warning:session_destroy() Trying to destroy uninitialized session

[bikashliju]

1.session_destroy() Trying to destroy uninitialized session
2.Cannot modify header information - headers already sent by (output started at C:\xampp\xampplite\htdocs\backup\logout.php:3)

<?php
session_destroy();
header( 'Location: http://localhost/backup/login.php');
?>

exicuting the code i got this type of warning
can someone explain what is unitialized session

[Dormilich]

can someone explain what is unitialized session

using session functions without calling session_start() beforehand

[Markus]

And for the second error, which is created by the first error, read this.

[bikashliju]

thanx a lot sir