catgets implementation is defined in the X/Open Portability
Guide, Volume 3, XSI Supplementary Definitions, Chapter 5. But the
process of creating this standard seemed to be too slow for some of
the Unix vendors so they created their implementations on preliminary
versions of the standard. Of course this leads again to problems while
writing platform independent programs: even the usage of
does not guarantee a unique interface.
Another, personal comment on this that only a bunch of committee members could have made this interface. They never really tried to program using this interface. It is a fast, memory-saving implementation, an user can happily live with it. But programmers hate it (at least I and some others do...)
But we must not forget one point: after all the trouble with transferring the rights on Unix(tm) they at last came to X/Open, the very same who published this specification. This leads me to making the prediction that this interface will be in future Unix standards (e.g. Spec1170) and therefore part of all Unix implementation (implementations, which are allowed to wear this name).