Inquiry about class variable declarations in C++

Question

I have a class to represent a 3D vector of floats:

class Vector3D
{
    public:

    float x, y, z;
    float * const data;

    Vector3D() : x(0.0), y(0.0),         


        

Answer 1

Your solution is not valid, but if you can ensure (or know) that your compiler will "do the right thing" (in particular by controlling padding between the x, y and z elements) you will be ok. In this case though I'd remove the data member altogether and use operator[].

I've seen something like this used on occasion. It runs into exactly the same issues, but does save you storing that data pointer, and allows for a nicer v[0] syntax rather than v.data[0].

class Vector3D
{
    public:

    float x, y, z;
    float& operator[](int i) { return *(&x+i); }
    const float& operator[](int i) const { return *(&x+i); }

    Vector3D() : x(0.0), y(0.0), z(0.0) {}
}

EDIT: Prompted by ildjam heres a compliant version using accessors rather than members, that is similar.

class Vector3D
{
    public:
      float& operator[](int i) { return v[i]; }
      const float& operator[](int i) const { return v[i]; }

      float& x() { return v[0]; }
      float  x() const { return v[0]; }
      float& y() { return v[1]; }
      float  y() const { return v[1]; }
      float& z() { return v[2]; }
      float  z() const { return v[2]; }

      Vector3D() : v() {}
    private:    
      float v[3];
};