php - Call to undefined function error -

i getting call undefined function error, when have defined function. here code:

foreach($db->query("select * 'members' username = '$user'") $row) {     echo "rank: ".get_rank_tag($user)."<br>"; } 

here class get_rank_tag() function

include('password.php');  class user extends password {   private $_db;    function __construct($db) {     parent::__construct();     $this->_db = $db;   }    public function get_rank_tag($user){         try {         $stmt = $this->_db->prepare('select rank members username = $user ');         $stmt->execute();         $row = $stmt->fetch();         if($row['rank']==0){return "<span class='label label-default'>default</span>";}         elseif($row['rank']==1){return "<span class='label label-success'>vip</span>";}         elseif($row['rank']==2){return "<span class='label label-success'>mvp</span>";}         elseif($row['rank']==3){return "<span class='label label-success'>elite</span>";}         elseif($row['rank']==4){return "<span class='label label-success'>master</span>";}         elseif($row['rank']==5){return "<span class='label label-success'>champion</span>";}         elseif($row['rank']==6){return "<span class='label label-primary'>jm</span>";}         elseif($row['rank']==7){return "<span class='label label-primary'>trusted</span>";}         elseif($row['rank']==8){return "<span class='label label-info'>gm</span>";}         elseif($row['rank']==9){return "<span class='label label-info'>gm+</span>";}         elseif($row['rank']==10){return "<span class='label label-warning'>admin</span>";}         elseif($row['rank']==11){return "<span class='label label-danger'>owner</span>";}      } catch(pdoexception $e) {         echo '';      }   }  } 

i bit of beginner php, please bear me.

are sure have instance of user class? sure have instantiated class php won't able identify function.