Re: Does passing an uninitialized array variable initialize it? (PHP 5)

On Tue, 31 Jul 2007 03:20:15 +0200, Jerry Stuckle <jstucklex@xxxxxxxxxxxxx> wrote:

Rik wrote:
On Tue, 31 Jul 2007 02:38:04 +0200, Jerry Stuckle <jstucklex@xxxxxxxxxxxxx> wrote:
I take this back - the result of the operation is unpredictable. That's because:

$rank[$i] = trim($rank[$i++]);

$rank[$i++]

is evaluated as $rank[$i]. However, when

$rank[$i]

is evaluated, does it use the old or the new version of $i?
This is indeed dubious. Which of the '[' gets evaluated first? Allthough, left-associtivity might indicate the first one should be evaluated first (PHP4 behaviour).
However, for:
$array[$i] = $i++;
Precedence as defined should kick in clearly. The '[' isn't in the table just for show.

The bottom line: don't change a value and use it in the same statement. Results are unpredictable.
And makes for more readable code indeed. However, if I read the documentation I fully expect the PHP4 result from my example, not the PHP5 one...
--Rik Wasmus

He, still trouble with my sig-seperator? :P

Rik,

The key here is, precedence defines the order of OPERATOR evaluation - but not the order of OPERAND evaluation. A subtle, but important difference in cases like this.

For instance, it defines that '++' will be evaluated before '[]',

Well, the other way around.

it doesn't define whether [$i] will use the old or new value of $i++. So even though [$i] is evaluated before [$i++], $i++ is evaluated first and the value of $i is unpredictable.

Hmm, you've got a point there. However, I still wonder what warrented the change from PHP4 to PHP5. Maybe it's got something to do with the fact references are more integrated, but that's just a wild guess.

What IS clear however, is that this is a nice example why one-liners are overrated. Nothing wrong with a few lines if it just clarifies things more, especially if it takes close to no extra CPU time and/or memory.
--
Rik Wasmus
.

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