What are some best practices for maintaining user input values in PHP forms?

When submitting a form, it is important to maintain user input values in case of validation errors so that users do not have to re-enter all their information. One way to achieve this is by using PHP to store the input values in session variables and repopulate the form fields with these values if validation fails. 

// Start the session
session_start();

// Check if form is submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Store user input values in session variables
    $_SESSION['username'] = $_POST['username'];
    $_SESSION['email'] = $_POST['email'];
    
    // Perform form validation
    // If validation fails, redirect back to the form
    if (/* validation fails */) {
        header("Location: form.php");
        exit();
    }
}

// Repopulate form fields with user input values
$username = isset($_SESSION['username']) ? $_SESSION['username'] : '';
$email = isset($_SESSION['email']) ? $_SESSION['email'] : '';
?>

<form method="post" action="process_form.php">
    <input type="text" name="username" value="<?php echo $username; ?>" />
    <input type="email" name="email" value="<?php echo $email; ?>" />
    <button type="submit">Submit</button>
</form>

Keywords

Sanitization Validation Form validation Input filtering Security

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