How can PHP developers ensure clean and secure output when dealing with user input and data from databases?

PHP developers can ensure clean and secure output by using functions like htmlentities() or htmlspecialchars() to encode user input before displaying it on the webpage. Additionally, when retrieving data from databases, developers should use prepared statements with parameterized queries to prevent SQL injection attacks. It's crucial to validate and sanitize user input before processing or storing it to ensure the security and integrity of the application. 

// Example of using htmlentities() to encode user input before displaying it
$userInput = "<script>alert('XSS attack');</script>";
echo htmlentities($userInput);

// Example of using prepared statements with PDO to retrieve data from a database
$pdo = new PDO("mysql:host=localhost;dbname=mydatabase", "username", "password");
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");
$stmt->bindParam(':username', $username, PDO::PARAM_STR);
$stmt->execute();
$userData = $stmt->fetch();

Keywords

input validation SQL injection htmlspecialchars prepared statements data sanitization

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