How friend function in c plus plus created?

Answer 1

Within a class declaration, include the following:

friend ;

For example:

friend class MyClass; // friend class

friend void MyClass::SomeFunction(); // friend class method.

friend void MyFunction(); // friend function.

When declaring friend functions and friend class methods, you must declare an unambiguous prototype, including its return type and its parameter types, and all instances of the const keyword. If the function prototype is contained in another file, that file must also be included in the class declaration file.

Friends can be declared anywhere in a class declaration. However, friends cannot be inherited so it doesn't matter if they're declared public, private or protected (access specifiers have no meaning to friends). But be aware that friends have privileged access to all members, including private and protected members. This is said to undermine the fundamentals of encapsulation, however the purpose of a friend is to extend the class interface, and is no more an undermining of encapsulation than is public inheritance. However, access should be limited to as few friends as possible; a class with many friends implies a fundamental design flaw in the class.