php $_GET / $_POST / $_SESSION

• PHP uses predefined variables to provide access to
important information about the server and requests
from a browser.
• PHP provides a large number of predefined variables to
any script which it runs. PHP provides an additional set
of predefined arrays containing variables from the web
server the environment, and user input.
• We can access predefined variables in any scope - any if
block, any for block. It means every where in PHP block.
• There are many predefined variables provided by PHP
but this week you will learn just $_GET, $_POST,
$_SESSION because there are common things you need
to know.

HANDLING USER
INPUT WITH $_GET / $_POST

Before knowing $_GET and $_POST
You have to know ‘HTTP data sending method’ first.
• HTTP is how webpage runs. it is agreement between web
server and web browser. That is how server and browser
communicate to each other.
• HTTP sending method is about how much secure browser
send data to server. (data which comes from user input).
- GET method is less secure but easier.
With this method we can send data by submitting form or put
it directly in address bar but web user can see datas in
address bar.
( http://webserver/calculate.php?a=10&b=5 )
- POST method is better secure but more difficult.
With this method we can send data by only submitting form
and web user cannot see datas in address bar.
( http://webserver/calculate.php )

THE WAY OF $_GET
• We have 2 ways to send data from one php
page to another one php page (or itself).
– First is using form submission.
• Important to set method=“get”
– Second is specifying data as key-value pair directly
after URL.

• When datas are sent to destination page you
will see the URL in address bar
• In destination page you can use $_GET[‘key or
name of data’]; in PHP block to access datas
sent from source page.

THE WAY OF $_POST
• We have 1 way to send data from one php
page to another one php page (or itself).
– It is using form submission.
• Important to set method=“post”

• When datas are sent to destination page you
will see the URL in address bar
• In destination page you can use $_POST[‘key or
name of data’]; in PHP block to access datas
sent from source page.

STORING USER’S STATE OR
TEMPORARY INFO WITH
$_SESSION

Before knowing $_SESSION
• Session provides a way to identify a user across more than
one page request or visit to a Web site and to store
information about that user.
• Session is like transaction, at 7-11 cashier you buy 3 things -
Lays, Coke, Mama. Cashier staff calculates the price one by
one by scanning your things’ barcode. She does three times
then press ‘Enter’ to finish to process. The whole process just
now is 1 transaction.
• The same way when you go to facebook.com website. You
may first go to your profile first then you go to your friends’
profile, leave some comments. You found your friend of
friend looks nice, you go to his/ her profile and try to see
information, photos, marriage status. You may go 5-6 pages
already but that is 1 session.

• Session may start when you first come to web site at any
page or logged in success.
• After session started, web server can store your state
(your information, your input, your IP address, Item you
want to buy etc).
• Web server can destroy your session
- by program (such as when you click logout) or
- by timing which is when you are inactive (sleep in front
your
• computer or you did not go any page within the same
web site) within defined interval (such as 30 minutes).
We call this ‘Session timeout’.

Starting a session.
• Before you can begin storing user information
in your PHP session, you must first start the
session. When you start a session, it must be
at the very beginning of your code, before any
HTML or text is sent.
• Below is a simple script that you should place
at the beginning of your PHP code to start up
a PHP session.

<?php
session_start(); // start up your PHP session!
?>
<html>
.
.
.
</html>

Storing / Getting data.
• When you want to store user data in a session
use the $_SESSION associative array. This is
where you both store and retrieve session
data.

<?php
?>
<html>
<body>
<?php
$_SESSION[‘views’])=1; // store session data
print “view is =“.$_SESSION[‘views’]; // retrieve data
?>
</body>
</html>

Check if particular session data exists.
• isset() function comes in handy. isset is a
function that takes any variable you want to
use and checks to see if it has been set. That
is, it has already been assigned a value.
• With our previous example, we can create a
very simple pageview counter by using isset to
check if the pageview variable has already
been created. If it has we can increment our
counter. If it doesn't exist we can create a
pageview counter and set it to one. Here is
the code to get this job done:

<?php
?>
<html>
<body>
<?php
if(isset($_SESSION[‘views’]))
$_SESSION[‘views’])= $_SESSION[‘views’]+1;
else
$_SESSION[‘views’])=1;
print “view is =“.$_SESSION[‘views’];
?>
</body>
</html>

Destroying session
• You may remove some datas in someone’s
session such as session data named ‘cart’
when shopping cart is checked out.

<?php
?>
<html>
<body>
<?php
// Remove only session data name ‘cart’
if(isset($_SESSION[‘cart’])) unset($_SESSION[‘cart’]) ;
?>
</body>
</html>

• You can also destroy someone’s whole session
when he clicked log out button.

<?php
?>
<html>
…
</html>
<?php
session_destroy(); // destroy your PHP session!
?>

Setting up session timeout interval.
• If you want your session of visitor to be
destroy if your visitor are inactive (did not
open any page for a while) for an interval you
desire, you can easily set it as below:
• Note that number is second. So 1800 is 30
minutes.

<?php
ini_set(‘session.gc_maxlifetime’,’1800’);
?>
<html>
…
</html>

php $_GET / $_POST / $_SESSION

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