What is the friend keyword in C++?
Written By - Md Altaf
The friend keyword in C++ allows the programmer to declare friend functions and classes. Let us understand further what are friend functions and classes.
Data hiding is an important concept of Object-Oriented Programming (OOP). It as achieved with the help of classes and access specifiers. They restrict non-member functions from accessing private and protected data members, therefore, hiding data.
Sometimes, due to this restriction, programmers end up writing long codes which can be otherwise done with a shorter method but compromising data hiding.
To solve this, a friend keyword is used. By declaring a friend function, we allow the function to access public and private variables of the class without being a member of the function. Similarly, we can declare a friend class in which all the member functions of the friend class becomes friend functions.
For example,
class frnd{
private:
void somefunc();
};
int frndFUNC(int a) {}
class A{
friend class frnd;
friend int frndFUNC(int a);
};
Here, both somefunc() and frndFUNC() can access the private and protected members of class A without being the members of class A.
Some important points about friend functions and classes:
- Declarations of friend functions and classes are always made inside the class definition(can be anywhere either in public and private)
- Friend functions and classes are declared by the implementor i.e. only the class can define its friend functions and classes, a function or class cannot declare itself a friend of a class
- Friend classes can access the data members of the class but not vice versa i.e. Class frndcan access the data members of class A but class A cannot access members of class frnd.
- Friend functions are not inherited.
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