Problem with ostream overloading

[GriffinWolf]

Okay. I have searched both my textbook and the internet for the past few hours, and I've made progress in various ways - but I'm still having a problem with my code to overload the ostream operator (<<).

I'm trying to include all relevent information, please ask if there's anything I left out. Most likely it's going to be one of those really, really stupid, simple things... so any and all help appreciated. This is part of a uni assignment, which is 95% done, except for this one function...

I have a class called set, with various functions declared and working. I'm now trying to use the ostream overloader to output the contents of a set.

Here is the declaration in the header file:

friend ostream operator<<(ostream &os, const set mySet);

Private data for class set:

private:
  vector <bool> setlist;  // indicates set elements as true
  int cardinality; // number of (true) items in set 

And here is the code I have in set.cpp:

ostream operator<<(ostream &os, const set mySet)
{
    mySet.display();
    return os;
}

It is on line 4 of the code in set.cpp that I'm encountering problems. There's a squiggly red line underneath it, it won't compile, and the error message is "within this context".

Thanks in advance :)

[Duthomhas]

The insertion operator should be defined as:

ostream& operator<<( ostream& outs, const myType& myData )
{
    ...
    return outs;
}

Notice how everything is passed by reference.

BTW, avoid variable names like 'os', because that gives you 'is' for the extraction operator (>>), and using 'is' for variable names is a bad idea, even in C++.

Hope this helps.

[edit] One more thing. How does mySet.display(); write to the argument ostream?

[GriffinWolf]

Thankyou so much. It appears to be working now. :)

One more thing. How does mySet.display(); write to the argument ostream?

I'm sorry, I don't understand the question. ? Display is a void function that outputs the data (I'm thinking I will replace that line with the actual display function code).

[Duthomhas]

The whole point of the insertion operator is to write data to the argument stream (which you have named 'os'). To what stream does mySet.display(); write? It certainly can't be 'os'...

[GriffinWolf]

Maybe I'm being particularly dim tonight (in which case I should probably remove myself from coding until I've had some sleep) but what you're asking is just going way over my head. I'm only a beginner at C++, and we haven't covered anything in class about writing data.

Here is the function display, if that helps answer your question. (And it's just now that I remember that display is a hideously written piece of inefficient code... but it worked, and for the purpose of submitting the assignment that was good enough at the time.)

 void set::display()const
{
   // pre : none
   // displays the elements of this set enclosed in braces and separated by commas eg {1,2,3} or {}
   //(do not use backspace, delete etc)
	unsigned int highest = getLargest();

	cout << "{";
	if (cardinality == 0)
		cout << "}" << endl;
	for (unsigned int i = 0; i < setlist.size(); i++)
	{
		if (i == highest)
			cout << highest << "}" << endl;
		else if (setlist.at(i) == true)
			cout << i << ",";
	}
} 

I also took your advice and renamed os.