Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site brl-tgr.ARPA
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!harvard!seismo!brl-tgr!tgr!lcc.niket@UCLA-LOCUS.ARPA
From: lcc.niket@UCLA-LOCUS.ARPA (Niket K. Patwardhan)
Newsgroups: net.lang.c
Subject: Re: C programming hint
Message-ID: <14@brl-tgr.ARPA>
Date: Fri, 19-Jul-85 07:12:09 EDT
Article-I.D.: brl-tgr.14
Posted: Fri Jul 19 07:12:09 1985
Date-Received: Sat, 20-Jul-85 12:34:56 EDT
Sender: news@brl-tgr.ARPA
Lines: 19

I scanned the C standards draft a while ago and remembered there was something
about builtins. Well, I went back and checked, and found there isn't any
declaration as such, but it does say (Page 68, Introduction of Library section)
that

"One implication of this restriction <....external identifiers starting with
_ are reserved ....> is that implementations may provide special semantics
for names starting with underscore. For example, _builtin_abs could be used
to <.....define an inline abs>."

It also warns that any function defined in a header file could be a macro,
and that if you wanted your own function you should use the #undef directive
to nullify any such macro definition before using your function. Thus an
implementor says

#define abs _builtin_abs

in his header file, and users would get the builtin abs normally. If they wanted
to use their own abs, they would #undef abs before using it.