A Comprehensive Guide to PHP Superglobals: Understanding Cookies

PHP superglobals are built-in variables that are always accessible, regardless of scope. One of these superglobals is $_COOKIE, which is used to handle cookies in PHP.

What are Cookies?

• Definition: Cookies are small pieces of data stored on the user's computer by the web browser while browsing a website.
• Purpose: They are used to remember information about the user, such as login credentials or preferences.

The $_COOKIE Superglobal

• Definition: $_COOKIE is an associative array in PHP that contains all cookies sent by the client to the server.
• Accessing Cookies: You can access cookie values using their names as keys in the $_COOKIE array.

Setting Cookies

To set a cookie in PHP, you use the setcookie() function:

setcookie("username", "JohnDoe", time() + (86400 * 30), "/"); // 86400 = 1 day

• Parameters:
  • Name: The name of the cookie ("username" in this example).
  • Value: The value of the cookie ("JohnDoe").
  • Expiration: The time until the cookie expires (in this case, 30 days from now).
  • Path: The path on the server where the cookie will be available ("/" means it is available across the entire domain).

Retrieving Cookies

To retrieve a cookie, simply access it through the $_COOKIE superglobal:

if (isset($_COOKIE["username"])) {
    echo "Username is: " . $_COOKIE["username"];  
} else {
    echo "Username cookie is not set.";
}

• Checking Existence: Always check if a cookie is set using isset() to avoid errors.

Deleting Cookies

To delete a cookie, you can set its expiration date to a past time:

setcookie("username", "", time() - 3600, "/"); // Deletes the cookie

Key Concepts to Remember

• Cookies are stored on the client's machine and sent to the server with every request.
• The $_COOKIE array is used to access cookie values.
• Always check if a cookie exists before accessing it.
• Cookies can be set to expire after a certain period or can be deleted by setting a past expiration date.

By understanding how to use cookies in PHP through the $_COOKIE superglobal, you can enhance user experience by remembering user preferences and maintaining session states.