How to set and get session variables in PHP?
Jul 12, 2025 am 03:10 AM
To set and get session variables in PHP, you must first always call session_start() at the top of the script to start the session. 1. When setting session variables, use the $_SESSION hyperglobal array to assign values ??to specific keys, such as $_SESSION['username'] = 'john_doe'; It can store strings, numbers, arrays and even objects, but avoid storing too much data to avoid affecting performance. 2. When obtaining session variables, you need to call session_start() first, and then access the $_SESSION array through the key, such as echo $_SESSION['username']; It is recommended to use isset() to check whether the variable exists to avoid errors. 3. Notes include: make sure session_start() is called before any output; make sure the client enables cookies; session_start() is still required before redirection; and do not manually serialize or modify session data unless the purpose of the operation is clearly known. Follow these steps to use the PHP session functionality correctly.
Setting and getting session variables in PHP is straightforward once you understand the basics of how sessions work. The key points are: always start the session with session_start() , use the $_SESSION superglobal to set or retrieve data, and remember that sessions persist across multiple pages as long as they're properly initialized.
Starting the Session
Before you can set or get any session variables, you need to start the session using session_start() . This must be called before any output is sent to the browser — even a blank space or newline will cause it to fail.
-
Do this:
<?php session_start();
Don't do this:
<?php echo "Hello"; session_start(); // This will throw an error
Also, make sure you call session_start() on every page where you want to access session data.
Setting Session Variables
Once the session is started, setting a session variable is as simple as assigning a value to an index in the $_SESSION array.
For example:
<?php session_start(); $_SESSION['username'] = 'john_doe';
You can store all kinds of data — strings, numbers, arrays, even objects (though that's more advanced). Just keep in mind that storing large amounts of data in sessions can affect performance or scalability.
Here's another example:
$_SESSION['user_preferences'] = [
'theme' => 'dark',
'notifications' => true
];Getting Session Variables
To retrieve a session variable, just access the corresponding key from the $_SESSION array after starting the session.
Like this:
<?php session_start(); echo 'Welcome back, ' . $_SESSION['username'];
It's a good idea to check if a session variable exists before trying to use it, especially if it might not have been set yet:
if (isset($_SESSION['username'])) {
echo 'Welcome back, ' . $_SESSION['username'];
} else {
echo 'You are not logged in.';
}A Few Common Gotchas
- Make sure
session_start()is at the very top of your script — no output before it. - Sessions rely on cookies by default, so make sure the client allows cookies.
- If you're redirecting after setting session data, remember that
session_start()still needs to be called before the redirect happens. - Don't serialize or manually manipulate session data unless you know what you're doing — PHP handles it internally.
That's basically it. Sessions are a powerful way to maintain user state across requests, and using them correctly make building things like login systems much easier.
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