Help in php login code

PHP
1

Hi I am getting the below error with my code. Please help me correcting. I have tried many things but it does not work.

Call to a member function real_escape_string() on a non-object in C:\xampp\htdocs\elearning\teacher_modal.php on line 45

<?php
            if (isset($_POST['login_teacher'])) {

                function clean($str) {
                    $str = @trim($str);
                    if (get_magic_quotes_gpc()) {
                        $str = stripslashes($str);
                    }
                    return mysql_real_escape_string($str);
                }

                $username = clean($_POST['username']);
                $password = clean($_POST['password']);

                $query = mysql_query("select * from teacher where username='$username' and password='$password'") or die(mysql_error());
                $count = mysql_num_rows($query);
                $row = mysql_fetch_array($query);


                if ($count > 0) {
                    session_start();
                    session_regenerate_id();
                    $_SESSION['id'] = $row['teacher_id'];
                    header('location:teacher_home.php');
                    session_write_close();
                    exit();
                } else {
                    session_write_close();
                    ?>
                    <div class="pull-right">   
                        <button type="button" class="close" data-dismiss="alert">&times;</button>
                        <div class="alert alert-danger"><i class="icon-remove-sign"></i>&nbsp;Access Denied</div>
                    </div>
                    <?php
                    exit();
                }
            }
            ?>
2

Dupe thread. Please keep discussions there…