c++ - Definition of the static data member -

i'm reading scott meyers' c++ , come across example:

class gameplayer{ private:     static const int numturns = 5;     int scores[numturns];     // ... }; 

what see above declaration numturns, not definition.

why not definition? looks initialize static data member 5.

i don't understand means declare not define variable value 5. can take address of variable fine.

class { public:     void foo(){ const int * p = &a; } private:     static const int = 1; };  int main () {     a;     a.foo(); } 

demo

because isn't definition. static data members must defined outside class definition.

[class.static.data] / 2

the declaration of static data member in class definition is not definition , may of incomplete type other cv-qualified void. definition static data member shall appear in namespace scope enclosing member’s class definition.

as taking address of static member without defining it, compile, shouldn't link.