c++ - operator

I didn't find any thing that could help me in this subject...
I'm trying to over load the << operator, this is my code:

 ostream& Complex::operator<<(ostream& out,const Complex& b){
    out<<"("<    return out;
}    

this is the declaration in the H file:

 ostream& operator<<(ostream& out,const Complex& b);

I get this error:
error: std::ostream& Complex::operator<<(std::ostream&, const Complex&) must take exactly one argument

what and why I'm doing wrong?
thanks

Answer

your operator << should be free function, not Complex class member in your case.

If you did your operator << class member, it actually should take one parameter, which should be stream. But then you won't be able to write like

std::cout << complex_number;

but

complex_number << std::cout;

which is equivalent to

complex_number. operator << (std::cout);

It is not common practice, as you can note, that is why operator << usually defined as free function.