What are best practices for handling form validation in PHP?

When handling form validation in PHP, it is important to validate user input to ensure data integrity and security. Best practices include using server-side validation to prevent malicious input, displaying clear error messages to users, and sanitizing input data before processing it. Additionally, using PHP functions like filter_var() or regular expressions can help validate different types of input. 

// Example of handling form validation in PHP
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST["username"];
    $email = $_POST["email"];
    
    // Validate username
    if (empty($username)) {
        $errors[] = "Username is required";
    }
    
    // Validate email
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        $errors[] = "Invalid email format";
    }
    
    // Display error messages
    if (!empty($errors)) {
        foreach ($errors as $error) {
            echo $error . "<br>";
        }
    } else {
        // Process form data
        // Sanitize input data before use
        $username = htmlspecialchars($username);
        $email = filter_var($email, FILTER_SANITIZE_EMAIL);
        
        // Further processing...
    }
}

Keywords

filter_var htmlspecialchars validation library error messages client-side validation

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