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A PHP session variable is used to store information about, or change settings for a user session. Session variables hold information about one single user, and are available to all pages in one application.A session creates a file in a temporary directory on the server where registered session variables and their values are stored. This data will be available to all pages on the site during that visit.
A session ends when the user loses the browser or after leaving the site, the server will terminate the session after a predetermined period of time, commonly 30 minutes duration.
Starting a PHP Session:
A PHP session is easily started by making a call to the session_start() function.This function first checks if a session is already started and if none is started then it starts one. It is recommended to put the call to session_start() at the beginning of the page.
Session variables are stored in associative array called $_SESSION[]. These variables can be accessed during lifetime of a session.
The following example starts a session then register a variable called counter that is incremented each time the page is visited during the session.
Make use of isset() function to check if session variable is already set or not.
Put this code in a test.php file and load this file many times to see the result:
<?php
session_start();
if( isset( $_SESSION['counter'] ) )
{
$_SESSION['counter'] += 1;
}
else
{
$_SESSION['counter'] = 1;
}
$msg = “You have visited this page “. $_SESSION['counter'];
$msg .= “in this session.”;
?>
<html>
<head>
<title>Setting up a PHP session</title>
</head>
<body>
<?php echo ( $msg ); ?>
</body>
</html>
Destroying a PHP Session:
A PHP session can be destroyed by session_destroy() function. This function does not need any argument and a single call can destroy all the session variables. If you want to destroy a single session variable then you can use unset() function to unset a session variable.
Here is the example to unset a single variable:
<?php
unset($_SESSION['counter']);
?>
Here is the call which will destroy all the session variables:
<?php
session_destroy();
?>
Turning on Auto Session:
You don’t need to call start_session() function to start a session when a user visits your site if you can set session.auto_start variable to 1 in php.ini file.
Sessions without cookies:
There may be a case when a user does not allow to store cookies on their machine. So there is another method to send session ID to the browser.
Alternatively, you can use the constant SID which is defined if the session started. If the client did not send an appropriate session cookie, it has the form session_name=session_id. Otherwise, it expands to an empty string. Thus, you can embed it unconditionally into URLs.
The following example demonstrates how to register a variable, and how to link correctly to another page using SID.
<?php
session_start();
if (isset($_SESSION['counter'])) {
$_SESSION['counter'] = 1;
} else {
$_SESSION['counter']++;
}
?>
$msg = “You have visited this page “. $_SESSION['counter'];
$msg .= “in this session.”;
echo ( $msg );
<p>
To continue click following link <br />
<a href=”nextpage.php?<?php echo htmlspecialchars(SID); >”>
</p>
The htmlspecialchars() may be used when printing the SID in order to prevent XSS related attacks.
A session ends when the user loses the browser or after leaving the site, the server will terminate the session after a predetermined period of time, commonly 30 minutes duration.
Starting a PHP Session:
A PHP session is easily started by making a call to the session_start() function.This function first checks if a session is already started and if none is started then it starts one. It is recommended to put the call to session_start() at the beginning of the page.
Session variables are stored in associative array called $_SESSION[]. These variables can be accessed during lifetime of a session.
The following example starts a session then register a variable called counter that is incremented each time the page is visited during the session.
Make use of isset() function to check if session variable is already set or not.
Put this code in a test.php file and load this file many times to see the result:
<?php
session_start();
if( isset( $_SESSION['counter'] ) )
{
$_SESSION['counter'] += 1;
}
else
{
$_SESSION['counter'] = 1;
}
$msg = “You have visited this page “. $_SESSION['counter'];
$msg .= “in this session.”;
?>
<html>
<head>
<title>Setting up a PHP session</title>
</head>
<body>
<?php echo ( $msg ); ?>
</body>
</html>
Destroying a PHP Session:
A PHP session can be destroyed by session_destroy() function. This function does not need any argument and a single call can destroy all the session variables. If you want to destroy a single session variable then you can use unset() function to unset a session variable.
Here is the example to unset a single variable:
<?php
unset($_SESSION['counter']);
?>
Here is the call which will destroy all the session variables:
<?php
session_destroy();
?>
Turning on Auto Session:
You don’t need to call start_session() function to start a session when a user visits your site if you can set session.auto_start variable to 1 in php.ini file.
Sessions without cookies:
There may be a case when a user does not allow to store cookies on their machine. So there is another method to send session ID to the browser.
Alternatively, you can use the constant SID which is defined if the session started. If the client did not send an appropriate session cookie, it has the form session_name=session_id. Otherwise, it expands to an empty string. Thus, you can embed it unconditionally into URLs.
The following example demonstrates how to register a variable, and how to link correctly to another page using SID.
<?php
session_start();
if (isset($_SESSION['counter'])) {
$_SESSION['counter'] = 1;
} else {
$_SESSION['counter']++;
}
?>
$msg = “You have visited this page “. $_SESSION['counter'];
$msg .= “in this session.”;
echo ( $msg );
<p>
To continue click following link <br />
<a href=”nextpage.php?<?php echo htmlspecialchars(SID); >”>
</p>
The htmlspecialchars() may be used when printing the SID in order to prevent XSS related attacks.
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