Session and Cookies

This covers the working of session and cookies

1. Unit 8 Remembering Users with Cookies and Sessions

2. Cookie O ften used to identify a user I s a small file that the server embeds on the user's computer Each time the same computer requests a page with a browser, it will send the cookie too With PHP, we can both create and retrieve cookie values

3. Starting a page with setcookie ( )

4. Setting cookie expiration

5. Session Session variables store user information to be used across multiple pages (e.g. username, favorite color, etc ) By default, session variables last until the user closes the browser Session variables hold information about one single user, and are available to all pages in one application

6. Activating Sessions U se a cookie called PHPSESSID When we start a session on a page, the PHP interpreter checks for the presence of this cookie and sets it if it doesn't exist. V alue of the PHPSESSID cookie is a random alphanumeric string. Each web client gets a different session ID The session ID in the PHPSESSID cookie identifies that web client uniquely to the server. That lets the interpreter maintain separate piles of data for each web client.

7. Client and server communication when starting a session

8. Counting page accesses with a session

9. Saving form data in a session

10. Printing session data

11. Log in form

12. Logging out

13. Why setcookie ( ) and session_start ( ) Want to Be at the Top of the Page? B efore HTML is sent there is a section of the response that contains headers These don't get displayed on screen but are commands or information from the server for the web client such as " this page was generated at such-and-such a time ,“ "please don't cache this page ,“ "please remember that the cookie named userid has the value ralph ."

14. All of the headers in the response from the web server to the web client have to be at the beginning of the response,(body), which is the HTML that controls what the browser actually displays. Once some of the body is sent— even one line—no more headers can be sent. Functions such as setcookie ( ) and session_start ( ) add headers to the response

15. In order for the added headers to be sent properly, they must be added before any output starts That's why they must be called before any print statements or any HTML