Member Functions

A member function is a function that belongs to a class.

Member functions describe object behavior.

class Student {
public:
    void display();
};

Why Member Functions Matter

Member functions can work with the object's data.

class Counter {
private:
    int value = 0;

public:
    void increment() {
        value++;
    }

    int getValue() const {
        return value;
    }
};

Each object has its own value.

Defining Inside the Class

Short functions are often defined inside the class.

class Calculator {
public:
    int add(int a, int b) const {
        return a + b;
    }
};

Defining Outside the Class

You can declare the function inside the class and define it outside using ::.

class Calculator {
public:
    int multiply(int a, int b) const;
};

int Calculator::multiply(int a, int b) const {
    return a * b;
}

The Calculator:: part means:

This function belongs to the Calculator class.

Const Member Functions

If a member function does not modify the object, mark it with const.

void display() const;

This tells the compiler and reader:

Calling this function should not change the object's state.

Member Function vs Normal Function

Normal function:

void printStudent(Student s);

Member function:

student.display();

The member function belongs to the object and can access its private data.

Viva Answer

A member function is a function declared inside a class. It defines object behavior and can access the object's data members. Member functions can be defined inside the class or outside using the scope resolution operator ::.

Quick Check

• What is a member function?
• What does ClassName::functionName mean?
• Why mark a function const?
• How is a member function different from a normal function?