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From: gwyn@brl-smoke.UUCP
Newsgroups: comp.lang.c
Subject: Re: pre#defines for system and machine
Message-ID: <5573@brl-smoke.ARPA>
Date: Wed, 28-Jan-87 01:40:03 EST
Article-I.D.: brl-smok.5573
Posted: Wed Jan 28 01:40:03 1987
Date-Received: Thu, 29-Jan-87 05:49:09 EST
References: <2144@brl-adm.ARPA> <5497@brl-smoke.ARPA> <3952@utcsri.UUCP> <556@omssw2.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 13

The point about using lower-level "feature defines" like #ifdef TCGETA
is well taken, but there is also use for higher-level non-feature
conditionalization.  For example, my most common conditional seems to
be #if BRL_System_V_emulation_really_running_on_a_4BSD_kernel
(or equivalent).  I know of no reliable way to test combinations of
features to determine high-level properties like that.

I could also really use #if_header_exists "header_name" but I doubt we
could come up with a good way to wedge this into C portably.  However,
there might be hope; a small subgroup of X3J11 is working on defining
minimum syntax for portable filenames for use in #include "header_name"
directives.  Several of us feel that that is needed to plug a major hole
in the facilities a maximally-portable C application can rely on.