Session variables in PHP

Introduction

Session variables let you save information about a user while they browse your website. This helps keep data like login status or preferences as they move between pages.

Remember if a user is logged in across different pages.

Store items in a shopping cart while the user shops.

Keep track of user preferences like language or theme.

Save temporary data during a multi-step form.

Pass data between pages without showing it in the URL.

Syntax

PHP

<?php
session_start();
$_SESSION['key'] = 'value';
$value = $_SESSION['key'];
?>

You must call session_start() at the very start of your PHP script before any output.

Session variables are stored in the $_SESSION superglobal array.

Examples

Save the username 'Alice' in a session variable.

PHP

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

Retrieve and show the username stored in the session.

PHP

<?php
session_start();
echo $_SESSION['username'];
?>

Add an item to a shopping cart stored in the session.

PHP

<?php
session_start();
if (isset($_SESSION['cart'])) {
    $_SESSION['cart'][] = 'item1';
} else {
    $_SESSION['cart'] = ['item1'];
}
?>

Sample Program

This program starts a session, saves the user's name and role, then prints them out.

PHP

<?php
session_start();

// Save user info
$_SESSION['user'] = 'Bob';
$_SESSION['role'] = 'admin';

// Show saved info
echo "User: " . $_SESSION['user'] . "\n";
echo "Role: " . $_SESSION['role'] . "\n";
?>

Important Notes

Always call session_start() before using $_SESSION.

Session data is stored on the server, so it is more secure than cookies.

To remove a session variable, use unset($_SESSION['key']);.

Summary

Session variables store user data across pages.

Use session_start() to begin using sessions.

Access session data with the $_SESSION array.

Practice

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

easy

A. To connect to a database

B. To send output to the browser

C. To begin a session and enable session variables

D. To include another PHP file

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: Identify the purpose of session variables

   Session variables store user data across multiple pages, but they only work if a session is started first.

3. Final Answer:

   To begin a session and enable session variables -> Option C

4. Quick Check:

   session_start() = start session [OK]

Hint: Remember: session_start() must be called before using $_SESSION [OK]

Common Mistakes:

• Thinking session_start() connects to a database
• Using session variables without calling session_start()
• Confusing session_start() with output functions

2. Which of the following is the correct way to set a session variable named user with the value "Alice"?

easy

A. $_SESSION['user'] = 'Alice';

B. session['user'] = 'Alice';

C. set_session('user', 'Alice');

D. session_start['user'] = 'Alice';

Solution

1. Step 1: Recall the syntax for setting session variables

   Session variables are stored in the global $_SESSION array, so you assign values like $_SESSION['key'] = value;.

2. Step 2: Check each option's syntax

   $_SESSION['user'] = 'Alice'; uses the correct $_SESSION superglobal with proper array syntax and assignment.

3. Final Answer:

   $_SESSION['user'] = 'Alice'; -> Option A

4. Quick Check:

   $_SESSION['key'] = value [OK]

Hint: Use $_SESSION['name'] = value to set session data [OK]

Common Mistakes:

• Using session without the $_SESSION superglobal
• Trying to call session_start as an array
• Using undefined functions like set_session()

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

session_start();
$_SESSION['count'] = 1;
$_SESSION['count']++;
echo $_SESSION['count'];

medium

A. 1

B. 0

C. Error

D. 2

Solution

1. Step 1: Analyze session variable initialization and increment

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

2. Step 2: Determine the final value of $_SESSION['count']

   After increment, the value becomes 2, which is then printed by echo.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   1 incremented by 1 = 2 [OK]

Hint: Increment session variable with ++ after setting it [OK]

Common Mistakes:

• Forgetting to call session_start() before using $_SESSION
• Assuming $_SESSION['count'] stays 1 after ++
• Expecting an error due to session usage

4. Identify the error in this PHP code snippet:

$_SESSION['user'] = 'Bob';
echo $_SESSION['user'];

medium

A. Missing session_start() before using $_SESSION

B. Incorrect array syntax for $_SESSION

C. Cannot assign string to $_SESSION

D. Echo statement syntax is wrong

Solution

1. Step 1: Check for session initialization

   The code uses $_SESSION but does not call session_start() first, which is required to access session variables.

2. Step 2: Verify syntax correctness

   The array syntax and echo statement are correct, and assigning a string to $_SESSION is valid.

3. Final Answer:

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

4. Quick Check:

   Always call session_start() before $_SESSION [OK]

Hint: Always start session with session_start() before $_SESSION use [OK]

Common Mistakes:

• Using $_SESSION without session_start()
• Thinking $_SESSION needs special syntax
• Assuming 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 using session variables?

hard

A. session_start();
$_SESSION['visits']++;
echo $_SESSION['visits'];

B. session_start();
if (!isset($_SESSION['visits'])) {
$_SESSION['visits'] = 1;
} else {
$_SESSION['visits']++;
}
echo $_SESSION['visits'];

C. session_start();
$_SESSION['visits'] = 1;
echo $_SESSION['visits'];

D. if (!isset($_SESSION['visits'])) {
$_SESSION['visits'] = 1;
} else {
$_SESSION['visits']++;
}
echo $_SESSION['visits'];

Solution

1. Step 1: Ensure session is started

   Calling session_start() is necessary to use session variables.

2. Step 2: Check visit count logic

   The code checks if $_SESSION['visits'] exists; if not, it sets it to 1. Otherwise, it increments the count. This correctly tracks visits.

3. Step 3: Verify output

   Finally, it echoes the current visit count, showing how many times the user visited during the session.

4. Final Answer:

   Code snippet with session_start() and visit count check -> Option B

5. Quick Check:

   Initialize then increment visits with session_start() [OK]

Hint: Always check isset() before incrementing session counters [OK]

Common Mistakes:

• Forgetting session_start() before using $_SESSION
• Not checking if session variable exists before increment
• Resetting visit count every page load