c++11 - Access static constexpr std::array without out-of-class definition -

i have class defines arrays.

points.hpp

class points {  public:      static constexpr std::array< double, 1 > a1 = { {             +0.0 } };      static constexpr std::array< double, 2 > a2 = { {             -1.0 / std::sqrt( 3.0 ),             +1.0 / std::sqrt( 3.0 ) } };  }; 

my main file uses these arrays.

main.cpp

#include "points.hpp"  int main() {     // example on how access point.     auto point = points::a2[0];      // point. } 

when compile code, using c++11 , g++ 4.8.2, following linker error:

undefined reference `points::a2' 

i attempted create points.cpp file compiler can create object file it.

points.cpp

#include "points.hpp" 

but did not fix linker error.

i under impression possible initialize variables static constexpr in c++11 in class declaration, , access them way i'm doing it, shown in question: https://stackoverflow.com/a/24527701/1991500

do need make constructor points , instantiate class? doing wrong?

any feedback appreciated! thanks!

as per @dyp suggestion, looked definition of static data members.

my problem requires me define static member variables of points class.

following examples in these questions:

is constexpr array odr-used when subscripted?

and

defining static members in c++

i need add:

// in .cpp constexpr std::array< double, 1 > points::a1;