? PHP Session Variables

?️ Quick Overview

Sessions are used to store data across multiple pages. Unlike cookies, which are stored on the client's browser, session data is stored on the server. The session variables are unique to each user and last until the user closes the browser or the session is destroyed.

? Key Concepts

• Sessions store user-specific data on the server
• Each user gets a unique session ID
• Session data persists across multiple pages
• Sessions end when destroyed or expired

? Syntax / Theory

Before using session variables, the session must be initialized using session_start(). This function must be called before any HTML output.

// Start a new or existing session
session_start();

? Code Example: Starting a Session

// Initialize session and store values
<?php
session_start();
$_SESSION["username"] = "JohnDoe";
$_SESSION["email"] = "john@example.com";
echo "Session variables are set!";
?>

? Code Example: Accessing Session Variables

// Access stored session values safely
<?php
session_start();
if(isset($_SESSION["username"]) && isset($_SESSION["email"])) {
echo "Welcome " . $_SESSION["username"];
echo "<br>Email: " . $_SESSION["email"];
} else {
echo "No session variables are set.";
}
?>

? Live Output / Explanation

The isset() function ensures that session variables exist before accessing them, preventing warnings and errors.

?️ Additional Example: Destroying a Session

// Clear and destroy session data
<?php
session_start();
session_unset();
session_destroy();
echo "Session destroyed successfully!";
?>

? Use Cases

• User authentication systems
• Shopping carts in e-commerce
• Maintaining user preferences
• Multi-page form handling