Session in PHP

The main difference between sessions and cookies is that a session can hold multiple variables, and you need not have to set cookies for every variable. By default, the session data is stored in the cookie wich has an expiry date of zero, which means that the session remains active only as long as the browser.Once you close the browser, all the stored information is lost. This behavior can be modified by changing the “session. cookie_lifetime” setting in “php.ini” from zero to whatever you want the cookie lifetime to be.

Before starting to work with sessions, you must explicitly start a session using “session_start()” function. If you want sessions to start themselfs automatically, you should enable the “session.auto_start” setting in PHP’s configuration file.

After starting a session, you can access to the session ID via the “session_id()” function. After completing the work, you can destroy the session using “session_destroy()”.

the main objective of the session is to hold the values of variables. You must register session variables using the “session_register()” function, before trying to read them on a session-enabled page. Remember that a “session_register()” requires you to pass as an argument "variable name", and not the variable itself:

you can test if a variable is assigned using the “isset()” function.

To remove the registered variables, you need to use the session_unset() function. This function when called destroys all variables associated with a session, both in the the script and within session file .