Note:
As of PHP 4.1.0, $_SESSION is available as a
global variable just like $_POST,
$_GET, $_REQUEST and so on.
Unlike $HTTP_SESSION_VARS,
$_SESSION is always global. Therefore, you do not
need to use the global
keyword for $_SESSION. Please note that this
documentation has been changed to use
$_SESSION everywhere. You can substitute
$HTTP_SESSION_VARS for
$_SESSION, if you prefer the former. Also note
that you must start your session using session_start()
before use of $_SESSION becomes available.
The keys in the $_SESSION associative
array are subject to the
same limitations as regular variable names in PHP, i.e. they cannot
start with a number and must start with a letter or underscore.
For more details see the section on
variables in this manual.
If register_globals
is disabled, only members of the global associative array
$_SESSION can be registered as session
variables. The restored session variables will only be available
in the array $_SESSION.
Use of $_SESSION (or
$HTTP_SESSION_VARS with PHP 4.0.6 or less) is
recommended for improved security and code readability. With
$_SESSION, there is no need to use the
session_register(),
session_unregister(),
session_is_registered() functions. Session variables
are accessible like any other variables.
Example #1
Registering a variable with $_SESSION.
<?php
session_start();
// Use $HTTP_SESSION_VARS with PHP 4.0.6 or less
if (!isset($_SESSION['count'])) {
$_SESSION['count'] = 0;
} else {
$_SESSION['count']++;
}
?>
Example #2
Unregistering a variable with $_SESSION and
register_globals disabled.
<?php
session_start();
// Use $HTTP_SESSION_VARS with PHP 4.0.6 or less
unset($_SESSION['count']);
?>
Caution
Do NOT unset the whole $_SESSION with
unset($_SESSION) as this will disable the
registering of session variables through the
$_SESSION superglobal.
Warning
You can't use references in session variables as there is no feasible way
to restore a reference to another variable.
If register_globals
is enabled, then each global variable can be registered as session
variable. Upon a restart of a session, these variables will be restored
to corresponding global variables. Since PHP must know which global
variables are registered as session variables, users need to register
variables with session_register() function.
You can avoid this by simply setting entries in
$_SESSION.
If register_globals
is enabled, then the global variables and the
$_SESSION entries will automatically reference the
same values which were registered in the prior session instance.
However, if the variable is registered by $_SESSION
then the global variable is available since the next request.
There is a defect in PHP 4.2.3 and earlier. If you register a new
session variable by using session_register(), the
entry in the global scope and the $_SESSION entry will
not reference the same value until the next
session_start(). I.e. a modification to the newly
registered global variable will not be reflected by the
$_SESSION entry. This has been corrected in PHP 4.3.0.
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