Loggedin variable in session save?

Is it save to store a variable "loggedin" in a session, to indicate that someone has logged in?

For example:

login.php

if($login)
{
...
session_register("loggedin");
}

if($loggedin)
{
displaysecrettext();
}
else
{
redirect("login.php");
}

There is a function session_is_registered()
this function for :
Find out if a variable is registered in a session.

For example:

if($login)
{
...
session_register("loggedin");
}

session_star();
$login = session_is_registered("loggerin");

if($login){
displaysecrettext(); }
else{
Header("Location: login.php");
}

Thanks for your quick reply! Is there a pratical difference between your code and the code below?

if($login)
{
...
$loggedin=true;
session_register("loggedin");
}

session_star();
$login = $loggedin;

if($login){
displaysecrettext(); }
else{
Header("Location: login.php");
}

yes , at my code is check if $login is logged or not

Thanks, now i get it 🙂