PHP
Storing data with $_SESSION
Learn to write data to the $_SESSION superglobal and carry it across pages.
The $_SESSION superglobal
$_SESSION is a superglobal array: it is accessible globally, even inside functions. After session_start() you write data as $_SESSION['key'] = value.
The data is saved to a session file on the server. On later requests with the same session id, PHP loads this file and $_SESSION is ready.
This lets you carry a username, cart contents or theme choice across pages.
Data persists across pages
The power of sessions is persistence. If you write $_SESSION['cart'] = 3 on page_a.php, you read the same value on page_b.php after calling session_start().
The reason: both pages share the same session id. The browser cookie sends the id on every request; PHP loads the right file.
The data survives until you close the session with session_destroy() or the cookie expires.
Exercise Write a user and role to $_SESSION
Call session_start(). Set $_SESSION['user'] to 'Alex' and $_SESSION['role'] to 'admin'. Then print both on separate lines with echo.
Show example solution
Call session_start, assign two keys, then echo $_SESSION['user'] and echo $_SESSION['role'].
Example solution:
<?php
// Write a username and role to $_SESSION, then print them
session_start();
$_SESSION['user'] = 'Alex';
$_SESSION['role'] = 'admin';
echo $_SESSION['user'] . "\n";
echo $_SESSION['role'] . "\n";
Test yourself
-
Which superglobal stores session data?
- $_SESSION
- $_POST
- $_GET
- $_COOKIE
Show answer
$_SESSION — Correct. The $_SESSION superglobal carries session data across pages.
-
Write a username to the session
<?php
session_start();
____
$_SESSION['cart'] = ['item' => 'book'];
echo $_SESSION['user'];
Show answer
<?php
session_start();
$_SESSION['user'] = 'Alex';
$_SESSION['cart'] = ['item' => 'book'];
echo $_SESSION['user'];
-
Match the write and read flow
- $_SESSION['x'] = 5
- Data is written on page A
- session_start()
- Called first on page B
- echo $_SESSION['x']
- Prints 5 on page B
- session_id()
- Returns the session id
Next lesson: Reading from a session
