How does PHP calculate the difference between two dates for several months?

How does PHP calculate the gap between two dates for several months? & Lt ;? Phpfunction & nbsp; getMonthNum (& nbsp; $ date1, & nbsp; $ date2, & nbsp; $ tags = '-' & nbsp;) {& nbsp; $ date1 & nbsp ;=& nbsp; explode ($ tags, $ date PHP how to calculate the gap between the two dates for several months?

 function getMonthNum( $date1, $date2, $tags='-' ){
  $date1 = explode($tags,$date1);
  $date2 = explode($tags,$date2);
  return abs($date1[0] - $date2[0]) * 12 + abs($date1[1] - $date2[1]);
 }

echo getMonthNum("2013-02-01","2014-01-01",'-');

?>

The code above calculates a difference of 13 months. I don't know how to change it to be normal? Php date:
------ Solution --------------------
Remove abs
-11 indicates that is 11 months earlier
Of course, you can also return the entire abs value, but you only know that the difference is 11 months, but you do not know whether it is more or less.
------ Solution --------------------

function getMonthNum($date1,$date2){
$date1_stamp=strtotime($date1);
$date2_stamp=strtotime($date2);
list($date_1['y'],$date_1['m'])=explode("-",date('Y-m',$date1_stamp));
list($date_2['y'],$date_2['m'])=explode("-",date('Y-m',$date2_stamp));
return abs($date_1['y']-$date_2['y'])*12 +$date_2['m']-$date_1['m'];
 }
 
echo getMonthNum("2013-02-01","2014-01-01");

echo getMonthNum("20130201","20140101");

echo getMonthNum("201302","201401");

------ Solution --------------------

 function getMonthNum( $date1, $date2, $tags='-' ){
  $date1 = explode($tags,$date1);
  $date2 = explode($tags,$date2);
  if ($date1[0]>=$date2[0]){
  return abs($date1[0] - $date2[0]) * 12 + abs($date1[1] - $date2[1]);
  }
  else{
  return abs($date2[0] - $date1[0]) * 12 - abs($date1[1] - $date2[1]);
  }
 }

echo getMonthNum("2013-02-01","2014-01-01",'-');

?>

------ Solution --------------------
The above is wrong ..... Resend:

function getMonthNum($date1,$date2){