How cookies work in PHP - Try It Yourself

How cookies work

📖 Scenario: You are building a simple website that remembers a visitor's name using cookies. When the visitor enters their name, the website saves it in a cookie so that next time they visit, the site greets them by name automatically.

🎯 Goal: Create a PHP script that sets a cookie with the visitor's name, reads the cookie on subsequent visits, and displays a greeting message using the stored name.

📋 What You'll Learn

Create a variable to hold the visitor's name

Set a cookie with the visitor's name that expires in 1 hour

Check if the cookie exists and read the visitor's name from it

Display a greeting message using the visitor's name from the cookie

💡 Why This Matters

🌍 Real World

Cookies are used by websites to remember users and their preferences, making visits more personal and convenient.

💼 Career

Understanding how cookies work is important for web developers to manage user sessions, preferences, and authentication.

1

Create a variable with the visitor's name

Create a variable called $visitorName and set it to the string 'Alice'.

PHP

<?php

// Create a variable called $visitorName and set it to 'Alice'
// Your code here

Hint

Use $visitorName = 'Alice'; to create the variable.

2

Set a cookie with the visitor's name

Use the setcookie function to set a cookie named 'user' with the value of $visitorName that expires in 3600 seconds (1 hour).

PHP

<?php

$visitorName = 'Alice';

// Set a cookie named 'user' with value $visitorName that expires in 1 hour
// Your code here

Hint

Use setcookie('user', $visitorName, time() + 3600); to set the cookie.

3

Check if the cookie exists and read its value

Use an if statement to check if the cookie named 'user' exists in $_COOKIE. If it exists, create a variable called $nameFromCookie and set it to the cookie's value.

PHP

<?php

$visitorName = 'Alice';

setcookie('user', $visitorName, time() + 3600);

// Check if cookie 'user' exists and assign its value to $nameFromCookie
// Your code here

Hint

Use if (isset($_COOKIE['user'])) { $nameFromCookie = $_COOKIE['user']; } to read the cookie.

4

Display a greeting message using the cookie value

Use echo to print the greeting message Hello, followed by the value of $nameFromCookie. If $nameFromCookie is not set, print Hello, guest instead.

PHP

<?php

$visitorName = 'Alice';

setcookie('user', $visitorName, time() + 3600);

if (isset($_COOKIE['user'])) {
    $nameFromCookie = $_COOKIE['user'];
}

// Print greeting message using $nameFromCookie or 'guest'
// Your code here

Hint

Use echo "Hello, $nameFromCookie"; if the cookie exists, otherwise echo "Hello, guest";.

Practice

1. What is the primary purpose of cookies in PHP?

easy

A. To execute server-side scripts

B. To style web pages dynamically

C. To create database connections

D. To store small pieces of data on the user's computer

Solution

1. Step 1: Understand what cookies do

   Cookies save small data on the user's computer to remember information like preferences or login status.

2. Step 2: Identify the correct purpose

   Among the options, only storing small data on the user's computer matches the purpose of cookies.

3. Final Answer:

   To store small pieces of data on the user's computer -> Option D

4. Quick Check:

   Cookies store data = B [OK]

Hint: Cookies save data on user device, not server tasks [OK]

Common Mistakes:

• Confusing cookies with server-side code execution
• Thinking cookies style web pages
• Assuming cookies manage database connections

2. Which of the following is the correct syntax to set a cookie named user with value John in PHP?

easy

A. setcookie('user', 'John');

B. cookie_set('user', 'John');

C. set_cookie('user', 'John');

D. setcookie(user, John);

Solution

1. Step 1: Recall the PHP function to set cookies

   The correct PHP function is setcookie() with parameters as strings.

2. Step 2: Check syntax correctness

   setcookie('user', 'John'); uses correct function name and quotes around parameters, making it valid syntax.

3. Final Answer:

   setcookie('user', 'John'); -> Option A

4. Quick Check:

   Correct function and quotes = A [OK]

Hint: Use setcookie() with quoted strings for name and value [OK]

Common Mistakes:

• Using wrong function names like cookie_set or set_cookie
• Forgetting quotes around cookie name or value
• Passing variables without quotes incorrectly

3. What will be the output of the following PHP code?

setcookie('color', 'blue');
if(isset($_COOKIE['color'])) {
    echo $_COOKIE['color'];
} else {
    echo 'No cookie set';
}

medium

A. blue

B. No cookie set

C. Undefined index error

D. Syntax error

Solution

1. Step 1: Understand when cookies are available

   Cookies set by setcookie() are available on the next page load, not immediately in the same script.

2. Step 2: Check the condition in the code

   Since the cookie is not yet set in $_COOKIE during this script run, isset($_COOKIE['color']) is false, so it prints 'No cookie set'.

3. Final Answer:

   No cookie set -> Option B

4. Quick Check:

   Cookie available next request = A [OK]

Hint: Cookies appear in $_COOKIE on next page load, not immediately [OK]

Common Mistakes:

• Expecting cookie immediately after setcookie() in same script
• Assuming $_COOKIE is updated instantly
• Confusing cookie setting with session variables

4. Identify the error in this PHP code snippet that tries to set a cookie:

setcookie('theme', 'dark', time() + 3600)
echo 'Cookie set!';

medium

A. Missing semicolon after setcookie() call

B. Incorrect function name

C. Wrong parameter order in setcookie()

D. Cookies cannot be set with expiration time

Solution

1. Step 1: Check PHP syntax rules

   Each PHP statement must end with a semicolon (;). The setcookie() call is missing this.

2. Step 2: Verify function name and parameters

   The function name and parameters are correct, and expiration time is valid.

3. Final Answer:

   Missing semicolon after setcookie() call -> Option A

4. Quick Check:

   Semicolon missing = C [OK]

Hint: Always end PHP statements with semicolon [OK]

Common Mistakes:

• Forgetting semicolon at end of function calls
• Thinking expiration time is invalid
• Confusing function names

5. You want to create a cookie that lasts for 7 days, is only accessible over HTTPS, and cannot be accessed by JavaScript. Which of the following setcookie() calls correctly achieves this?

hard

A. setcookie('session', 'active', time() + 604800);

B. setcookie('session', 'active', time() + 604800, '/', '', false, true);

C. setcookie('session', 'active', time() + 604800, '/', '', true, true);

D. setcookie('session', 'active', time() + 604800, '/', '', true, false);

Solution

1. Step 1: Calculate expiration time for 7 days

   7 days = 7 * 24 * 3600 = 604800 seconds, so time() + 604800 is correct.

2. Step 2: Set secure and httponly flags

   To make cookie HTTPS-only, set the secure flag to true. To improve security, httponly should also be true.

3. Step 3: Check options

   setcookie('session', 'active', time() + 604800, '/', '', true, true); sets secure and httponly to true, matching requirements. Others either disable secure or httponly or omit parameters.

4. Final Answer:

   setcookie('session', 'active', time() + 604800, '/', '', true, true); -> Option C

5. Quick Check:

   Secure and httponly true for HTTPS cookie = D [OK]

Hint: Use secure=true and httponly=true for HTTPS cookies [OK]

Common Mistakes:

• Not setting secure flag to true for HTTPS-only cookies
• Omitting httponly flag for security
• Incorrect expiration time calculation