Cookies

Storing data at client machine.The expires time is in seconds.

Setting a session cookie
<?php
setcookie('Cookie_name','value','expire_time');
// If expire_time set to 0, or omitted, the cookie will expire at the end of the session (when the browser closes).
?>

Setting a persistant cookie
<?php
setcookie('Cookie_name','value',mktime.time()+60*60); // Expires after 60 min.
?>

Reading a cookie
<?php
echo $_COOKIE['Cookie_name'];
?>

Deleting the Cookies
<?php
setcookie('Cookie_name','',mktime.time()-60); // Set expire time to negative time deletes a cookie.
?>

Other Optional Parameters
Path, Domain, and Secure parameters can also be set to restrict a cookie to a certain path, domain or
in the case of the Secure parameter, limit the cookie to only be set if the request came in over an SSL
connection.

Common Problem : Short expiry cookies depend on users having their system clocks set correctly.
Solution : Don't depend on the users having their clocks set right. Embed the timeout based on your server's
clock in the cookie.
Example:
At the cookie setting script :
<?php
$variable = 'Data to be stored in cookie'; // Data to be store
$value = time()+60 .':'.$varaible; // Concatenate the current(server) time + Data to be store
setcookie('Cookie_name',$value);
?>
At the receiving (getting cookie)script :
<?php
$value = $_COOKIE['Cookie_name']; // Getting the whole string stored in cookie
$valueArray = explode(':',$value);

if($valueArray[0]<=time()){ // Is valid cookie
    $variable = $valueArray[1];
}else{ // Expired cookie
    setcookie('Cookie_name','',mktime.time()-60); // deleting the cookie
}
?>