Emacs lisp: Get directory name (not path) from the path

I am looking for a simple and portable way of obtaining the last component of the directory path or the directory itself from the path. The semantics of the function should be something like this: ``` (get-dirname-nonpath "/some/dir/") ;; should return "dir" (get-dirname-nonpath "C:\Windows\Path") ;; should return "Path" (get-dirname-nonpath "/some/path/to/my/source.ext") ;; returns "my" ``` In the last example it is also fine if the function returns "source.ext" instead of "my", especially if that would make it shorter. Looking at the emacs, I am unable to find a built-in function that would help in achieving this: Of course, I could do some string manipulation with (back)slashes, but that looks messy and more like a hack. What is the right way to do it in a robust (OS-oblivious) manner? EDIT: The best I could find so far is: `(file-name-nondirectory (directory-file-name ...))`