PHP
Starting a session with session_start()
Learn to start a session with session_start() and the session cookie.
What does session_start() do?
HTTP is stateless: each request is independent of the previous one. PHP overcomes this with session_start().
When you call it, PHP sends a session cookie to the browser and opens a separate data area on the server for each user. This area lives in the $_SESSION superglobal.
The cookie carries a unique session id; PHP uses it to find the right data. Call it once at the top of the page, before any output.
The session id and cookie
Every session has a unique identifier: the session id. PHP reads or sets it with session_id(). On the first session_start() call, the id is generated automatically.
The browser stores this id in a cookie named PHPSESSID (default). On later requests the browser sends the cookie back; PHP reads the id and loads the matching $_SESSION data.
You can rename the cookie in php.ini with session.name. The session lives until the cookie expires.
Exercise Print the session status with session_start
Call session_start(). Then, with an if, print active when session_status() equals PHP_SESSION_ACTIVE.
Show example solution
Call session_start, compare session_status() === PHP_SESSION_ACTIVE in an if, and echo "active".
Example solution:
<?php
// Call session_start and print that the session is active
session_start();
if (session_status() === PHP_SESSION_ACTIVE) {
echo "active\n";
}
Test yourself
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When should session_start() be called?
- At the very end, after all output
- Before any output, at the top of the page
- Only after a database connection
- On the same line as echo
Show answer
Before any output, at the top of the page — Correct. session_start() must be called before output, or you get 'headers already sent'.
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Start the session
<?php
____
$_SESSION = ['counter' => 1];
echo $_SESSION['counter'];
Show answer
<?php
session_start();
$_SESSION = ['counter' => 1];
echo $_SESSION['counter'];
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Match the session concepts
- session_start()
- Starts the session
- $_SESSION
- Holds session data
- session_id()
- Returns the session id
- session_destroy()
- Destroys the session
Next lesson: Storing data with $_SESSION
