PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Implementing Simple Sessions
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Registering Session Variables
The way you register session variables has recently changed in PHP. Session variables
have been stored in the superglobal array $_SESSION since PHP 4.1.To create a session
variable, you simply set an element in this array, as follows:
$_SESSION[‘myvar’] = 5;
The session variable you have just created will be tracked until the session ends or until
you manually unset it.The session may also naturally expire based on the
session.gc_maxlifetime setting in the php.ini file.This setting determines the
amount of time (in seconds) that a session will last before it is ended by the garbage collector.
Using Session Variables
To bring session variables into scope so that they can be used, you must first start a session
calling session_start().You can then access the variable via the $_SESSION superglobal
array—for example, as $_SESSION[‘myvar’].
When you are using an object as a session variable, it is important that you include
the class definition before calling session_start() to reload the session variables.This
way, PHP knows how to reconstruct the session object.
On the other hand, you need to be careful when checking whether session variables
have been set (via, say, isset() or empty()). Remember that variables can be set by the
user via GET or POST.You can check a variable to see whether it is a registered session
variable by checking in $_SESSION.
You can check this directly using the following, for example:
if (isset($_SESSION[‘myvar’])) ...
Unsetting Variables and Destroying the Session
When you are finished with a session variable, you can unset it.You can do this directly
by unsetting the appropriate element of the $_SESSION array, as in this example:
unset($_SESSION[‘myvar’]);
Note that the use of session_unregister() and session_unset() is no longer
required and is not recommended.These functions were used prior to the introduction
of $_SESSION.
You should not try to unset the whole $_SESSION array because doing so will effectively
disable sessions.To unset all the session variables at once, use
$_SESSION = array();
When you are finished with a session, you should first unset all the variables and
then call
session_destroy();
to clean up the session ID.