PHP and P++

Treating everything as bytes is fine for filesystem APIs, but a big problem arises when you want to print path names; if you don't know the encoding, and the path name is not ASCII, you can't print them correctly. A slightly lesser problem is the reverse: when you receive a path name that happens to be in Unicode (because it comes from user input in Unicode, for example), and is non-ASCII.

If you care about those problems then you need to define the encoding of path names, and decide how to handle path names that aren't valid in the encoding.