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Unit 9: Web Techniques
The page created by above example contains a link to another page, shown in below given Notes
example, that uses the colour preferences by accessing the $_COOKIE array.
Using the colour preferences with cookies
<html>
<head>
<title>Front Door</title>
</head>
<?
php $bg = $_COOKIE[‘bg’];
$fg = $_COOKIE[‘fg’];
?>
<body bgcolor=”<?= $bg ?>” text=”<?= $fg ?>”>
<h1>Welcome to the Store</h1>
We have many fine products for you to view. Please feel free to browse the aisles and stop
an assistant at any time. But remember, you break it you bought it!<p> would you like to <a
href=”prefs.html”>change your preferences?</a> </body> </html>
There are plenty of caveats about the use of cookies. Not all clients support or accept cookies,
and even if the client does support cookies, the user may have turned them off. Furthermore,
the cookie specification says that no cookie can exceed 4 KB in size, only 20 cookies are allowed
per domain, and a total of 300 cookies can be stored on the client side. Some browsers may have
higher limits, but you cannot rely on that. Finally, you have no control over when browsers
actually expire cookies—if they are at capacity and need to add a new cookie, they may discard
a cookie that has not yet expired. You should also be careful of setting cookies to expire quickly.
Expiration times rely on the client’s clock being as accurate as yours. Many people do not have
their system clocks set accurately, so you cannot rely on rapid expirations.
Despite these limitations, cookies are very useful for retaining information through repeated
visits by a browser.
Do not use whitespace or semicolons in a cookie name otherwise it will be
invalid.
Develop a PHP program to set the preferences with cookies.
9.6.2 Sessions
PHP has built-in support for sessions, handling all the cookie manipulation for you to provide
persistent variables that are accessible from different pages and across multiple visits to the
site. Sessions allow you to easily create multipage forms (such as shopping carts), save user
authentication information from page to page, and store persistent user preferences on a site.
Each first-time visitor is issued a unique session ID. By default, the session ID is stored in a
cookie called PHPSESSID.
Every session has a data store associated with it. You can register variables to be loaded from
the data store when each page starts and saved back to the data store when the page ends.
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