PHP: Random string generator

A random string generator useful for random filenames or passwords

<?php
function gen_rand_str($max)
{
 $val = '';
 $charset = "abcdefghijkmnpqrstuvwxyz0123456789";
 for ($i = 0; $i < $max; $i++)
 {
  $val .= $charset[mt_rand(0, strlen($charset) - 1)];
 }
 return $val;
}
?> 

Usage

Pass as parameter the maximum number of characters to return.