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Friend Function

In C++, a friend function is a function that is not a member of a class but is granted special access to the private and protected members of that class. Friend functions it can be useful when need to allow an external function to access or modify the private members of a class without making those members public. Here's how define and use friend functions in C++:

Defining a Friend Function:

A friend function is declared in the class that wants to grant access to it using the friend keyword. It it can be declared in the class definition, but it is defined separately outside the class just like any other function. Here's an example:

Program:

class MyClass {
private:
    int privateData;

public:
    MyClass(int data) : privateData(data) {}

    // Declare a friend function
    friend void showPrivateData(const MyClass& obj);
};

// Define the friend function
void showPrivateData(const MyClass& obj) {
    // Access the private member 'privateData' of 'obj'
    std::cout << "Private Data: " << obj.privateData << std::endl;
}

In this example, showPrivateData is declared as a friend function inside the MyClass class. This means it has access to the private member privateData of objects of the MyClass class.

Using a Friend Function:

it can use a friend function just like any other function, even though it's not a member of the class:

Program:

int main() {
    MyClass obj(42);

    // Call the friend function to access privateData
    showPrivateData(obj);

    return 0;
}

In this main function, we create an object of MyClass and call the showPrivateData friend function to access and display the private data.

Important Notes:

Friend functions are not associated with any specific object of the class. They do not have a this pointer, as they are not members of the class. Instead, they operate on the objects passed as arguments.

Friend functions it can be defined outside the class or within the class declaration. it can also declare multiple friend functions inside a class.

Friend functions should be used judiciously, as they break encapsulation by allowing external access to private members. They are typically used when have a valid reason for allowing specific external functions or classes to access private members.

Friend functions it can be used for operator overloading, allowing to define custom behavior for operators like +, -, <<, etc., when working with objects of the class.

Overall, friend functions provide a way to maintain encapsulation while selectively granting access to certain external functions or classes when necessary.


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