echo don`t show when use unset global variables - php

Question

I have started a session on config page, then $_SESSION['logged_out'] = 1; and on index page that:
if(isset($_SESSION['logged_out']))
{
echo "You have been logged out !";
unset($_SESSION['logged_out']);
}
But the echo not workig, like unset is before him. And i don`t understand why, please help me.
EDITED:
Config page:
<?php
ini_set('display_errors',1);
error_reporting(E_ALL);
ob_start();
session_start();
include 'connection.php';
include 'functions.php';
$logged_in = 0;
if(isset($_SESSION['username']) && isset($_SESSION['password']))
{
$username = sec($link, $_SESSION['username']);
$password = sec($link, $_SESSION['password']);
$udata = get_row($link, "SELECT * FROM accounts WHERE Username= '$username' && Password= MD5('$password')");
if(isset($udata['ID']))
{
$logged_in = 1;
if(isset($_GET['logout']))
{
unset($_SESSION['username']);
unset($_SESSION['password']);
$_SESSION['logged_out'] = "1";
mysqli_query($link, "UPDATE accounts SET rpgon = '0' WHERE Username = '$username'");
header('location: index.php');
}
}
} ?>
Index page:
if(isset($_SESSION['logged_out']))
{
echo "You have been logged out !";
unset($_SESSION['logged_out']);
}?>
This is it ...

Answer 1

If echo doesn't show anything is because the if condition is evaluated to false. This mean that $_SESSION['logged_out'] isn't set.

Answer 2

You have to start_session() on every page that uses the $_SESSION. In fact if you are using $_SESSION anywhere in your site, its best to start it on all your pages.
So add start_session() just after the first <?php to ensure it is always started for all pages
<php
start_session();
. . .
if(isset($_SESSION['logged_out']))
{
echo "You have been logged out !";
unset($_SESSION['logged_out']);
}
Added after additional info given
I think this may be one of your problems
$udata = get_row($link,
"SELECT * FROM accounts
WHERE Username= '$username'
&& Password= MD5('$password')"
);
The && should be AND, then this query should return a result. You should really be checking the result status from all query command like so:
<?php
ini_set('display_errors',1);
error_reporting(E_ALL);
session_start();
ob_start();
include 'connection.php';
include 'functions.php';
$logged_in = 0;
if(isset($_SESSION['username']) && isset($_SESSION['password']))
{
$username = sec($link, $_SESSION['username']);
$password = sec($link, $_SESSION['password']);
$udata = get_row($link, "SELECT * FROM accounts
WHERE Username= '$username'
AND Password= MD5('$password')"
);
// this would have shown the error in the sql query
// if it had been here before
if ( ! $udate ) {
echo mysqli_error($link);
exit;
}
// now this if will be executed
// although this if is probably no longer required
if(isset($udata['ID']))
{
$logged_in = 1;
if(isset($_GET['logout']))
{
unset($_SESSION['username']);
unset($_SESSION['password']);
$_SESSION['logged_out'] = "1";
mysqli_query($link, "UPDATE accounts SET rpgon = '0' WHERE Username = '$username'");
header('location: index.php');
// you should also follow a header() call with an exit;
exit;
}
}
}
?>