Count the number of objects using Static member function in C++ Program

The goal here is to count the number of objects of a class that are being created using a static member function.

A static data member is shared by all objects of the class commonly. If no value is given, a static data member is always initialized with 0. A static member function can only use static data members of that class.

We are using a class Student here. We will declare a static data member count which will store the count of objects. A static member function rollCall(void) will display the count of objects as roll no.s of students in a class.

Approach used in the below program is as follows

• We declare a class Student which has public data members int rollno and static data member count.

• There is a constructor that calls rollcall() and initializes rollno with the count.

• There is a destructor that decreases count.

• Static member function rollcall() displays the count of objects as Student count and increments the count.

• Each time the object of Student is created, the constructor calls rollcall() and count is incremented. This count is assigned to rollno of that Student object.

• In the main, we created 4 objects of class Student as stu1, stu2, stu3, and stu4 and verified that count and rollno are the same as no. of objects.

Example

// C++ program to Count the number of objects
// using the Static member function
#include <iostream>
using namespace std;
class Student {
public:
 int rollno;
 static int count;
public:
 Student(){
rollCall();
rollno=count;
 }
 ~Student()
 { --count; }
 static void rollCall(void){
cout <<endl<<"Student Count:" << ++count<< "\n"; //object count
 }
};
int Student::count;
int main(){
 Student stu1;
 cout<<"Student 1: Roll No:"<<stu1.rollno;
 Student stu2;
 cout<<"Student 2: Roll No:"<<stu2.rollno;
 Student stu3;
 cout<<"Student 3: Roll No:"<<stu3.rollno;
 Student stu4;
 cout<<"Student 4: Roll No:"<<stu4.rollno;
 return 0;
}

Output

If we run the above code it will generate the following output ?

Student Count:1
Student 1: Roll No:1
Student Count:2
Student 2: Roll No:2
Student Count:3
Student 3: Roll No:3
Student Count:4
Student 4: Roll No:4