用静态成员的方法。这是实现这一目标的正确方法吗？性能将是一个关键点。

vector.h

#include <iostream>

class Vector3D {

public:
    Vector3D(double x=0.0, double y=0.0, double z=0.0) :
        x_(x),
        y_(y),
        z_(z) {};

    inline void print() const {
        std::cout << x_ << " " << y_ << " " << z_ << std::endl;
    }

    // Predefined Vectors
    static Vector3D ZERO;
    static Vector3D X;
    static Vector3D Y;
    static Vector3D Z;

    double x_, y_, z_;
};

vector .cpp

#include "vector.h"

// Predefined vectors
Vector3D Vector3D::ZERO = Vector3D(0.0f, 0.0f, 0.0f);
Vector3D Vector3D::X    = Vector3D(1.0f, 0.0f, 0.0f);
Vector3D Vector3D::Y    = Vector3D(0.0f, 1.0f, 0.0f);
Vector3D Vector3D::Z    = Vector3D(0.0f, 0.0f, 1.0f);

类可以这样使用:

main.cpp

#include "vector.h"

int main()
{
    Vector3D o = Vector3D::ZERO;
    Vector3D x = Vector3D::X;
    Vector3D y = Vector3D::Y;
    Vector3D z = Vector3D::Z;

    o.print();
    x.print();
    y.print();
    z.print();

    return 0;
}

Answer 1

您缺少 const 标识符。您不希望有人不小心修改零 =)

你也可以使用静态方法:

struct Vector3D
{
  //...

  static Vector3D const & ZERO()
  {
     static Vector3D zero_(0,0,0);
     return zero_;
  }
};