CodeIgnitor form validation class to allow only alphanum and spaces. My regex is ABSOLUTELY terrible (whose isn't?), so...this may not work and needs to be tested. If you find that the regex pattern needs to be tweaked, please come back and edit this gist.

alpha_num_spaces.php

<?php

function alpha_num_spaces($subject)
{

    $pattern = "#^[A-Z0-9 ]+$#i";
    $res = preg_match($pattern, $subject);
    
    if ($res == 1)
    {
        return TRUE;
    }
    else
    {
        return FALSE;
    }
}

?>