Question

I have code like this…

class Time
{
    public: 
        Time(int, int, int);
        void set_hours(int);
        void set_minutes(int);
        void set_seconds(int);

        int get_hours() const;
        int get_minutes() const;
        int get_seconds() const;

        static void fun() ;

        void printu() const;
        void prints();

    private:
        int x;
        int hours;
        int minutes;
        int seconds;
        const int i;
};

Why do I need to put const at last to make a function constant type but if i need to make a function, I can do this like…

static void Time::fun() 
{
    cout<<"hello";
}

Above function fun() is also in same class. I just want to know what is the reason behind this?

Answer 1

with a const instance method such as int get_hours() const;, the const means that the definition of int get_hours() const; will not modify this.

with a static method such as static void fun();, const does not apply because this is not available.

you can access a static method from the class or instance because of its visibility. more specifically, you cannot call instance methods or access instance variables (e.g. x, hours) from the static method because there is not an instance.

class t_classname {
public:
  static void S() { this->x = 1; } // << error. this is not available in static method
  void s() { this->x = 1; } // << ok
  void t() const { this->x = 1; } // << error. cannot change state in const method
  static void U() { t_classname a; a.x = 1; } // << ok to create an instance and use it in a static method
  void v() const { S(); U(); } // << ok. static method is visible to this and does not mutate this.

private:
  int a;
};