Php获得最新日期

I'm working in php and I have a list of dates in string format. I'd like to get the newest one, and have the function return it.. I can't seem to get this to work.. Maybe someone can help me out..

<?php
    $list_of_dates = array("04/17/1999 05:15 AM - CST", "04/17/2000 05:18 AM - CST", "04/17/2000 05:19 AM - CST");

    function getLatestDate($in){
        $ret = ""; 
        foreach($in as &$date){
         $cnt = strtotime($date);
         if(strtotime($ret) > $cnt){
            $ret = $date;
         }
        }

        return $ret;
    }
?>

Your condition seems to be reversed:

if(strtotime($ret) > $cnt){
        $ret = $date;
     }

Should be:

if ($ret === '' || strtotime($ret) < $cnt){
        $ret = $date;
     }

You will want to overwrite $ret if its value is lower (older) than $cnt. In the first iteration $ret will be the empty string, so you will always want to overwrite that; of course, strtotime('') will probably always be lower than anything else, but it's good form to make the distinction.