$_SESSION

Creating New Session
==========================
<?php 
session_start();
/*session is started if you don't write this line can't use $_Session  global variable*/
$_SESSION["newsession"]=$value;
?>
Getting Session
==========================
<?php 
session_start();
/*session is started if you don't write this line can't use $_Session  global variable*/
$_SESSION["newsession"]=$value;
/*session created*/
echo $_SESSION["newsession"];
/*session was getting*/
?>
Updating Session
==========================
<?php 
session_start();
/*session is started if you don't write this line can't use $_Session  global variable*/
$_SESSION["newsession"]=$value;
/*it is my new session*/
$_SESSION["newsession"]=$updatedvalue;
/*session updated*/
?>
Deleting Session
==========================
<?php 
session_start();
/*session is started if you don't write this line can't use $_Session  global variable*/
$_SESSION["newsession"]=$value;
unset($_SESSION["newsession"]);
/*session deleted. if you try using this you've got an error*/
?>

Be carefull with $_SESSION array elements when you have the same name as a normal global.The following example leads to unpredictable behaviour of the $wppa array elements, some are updated by normal code, some not, it is totally unpredictable what happens.<?phpglobal $wppa;$wppa = array( 'elm1' => 'value1', 'elm2' => 'value2', ....etc...);if ( ! session_id() ) @ session_start();if ( ! isset($_SESSION['wppa']) $_SESSION['wppa'] = array();if ( ! isset($_SESSION['wppa']['album']) ) $_SESSION['wppa']['album'] = array();$_SESSION['wppa']['album'][1234] = 1;$wppa['elm1'] = 'newvalue1';print_r($_SESSION); ?>This will most likely display Array ( [wppa] => Array ( [album] => Array ( [1234] => 1 ) [elm1] => 'newvalue1' [elm2] => 'value2' ... etc ...But setting $wppa['elm1'] to another value or referring to it gives unpredictable results, maybe 'value1', or 'newvalue1'. The most strange behaviour is that not all elements of $wppa[xx] show up as $_SESSION['wppa'][xx].

Please note that if you have register_globals to On, global variables associated to $_SESSION variables are references, so this may lead to some weird situations.<?phpsession_start();$_SESSION['test'] = 42;$test = 43;echo $_SESSION['test'];?>Load the page, OK it displays 42, reload the page... it displays 43.The solution is to do this after each time you do a session_start() :<?phpif (ini_get('register_globals')){    foreach ($_SESSION as $key=>$value)    {        if (isset($GLOBALS[$key]))            unset($GLOBALS[$key]);    }}?>