Comment calculer le nombre de jours entre les dates en PHP

$date_1 = date('Y-m-d');
$date_2= '2012-07-16';
$date1_arr = explode("-",$date_1);
$date2_arr = explode("-",$date_2);
$day1 = mktime(0,0,0,$date1_arr[1],$date1_arr[2],$date1_arr[0]);
$day2 = mktime(0,0,0,$date2_arr[1],$date2_arr[2],$date2_arr[0]);
$days = round(($day2 - $day1)/3600/24);
echo $days; exit;

<?php
$datetime1 = new DateTime(&#39;2009-10-11&#39;);
$datetime2 = new DateTime(&#39;2009-10-13&#39;);
$interval = $datetime1->diff($datetime2);
echo $interval->format(&#39;%R%a days&#39;);
?>

<?php
$datetime1 = date_create(&#39;2009-10-11&#39;);
$datetime2 = date_create(&#39;2009-10-13&#39;);
$interval = date_diff($datetime1, $datetime2);
echo $interval->format(&#39;%R%a days&#39;);
?>