Question

I was asked to provide solution for the following problems:

There is a structure defining some int parameters:

struct B {
  int a;
  int b;
};

One wanted to define this structure as const static members in other classes (not only for this class A – there are other classes expected to have the same set of constants) .

And one wanted to use them as real integral constants:

// .h file
class A {
public:
  static const B c; // cannot initialize here - this is not integral constant
};
// .cpp file
const B A::c = {1,2};

But cannot use this constant to make for example an array:

float a[A::c.a];

Any advice?

Answer 1

If you make A::c constexpr you can initialise it inline and use its members as a constant:

struct A {
    static constexpr B c = {1, 2};
};

float a[A::c.a];