constexpr_offset_of.cpp

#include <iostream>

struct Foo
{
  int a;
  int b;
};

template<typename T, typename Struct>
constexpr size_t offset_of(T Struct::*member) {
  using pointer = Struct*;
  return size_t(&(pointer(nullptr)->*member));
}

enum : size_t {
  offset_of_Foo_a = offset_of(&Foo::a),
  offset_of_Foo_b = offset_of(&Foo::b),
};

int main() {
  std::cout<< "offset_of_Foo_a: " << offset_of_Foo_a << "\n";
  std::cout<< "offset_of_Foo_b: " << offset_of_Foo_b << "\n";
  return 0;
}