C++ Primer, Fifth Edition

Declaring static Members

We say a member is associated with the class by adding the keyword static to its declaration. Like any other member, static members can be public or private. The type of a static data member can be const, reference, array, class type, and so forth.

As an example, we’ll define a class to represent an account record at a bank:

class Account {public:    void calculate() { amount += amount * interestRate; }    static double rate() { return interestRate; }    static void rate(double);private:    std::string owner;    double amount;    static double interestRate;    static double initRate();};

The static members of a class exist outside any object. Objects do not contain data associated with static data members. Thus, each ...