To access cookie data in PHP, you need to use a $_COOKIE hyperglobal array that stores all cookies sent by the browser with the current request in key-value pairs. When reading, you should first use isset() to check whether it exists, such as $_COOKIE['user']; note that cookies are only available after page refresh, and their scope is affected by paths, domain names and security flags. Common errors include immediate access after setting, spelling errors, failure to check for existence, and mistakenly considering cookies to be safe and reliable. If multiple values ??need to be stored, you can use json_encode encoding to store and decode verification data when read.

To access cookie data in PHP, you use the $_COOKIE superglobal array. This array holds all the cookies sent by the browser with the current request. Each cookie is stored as a key-value pair, where the key is the cookie name and the value is its content.

How to Read a Cookie

Once a cookie has been set — either by your own code using setcookie() or by another script — you can access it using $_COOKIE['cookie_name'] .

For example:

 if (isset($_COOKIE['user'])) {
    echo 'Welcome back, ' . $_COOKIE['user'];
} else {
    echo 'New visitor';
}

A few things to note:

• Always check if a cookie exists using isset() before trying to access it.
• Cookie values ??are strings; if you need other types, you'll have to convert them manually.
• Cookies are only available after the page reloads — setting one doesn't make it appear in $_COOKIE immediately.

Understanding Cookie Scope

Cookies are not always available everywhere on your site. Their availability depends on how they were set:

• Path : A cookie set with setcookie('user', 'John', '/', ...) will be available throughout the entire domain.
• Domain : If you're working with subdomains, you might need to specify the domain like .example.com .
• Secure & HttpOnly flags : These don't affect $_COOKIE , but they do impact security and accessibility from JavaScript.

If a cookie isn't showing up in $_COOKIE , double-check the path and domain used when it was created.

Common Mistakes When Accessing Cookies

It's easy to run into issues if you're not careful. Here are some common pitfalls:

• ? Trying to access a cookie right after setting it — remember, it's only available on the next request.
• ? Using incorrect names or misspelling the cookie key.
• ? Not checking whether the cookie exists first with isset() or array_key_exists() .
• ? Assuming cookies are secure — they're client-side and can be manipulated.

Also, keep in mind that browsers may block third-party cookies depending on privacy settings, especially in cross-site contexts.

Handling Multiple Cookie Values

Sometimes, you may want to store more than a single value in a cookie. Since cookies can only hold strings, you'll need to serialize or structure the data yourself.

One approach is to store JSON-encoded data:

 // Setting multiple values
$data = ['user' => 'John', 'role' => 'editor'];
setcookie('userdata', json_encode($data), time() 3600, '/');

// Reading it back
if (isset($_COOKIE['userdata'])) {
    $userData = json_decode($_COOKIE['userdata'], true);
    echo 'User role: ' . $userData['role'];
}

Just remember to decode and validate the data each time you read it.

That's basically it for accessing cookies via $_COOKIE . It's straightforward once you understand how cookies are stored and retrieved. Just watch out for timing, scope, and data format — those are the most common gotchas.

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