PHP时间比较和时间差如何计算

<?php   
 $zero1=date(“y-m-d h:i:s”);   
 $zero2=”2010-11-29 21:07:00′;   
 echo “zero1的时间为：”.$zero1.”<br>”;   
 echo “zero2的时间为：”.$zero2.”<br>”;   
 if(strtotime($zero1)<strtotime($zero2)){   
  echo “zero1早于zero2′;   
 }else{   
  echo “zero2早于zero1′;   
 }   
 ?>

<?php   
$zero1=strtotime (date("y-m-d h:i:s")); //当前时间  ,注意H 是24小时 h是12小时 
$zero2=strtotime ("2014-1-21 00:00:00");  //过年时间，不能写2014-1-21 24:00:00  这样不对 
$guonian=ceil(($zero2-$zero1)/86400); //60s*60min*24h   
echo "离过年还有<strong>$guonian</strong>天！";   
?>

<?php
//PHP计算两个时间差的方法 
$startdate="2010-12-11 11:40:00";
$enddate="2012-12-12 11:45:09";
$date=floor((strtotime($enddate)-strtotime($startdate))/86400);
$hour=floor((strtotime($enddate)-strtotime($startdate))%86400/3600);
$minute=floor((strtotime($enddate)-strtotime($startdate))%86400/60);
$second=floor((strtotime($enddate)-strtotime($startdate))%86400%60);
echo $date."天<br>";
echo $hour."小时<br>";
echo $minute."分钟<br>";
echo $second."秒<br>";

?>

<?php
/**
 * 时间差计算
 *
 * @param Timestamp $time
 * @return String Time Elapsed
 * @author Shelley Shyan
 * @copyright http://phparch.cn (Professional PHP Architecture)
 */
function time2Units ($time)
{
   $year   = floor($time / 60 / 60 / 24 / 365);
   $time  -= $year * 60 * 60 * 24 * 365;
   $month  = floor($time / 60 / 60 / 24 / 30);
   $time  -= $month * 60 * 60 * 24 * 30;
   $week   = floor($time / 60 / 60 / 24 / 7);
   $time  -= $week * 60 * 60 * 24 * 7;
   $day    = floor($time / 60 / 60 / 24);
   $time  -= $day * 60 * 60 * 24;
   $hour   = floor($time / 60 / 60);
   $time  -= $hour * 60 * 60;
   $minute = floor($time / 60);
   $time  -= $minute * 60;
   $second = $time;
   $elapse = ‘‘;

   $unitArr = array(‘年‘  =>‘year‘, ‘个月‘=>‘month‘,  ‘周‘=>‘week‘, ‘天‘=>‘day‘,
                    ‘小时‘=>‘hour‘, ‘分钟‘=>‘minute‘, ‘秒‘=>‘second‘
                    );

   foreach ( $unitArr as $cn => $u )
   {
       if ( $$u > 0 )
       {
           $elapse = $$u . $cn;
           break;
       }
   }

   return $elapse;
}

$past = 2052345678; // Some timestamp in the past
$now  = time();     // Current timestamp
$diff = $now - $past;

echo ‘发表于‘ . time2Units($diff) . ‘前‘;
?>