To access session data in PHP, you must first start the session and then operate through the $_SESSION hyperglobal array. 1. The session must be started with session_start(), and the function must be called before any output; 2. When accessing session data, check whether the key exists. You can use isset($_SESSION['key']) or array_key_exists('key', $_SESSION); 3. To set or update session variables, you only need to assign values ??to the $_SESSION array without manually saving; 4. To clear the available unset($_SESSION['key']) for specific data, you can set $_SESSION to an empty array. To completely end the session, you must call session_unset() and session_destroy(). At the same time, pay attention to manually deleting the client's session cookies to complete the cleaning.
In PHP, accessing session data is straightforward once the session has been started. The key is to use the $_SESSION superglobal array, which holds all session variables you've set.
Starting a Session
Before you can access or store any session data, you need to start the session using session_start() . This function must be called before any output is sent to the browser — even a blank line or space counts.
<?php session_start(); ?>
A common mistake is forgetting to call this at the top of every page where you want to access session data. Also, don't put anything (including HTML or echo statements) before the <?php tag if you're using session_start() there.
Accessing Stored Session Data
Once the session is started, you can access stored values ??just like you would with any associated array:
echo 'Welcome back, ' . $_SESSION['username'];
Make sure the key exists before trying to access it — otherwise, you might trigger a notice or warning.
Here's how to safely check for a session variable:
- Use
isset($_SESSION['key'])to see if it's been set - Or use
array_key_exists('key', $_SESSION)if you want to distinguish betweennulland not-set
If you're debugging or just want to see what's in the session, print_r($_SESSION); can help.
Setting and Updating Session Variables
You can add or update session data anytime after starting the session:
$_SESSION['user_id'] = 123; $_SESSION['logged_in'] = true;
These will persist across requests as long as the session is active. If you change a value later in the script, the session will hold the updated version.
One thing to note:
You don't have to "save" the session manually — PHP handles that automatically when the script ends.
Destroying or Clearing Session Data
To remove specific data, use unset() :
unset($_SESSION['user_id']);
To clear everything in the session:
$_SESSION = [];
And if you want to completely end the session (like during logoout), you should also call session_destroy() :
session_unset(); session_destroy();
Keep in mind that session_destroy() only removes the data on the server — you still need to unset the session cookie on the user's side for full cleanup.
Basically that's it.
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