Learning MySQL

The PHP Predefined Superglobal Variables

Superglobal variables are automatically created and initialized by the PHP engine, and are accessible throughout the script. We’ve already seen the $_GET and $_POST associative arrays that contain data passed to the script from a form using the GET or POST method, respectively.

The array $_SESSION contains data related to a user’s interaction with a web application within a single session; we describe sessions and this variable in Sessions,” later in this chapter.

The $_COOKIE array contains cookie data provided by the user’s browser. Cookies are strings that are passed back and forth between the web server and browser to maintain a unique key. They are useful for storing information on a user on the user’s computer; you can use the PHP set_cookie() function to send a cookie to the user’s browser. Each subsequent time the user visits your site, his browser automatically provides the cookie data. Cookies can be set to expire once the user closes their browser, at a later date, or never. A good use for cookies is to remember what news articles users have read and to show them new articles that they haven’t read yet. Note that cookies should never be used to store confidential information, as they are not secure. In addition, they shouldn’t be used to store information critical to your application, since users can move among computers, or modify or delete cookies at any time. Cookies have been widely abused by companies trying to track user web ...