PHP : CodeIgniter mysql_real_escape_string 警告

/**
     * Escape String
     *
     * @access    public
     * @param    string
     * @param    bool    whether or not the string will be used in a LIKE condition
     * @return    string
     */
    function escape_str($str, $like = FALSE)
    {
        if (is_array($str))
        {
            foreach ($str as $key => $val)
               {
                $str[$key] = $this->escape_str($val, $like);
               }

               return $str;
           }

        if (function_exists(‘mysql_real_escape_string‘) AND is_resource($this->conn_id))
        {
            $str = mysql_real_escape_string($str, $this->conn_id);
        }
                elseif (function_exists(‘mysql_real_escape_string‘))
        {
            if (is_object($this->conn_id)) {
                            $str = mysql_real_escape_string($str, $this->conn_id);
                        } else {
                            $str = addslashes($str);
                        }
        }
elseif (function_exists(‘mysql_escape_string‘))
        {
            $str = mysql_escape_string($str);
        }
        else
        {
            $str = addslashes($str);
        }

        // escape LIKE condition wildcards
        if ($like === TRUE)
        {
            $str = str_replace(array(‘%‘, ‘_‘), array(‘\\%‘, ‘\\_‘), $str);
        }

        return $str;
    }