A static data member is a variable shared by all objects of a class. static keyword is used to declare the static variable. Only one copy of the variable exists. If one object changes it, all objects see the changed value.

• Declare inside class
• Define outside class

  Real-Life Example

  Suppose a school has 500 students.

  • Every student has a different name.
  • But all students belong to the same school.

  The school name is common to all students, so it can be stored as a static data member.

  Syntax

  class ClassName
  {
  public:
  static dataType variableName;
  };

  dataType ClassName::variableName = value;

  Whenever an object is created, the count increases. Since all objects share the same count variable, we use a static data member.

  Program example 1 of using static variable

  #include <iostream>
  using namespace std;

  class Student
  {
  public:
  static int fee; // Declaration
  };

  // Definition
  int Student::fee = 2000;

  int main()
  {
  Student s1, s2;

  cout << “Fee of Student 1 = ” << s1.fee << endl;
  cout << “Fee of Student 2 = ” << s2.fee << endl;

  return 0;
  }

  Example 2

  #include <iostream>
  using namespace std;

  class Student
  {
  public:
  static int count;

  Student()
  {
  count++;
  }
  };

  int Student::count = 0;

  int main()
  {
  Student s1;
  Student s2;
  Student s3;

  cout << “Total Objects = ” << Student::count;

  return 0;
  }

  Output:

  Total Objects = 3

  A static function is a class function that can be called without creating an object.

  Static function is

  • Declared using the static keyword.
  • Belongs to the class, not to objects.
  • Can be called without creating an object.
  • Called using the class name.
  • Can directly access only static data members.

  Syntax of static member function

  class ClassName
  {
  public:
  static void functionName()
  {
  // code
  }
  };

  Calling

  ClassName::functionName();

  Program Example 1:

  A college has a common exam fee for all students. The fee is stored as a static data member, and a static function is used to display it.

   

  #include <iostream>
  using namespace std;

  class Student
  {
  public:
  static int fee; // Static data member

  static void showFee(); // Static function
  };

  int Student::fee = 2000;

  // Definition of static function
  void Student::showFee()
  {
  cout << “Exam Fee = ” << fee;
  }

  int main()
  {
  Student::showFee(); // Calling without object

  return 0;
  }

  Output:

  Exam Fee = 2000