session in php

[lionell1988]

ho fatto una pag di prova col seguente codice

<?php
$var="cia";
session_start();
$_SESSION['user']=$var;
?>

ma mi dà questi errori :
Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at C:\xampp\htdocs\session.php:9) in C:\xampp\htdocs\session.php on line 11

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\xampp\htdocs\session.php:9) in C:\xampp\htdocs\session.php on line 11

????????