PHP Sessions
A session is a way to store information (in variables) to be used across multiple pages.
Unlike a cookie, the information is not stored on the users computer.
What is a PHP Session?
When you work with an application, you open it, do some changes, and then you close it. This is much like a Session. The computer knows who you are. It knows when you start the application and when you end. But on the internet there is one problem: the web server does not know who you are or what you do, because the HTTP address doesn’t maintain state.
Session variables solve this problem by storing user information to be used across multiple pages (e.g. username, favorite color, etc). By default, session variables last until the user closes the browser.
So; Session variables hold information about one single user, and are available to all pages in one application.
Tip: If you need a permanent storage, you may want to store the data in a database.
Start a PHP Session
A session is started with the session_start() function.
Session variables are set with the PHP global variable: $_SESSION.
Now, let’s create a new page called «demo_session1.php». In this page, we start a new PHP session and set some session variables:
Example
// Set session variables
$_SESSION[«favcolor»] = «green»;
$_SESSION[«favanimal»] = «cat»;
echo «Session variables are set.»;
?>
Note: The session_start() function must be the very first thing in your document. Before any HTML tags.
Get PHP Session Variable Values
Next, we create another page called «demo_session2.php». From this page, we will access the session information we set on the first page («demo_session1.php»).
Notice that session variables are not passed individually to each new page, instead they are retrieved from the session we open at the beginning of each page ( session_start() ).
Also notice that all session variable values are stored in the global $_SESSION variable:
Example
// Echo session variables that were set on previous page
echo «Favorite color is » . $_SESSION[«favcolor»] . «.
«;
echo «Favorite animal is » . $_SESSION[«favanimal»] . «.»;
?>
Another way to show all the session variable values for a user session is to run the following code:
Example
How does it work? How does it know it’s me?
Most sessions set a user-key on the user’s computer that looks something like this: 765487cf34ert8dede5a562e4f3a7e12. Then, when a session is opened on another page, it scans the computer for a user-key. If there is a match, it accesses that session, if not, it starts a new session.
Modify a PHP Session Variable
To change a session variable, just overwrite it:
Example
// to change a session variable, just overwrite it
$_SESSION[«favcolor»] = «yellow»;
print_r($_SESSION);
?>
Destroy a PHP Session
To remove all global session variables and destroy the session, use session_unset() and session_destroy() :
Example
// remove all session variables
session_unset();
// destroy the session
session_destroy();
?>
$_SESSION
An associative array containing session variables available to the current script. See the Session functions documentation for more information on how this is used.
Notes
Note:
This is a ‘superglobal’, or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods.
See Also
User Contributed Notes 8 notes
Creating New Session
==========================
session_start ();
/*session is started if you don’t write this line can’t use $_Session global variable*/
$_SESSION [ «newsession» ]= $value ;
?>
Getting Session
==========================
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
==========================
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
==========================
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.
global $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 ;
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.
$_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() :
if ( ini_get ( ‘register_globals’ ))
foreach ( $_SESSION as $key => $value )
if (isset( $GLOBALS [ $key ]))
unset( $GLOBALS [ $key ]);
>
>
Regarding array keys, from http://php.net/manual/en/language.types.array.php, «Strings containing valid integers will be cast to the integer type».
The manual on $_SESSION says «An associative array». So an associative array is expected literally. It does no one any good if this bit of important info about accessing and storing session data remains buried in manual comments.
Session variables with a single number will not work, however «1a» will work, as will «a1» and even a just single letter, for example «a» will also work.
session_start ();
$_SESSION [ «1» ] = «LOGGED» ;
?>
2nd page
session_start ();
$_SESSION [ «a» ] = «LOGGED» ;
?>
2nd page
session_start ();
$_SESSION [ «a1» ] = «LOGGED» ;
?>
2nd page
Example from PHP.net manual on Session variables
$_SESSION [ 1 ][ 1 ] = ‘cake’ ; // fails