On PHPMaster.com today David Shirey has a written up a new tutorial introducing the ctype functions in PHP. This set of functions provides a handy way to more correctly check values to ensure they're valid (and contain what they should).
If you have a background in C, then you’re probably already familiar with the character type functions because that is where they come from (don’t forget that PHP is actually written in C). But if you’re into Python, then it’s only fair to point out that the PHP Ctype functions have absolutely nothing to do with the Python’s ctypes library. It’s just one of those tragic and totally unavoidable naming similarities.
He briefly explains how the functions work and at least one "gotcha" to watch out for if you're using them for input validation. He then goes through the list of the eleven ctype functions and briefly describes what they do. Some example code is also included showing how you can use them to validate a value based on the true/false return from the function call.