C++ Friend Function

🤝 C++ Friend Function – Let Outsiders Peek In

Normally, private members of a class are hidden from the outside world. But what if you want to give special access to a non-member function or another class? That’s where friend functions come in! 🔐

🔍 What is a Friend Function?

A friend function is not a member of the class, but it can access private and protected members like a close friend with VIP access. 😎

🔧 Example: A Friend Who Can Peek

#include <iostream>
using namespace std;

class SecretBox {
private:
    int secret = 42;

public:
    friend void peekInside(SecretBox);  // Declaring a friend
};

void peekInside(SecretBox box) {
    cout << "Peeking inside... secret is: " << box.secret << endl;
}

int main() {
    SecretBox myBox;
    peekInside(myBox);  // Accessing private data

    return 0;
}
  

🔐 How to Declare a Friend

• Use the keyword friend inside the class
• The function does not belong to the class, but it can access private data
• Definition of the function stays outside the class

👫 Friend Class (Yes, That Too!)

You can also make an entire class a friend of another. That means all its member functions can access private/protected members of the friend class.

🔧 Example: Friend Class

#include <iostream>
using namespace std;

class Engine;

class Car {
private:
    int speed = 180;

public:
    friend class Engine;  // Engine is now a friend
};

class Engine {
public:
    void showSpeed(Car c) {
        cout << "Accessing Car speed: " << c.speed << " km/h" << endl;
    }
};

int main() {
    Car myCar;
    Engine v8;
    v8.showSpeed(myCar);

    return 0;
}
  

📌 Summary

• Friend function can access private/protected data
• Use friend keyword inside the class
• Friend functions are not class members
• You can also declare a whole friend class

Think of friend functions as “trustworthy outsiders” — not family, but close enough to see your secrets! 🧑‍🤝‍🧑🔍