Lecture 131:- Friend Keyword In C++

In C++, the friend keyword is used to grant access to private or protected members of a class to functions or other classes that are not part of the class itself. This allows external entities to access private or protected members, breaking the encapsulation principle, but it can be useful in specific scenarios.

When a function or class is declared as a friend of another class, it can access the private and protected members of that class as if they were its own members.

Here's how the friend keyword is used:

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class MyClass { private: int privateData; public: MyClass(int data) : privateData(data) {} friend void friendFunction(MyClass &obj); }; void friendFunction(MyClass &obj) { // Friend function can access private member std::cout << "Friend Function: " << obj.privateData << std::endl; } int main() { MyClass myObj(42); friendFunction(myObj); return 0; }

In this example, friendFunction is declared as a friend of the MyClass class. As a result, it can access the private member privateData of the class.

The friend keyword can also be used to declare entire classes as friends:

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class AnotherClass { public: void accessPrivateData(MyClass &obj) { std::cout << "AnotherClass: " << obj.privateData << std::endl; } }; class MyClass { private: int privateData; friend class AnotherClass; // Declare AnotherClass as a friend public: MyClass(int data) : privateData(data) {} }; int main() { MyClass myObj(42); AnotherClass anotherObj; anotherObj.accessPrivateData(myObj); return 0; }

Here, AnotherClass is declared as a friend of MyClass, so it can access the private member privateData.

It's important to use the friend keyword judiciously, as it can potentially break encapsulation and make your code less maintainable. In many cases, there are alternative approaches to achieve the desired functionality without relying on friend classes or functions.