Can I initialize static const class member?

I want to run this code:

struct A {
    static const string d[] = {"1", "2"};    
};

And get an error:

error: in-class initialization of static data member ‘const string A::d []’ of incomplete type
     static const string d[] = {"1", "2"};
                         ^
error: non-constant in-class initialization invalid for non-inline static member ‘A::d’
     static const string d[] = {"1", "2"};
                                        ^
note: (an out of class initialization is required)

Here I find information that now I can initialize what I want. So what the problem?

If I add inline then it will work:

struct A {
    static const inline string d[] = {"1", "2"};    
};