In addition to the note made by "Francis dot a at gmx dot net" you should not normally be using a function such as sizeof() or count() in a control structure such as FOR because the same value is being calculated repeatedly for each iteration. This can slow things down immensely, regardless of whether you pass by value or reference.
It is generally much better to calculate the static values before the defining the looping control structure.
Example:
<?php
$intSize = sizeof($arrData);
for($i = 0; $i < $intSize; $n++) {
}
?>
in the example below, you would get the same result if you change the function to something like:
function test_ref(&$arr) {
$time = time();
$size = sizeof($arr); // <--- this makes difference...
for($n=0; $n<$size; $n++) {
$x = 1;
}
echo "<br />The function using a reference took ".(time() - $time)." s";
}
I don't know if this is a bug (I'm using PHP 5.01) but you should be careful when using references on arrays.
I had a for-loop that was incredibly slow and it took me some time to find out that most of the time was wasted with the function sizeof() at every loop, and even more time I spent finding out that this problem it must be somehow related to the fact, that I used a reference of the array. Take a look at the following example:
function test_ref(&$arr) {
$time = time();
for($n=0; $n<sizeof($arr); $n++) {
$x = 1;
}
echo "<br />The function using a reference took ".(time() - $time)." s";
}
function test_val($arr) {
$time = time();
for($n=0; $n<sizeof($arr); $n++) {
$x = 1;
}
echo "<br />The funktion using a value took: ".(time() - $time)." s";
}
// fill array
for($n=0; $n<2000; $n++) {
$ar[] = "test".$n;
}
test_ref($ar);
test_val($ar);
echo "<br />Done";
When I tested it, the first function was done after 9 seconds, while the second (although the array must be copied) was done in not even one.
The difference is inproportional smaller when the array size is reduced:
When using 1000 loops the first function was running for 1 second, when using 4000 it wasn't even done after 30 Seconds.
Re-using variables which where references before, without unsetting them first, leads to unexpected behaviour.
The following code:
<?php
$numbers = array();
for ($i = 1; $i < 4; $i++) {
$numbers[] =
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