Problems overloading the operator<< ( multiple definition)

[olredixsis]

Hmm... I think you should try an upcasting since the Word class is a subclass of HTMLElement class. I'll will look your code later, I'm a bit busy right now.

[h4x0rmx]

Thanks! I'll wait for your answer!

[olredixsis]

What error(s) did you get?

[h4x0rmx]

I don't get any errors. It works as expected when I have single objects derived from HTMLElement, but when I have a LinkedList<HTMLElement>, only the HTMLElement versin of << gets called, ignoring the ones specific for the derived clases.
That's why I'm asking if I have to do some kind of casting... it would be cool to have the code figure out by itself what it function it should use.

[olredixsis]

did you revise your code for word.h

#ifndef WORD_H_
#define WORD_H_

#include "HTMLElement.h"
#include "URL.h"
#include <string>
#include <iostream>

// Forward declare Word 
class Word;
// Prototype operator<<.

ostream& operator<<(ostream& ostrw, const Word& w);

class Word :public HTMLElement {
public:
	Word(std::string v, URL u);
	std::string &getURL();
	friend ostream& operator<<(ostream& ostrw, const Word& w);
private:
	URL url;
};
#endif 

[h4x0rmx]

that's exactly what I have :\

[olredixsis]

Try deleting the operator << for the subclass Word and use the operator << of base class HTMLElement.

word.h must inherit the operator << from its base class I think?

overloading operator can be inherited right?

correct me if I'm wrong. :)

[h4x0rmx]

The subclass should have its own operator <<, it should not inherit.
The subclasses have other variables/methods that I'd like to include. :)

[firedraco]

If you are defining the operators the way you are (as global friends), then they will NOT be inherited.

[Disch]

I think I know what the problem is here... but let me make sure I have everything right.

1) You want to output stuff for HTMLElement and Word
2) You figured you could output via the << operator
3) You have a container of HTMLElement* (which may be of HTMLElements or Words or other derived types)
4) You want each type to print things in its own way.

Assuming I have all of this right so far....


This screams polymorphism. And unfortuantely you can't make the << operator virtual in this case. So instead, make a virtual Print function:

class HTMLElement:
{
public:
    virtual void Print(std::ostream& out) const
    {
        out << "whatever";
    }
    //... 

Put the same thing in Word. And instead of doing cout << *ptr; , you do ptr->Print(cout);


EDIT:

a nice perk to this approach is that you can overload << too, and make it fake virtual by having it call Print:

// you only have to write this for HTMLElement, and it will work as
//   desired for all derived types
std::ostream& operator << (std::ostream& out, const HTMLElement& el)
{
    el.Print(out);
    return out;
}

[h4x0rmx]

Right, the I'm using polymorphism... sorry if I wasn't clear enough.

I really appreciate your help!

[olredixsis]

Good for you. :)