How cookies work in PHP - Quick Revision & Summary

Recall & Review

beginner

What is a cookie in web development?

A cookie is a small piece of data stored on the user's computer by the web browser. It helps websites remember information about the user, like login status or preferences.

beginner

How does a server send a cookie to a browser in PHP?

The server sends a cookie using the setcookie() function before any output is sent. This function sets the cookie name, value, and optional parameters like expiration time.

beginner

Where are cookies stored and how are they sent back to the server?

Cookies are stored in the user's browser. When the browser makes a request to the same server, it sends the stored cookies automatically in the HTTP headers.

beginner

What is the purpose of the cookie expiration time?

The expiration time tells the browser how long to keep the cookie. If no expiration is set, the cookie lasts only for the browser session and is deleted when the browser closes.

beginner

How can you access a cookie value in PHP?

You can access cookie values using the $_COOKIE superglobal array with the cookie's name as the key, for example, $_COOKIE['username'].

Which PHP function is used to send a cookie to the browser?

A setcookie()

B cookie_send()

C send_cookie()

D cookie_set()

The correct function to send a cookie in PHP is setcookie().

Where are cookies stored after being sent by the server?

A On the user's browser

B On the server

C In the PHP script

D In the database

Cookies are stored on the user's browser and sent back to the server with each request.

What happens if you don't set an expiration time for a cookie?

A The cookie is stored on the server

B The cookie lasts forever

C The cookie lasts only for the browser session

D The cookie is deleted immediately

Without an expiration time, the cookie lasts only for the current browser session.

How do you access a cookie named 'user' in PHP?

A getcookie('user')

B $_COOKIE['user']

C cookie['user']

D $_SESSION['user']

Cookie values are accessed using the $_COOKIE array with the cookie name as the key.

When must you call setcookie() in a PHP script?

A Only inside functions

B After HTML content is printed

C Anywhere in the script

D Before any output is sent to the browser

Cookies must be sent before any output because they are part of HTTP headers.

Explain how cookies are created, stored, and sent back to the server in PHP.

Think about the journey of a cookie from server to browser and back.

Describe the role of cookie expiration time and what happens if it is not set.

Consider how long the cookie stays on the user's device.

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