I remember when years ago and i still was fresh to this i was searching like a function like this all the time and trying to make one without much success.
I guess i was over thinking all the loops at the time, guess i got a lil smarter with the years. xD cause it's really simple.
Anyways this lists all sub-directories of a specified folder.
[Edit] Don't be silly and try to scan your entire hdd it will take ages. it's not meant for huge file structures.
Functions:
Example:
UDF: