What are the implications of not following best practices for handling special characters in PHP, especially in terms of data integrity and output consistency?

Not following best practices for handling special characters in PHP can lead to data corruption, security vulnerabilities, and inconsistent output. To ensure data integrity and output consistency, it is important to properly sanitize and validate input data, encode special characters when necessary, and use secure functions for processing user input.

// Example of sanitizing input data to handle special characters
$user_input = $_POST['user_input'];
$clean_input = htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');