This function is missing on some platforms:
mingw.
@item
-On Ultrix 4.3, @code{getgroups (0, 0)} always fails. See macro
+On some platforms, this function fails to reject a negative count,
+even though that is less than the size that would be returned:
+FreeBSD 7.2.
+@item
+On Ultrix 4.3, @code{getgroups (0, NULL)} always fails. See macro
@samp{AC_FUNC_GETGROUPS}.
+@item
+On very old systems, this function operated on an array of @samp{int},
+even though that was a different size than an array of @samp{gid_t}.
@end itemize
Portability problems not fixed by Gnulib:
@itemize
+@item
+It is unspecified whether the effective group id will be included in
+the returned list, nor whether the list will be sorted in any
+particular order. For that matter, some platforms include the
+effective group id twice, if it is also a member of the current
+supplemental group ids.
@end itemize