C++ Primer, Fifth Edition

Using a Class static Member

We can access a static member directly through the scope operator:

double r;r = Account::rate(); // access a static member using the scope operator

Even though static members are not part of the objects of its class, we can use an object, reference, or pointer of the class type to access a static member:

Account ac1;Account *ac2 = &ac1;// equivalent ways to call the static member rate functionr = ac1.rate();      // through an Account object or referencer = ac2->rate();     // through a pointer to an Account object

Member functions can use static members directly, without the scope operator:

class Account {public:    void calculate() { amount += amount * interestRate; }private:    static double interestRate;    // ...