What are common validation steps to consider when checking form field values in PHP?

When checking form field values in PHP, it is important to validate the data to ensure it meets the expected criteria. Common validation steps include checking for required fields, validating email addresses, ensuring numeric values are within a certain range, and sanitizing input to prevent SQL injection attacks. 

// Example of validating a form field for required input
if(empty($_POST['username'])) {
    $errors[] = 'Username is required';
}

// Example of validating an email address
if(!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {
    $errors[] = 'Invalid email address';
}

// Example of validating a numeric value within a range
$age = $_POST['age'];
if(!is_numeric($age) || $age < 18 || $age > 100) {
    $errors[] = 'Age must be between 18 and 100';
}

// Example of sanitizing input to prevent SQL injection
$username = mysqli_real_escape_string($conn, $_POST['username']);
$email = mysqli_real_escape_string($conn, $_POST['email']);

Keywords

PHP form validation input filtering error handling data sanitization

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