How can input validation and sanitization functions improve the security and reliability of PHP registration forms interacting with a MySQL database?

Input validation and sanitization functions can improve the security and reliability of PHP registration forms interacting with a MySQL database by ensuring that the data entered by users is clean, correct, and safe to use. Validation functions can check for the presence of required fields, correct data formats (such as email addresses), and acceptable input values. Sanitization functions can help prevent SQL injection attacks by escaping special characters that could be used to manipulate database queries.

// Example of input validation and sanitization for a registration form
$name = $_POST['name'];
$email = $_POST['email'];
$password = $_POST['password'];

// Validate input
if(empty($name) || empty($email) || empty($password)) {
    echo "All fields are required.";
    exit;
}

if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    echo "Invalid email format.";
    exit;
}

// Sanitize input
$name = htmlspecialchars($name);
$email = filter_var($email, FILTER_SANITIZE_EMAIL);
$password = password_hash($password, PASSWORD_DEFAULT);

// Now $name, $email, and $password can be safely used in a MySQL query