rsync uses popt(3) rather than getopt(3). rsync explains why at https://github.com/WayneD/rsync/tree/master/popt

1) popt is fully reentrant
2) popt can parse arbitrary argv[] style arrays while 
   getopt(2) makes this quite difficult
3) popt allows users to alias command line arguments
4) popt provides convience functions for parsing strings
   into argv[] style arrays
[download]

popt is a library from Redhat that's only common on Linux. If you just want to do it like rsync does, getopt is pretty close.