PHP and XHTML Forms
Getting data from the user
Forms
●
●
●
If we can't get any data from the user, there's not
a lot of point in tailoring a page for that user
One of the main ways we get data from the user
is through forms
– The other main way is direct from the browser,
which sends strings identifying itself, language,
operating system etc
We studied XHTML forms when we looked at
JavaScript in CS15020
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XHTML Forms
●
If you recall, we had:
– <form action="">
–
http://users.aber.ac.uk/ais/examples/JavaScript/inputexample.html
Why? Because we weren't sending the result of
the form anywhere; we were handling it on the
client side with the JavaScript we wrote
● But now, we want to send the content of the form
elements back to a PHP script on the server
● The action is the name of the script
● And we need a <input type="submit" ...> which
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gives
to submit
the form too
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GET and POST
●
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There are two methods for sending the
data to a script
GET <form action="my.php" method="get">
POST <form
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action="my.php" method="post">
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GET
●
●
●
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Passes the data as part of the URL – you
will have noticed this before, in your
browser, I am sure
The HTTP request is just headers
There's a character limit – beware! And it's
browser dependent
ASCII only – no special characters allowed
–
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Problem if, say, user has a name or
address with
an accented character
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POST
●
Sends the data as name-value pairs, in the
body of the HTTP request
–
●
which is only seen by the server
Because the data is in the body,
–
–
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there is effectively no size limit,
it can contain any characters
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$_GET
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In PHP, there is a variable $_GET
Used to access the contents of a form
submitted with the GET method
●
http://users.aber.ac.uk/ais/examples/php/inputexample.html
●
●
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Almost the same as we did for JavaScript, but
without the JavaScript
The form is identical apart from the form's
action and method, and the final button (it is a
type=submit rather than a type=button and it
doesn't call a JavaScript function)
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$_GET – the PHP script
<p>Here is what you ordered:</p>
<ul>
<li><?php echo $_GET["drink"];?></li>
<?php
if (array_key_exists("sugar", $_GET))
echo "<li>" . $_GET["sugar"] . "</li>";
if (array_key_exists("cinnamon", $_GET))
echo "<li>" . $_GET["cinnamon"] . "</li>";
?>
<li><?php echo $_GET["creamormilk"];?></li>
</ul>
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When to use GET
●
Notice the URL bar when we use GET
✔
✗
It contains our variables – so we can bookmark it
But therefore it shouldn't be used for sensitive
information (passwords, bank details, etc)
And it has a character limit (browser
dependent, but to be safe, recommendation
is to keep within 256 – and ASCII only)
● If information is not sensitive, and character
limit is not a problem, then use GET
✗
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$_POST
●
●
●
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PHP has a variable $_POST, which
does much the same as $_GET, but for
data submitted using the POST method
We can re-write our last example, using
the post method instead of the get
method
All that changes is GET => POST in a
few places
http://users.aber.ac.uk/ais/examples/php/postexample.html
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$_POST – the PHP script
<p>Here is what you ordered:</p>
<ul>
<li><?php echo $_POST["drink"];?></li>
<?php
if (array_key_exists("sugar", $_POST))
echo "<li>" . $_POST["sugar"] . "</li>";
if (array_key_exists("cinnamon", $_POST))
echo "<li>" . $_POST["cinnamon"] . "</li>";
?>
<li><?php echo $_POST["creamormilk"];?></li>
</ul>
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When to use POST
●
Did you notice the URL?
✔
✗
It didn't contain any variables – so it's more
secure
But that means you can't bookmark it and
expect the same results another time
There is no (practical) limit to how much
data can be passed
● Use POST for sensitive data, or if the
amount of data is too large for GET
✔
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Just associative arrays
●
$_GET and $_POST are in effect no more
than associative arrays
–
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(arrays indexed by key, not by number)
So you can use all the usual array
functions on them
–
as I did in my example – using
array_key_exists("sugar", $_POST)
That makes it very easy to handle input
from forms in your script
● Use reference material when you need a
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function
like this (e.g.
use w3schools!)
●
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Suggestion
●
●
●
Grab my code (PHP in these slides,
XHTML from the web link) and try it for
yourself
Write your own examples, based on my
code
This stuff is crucial; please do make sure
you understand it
–
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Don't leave it – do it now!
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