What is friend ostream

Question

I\'m a bit confused about what exactly this line of code means in my header file.

friend ostream & operator << (ostream &, const something &         


        

Answer 1

A C++ class may declare another class or a function to be a friend. Friendly classes and methods may access private members of the class. So, the free operator method <<, not defined in any class, may insert somethings into a stream and look at and use the private members of something to do its work. Suppose something were complex:

class complex {
    private:
       double re;
       double im;
    public:
       complex(double real = 0.0, double imag = 0.0) : re(real), im(imag) {}
       friend ostream & operator<<(ostream& os, complex& c);
};

ostream & operator<<(ostream& os, complex& c){
    os << c.re << std::showpos << c.im;
    return os;
}