How sessions work in PHP - Quick Revision & Summary

Recall & Review

beginner

What is a session in PHP?

A session in PHP is a way to store information (variables) to be used across multiple pages by the same user. It helps keep data like login status or preferences while the user browses the website.

beginner

How does PHP identify a user session?

PHP uses a unique session ID stored in a cookie on the user's browser. This ID links the user to their stored session data on the server.

beginner

What function starts a session in PHP?

The function session_start() starts a new session or resumes an existing one. It must be called before any output is sent to the browser.

intermediate

Where does PHP store session data?

PHP stores session data on the server, usually in temporary files. The session ID in the user's cookie tells PHP which data belongs to that user.

beginner

How do you store and access session variables in PHP?

Use the $_SESSION superglobal array. For example, $_SESSION['username'] = 'Alice'; stores data, and you can access it later with $_SESSION['username'].

Which PHP function is used to start or resume a session?

A init_session()

B start_session()

C begin_session()

D session_start()

The correct function to start or resume a session in PHP is session_start().

Where is the session ID usually stored on the client side?

A In the URL only

B In a cookie

C In a hidden form field

D In local storage

PHP stores the session ID in a cookie on the user's browser by default.

What superglobal array holds session variables in PHP?

A $_SESSION

B $_POST

C $_GET

D $_COOKIE

Session variables are stored in the $_SESSION array.

When must session_start() be called in a PHP script?

A Only on the login page

B After HTML content is sent

C Before any output is sent to the browser

D At the end of the script

session_start() must be called before any output to avoid errors.

Where is session data stored in PHP?

A On the server

B In the user's browser

C In the database only

D In the URL

Session data is stored on the server, linked by the session ID.

Explain how PHP uses sessions to remember user information across pages.

Think about how PHP links a user to their data using a unique ID.

Describe the steps to store and retrieve a username using PHP sessions.

Remember the order and the special array used.

Practice

1. What is the main purpose of using sessions in PHP?

easy

A. To remember user data across multiple pages

B. To store data permanently on the user's computer

C. To speed up the website loading time

D. To create a new database connection

Solution

1. Step 1: Understand what sessions do

   Sessions keep track of user information as they move between pages on a website.

2. Step 2: Compare options

   Only To remember user data across multiple pages correctly describes this purpose. Options A, C, and D describe unrelated functions.

3. Final Answer:

   To remember user data across multiple pages -> Option A

4. Quick Check:

   Sessions remember user data = B [OK]

Hint: Sessions remember data across pages, not store on user PC [OK]

Common Mistakes:

• Confusing sessions with cookies stored on user device
• Thinking sessions speed up page loading
• Believing sessions create database connections

2. Which PHP function must be called before using $_SESSION variables?

easy

A. session_end()

B. session_open()

C. session_init()

D. session_start()

Solution

1. Step 1: Identify the correct function to start a session

   The function session_start() initializes a session or resumes the current one.

2. Step 2: Check other options

   Functions like session_end(), session_open(), and session_init() do not exist in PHP.

3. Final Answer:

   session_start() -> Option D

4. Quick Check:

   Start session with session_start() = C [OK]

Hint: Always call session_start() before accessing $_SESSION [OK]

Common Mistakes:

• Using non-existent functions like session_end()
• Forgetting to call session_start() before $_SESSION
• Calling session_start() after outputting HTML

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

<?php
session_start();
$_SESSION['count'] = 1;
$_SESSION['count']++;
echo $_SESSION['count'];
?>

medium

A. 2

B. Error

C. 0

D. 1

Solution

1. Step 1: Analyze session variable assignment and increment

   The code sets $_SESSION['count'] to 1, then increments it by 1, making it 2.

2. Step 2: Output the session variable

   The echo statement prints the current value, which is 2.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   1 incremented by 1 = 2 [OK]

Hint: Increment after setting 1 results in 2 [OK]

Common Mistakes:

• Assuming the value stays 1 without increment
• Thinking session variables reset each time
• Expecting an error without session_start()

4. Identify the error in this PHP code snippet:

<?php
$_SESSION['user'] = 'Alice';
echo $_SESSION['user'];
?>

medium

A. Cannot assign string to $_SESSION

B. Incorrect variable name, should be $SESSION

C. Missing session_start() before using $_SESSION

D. Echo statement syntax is wrong

Solution

1. Step 1: Check session initialization

   The code uses $_SESSION without calling session_start() first, which is required.

2. Step 2: Verify other options

   Variable name $_SESSION is correct, strings can be assigned, and echo syntax is valid.

3. Final Answer:

   Missing session_start() before using $_SESSION -> Option C

4. Quick Check:

   session_start() needed before $_SESSION = A [OK]

Hint: Always call session_start() before $_SESSION usage [OK]

Common Mistakes:

• Forgetting session_start() causes undefined $_SESSION
• Confusing $_SESSION with $SESSION
• Thinking echo syntax is incorrect

5. You want to count how many times a user visits a page during a session. Which code snippet correctly implements this?

hard

A. <?php
$_SESSION['visits'] = 1;
echo $_SESSION['visits'];
?>

B. <?php
session_start();
if (!isset($_SESSION['visits'])) {
$_SESSION['visits'] = 1;
} else {
$_SESSION['visits']++;
}
echo "Visits: " . $_SESSION['visits'];
?>

C. <?php
session_start();
$_SESSION['visits']++;
echo $_SESSION['visits'];
?>

D. <?php
session_start();
$_SESSION['visits'] = 0;
echo $_SESSION['visits'];
?>

Solution

1. Step 1: Check session initialization and visit count logic

   <?php session_start(); if (!isset($_SESSION['visits'])) { $_SESSION['visits'] = 1; } else { $_SESSION['visits']++; } echo "Visits: " . $_SESSION['visits']; ?> starts the session, checks if 'visits' exists, initializes or increments it properly.

2. Step 2: Review other options for errors

   <?php $_SESSION['visits'] = 1; echo $_SESSION['visits']; ?> lacks session_start(), <?php session_start(); $_SESSION['visits']++; echo $_SESSION['visits']; ?> increments without initialization, <?php session_start(); $_SESSION['visits'] = 0; echo $_SESSION['visits']; ?> resets visits to 0 every time.

3. Final Answer:

   The code snippet that initializes visits=1 if not set, else increments -> Option B

4. Quick Check:

   Initialize then increment visits with session_start() = A [OK]

Hint: Initialize visits if not set, then increment [OK]

Common Mistakes:

• Not calling session_start() before $_SESSION
• Incrementing without checking if variable exists
• Resetting counter on every page load