Xref: utzoo comp.lang.c:23259 comp.lang.c++:5207 gnu.g++:471
Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!hplabs!hplabsz!sartin
From: sartin@hplabsz.HPL.HP.COM (Rob Sartin)
Newsgroups: comp.lang.c,comp.lang.c++,gnu.g++
Subject: Re: A solution to the multiple inclusion problem
Keywords: #include c
Message-ID: <4207@hplabsz.HPL.HP.COM>
Date: 24 Oct 89 19:35:57 GMT
References: <14240@well.UUCP> <1989Oct23.191634.6345@cs.rochester.edu> <1659@atanasoff.cs.iastate.edu>
Reply-To: sartin@hplabsz.UUCP (Rob Sartin)
Distribution: comp
Organization: Hewlett-Packard, Software Technology Lab
Lines: 35

In article <1659@atanasoff.cs.iastate.edu> hascall@atanasoff.UUCP (John Hascall) writes:
>    Since the impending ANSI standard requires that including a file more
>    than once have exactly the same effect as including it once...why can't
>    a compiler just ignore #includes for files it has already #included???
>    (at least for the "standard" includes)

That introduces some potential oddities for <assert.h> which doesn't try
to prevent from being included twice.  My C++ 2.0 assert.h includes a
comment that says:

/* This header file intentionally has no wrapper, since the user
*  may want to re-include it to turn off/on assertions for only
*  a portion of the source file.
*/

>    but, does anyone do this thing in the *same* file??

=begin foo.c
#define NDEBUG
#include <assert.h>
int tested_function()
{
...
}

#undef NDEBUG
#include <assert.h>
int untested_function()
{
}
=end foo.c

Rob Sartin			internet: sartin@hplabs.hp.com
Software Technology Lab 	uucp    : hplabs!sartin
Hewlett-Packard			voice	: (415) 857-7592