深入for,while,foreach遍历时间比较的详解

<?php
$arr = array();
for($i = 0; $i < 50000; $i++){
$arr[] = $irand(1000,9999);
}
function GetRunTime()
{
list($usec,$sec)=explode(" ",microtime());
return ((float)$usec+(float)$sec);
}
/=============================================/
$time_start = GetRunTime();
for($i = 0; $i < count($arr); $i++){
$str = $arr[$i];
}
$time_end = GetRunTime();
$time_used = $time_end - $time_start;
echo 'Used time of for:'.round($time_used, 7).'(s)<br /><br />';
unset($str, $time_start, $time_end, $time_used);
/=============================================/
$time_start = GetRunTime();
while(list($key, $val) = each($arr)){
$str = $val;
}
$time_end = GetRunTime();
$time_used = $time_end - $time_start;
echo 'Used time of while:'.round($time_used, 7).'(s)<br /><br />';
unset($str, $key, $val, $time_start, $time_end, $time_used);
/=============================================/
$time_start = GetRunTime();
foreach($arr as $key => $val){
$str = $val;
}
$time_end = GetRunTime();
$time_used = $time_end - $time_start;
echo 'Used time of foreach:'.round($time_used, 7).'(s)<br /><br />';
?>