codeigniter: change html class when there is a form validation error?

Question

when using CodeIgniter's form validation, I see that there is a form_error() function for printing out an error if one exists, and an empty html tag if not. Is there an easy way to do a boolean test if there is an error for a particular field or not? I'd like to change the class of the input element itself instead of just printing out an error. What is the best way to accomplish this?

Answer 1

I'm not somewhere where I can test this, but wouldn't this work?

<?php
if (!empty(form_error('username')))
{
    $class = "error";
}
else
{
    $class = "valid";
}
?>

<input type="text" name="username" class="<?= $class ?>" value="<?= set_value('username') ?>" />

Answer 2

Looking at the source (line 207 of https://github.com/EllisLab/CodeIgniter/blob/v2.1.0/system/libraries/Form_validation.php), form_error() returns an empty string if there is no error associated with the given field. You could check to see what the method returns and use that as the condition for changing the element's class.