php session function says deprecated

Question

I'm building a type of mini cms but when i try to use sessions i get this error:

Deprecated: Function session_is_registered() is deprecated in index.php on line 4 , where the code i use is:

<?php
session_start(); //Start the session
define(ADMIN,$_SESSION['name']); //Get the user name from the previously registered super global variable
if(!session_is_registered("admin")){ //If session not registered
header("location:login.php"); // Redirect to login.php page
}
else //Continue to current page
header( 'Content-Type: text/html; charset=utf-8' );
?> 

It also says something about header already sent...

Answer 1

The session_is_registered is deprecated, just use isset to check:

if(!isset($_SESSION['admin'])){

And for header already sent notice, you should make sure there is no output before session_start() and any head() function.

Your case is most caused by the deprecated notice if your display_errors config is on.