Static Data Member | OOPS

STATIC Data Members

Static keyword has different meanings when used with different types. We can use static keyword with:

1. Static Variables : Variables in a function, Variables in a class
2. Static Members of Class : Class objects and Functions in a class

We can define class members static using static keyword. When we declare a member of a class as static it means no matter how many objects of the class are created, there is only one copy of the static member.

A static member is shared by all objects of the class. We can't put it in the class definition but it can be initialized outside the class as done in the following example by redeclaring the static variable, using the scope resolution operator :: to identify which class it belongs to.

What is a Static Function?

A function that is declared static using the ‘static‘ keyword becomes a static function in C++.

Syntax of the Static Function:

static <return_type> <function_name>(<arguments>){
    //code
}

When a function inside a class is declared as static, it can be accessed outside the class using the class name and scope resolution operator (::), without creating any object.

A static member method has access only to the static members of the class, we can not call any non-static functions inside it.

All objects in the class share the same copy of the static function. It is useful in manipulating global static variables, which are again shared by all objects.

Since the static function is not bounded by the object of the class, it does not has access to the this keyword.

CODE

#include <iostream>

using namespace std;

class Student {

    static int totalStudents;      

    // total number of students present

    public :

    int rollNumber;

    int age;

    Student() {

        totalStudents++;

    }

    int getRollNumber() {

        return rollNumber;

    }

    static int getTotalStudent() {

        return totalStudents;

    }

   

};

int Student :: totalStudents = 0;  

// initialze static data members 

int main() {

    Student s1;

    Student s2;

    Student s3, s4, s5;

    // cout << Student :: totalStudents << endl;

    cout << Student :: getTotalStudent() << endl;

}

KEY-NOTES

• The static data member belongs to the class, not to any particular object. 
• For initializing the static data member, we need to change it through class by using the scope resolution operator (iff the data member is public).
• int Student :: totalStudents = 0;
• In static functions, we can use only static data members.
• Other non-static functions can also use static data members.
• We can call static functions within a static function.
• We cannot use this keyword in static member functions.
• We cannot call any static data member through an object.

Share this post