mysqli : 严格的标准:只应通过引用传递变量

My code (i'm beginning) :

<?php
class Sql{

    private $db;
    private $user;
    private $pwd;
    private $url;

    private $param;

    private $mysqli;

    function __construct($db, $user, $pwd, $url){
        $this->db = $db;
        $this->user = $user;
        $this->pwd = $pwd;
        $this->url = $url;


    }

    /**
     * mysqli::connection()
     * 
     * @return 
     */
    public function connection()
    {
        try{
            $this->mysqli = new mysqli($this->db, $this->user, $this->pwd, $this->url);
        }catch(Exception $e){
            throw new Exception("Impossible de se connecter à la base " . $this->db);
        }
    }

    public function select($query, $param, $debug=false){

        $this->connection();

        $r = $this->InitialiseResult("select");

        if (!($stmt = $this->mysqli->prepare($query))) {
            echo "Echec de la préparation : (" . $this->mysqli->errno . ") " . $this->mysqli->error;
        }

        //Param
        for($i=0;$i<sizeof($param);$i++){
            if (!$stmt->bind_param($param[$i][0], mysqli_real_escape_string($this->mysqli, $param[$i][1]))) {
                echo "Echec lors du liage des paramètres : (" . $stmt->errno . ") " . $stmt->error;
            }
        }

        if (!$stmt->execute()) {
            echo "Echec lors de l'exécution : (" . $stmt->errno . ") " . $stmt->error;
        }

        if (!($res = $stmt->get_result())) {
            echo "Echec lors de la récupération du jeu de résultats : (" . $stmt->errno . ") " . $stmt->error;
        }else{

            $r["state"] = true;
            $r["rows"] = $res->fetch_assoc();
            $r["num_rows"] = $res->num_rows;

            if($debug)
                var_dump($r);

        }

        return $r;

    }


    /**
     * mysqli::InitialiseResult()
     *
     * @param mixed $p
     * @return
     */
    public function InitialiseResult($p)
    {
        $r = array(); //on écrase
        $r["state"] = false;

        switch($p){
            case "select":

                $r["rows"] = array();
                $r["num_rows"] = 0;
                break;

        }

        return $r;
    }
}
?>

我尝试将 $param 放在一个属性中并使用它是 mysqli_real_escape_string() 但错误仍然存​​在.