Difference Between Sessions and Cookies in PHP: Learn How to Use Them

Both sessions and cookies are essential components of PHP that help manage and preserve user data across various web pages.

They are fundamental tools for preserving user state, ensuring seamless navigation, and enabling functionalities such as user authentication, shopping carts, and personalized experiences.

Sessions and cookies both store data, but they operate differently, each with special features, applications, and implementation strategies.

Let us examine the key distinctions between PHP sessions and cookies and how to use each in your projects.

What Are Cookies in PHP?

Cookies are small pieces of data stored directly in the user’s browser.

Cookies are created by the server and sent to the user’s browser during an HTTP response.

Then the browser will store these cookies and send them back to the server with subsequent requests, allowing the server to identify users and maintain their state across multiple visits or pages.

Characteristics of Cookies

• Client-Side Storage: Cookies are kept on the client’s device, which is the browser, where the user can view and change them.
• Size Limit: Typically, cookies can store up to 4KB of data, which makes them ideal for small amounts of information like user preferences, session identifiers, or tokens.
• Expiration Date: Cookies can have an expiration time, meaning they can persist across browser sessions, even after the browser is closed and reopened, or be set to expire at the end of the session.
• Security Concerns: Because cookies are stored on the client-side, they are more vulnerable to manipulation, theft, or tampering, especially in cases of cross-site scripting (XSS) attacks.

How to Set Cookies in PHP

Setting a cookie in PHP is straightforward using the setcookie() function. This function should be called before any HTML output.

// Syntax for setting a cookie
setcookie(name, value, expire, path, domain, secure, httponly);

Here’s a practical example of setting a cookie in PHP:

// Setting a cookie that expires in one day
setcookie("username", "JohnDoe", time() + (86400 * 1), "/"); // 86400 = 1 day

In this example:

• "username" is the name of the cookie.
• "JohnDoe" is the value assigned to the cookie.
• time() + (86400 * 1) defines the expiration time (one day).
• "/" specifies the path for which the cookie is available (“/” makes it available across the entire domain).

Retrieving Cookies in PHP

To retrieve the value of a cookie, use the $_COOKIE superglobal array:

if(isset($_COOKIE["username"])) {
    echo "Welcome, " . $_COOKIE["username"];
} else {
    echo "Cookie not found.";
}

Deleting Cookies

To delete a cookie, set the expiration time to a past date:

setcookie("username", "", time() - 3600, "/");

This will remove the "username" cookie by forcing it to expire immediately.

What Are Sessions in PHP?

Sessions, on the other hand, are stored on the server and offer a more secure way to maintain user data across different pages.

When a session is started, PHP creates a unique session ID for each user and stores it on the server, while the session ID is sent to the user’s browser as a cookie or passed via URL.

Key Characteristics of Sessions:

• Server-Side Storage: Unlike cookies, session data is stored on the server, making it more secure and inaccessible to the user.
• Larger Data Capacity: Since the data is stored on the server, there is no practical limit to the amount of information you can store in a session.
• Temporary: Sessions typically last only as long as the browser is open. Once the browser is closed or the user logs out, the session is destroyed unless otherwise configured.
• More Secure: Because the actual data is stored on the server, sessions offer better security than cookies. However, session hijacking (when a malicious user gains access to a valid session) remains a concern, which is why additional security measures such as session regeneration and HTTPS should be employed.

How to Start a Session in PHP

Starting a session in PHP is simple and can be done using the session_start() function.

This function must be called at the beginning of the script, before any HTML output.

// Starting a session
session_start();

Storing Data in a Session

Once a session is started, you can store and retrieve data using the $_SESSION superglobal array:

// Storing session data
$_SESSION["username"] = "JohnDoe";
$_SESSION["user_id"] = 101;

Retrieving Session Data

// Accessing session data
session_start();
if(isset($_SESSION["username"])) {
    echo "Welcome, " . $_SESSION["username"];
}

Ending a Session

To end a session, you can use the session_destroy() function, which removes all session data stored on the server. Make sure to also unset the session variables.

// Ending a session
session_start();
session_unset(); // Unset all session variables
session_destroy(); // Destroy the session

Cookies vs Sessions: Key Differences

While both cookies and sessions are used to store user-related data, they differ greatly in terms of their use cases, security implications, and the manner and location in which the data is stored.

Here is a list of the main distinctions:

When to Use Cookies in PHP

Cookies are most suitable when:

• Small amounts of information must be stored, such as user preferences and pages that have been visited recently.
• You want the information to stay in place for several sessions (for example, remember me functionality).
• The data is not sensitive, and security is not a primary concern.

For example, it is common practice to use cookies to store a user’s preferred theme on a website.

Even if the user closes the browser and revisits the site later, the theme preference can be retained.

When to Use Sessions in PHP

Sessions should be used when:

• You need to store larger amounts of data (e.g., shopping cart information, user login credentials).
• Security is a concern, and you don’t want the user to access or modify the data.
• Once the user logs out or exits the browser, the data should be deleted because it is only temporary.

Because sensitive data, like user IDs and login status, should not be exposed in cookies, user authentication systems, for instance, typically rely on sessions.

Conclusion

The differences in data storage, security, and usage dictate when and how to use sessions and cookies, two essential PHP tools for preserving user state.

Cookies provide a lightweight solution for storing small, non-sensitive data that needs to persist across sessions, while sessions offer a secure, server-side alternative for handling sensitive or temporary information.

By understanding the distinctions and proper use cases for each, it will help you enhance the functionality and security of your PHP applications.