PHP
Reading cookies with $_COOKIE
Learn to read cookies sent by the browser with the $_COOKIE superglobal.
The $_COOKIE superglobal
After a cookie is created with setcookie(), the browser stores it. On the next request the browser sends it back; PHP fills the $_COOKIE superglobal with this data.
Each cookie name becomes a key: $_COOKIE['lang']. You can also iterate it as an array.
Important: in the same request where setcookie() is called, the cookie is not yet in $_COOKIE; you wait for the browser to send it back.
Checking a cookie with isset
A cookie may be undefined: the browser may not have sent it yet, or may have deleted it. Reading $_COOKIE['theme'] directly raises a warning in PHP 8.
First check the key with isset($_COOKIE['theme']). If true, read safely; if false, use a default value.
Tip: $_COOKIE['theme'] ?? 'light' gives both the check and a default in one line.
Exercise Read a default theme from a missing cookie
With if/else, check isset($_COOKIE['theme']): if defined, assign $_COOKIE['theme'] to $theme; otherwise assign 'light'. Then echo $theme.
Show example solution
Use if(isset($_COOKIE['theme'])) to set $theme from the cookie, else 'light', then echo $theme.
Example solution:
<?php
// Print the default theme if $_COOKIE['theme'] is missing
if (isset($_COOKIE['theme'])) {
$theme = $_COOKIE['theme'];
} else {
$theme = 'light';
}
echo $theme . "\n";
Test yourself
-
When does a cookie appear in $_COOKIE?
- Immediately in the same request setcookie is called
- Only when session_start is called
- On the next request, when the browser sends the cookie back
- After the cookie is deleted
Show answer
On the next request, when the browser sends the cookie back — Correct. The cookie appears in $_COOKIE only on a later request when the browser sends it back.
-
Read the cookie value
<?php
$cfg = ['default' => 'light'];
____
echo $theme;
Show answer
<?php
$cfg = ['default' => 'light'];
$theme = $_COOKIE['theme'];
echo $theme;
-
Match the cookie reading tools
- $_COOKIE['k']
- Reads the cookie value
- isset()
- Checks the key
- ?? 'default'
- Gives default if undefined
- empty()
- Checks if empty
Next lesson: Cookie expiration
