allowing only letters and numbers

[Lodius2000]

is there a php function to validate a textbox entry that will only allow a combination of letters and/or numbers, I am trying to set up a username submission form and I want only letters and/or numbers in the username, no spaces, no punctuation, no nothing,

 

if there isnt a function what could be my way of invalidating special characters and spaces and all that, I would like it to roughly match my current sytax for error validation which is.

 

//check that username is less or equal to than 14 characters
if (strlen(trim($_POST['username'])) <= 14) {
	$errors[]= "Your username must be 14 characters or less.";
}

 

thanks for your help

[p2grace]

Awesome command:

 

<?php
$clean = ctype_alnum($string);  // returns true if only letters and numbers returns false otherwise.
?>

 

 

http://www.php.net/manual/en/function.ctype-alnum.php

[sasa]

if (preg_match('/[^A-z0-9]/',trim($_POST['username']))) echo 'wrong'; else echo 'OK';