Friend function

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Friend function is a function, which can access the private and protected data member of a class. Using keyword friend, we can make function a friend function.
Below is the prototype for friend function

friend <return-type>  function(<className>);

Example:

#include <iostream>
using namespace std;
class base {
    unsigned int m_int;
public:
    base() {
        m_int = 20;
    }
    friend ostream& operator<<(ostream& s, const base& b); 
};

//Source File
ostream& operator<<(ostream& s, const base& b) {
    s << b.m_int ;
    return s;
}

int main() {
    base b;
    cout << b << endl;
    return 0;
}

The above example to print the object  using friend operator<< function is one of the typical example of friend function.

Points to Remember

  • In friend function definition, neither class name nor scope resolution operator required. This means friend function is not in the scope of a class.
  • For friend function, friend keyword is required only in declaration.
  • friend function is called without using object or class name.
  • friend function declaration can be kept in private or public section of a class.
  • friend function can access data member(private or protected) directly using dot operator as seen in the above example.

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