[WordPress] Occasionally, I've been parsing out data provided to me by third-parties and there have been hidden ASCII characters that can muck up programmatically inserting data into the database. Here's a simple regex for stripping out everything *except* alphanumeric characters.

strip-hidden-ascii-chars.php

<?php
// Replace anything that is not an 'a-z', 'A-Z', or '0-9' from the given $value
$value = preg_replace( "/[^a-zA-Z0-9\s]/", "", $value );

/*
 * Read the comments below to see some of the available functions WordPress provides for evaluating the validity of the characters in the input string.
 * /

For those who are looking for a WordPress-based solution (which is what this particular gist was used for), there's a nice function that someone mentioned in this comment.

Specifically, wp_check_invalid_utf8 which can be found [http://core.trac.wordpress.org/browser/tags/3.5.1/wp-includes/formatting.php#L499](in the source in Trac).