Starting and using sessions in PHP - Cheat Sheet & Quick Revision

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. It helps keep user data while they browse a website.

beginner

How do you start a session in PHP?

Use the function session_start(); at the very beginning of your PHP script before any output. This creates or resumes a session.

beginner

How do you store data in a PHP session?

You store data by assigning values to the $_SESSION superglobal array, like $_SESSION['key'] = 'value';.

beginner

How do you access session data on another page?

First, call session_start(); on the page, then read the data from $_SESSION['key'].

intermediate

What must you avoid before calling session_start();?

You must avoid sending any output (like HTML or echo) before session_start(); because it sends HTTP headers.

Which PHP function starts or resumes a session?

A session_start()

B start_session()

C begin_session()

D init_session()

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

Where should session_start() be placed in your PHP script?

A After HTML output

B Anywhere in the script

C Before any output

D Inside a function only

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

How do you store a user's name in a session variable?

A set_session('name', 'John');

B session['name'] = 'John';

C session->name = 'John';

D $_SESSION['name'] = 'John';

Use the superglobal array $_SESSION to store session data like $_SESSION['name'] = 'John';.

What happens if you try to access $_SESSION without calling session_start()?

A You get an error or empty data

B Session data is automatically loaded

C Session is created automatically

D Nothing happens, it works fine

Without session_start(), PHP does not load session data, so $_SESSION will be empty or cause errors.

Which superglobal array holds session variables?

A $_POST

B $_SESSION

C $_GET

D $_COOKIE

Session variables are stored in the $_SESSION superglobal array.

Explain how to start a session and store a user's favorite color in PHP.

Remember to start the session first, then save data in $_SESSION.

Describe why it is important to call session_start() before any output in PHP.

Think about how PHP sends session cookies in headers.

Practice

1. What is the main purpose of using session_start() in PHP?

easy

A. To begin a session and enable storing data across pages

B. To end a session and clear all session data

C. To connect to a database for user authentication

D. To send cookies to the user's browser

Solution

1. Step 1: Understand what session_start() does

   This function initializes a session or resumes the current one based on a session identifier passed via a cookie or URL.

2. Step 2: Recognize session purpose

   Sessions allow data to be saved and accessed across multiple pages for the same user, such as login status or preferences.

3. Final Answer:

   To begin a session and enable storing data across pages -> Option A

4. Quick Check:

   session_start() starts session = D [OK]

Hint: Remember: session_start() must run before any output [OK]

Common Mistakes:

• Thinking session_start() ends a session
• Confusing sessions with database connections
• Calling session_start() after HTML output

2. Which of the following is the correct way to start a session in PHP?

easy

A. session.begin();

B. start_session();

C. session_start();

D. begin_session();

Solution

1. Step 1: Recall PHP session function syntax

   The correct function to start a session is session_start() with an underscore and parentheses.

2. Step 2: Check other options for syntax errors

   Options B, C, and D are not valid PHP functions and will cause errors.

3. Final Answer:

   session_start(); -> Option C

4. Quick Check:

   Correct PHP session start syntax = A [OK]

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

Common Mistakes:

• Using wrong function names like start_session()
• Missing parentheses after session_start
• Using camelCase instead of underscore

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

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

medium

A. user

B. Alice

C. Array

D. Undefined index error

Solution

1. Step 1: Start session and assign value

   The code starts a session and sets the session variable 'user' to 'Alice'.

2. Step 2: Output the session variable

   Using echo $_SESSION['user']; prints the value stored, which is 'Alice'.

3. Final Answer:

   Alice -> Option B

4. Quick Check:

   $_SESSION['user'] = 'Alice' outputs Alice [OK]

Hint: Session variables store values like arrays [OK]

Common Mistakes:

• Expecting 'user' instead of its value
• Forgetting to call session_start() first
• Confusing session variables with regular variables

4. Identify the error in this PHP code snippet:

<?php
$_SESSION['count'] = 1;
echo $_SESSION['count'];
?>

medium

A. Cannot echo session variables

B. Incorrect variable name $_SESSION

C. Session variables must be integers only

D. Missing session_start() before using $_SESSION

Solution

1. Step 1: Check session initialization

   The code uses $_SESSION but never calls session_start() to begin the session.

2. Step 2: Understand session usage rules

   Without calling session_start(), PHP does not know which session to use, causing errors or empty values.

3. Final Answer:

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

4. Quick Check:

   Always call session_start() before $_SESSION [OK]

Hint: Always start session before accessing $_SESSION [OK]

Common Mistakes:

• Using $_SESSION without session_start()
• Assuming $_SESSION works like normal variables
• Trying to echo $_SESSION without initialization

5. You want to count how many times a user visits a page using sessions. Which code correctly increments the visit count each time the page loads?

<?php
// Fill in the missing part

if (isset($_SESSION['visits'])) {
    $_SESSION['visits']++;
} else {
    $_SESSION['visits'] = 1;
}
echo "Visit number: " . $_SESSION['visits'];
?>

hard

A. session_start();

B. session_destroy();

C. session_unset();

D. session_write_close();

Solution

1. Step 1: Recognize session must be started

   To use $_SESSION variables, the session must be started with session_start(); at the top.

2. Step 2: Understand the code logic

   The code checks if 'visits' exists in the session, increments it if yes, or sets it to 1 if no, then prints the count.

3. Final Answer:

   session_start(); -> Option A

4. Quick Check:

   Start session before using $_SESSION to track visits [OK]

Hint: Always call session_start() before session variables [OK]

Common Mistakes:

• Forgetting session_start() causes no session data
• Using session_destroy() resets visits
• Confusing session_unset() with starting session