Php function to determine if a string consist of only alphanumerical characters?

Question

Is there a Php function to determine if a string consist of only ASCII alphanumerical characters?

Note: I'm sorry if the question sounds dumb to some, but I couldn't easily find such a function in the Php manual.

Answer 1

Try ctype_alnum

Answer 2

preg_match('/^[a-z0-9]+$/i', $str);

Edit: John T's answer is better. Just providing another method.