c99/c++ localised variable definition

[Andrew Reilly]

On Mon, Jan 31, 2005 at 10:26:30AM +0000, Paul Richards wrote:
> 3) Usage in for loops may be more useful than other uses.
[snip]
> I think the loop usage though is one clear example where it is
> clearer. I think there are others as well; where the usage of the
> variable is clearly localised it is much easier to see a local
> definition than to have to jump back and forth to find out what
> variables are.

I'd just like to raise a dissenting voice to this particular
point.  I find the for-loop initialization syntax a pernicious
source of errors, mainly because of the non-intuitive scope of
the definition.  I.e., it looks like it's equivalent to "int i;
for (i = 0;;)" but it isn't.

If you carelessly c++-ify a loop like:

	for (int i = 0; i < N; i++)
	{
		if (some_condition(i)) break;
	}
	do_something_with(i);	/* use finishing index */

you can miss the fact that the value of i is used outside of the
loop.  The newly created scope for "i" shadows the presumably
pre-existing definition of i at the top of the function, which
is what do_something_with() gets to see.

Const friendliness and some minor economy of thought are perhaps
valid benefits of this style, but I don't think sufficient to
change the style.

Cheers,

-- 
Andrew