Re: Can I avoid using a global?!

From:

mike3 <mike4ty4@yahoo.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 22 Nov 2011 12:48:35 -0800 (PST)

Message-ID:

<1daeecc6-148d-4711-aca5-fbef2a063dfd@q39g2000prg.googlegroups.com>

On Nov 22, 4:03 am, Goran <goran.pu...@gmail.com> wrote:

On Nov 22, 11:09 am, mike3 <mike4...@yahoo.com> wrote:

On Nov 22, 2:36 am, Goran <goran.pu...@gmail.com> wrote:

On Nov 22, 5:08 am, mike3 <mike4...@yahoo.com> wrote:

Hmm. Now I've got another question. In this program, I have a numbe=

of
objects that represent various parts of the screen to draw in
("windows").
These are "global" to the source code file that handles the display=

but
are not accessed anywhere outside that -- or at least not visibly,
since
there are functions that can be called from outside that use them. =

this
global bad? If so, what can be done to replace it?

Namely, I've got some stuff like:

--- Code ---
DisplayWindow *msgWnd, *gameWnd, *statsWnd;
("globals" within the source file UH OH)

...
(Functions that use them -- this is all you see from "outside")
void InitializeGameDisplay()
{
...}

Your problems start this function. If you don't call it before any
other function, your code will pretty likely crash (e.g. because it
initializes your "globals", and some other function uses them, and if
Init... wasn't called...). And there's a way to explain, through code
organization, proper call order. E.g.

class GameDisplay
{
private:
  DisplayWindow gameWindow, msgWnd, statsWnd;
public:
  void Whatever()
  { use gameWnd, msgWnd, statsWnd... }

};

If you do the above, you can't make a mistake and not call Init (Init
just became the constructor of your GameDisplay). So perhaps you
should try this line of thinking.

Yes, I know -- I didn't like the "Init()" function there either --
"Init()"
functions are bad.

And then, in your main() (warning: IMAGINARY CODE):

int main()
{
  GameDisplay display;
  Game game(display);
  game.Run();
  return EXIT_SUCCESS;

}

Goran.

Just thought of something like that. But isn't "game" a singleton
there?

No. Singleton is a design pattern that ensures you can't possibly
have, at any given time, more than one object of a certain type, and
provides a way to access that sole instance. "Game" and "game" aren't
that. Don't equate a singleton with a local variable ;-).

So singleton isn't just "having an object of which you happen to only
have one of".

Or is the "bad" kind of singleton the one
that acts like a type of global (i.e. if "Game game" were outside
main() and accessed all over the program)?

Yes. You also seem to equate a singleton with a global variable ;-).
Not the same either.

Goran.

I've heard that they can _act_ like a global, not that they _ARE_ a
global.