Question

I’m having some trouble overloading my stream extraction operator in C++ for a hw assignment. I’m not really sure why I am getting these compile errors since I thought I was doing it right… Here is my code:

Complex.h

#ifndef COMPLEX_H
#define COMPLEX_H

class Complex
{
    //friend ostream &operator<<(ostream &output, const Complex &complexObj) const;
     // note at bottom regarding friend function
public:
    Complex(double = 0.0, double = 0.0); // constructor
    Complex operator+(const Complex &) const; // addition
    Complex operator-(const Complex &) const; // subtraction
    void print() const; // output
private:
    double real; // real part
    double imaginary; // imaginary part
};

#endif

Complex.cpp

#include <iostream>
#include "Complex.h" 
using namespace std;

// Constructor
Complex::Complex(double realPart, double imaginaryPart) : real(realPart), imaginary(imaginaryPart)
{
}

// addition operator
Complex Complex::operator+(const Complex &operand2) const
{
    return Complex(real + operand2.real, imaginary + operand2.imaginary);
}

// subtraction operator
Complex Complex::operator-(const Complex &operand2) const
{
    return Complex(real - operand2.real, imaginary - operand2.imaginary);
}

// Overload << operator
ostream &Complex::operator<<(ostream &output, const Complex &complexObj) const 
{
    cout << '(' << complexObj.real << ", " << complexObj.imaginary << ')';
    return output;  // returning output allows chaining
}

// display a Complex object in the form: (a, b)
void Complex::print() const
{
    cout << '(' << real << ", " << imaginary << ')';
}

main.cpp

#include <iostream>
#include "Complex.h"
using namespace std;
int main()
{
    Complex x;
    Complex y(4.3, 8.2);
    Complex z(3.3, 1.1);

    cout << "x: ";
    x.print();
    cout << "\ny: ";
    y.print();
    cout << "\nz: ";
    z.print();

    x = y + z;
    cout << "\n\nx = y + z: " << endl;
    x.print();
    cout << " = ";
    y.print();
    cout << " + ";
    z.print();

    x = y - z;
    cout << "\n\nx = y - z: " << endl;
    x.print();
    cout << " = ";
    y.print();
    cout << " - ";
    z.print();
    cout << endl;
}

Compile erros:

complex.cpp(23) : error C2039: '<<' : is not a member of 'Complex'
complex.h(5) : see declaration of 'Complex'
complex.cpp(24) : error C2270: '<<' : modifiers not allowed on nonmember functions
complex.cpp(25) : error C2248: 'Complex::real' : cannot access private member declared in class 'Complex'
complex.h(13) : see declaration of 'Complex::real'
complex.h(5) : see declaration of 'Complex'
complex.cpp(25) : error C2248: 'Complex::imaginary' : cannot access private member declared in class 'Complex'
complex.h(14) : see declaration of 'Complex::imaginary'
complex.h(5) : see declaration of 'Complex'

Thanks!

Edit:

I wasn't sure about declaring the friend function in the header file or not.  When I do, I get these errors:
c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2143: syntax error : missing ';' before '&'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2433: 'ostream' : 'friend' not permitted on data declarations
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2061: syntax error : identifier 'ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2805: binary 'operator <<' has too few parameters
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2872: 'ostream' : ambiguous symbol
1>        could be 'c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : int ostream'
1>        or       'c:\program files\microsoft visual studio 9.0\vc\include\iosfwd(708) : std::ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2143: syntax error : missing ';' before '&'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2086: 'int ostream' : redefinition
1>        c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : see declaration of 'ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2872: 'ostream' : ambiguous symbol
1>        could be 'c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : int ostream'
1>        or       'c:\program files\microsoft visual studio 9.0\vc\include\iosfwd(708) : std::ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2872: 'ostream' : ambiguous symbol
1>        could be 'c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : int ostream'
1>        or       'c:\program files\microsoft visual studio 9.0\vc\include\iosfwd(708) : std::ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2065: 'output' : undeclared identifier
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2059: syntax error : 'const'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(24) : error C2143: syntax error : missing ';' before '{'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(24) : error C2447: '{' : missing function header (old-style formal list?)
1>Generating Code...
1>Compiling...
1>main.cpp
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2143: syntax error : missing ';' before '&'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2433: 'ostream' : 'friend' not permitted on data declarations
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2061: syntax error : identifier 'ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2805: binary 'operator <<' has too few parameters

Answer 1

Your commented-out declaration in the header is almost correct. Since it is a friend, it is not a member and thus cannot be const, so it should be:

friend std::ostream &operator<<(std::ostream &output, const Complex &complexObj);

Note also that you need to qualify ostream as std::ostream, since you should not use using namespace std; in a header file (you really shouldn’t need to use it anywhere; it’s generally better to just write out std:: when you want to use something from the standard library).

Likewise, in your source file, since it is not a member function, you do not prefix the operator definition with the class name, and it should be:

std::ostream &operator<<(std::ostream &output, const Complex &complexObj)