How can the PHP version on the server impact session management and variable access, especially when dealing with older code that relies on deprecated features?

When dealing with older code that relies on deprecated features, updating the PHP version on the server can impact session management and variable access. To address this issue, it is important to review the deprecated features being used in the code and update them to modern standards. Additionally, ensuring that the session management functions and variable access methods are compatible with the new PHP version is crucial to maintain the functionality of the code.

// Example of updating session management for compatibility with newer PHP versions
// Start the session
session_start();

// Check if a session variable is set
if (isset($_SESSION['user_id'])) {
    // Access the session variable
    $user_id = $_SESSION['user_id'];
    // Use the variable in the code
    echo "User ID: " . $user_id;
}