Why can't I access a friend function declared within a class?

Accessing Friend Functions Defined in a Class

In the provided code snippet, there are three friend functions declared as friends of the class A: fun, fun2, and fun3. While fun and fun3 can be accessed without any issues, accessing fun2 raises compilation errors. This is because fun2 is declared within the class declaration, which makes it a local entity only known within that scope.

To address this limitation, there are two primary approaches:

Defining Global Function Declarations:

In this approach, you can define the friend function fun2 outside the class declaration, as follows:

<code class="cpp">// In the global scope
void fun2();</code>

This makes the function declaration visible to the entire program and allows you to access it using the global namespace.

Using Friend Class Declarations:

Alternatively, you can use friend class declarations to grant access to member functions of a particular class. For example, you can create a class Friend that is declared as a friend of class A:

<code class="cpp">class Friend {
    friend void fun2();
};</code>

This allows any function defined within the Friend class to access the private and protected members of class A. However, this approach is not as flexible as defining the function globally, as it limits access to those functions within the scope of the Friend class.

By following these approaches, you can effectively access friend functions that are defined within a class, ensuring that they have the necessary privileges to interact with the class's members.

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