Why does the variable defined in the included script have no value?

I have this code in script.php:

<?php
session_start();

$user_session = $_SESSION['u_name'];

class check_sess {
    public function check_id_session($user_session, $db) { //email
        $stmt = $db->prepare('select id_user from users where email=?');
        $stmt->bind_param('s', $user_session);

        $stmt->execute();

        $stmt->bind_result($id);

        if ($stmt -> fetch()) {
            $id;
            echo $id; // here shows 20 for example
            return true;
        }
        else
        return false;

        $stmt->close();
        $db->close();
    }
}
?>

and in demo.php I have:

include 'script.php';
$val = new check_sess();
$val-> check_id_session($user_session, $db);
echo $id; //problem here. It is supposed echo 20

Why can't I do echo $id? There is no output in demo.ph开发者_JAVA百科p.

Read about variable scope. The variable $id does not exist outside the function. If you want the function to return $id, write return $id in the if ($stmt -> fetch()) { condition branch. You can then write:

include 'script.php';
$val = new check_sess();
$id = $val-> check_id_session($user_session, $db);
echo $id;

You need to return a value to access it in this way:

if ($stmt -> fetch()) {
     return $id; 
}

Except that won't work as you intended.

You need to assign $id first - and it looks like you're using some kind of framework; so you should first assign the value to $id, as a result from say, fetch(), and then return that value from the method, allowing you to access it.

your id is within a class and therefore in a different scope.

You can either write a getter for it or declare it as static, then you can access it without an instance:

class check_sess {
    static $id;
...
    if ($stmt -> fetch()) {
        self::$id = $id;
        echo self::$id; // here shows 20 for example
        return true;
    }
...
}

You can now access it anywhere in your code via

check_sess::$id