How can a custom PHP function be used to streamline form input handling and prevent errors in field values?

To streamline form input handling and prevent errors in field values, a custom PHP function can be created to sanitize and validate user input. This function can be used to remove any unwanted characters or tags from the input data, as well as check for the correct format of specific fields such as email addresses or phone numbers. By using this custom function for all form inputs, it ensures that the data is clean and safe to use in the application.

function sanitize_input($input) {
    $input = trim($input);
    $input = stripslashes($input);
    $input = htmlspecialchars($input);
    return $input;
}

// Example usage
$name = sanitize_input($_POST['name']);
$email = sanitize_input($_POST['email']);
$message = sanitize_input($_POST['message']);