Truncate a string without breaking a word

function truncate_str($string, $length = 80, $etc = '...',$break_words = false)
{
    if ($length == 0)
        return '';
 
    if (strlen($string) > $length) {
        $length -= strlen($etc);
        if (!$break_words)
            $string = preg_replace('/\s+?(\S+)?$/', '', substr($string, 0, $length+1));
 
        return substr($string, 0, $length).$etc;
    } else
        return $string;
}