Static Member Function and Variables in C++

In a C++ programming we can create static function and variable by using the “static” keyword.

Static Variables

In C++ programming we can create a static variable by placing the “static” keyword before the variable declaration.

Once a variables declared as static, only one copy of that variable is created for the whole class.

When a variable is declared as static, by default it is initialize to zero.

#include <iostream>

using namespace std;
class Example {
        static int x;
        int y;
        public:
                void show() {
                        y = 0;
                }

        void count() {
                ++x;
                ++y;
                cout << "\n value of x=" << x;
                cout << "\n value of y=" << y;
        }
};
int Example::x = 0; //initialization of static member variable 
int main() {
        Example a, b, c;
        a.show();
        b.show();
        c.show();
        a.count();
        b.count();
        c.count();
}

#include <iostream>

using namespace std;

class Example {

static int x;

int y;

public:

void show() {

y = 0;

}

void count() {

++x;

++y;

cout << "\n value of x=" << x;

cout << "\n value of y=" << y;

}

};

int Example::x = 0; //initialization of static member variable

int main() {

Example a, b, c;

a.show();

b.show();

c.show();

a.count();

b.count();

c.count();

}

Output

 value of x=1
 value of y=1
 value of x=2
 value of y=1
 value of x=3
 value of y=1

value of x=1

value of y=1

value of x=2

value of y=1

value of x=3

value of y=1

Note: In the above figure we have a two object (object 1 & object 2) we object occupies a separate memory for variable(for ex: for variable 1 , object1 and object2 both will occupy the memory) .

But when a variable declared as a static then only one memory location is occupy for all object.

Static function

In C++ programming we can create a static function by placing the “static” keyword before the function declaration .

A static function can only assess static member variable and member function.

In a C++ it is also possible to call a static member function without object.

Static public member function:

Example: WAP to declare public member function and call them from main().

#include <iostream>

using namespace std;
class Smember {
        static int a;
        public:
                static void count() {
                        a++;
                }

        static void show() {
                cout << a<<endl;
        }
};

int Smember::a = 2;

int main() {
        Smember::show(); // call show() without object
        Smember::count(); // call count() without object
        Smember::count();
        Smember::show();
}

#include <iostream>

using namespace std;

class Smember {

static int a;

public:

static void count() {

a++;

}

static void show() {

cout << a<<endl;

}

};

int Smember::a = 2;

int main() {

Smember::show(); // call show() without object

Smember::count(); // call count() without object

Smember::count();

Smember::show();

}

Static function can’t assess normal variable

A static function can only assess static variable .

A static function can’t access normal function.

If we try to access normal function within the static function then we will get an error.

  #include <iostream>

  using namespace std;
  class Smember {
      int a; // normal variable
      public:
          static void count() {
              a = 10;
          } // error, static function can’t access normal variable

      static void show() {
          cout << a; // error, static function can’t access normal variable
      }
  };

  int main() {
      Smember::show(); // call show() without object
      Smember::count(); // call count() without object
  }

#include <iostream>

using namespace std;

class Smember {

int a; // normal variable

public:

static void count() {

a = 10;

} // error, static function can’t access normal variable

static void show() {

cout << a; // error, static function can’t access normal variable

}

};

int main() {

Smember::show(); // call show() without object

Smember::count(); // call count() without object

}

Output

 error, static function can’t access normal variable

1	error, static function can’t access normal variable

Static Object

In a C++ programming like a static variable & function we can also declare a static object.

The object is a composition of one or more member variable of the class.

When we declare a static object by default it initializes all variables of class with zero.

#include <iostream>

using namespace std;

class Smember {
        int a;
        public:
                void show() {
                        cout << a << endl;
                }
        void increment() {
                a = 10;
        }
};

int main() {
        static Smember obj; // by default, static object initialize all variable of class  with zero
        obj.show();
        obj.increment();
        obj.show();
}

#include <iostream>

using namespace std;

class Smember {

int a;

public:

void show() {

cout << a << endl;

}

void increment() {

a = 10;

}

};

int main() {

static Smember obj; // by default, static object initialize all variable of class with zero

obj.show();

obj.increment();

obj.show();

}

Output

 0
 10