how to pass session_id() throught out the php pages?

when user clicks on login button(index.php) I am calling chechlogin.php where I am checking loginId an password as-

if($count==1)
{
// Register $myusername, $mypassword and redirect to file "login_success.php"
session_register("myusername");
session_register("mypassword"); 
$_SESSION['UserId'] = $myusername;
$_session['开发者_高级运维SessionId'] = session_id();
header("location:LoggedUser.php");
}

in LiggedUser.php

<?php session_start();  //starting session

if (!isset($_SESSION['SessionId']) || $_SESSION['SessionId'] == '') { header("location:index.php"); } ?>

Problem: It is always going back to index.php page although I am entering right userid and password.I think session_id() is not working properly or ??

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change $_session to $_SESSION.

btw session_register is deprecated and shouldn't be used. See session-register manual for details.

btw #2. You don't need to store sessionId in the $_SESSION, UserId is enough. So you code could look like:

login.php

if ($count == 1) {
    $_SESSION['UserId'] = $myusername;
    header ("location: LoggedUser.php");
    exit;
}

loggeduser.php

if (empty ($_SESSION['UserId'])) {
    header ("location:login.php");
    exit;
}

// user is logged 

EDIT: Exit added as Emil suggested.

---

Consider calling exit; after each header('Location: ...') call. Otherwise PHP will continue parsing the rest of the code, which may cause unpredictable errors.

header("Location: LoggedUser.php");
exit;