overloading <<

This is a discussion on overloading << within the C++ Programming forums, part of the General Programming Boards category; I'm trying to figure out how to overload << so I can print a complex number just by cout << ...

  1. #1
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    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

  2. #2
    Registered User hk_mp5kpdw's Avatar
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    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)
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  3. #3
    Registered User The Dog's Avatar
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    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;
    
    };

  4. #4
    Registered User Codeplug's Avatar
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    Remove the "const" as The Dog pointed out.

    "Go Dawgs!"
    gg (UGA grad)

  5. #5
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    595
    Thanks, guys.

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