Session vs cookie decision in PHP - Quick Revision & Key Differences

Recall & Review

beginner

What is a session in PHP?

A session in PHP is a way to store data on the server for a user to use across multiple pages. It keeps user information safe and private during their visit.

beginner

What is a cookie in PHP?

A cookie is a small piece of data stored on the user's browser. It helps remember information like login or preferences even after the browser is closed.

intermediate

When should you use a session instead of a cookie?

Use a session when you need to store sensitive data securely on the server or when data should not be visible or modifiable by the user.

beginner

What are the size limits for cookies?

Cookies are limited to about 4KB of data per cookie, so they are not suitable for storing large amounts of information.

intermediate

How does a session maintain user state differently from a cookie?

A session stores data on the server and uses a session ID cookie to link the user. Cookies store all data on the user's browser directly.

Which of the following stores data on the server side?

A Local Storage

B Cookie

C Session

D URL Parameters

Sessions store data on the server, while cookies and local storage store data on the client side.

What is the typical size limit for a cookie?

A 4KB

B 1MB

C 100KB

D No limit

Cookies are limited to about 4KB of data per cookie.

Which is safer for storing sensitive user data?

A Session

B Cookie

C Local Storage

D All are equally safe

Sessions keep data on the server, making them safer for sensitive information.

If you want to remember a user's preference after they close the browser, what should you use?

A Server variable

B Cookie

C Session

D Temporary file

Cookies can persist data on the user's browser even after closing it.

How does a session identify a user?

A By using IP address only

B By storing user data in the URL

C By saving data in local storage

D Using a session ID stored in a cookie

Sessions use a session ID cookie to link the user to their server-stored data.

Explain the main differences between sessions and cookies in PHP.

Think about where data is stored and how long it lasts.

Describe a scenario where using a session is better than a cookie.

Consider when you want to keep data hidden from the user.

Practice

1. Which of the following is the best reason to use a PHP session instead of a cookie?

easy

A. To reduce server memory usage

B. To save user preferences permanently on the browser

C. To store sensitive user data temporarily during a visit

D. To share data between different websites

Solution

1. Step 1: Understand session purpose

   Sessions store data on the server and are good for sensitive or temporary data during a visit.

2. Step 2: Compare with cookies

   Cookies store data on the user's browser and are better for non-sensitive, longer-term data.

3. Final Answer:

   To store sensitive user data temporarily during a visit -> Option C

4. Quick Check:

   Session = temporary sensitive data [OK]

Hint: Use sessions for sensitive, temporary data; cookies for long-term [OK]

Common Mistakes:

• Thinking cookies are safer than sessions
• Using sessions to store permanent data
• Confusing where data is stored

2. Which PHP code snippet correctly starts a session?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall PHP session syntax

   The correct function to start a session is session_start().

2. Step 2: Check other options

   Other options are not valid PHP functions and will cause errors.

3. Final Answer:

   <?php session_start(); ?> -> Option D

4. Quick Check:

   session_start() starts session [OK]

Hint: Remember exact function name: session_start() [OK]

Common Mistakes:

• Using incorrect function names
• Forgetting parentheses
• Confusing session_start with cookie functions

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

<?php
session_start();
$_SESSION['user'] = 'Alice';
setcookie('user', 'Bob', time() + 3600);
echo $_SESSION['user'] . ' & ' . $_COOKIE['user'];
?>

medium

A. Alice &

B. Bob & Alice

C. Alice & Alice

D. Bob & Bob

Solution

1. Step 1: Understand session and cookie values

   $_SESSION['user'] is set to 'Alice'. The cookie 'user' is set to 'Bob' but will be available on the next request only.

2. Step 2: Check echo output

   $_SESSION['user'] outputs 'Alice'. $_COOKIE['user'] is not set in this request (assuming no prior cookie), so it is empty. Output: Alice & (empty).

3. Final Answer:

   Alice & -> Option A

4. Quick Check:

   Session = Alice immediate, Cookie = next request [OK]

Hint: Session changes immediate; cookie available next request [OK]

Common Mistakes:

• Expecting cookie value immediately after setcookie()
• Mixing session and cookie values
• Assuming cookie overwrites session

4. Identify the error in this PHP code snippet:

<?php
setcookie('theme', 'dark');
session_start();
$_SESSION['theme'] = 'light';
?>

medium

A. session_start() must be called before setcookie()

B. No error, code is correct

C. $_SESSION cannot be set after setcookie()

D. setcookie() must be called before any output

Solution

1. Step 1: Recall header rules in PHP

   Both setcookie() and session_start() send HTTP headers and must be called before any output.

2. Step 2: Check order and output

   No output before either function. Order of setcookie() before session_start() is fine; multiple Set-Cookie headers are allowed.

3. Final Answer:

   No error, code is correct -> Option B

4. Quick Check:

   Headers before output, order OK [OK]

Hint: Call setcookie() and session_start() before any output [OK]

Common Mistakes:

• Thinking session_start() must come before setcookie()
• Ignoring header output rules
• Assuming $_SESSION depends on setcookie()

5. You want to remember a user's language preference safely for their entire visit but not after they close the browser. Which is the best choice?

hard

A. Store language in a session variable

B. Store language in a cookie with 1 year expiry

C. Store language in a cookie without expiry

D. Store language in a hidden form field

Solution

1. Step 1: Understand data lifetime needs

   The language preference should last only during the visit, not after browser closes.

2. Step 2: Match storage type to lifetime

   Sessions last until browser closes or session expires, so session variable fits. Cookies persist beyond browser close if expiry is set.

3. Final Answer:

   Store language in a session variable -> Option A

4. Quick Check:

   Temporary visit data = session [OK]

Hint: Use session for visit-only data, cookie for longer storage [OK]

Common Mistakes:

• Using cookies for temporary visit data
• Setting cookie without expiry expecting session behavior
• Using hidden fields for persistent data