static

The static storage class specifier has three different meanings.

1. Gives internal linkage to a variable or function declared at namespace scope.

   // internal function; can't be linked to
   static double semiperimeter(double a, double b, double c) {
       return (a + b + c)/2.0;
   }
   // exported to client
   double area(double a, double b, double c) {
       const double s = semiperimeter(a, b, c);
       return sqrt(s*(s-a)*(s-b)*(s-c));
   }
2. Declares a variable to have static storage duration (unless it is thread_local). Namespace-scope variables are implicitly static. A static local variable is initialized only once, the first time control passes through its definition, and is not destroyed every time its scope is exited.

   void f() {
       static int count = 0;
       std::cout << "f has been called " << ++count << " times so far\n";
   }
3. When applied to the declaration of a class member, declares that member to be a static member.

   struct S {
       static S* create() {
           return new S;
       }
   };
   int main() {
       S* s = S::create();
   }

   Note that in the case of a static data member of a class, both 2 and 3 apply simultaneously: the static keyword both makes the member into a static data member and makes it into a variable with static storage duration.