Session in PHP

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Session lets you store data of individual for accessing across multiple pages until the broswer is terminated i.e the data is stored for that period of access only. The session stores data for that access only and so very useful for tracking activity of user. Keep in mind that if we are accessing from two different browsers, both will have their own session data.

In PHP we need to manually start session before we can use session variables. This is done using session_start(). This function looks for the session id and if there is none it creates a new session id.
Session ID
Session ID is a unique string that is assigned to each session which lets PHP engine distinguish between different session and serve content/data of that session only. You can get session by using session_id() function.

$_SESSION is an array of all the session variables present. If you create an index in this array and assign any value to it, It will be automatically available in the session. You can use that at any page during that session and can be used in any scope i.e. it is superglobal.

// starting session
echo session_id()."<br>";
// Creating new index in session array
$_SESSION['user'] = "user1";
function abc(){
    // calling session array elememt inside of a function
    echo $_SESSION['user'];



session_start() will look for a session Id and it won't get one because this is the first time we have called session_start() So it will create a new Session ID.
The session Id will be different in your case. You can get $_SESSION['user'] in any other page and you will get this same value, you can try that by creating two pages and assigning value to a session array element in one page and then accessing that in another page.
But remember, before using $_SESSION you must call session_start() at every page you are using it. Here we demonstrated that we can use $_SESSION in any scope by using it inside of a function.
Try making a second page similar to this to test it.

// starting session
// accesing value of a variable defined on another page
echo $_SESSION['user'];



session_start() will look for a Session ID and it will get one this time as we have already started session in previous page.
In this page we are trying to access a variable we didn't create on this page. This should give an error in case of a normal variable but Session Array lets you access data you defined on some other page as well. So this should give output we assigned it on the first page.
You can also get Session ID on this page using function session_id() and you will get the same session Id you got on the first page provided you haven't terminated broswer in between or destroyed the session.

You can destroy a session using function session_destroy().

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