Static Members

A static data member belongs to the class, not to each individual object.

Normal data member:

Each object gets its own copy.

Static data member:

All objects share one copy.

Complete Example

#include <iostream>
using namespace std;

class Student {
private:
    int id;
    static int count;

public:
    Student() {
        ++count;
        id = count;
    }

    void display() const {
        cout << "Student ID: " << id << endl;
    }

    static int getCount() {
        return count;
    }
};

int Student::count = 0;

int main() {
    Student s1;
    Student s2;

    s1.display();
    s2.display();

    cout << "Total students: " << Student::getCount() << endl;

    return 0;
}

Output:

Student ID: 1
Student ID: 2
Total students: 2

Static Member Function

A static member function:

• Can be called using the class name.
• Can access static members directly.
• Cannot access non-static members directly because it has no this pointer.

Example:

Student::getCount();

Why Static Data Is Defined Outside

In classic C++, a static data member is declared inside the class and defined outside the class.

class Student {
    static int count;
};

int Student::count = 0;

Modern C++ also supports inline static data members, but the outside definition is still important for viva.

Viva Answer

A static data member belongs to the class and is shared by all objects. A static member function can be called using the class name and can access static members directly, but it cannot access non-static members directly because it has no this pointer.

Quick Check

1. Does each object get a separate copy of a static data member?
2. Can a static member function access id directly in the example?
3. Why can we call Student::getCount() without an object?