Significance of cookies

HTTP is stateless, so cookies give websites a memory. They enable:

• Session management: login state, shopping carts.
• Personalisation: language, theme, preferences.
• Tracking and analytics: counting visits, behaviour, advertising.
• Convenience: "remember me" and auto-filled details.

Creating a cookie in PHP

Syntax: setcookie(name, value, expire, path, domain, secure, httponly);

It must be called before any output (before <html>), because cookies travel in HTTP headers.

<?php
// Create: valid for 1 hour
setcookie("user", "Raiyan", time() + 3600, "/");
?>
<html><body>
<?php
if (isset($_COOKIE["user"])) {
    echo "Hello, " . $_COOKIE["user"];   // available from the next request
} else {
    echo "Cookie not set yet.";
}
?>
</body></html>

Destroying a cookie in PHP

There is no delete function. Set the same cookie with an expiry time in the past (same name, path, and domain):

<?php
setcookie("user", "", time() - 3600, "/");
unset($_COOKIE["user"]);   // also remove it from the current request
?>

The browser sees the cookie has expired and removes it.