/rootdir/sub1/sub2/sub3/sub4/
  -> \rootdir\sub1\sub2\sub3
/rootdir/sub1/sub2/sub3/file
  -> \rootdir\sub1\sub2
/rootdir/
  -> \
/rootfile
  -> \
/
  -> \
C:\
  -> C:\
reldir/sub1/
  -> reldir
reldir/file
  ->
reldir/
  ->
relfile
  ->