help overloading << and >> to display two values

Question

This may be a novice question, but I can't figure it out by inspecting the book I have. The class's constructor initializes two doubles, and I want the following code to output those two doubles with <<.

Complex x( 3.3, 1.1 );

cout << "x: " << x;

After this I need to overload >> to accept two doubles into these. This is my first question here, so if my information provided is lacking inform me

EDIT: I now have for the constructor and overloading statement this:

#include "Complex.h"

Complex::Complex( double realPart, double imaginaryPart )
: real( realPart ),
imaginary( imaginaryPart )
{

}

std::istream& operator>>(std::istream& strm, const Complex &c)
{
   double r,i;
   strm >> r >> i;
   c = Complex(r,i);
   return strm;
}

I know I have to change the "const Complex &c" and the "c = Complex(r,i);" but I'm not sure how to go about it. Also, I will say here that this is not about the std library's Complex class, although it is based on the same idea. So far everyone has been a great help, but I have a case of the dumb today.

Answer 1

operator<< :

std::cout is an std::ostream object, so you have to overload operator<< for ostream, which takes std::complex<double> as an argument, assuming you use std::complex<double> from the standard header complex. Since you shouldn't make internal changes to standard containers and classes, make it standalone.

#include <iostream>
#include <complex>

std::ostream& operator<<(std::ostream& strm, const std::complex<double>& c)
{
    strm << "real: " << c.real() << "imag: " << c.imag();
    return strm;
}

operator>> :

operator>> takes a std::istream object, which does the opposite of what std::ostream does. If you use streams for serialization like this, it's a good idea to enable exceptions for them too. Usually you only want to throw on std::ios::badbit.

#include <iostream>
#include <complex>

std::istream& operator>>(std::istream& strm, std::complex<double>& c)
{
    double r,i;
    strm >> r >> i;
    c = std::complex<double>(r,i);
    return strm;
}

If you needed access to internal members of the class, you would define the overloaded function as a friend. But since std::complex::real() and std::complex::imag() are a part of the public interface, that's not needed here. And for the istream example, we simply invoke the copy-constructor which is also a part of the public interface.

I assumed you wanted to use cin and cout here. But if you wanted to overload the operators for something else, the same applies. If you implement the operators inside a class definition, you have access to the this pointer, hence the operator function should only take one argument.