Data validation is an integral part of working with forms. Not only can invalid submitted data lead to security problems, but it can also break your webpage. Today, we'll take a look at how to remove illegal characters and validate data by using the "filter_var" function.

Using filter_var they create a simple form with email and URL input fields. Their script runs these through the FILTER_SANITIZE_EMAIL and FILTER_SANITIZE_URL respectively to see if they are valid. Later they add on a name and message field to make it into an email form (performing the checks on these with the FILTER_SANITIZE_STRING).

A link to download the source is also included.