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From: chris@umcp-cs.UUCP
Newsgroups: net.sources.d
Subject: Re: ifdef filter
Message-ID: <2496@umcp-cs.UUCP>
Date: Sat, 19-Jul-86 20:23:41 EDT
Article-I.D.: umcp-cs.2496
Posted: Sat Jul 19 20:23:41 1986
Date-Received: Sat, 19-Jul-86 23:38:51 EDT
References: <323@enmasse.UUCP> <924@cyb-eng.UUCP>
Reply-To: chris@maryland.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 48

In article <323@enmasse.UUCP> someone writes:
>It often happens that software packages are set up to run on so many
>configurations that it is hard to read the code because of all the
>ifdefs. ... That is, filter out everything that is not going to be
>expanded by cpp while retaining the ifdefs that are going to be expanded,
>just for comment value.

I can understand the desire for this: reading code before using it
is often a good idea.  However, I am not at all convinced that this
is a good way to make the code more readable.  I have run into this
`ifdef problem' in the past, and the best solution I have come up
with so far is to properly group the dependencies and to construct
system-independent routines or `define's so that no further `if's
are required:

	#ifdef xyzzy
	#define strchr index
	#define strrchr rindex
	#define input_pending(fd) funny_system_call(fd)
	#else /* xyzzy */
	#define	input_pending(fd) routine_to_do_input_pending(fd)
	#endif /* xyzzy */

	#if defined(a) || defined(b)
	#define memcpy(d, s, n) bcopy(s, d, n)
	#endif /* a || b */

	#ifdef gleep
	routine()		/* for gleep */
	{
		...
	}
	#else /* gleep */
	routine()		/* for everyone else */
	{
		...
	}
	#endif /* gleep */

and so forth.

Of course, doing this to an existing program is much more difficult
than simply weeding out irrelevant `ifdef's.  It does, however, maintain
portability.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu