Static member variable:

In object-oriented programming, the member variable is declared with the keyword of “static” is referred as static member variable.

• In memory, it allocates only one copy of the static member variable for that class.
• If changes are made to static variable, then it reflects to all other instances of that class.
• The static member variables can be re-declared and reuse outside the class using the scope resolution operator (::).
• The static member variables are used anywhere in the program. Even though it is declared outside or inside of the class.

Example:

Consider the example of static member variable declaration is as follows:

//Header file

#include<iostream>

using namespace std;

//class definition

class sample

{

  //declaration of instance variable

  int c;

  //declaration of static variable

  static int ct;

//access specifier

public:

  //constructor

  sample()

  {

  //increment the variable

  c = ++ct;

  }

//function definition

void show_code()

{

//display the output

cout << "Object number is: " << c << endl;

  }

//static member function definition

static void show_count()

{

  //display the output

cout << "The number of objects in the program: " << ct<< endl;

}

};

//definition of static member variable "ct"

int sample::ct=0;

//definition of main method

int main()

{

//Create two Objects for "sample" class

sample o1, o2;

//call the functions

o1.show_count();

o1.show_code();

o2.show_count();

o2.show_code();

//return statement

return 0;

}

Explanation:

• Here, the variable “ct” is declared as a static member variable in the class “sample”.
• In main() function,
  • Create two objects for “sample”class.
  • Call the show_count() function by using two objects such as “o1” and “o2”.
  • Call the show_code() function by using two objects such as “o1” and “o2”.
• Therefore, all the objects of the class have rights to access the static member variable “ct”.

Output:

The number of objects in the program: 2

Object number is: 1

The number of objects in the program: 2

Object number is: 2