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

The compiler has some flexibility in how it lays out the memory within a struct. The struct will never overlap another data structure, but it can inject unused space between elements. In the struct you give, some compilers might choose to add 4 bytes of extra space between z and data so that the data pointer can be aligned. Most compilers provide a way of packing everything tightly.

EDIT: There's no guarantee that the compiler will choose to pack x, y, and z tightly, but in practice they will be packed well because they are the first elements of the struct and because they're a power of two in size.