Access Modifiers

Jun 23, 2026Pheonix

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Access Modifiers in C++

Access modifiers control the visibility and accessibility of class members, forming the foundation of encapsulation in OOP.

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1. Introduction

C++ provides three access specifiers:

• public
• protected
• private

Default Behavior:

• class → members are private by default
• struct → members are public by default

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2. Public

Accessible from anywhere.

Example:

#include <iostream>
using namespace std;

class Student {
public:
    string name;

    void display() {
        cout << "Name: " << name << endl;
    }
};

int main() {
    Student s;
    s.name = "Alice";
    s.display();
    return 0;
}

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3. Private

Accessible only within the same class.

Example:

#include <iostream>
using namespace std;

class BankAccount {
private:
    double balance;

public:
    BankAccount(double initial) : balance(initial) {}

    void deposit(double amount) {
        if (amount > 0) balance += amount;
    }

    double getBalance() const {
        return balance;
    }
};

int main() {
    BankAccount acc(1000);
    acc.deposit(500);
    cout << "Balance: " << acc.getBalance() << endl;
    return 0;
}

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4. Protected

Accessible within the class and derived classes.

Example:

#include <iostream>
using namespace std;

class Vehicle {
protected:
    int speed = 0;

public:
    void accelerate(int inc) { speed += inc; }
};

class Car : public Vehicle {
public:
    void showSpeed() {
        cout << "Speed: " << speed << " km/h\n";
    }
};

int main() {
    Car c;
    c.accelerate(80);
    c.showSpeed();
    return 0;
}

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5. Summary Table

Specifier	Same Class	Derived Class	Outside Class
public	Yes	Yes	Yes
protected	Yes	Yes	No
private	Yes	No	No

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6. Friend Functions & Classes

friend keyword bypasses access rules.

class Box {
private:
    int length;

public:
    friend void printLength(Box b);
};

void printLength(Box b) {
    cout << "Length: " << b.length << endl;
}

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7. Relationship with Inheritance

Access modifiers affect how base class members are inherited (see Inheritance documentation).

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8. Best Practices

1. Make data members private by default.
2. Provide public getters/setters or methods.
3. Use protected only when needed for inheritance.
4. Minimize use of friend.
5. Follow const-correctness.

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