overloading <<

I'm trying to figure out how to overload << so I can print a complex number just by

cout << c_num;

I'm getting a compilation error saying
k:\cfiles\cis285\complex\complex.h(24) : error C2270: '<<' : modifiers not allowed on nonmember functions

How can I correct this?

(The error message references the line that begins:
"friend ostream& operator<<..."

Code:

#ifndef _complex_h
#define _complex_h

#include <iostream>
using namespace std;


class Complex{
public:
	Complex(double re = 0, double im = 0){_real = re, _imag = im;}
	Complex operator+( const Complex& num2) const {
		Complex result(_real + num2._real, _imag + num2._imag);
		return result;}
	Complex operator-( const Complex& num2) const {
		Complex result(_real - num2._real, _imag - num2._imag);
		return result;}
	friend ostream& operator<<( ostream& os, const Complex& cnum) const {
		return os << cnum._real	<< " + " << cnum._imag << "i";}

	
//	void print() {
//		cout << _real << " + " << _imag << "i";}


private:
	double _real, _imag;

};

#endif

There is a built in STL container for complex numbers, the << operator is already taken care of:

Code:

#include <complex>
#include <iostream>
using namespace std;

int main()
{
    complex<double> c1(3.2,6.1);
    cout << "Complex value c1: " << c1 << endl;
    return 0;
}

Should output something along the lines of:
Complex value c1: (3.2,6.1)

Code:

class Complex{
public:
	Complex(double re = 0, double im = 0){_real = re, _imag = im;}
	Complex operator+( const Complex& num2) const {
		Complex result(_real + num2._real, _imag + num2._imag);
		return result;}
	Complex operator-( const Complex& num2) const {
		Complex result(_real - num2._real, _imag - num2._imag);
		return result;}
	//friend ostream& operator<<( ostream& os, const Complex& cnum) const {
	//	return os << cnum._real	<< " + " << cnum._imag << "i";}
	friend	ostream&	operator<<(ostream& os,const Complex& cnum){
		return os << cnum._real	<< " + " << cnum._imag << "i";
	}
		
//	void print() {
//		cout << _real << " + " << _imag << "i";}


private:
	double _real, _imag;

};

Remove the "const" as The Dog pointed out.

"Go Dawgs!"
gg (UGA grad)

Thanks, guys.