Actually if he has to create a files list that's not only platform specific it's likely to be filesystem specific.
In windows the function calls to enumerate a folder would be FindFirstFile() and FindNextFile() I have no idea what they would be on MAC or Linux.
The balance of the program... opening and crunching the files will likely be platform independent.
If our friend is on Linux he can use the Wine windows emulator or Parallels for Mac.