If I have a PHP string, how can I determine if it contains at least one non-ASCII character or not, in an efficient way? And by non-ASCII character, I mean any character tha
I suggest you look into utf8_encode or utf8_decode under PHP's manual:
http://www.php.net/manual/en/function.utf8-encode.php
Look into the examples down below as it may have something there that leads you to the right direction if not finding what you are looking for.