<?php // fixString.php
    require_once 'login.php';
    $connection = new mysqli($hn, $un, $pw, $db);
    if ($connection->connect_error)
        die($connection->connect_error);

    var_dump($_POST);
    $user = mysql_fix_string($connection, $_POST['user']);
    $pass = mysql_fix_string($connection, $_POST['pass']);
    $query = "SELECT * FROM customers WHERE name='$user' AND isbn='$pass'";
    $result = $connection->query($query);
    if (!$result)
        die($connection->error);

    echo $user . "<br>";
    echo $pass . "<br>";

    function mysql_fix_string($connection, $string)
    {
        if (get_magic_quotes_gpc()) // returns TRUE if magic quotes are active
            $string = stripslashes($string);
        return $connection->real_escape_string($string);
    }
?>

array(0) { }
Notice: Undefined index: user in C:xampphtdocsPHPfixString.php on line 8

Notice: Undefined index: pass in C:xampphtdocsPHPfixString.php on line 9