Path: utzoo!utgpu!watmath!cantuar!greg
From: greg@cantuar.UUCP (G. Ewing)
Newsgroups: comp.lang.c++
Subject: Re: Including header files minimally.
Message-ID: <867@cantuar.UUCP>
Date: 24 Nov 88 02:27:27 GMT
References: <3561@pt.cs.cmu.edu> <7860@nsc.nsc.com> <3614@pt.cs.cmu.edu> <559@redsox.UUCP>
Reply-To: greg@cantuar.UUCP (G. Ewing)
Organization: University of Canterbury, Christchurch, New Zealand
Lines: 39

Instead of including the same header file several times, what's
wrong with having the header file define a macro, including it
once, and then using the macro several times?

Using Larry Campbell (campbell@redsox.UUCP)'s example (sort of):

------------------------------message.h------------------------------
#define GENERATE_MESSAGES \
MSG(err_you_lose, "you lose big time, pal") \
MSG(err_get_real, "get real, pal") \
MSG(err_swap_mad, "swap read error, you lose your mind") \
#undef MSG
---------------------------end of message.h--------------------------

------------------------------message.c------------------------------
#include "message.h"

#define MSG(name, string) char name[] = string;
GENERATE_MESSAGES

#define MSG(name, string) extern char name[];
GENERATE_MESSAGES
---------------------------end of message.c--------------------------

Hmm... that perhaps wasn't the most useful of examples, but you get
what I mean, I hope. The point is that cpp could safely be hacked
to only ever include things once; anything that can be done with
multiply included files can also be done using macros.

Can anyone think of something that couldn't?

(P.S. I'd allow a backward-compatibility flag, before anyone jumps
on me...)

Greg Ewing				Internet: greg@cantuar.uucp
Spearnet: greg@nz.ac.cantuar		Telecom: +64 3 667 001 x8357
UUCP:	  ...!{watmath,munnari,mcvax,vuwcomp}!cantuar!greg
Post:	  Computer Science Dept, Univ. of Canterbury, Christchurch, New Zealand
Disclaimer: The presence of this disclaimer in no way implies any disclaimer.