Re: Meta-C question about header order

From	Kaz Kylheku <kaz@kylheku.com>
Newsgroups	comp.lang.c
Subject	Re: Meta-C question about header order
Date	2014-04-13 14:41 +0000
Organization	Aioe.org NNTP Server
Message-ID	<20140413072042.507@kylheku.com> (permalink)
References	<bqtj0hF60hpU1@mid.individual.net> <lnvbue8e6j.fsf@nuthaus.mib.org> <bqvbcrFhg97U3@mid.individual.net>

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On 2014-04-13, Jens Schweikhardt <usenet@schweikhardt.net> wrote:
> Keith Thompson <kst-u@mib.org> wrote
> 	in <lnvbue8e6j.fsf@nuthaus.mib.org>:
> # Jens Schweikhardt <usenet@schweikhardt.net> writes:
> #> hello, world\n
> #>
> #> consider a small project of 100 C source and 100 header files.
> #> The coding rules require that only C files include headers,
> #> headers are not allowed to include other headers (not sure if
> #> this is 100% the "IWYU - Include What You Use" paradigma).
> # 
> # That strikes me as a stupid^H^H^H^H^H^H suboptimal rule.
>
> I thought the same some time ago, but was able to leave the
> dark side behind me and become a good jedi.
>
> # You'll have headers that depend on other headers, but without that
> # relationship being expressed in the source.
>
> This is exactly what I want to avoid. I *want* the dependencies to be as
> clear as possible. I want to look at the include directives and have
> them stare right at me; it helps me realize when there is too much
> interdependency emerging and rethink modularization and write smaller
> sexier interfaces.

Also, here is the thing.  Suppose we have a module "g" which uses some data
structure and functions defined by "c" which is built up using data types "a"
and "b".

Module "g" might depend on "a" and "b" not only through "c",
but also directly.

This is why it is nice in "g.c" to also include the "a.h" and "b.h"
headers.

It is quite bothersome when "g.c" relies on the fact that, for instance sprintf
is declared because it happens that "c.h" contains interface that have FILE *
arguments, and includes <stdio.h> for that.  Then "g.c" is relying on the side
effect that "c.h" provides sprintf, which is brutally ugly, and shows that
attempts at automatic modularity through textual preprocessing are a failure.

In a language with real modularity, if we depended on a module C which depends
on some types in a standard I/O library, we would not inherit that entire
standard I/O library through B by accident: the module inheritance mechanism
"uses interface C" would not leak through irrelevant things, because C's
interface would in turn use only what it needs to, like the FILE * type.

With the enlightened inclusion approach, g.c has a right to use sprintf because
g.c contains, somewhere at the top, #include <stdio.h>.   This satisfies a
need in #include "c.h", and an *independent* need in the body of g.c.

When I'm reading g.c, I'm not bothered by things like "hey this uses malloc,
but it's not including <stdlib.h> anywhere!" (3 minutes later) Oh, it's
picking it up via foo.h (which needs stdlib.h for ldiv_t) and foo.h is included
by bar.h, which is included by xyzzy.h which g.c includes.

Thread

Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-12 19:37 +0000
  Re: Meta-C question about header order Keith Thompson <kst-u@mib.org> - 2014-04-12 13:51 -0700
    Re: Meta-C question about header order glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-13 00:11 +0000
    Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-13 11:40 +0000
      Re: Meta-C question about header order "BartC" <bc@freeuk.com> - 2014-04-13 13:10 +0100
      Re: Meta-C question about header order Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-13 06:29 -0700
      Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-13 14:41 +0000
    Re: Meta-C question about header order Ken Brody <kenbrody@spamcop.net> - 2014-04-15 10:36 -0400
  Re: Meta-C question about header order Richard Damon <Richard@Damon-Family.org> - 2014-04-12 16:58 -0400
    Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-13 03:40 +0000
      Re: Meta-C question about header order Ian Collins <ian-news@hotmail.com> - 2014-04-13 16:26 +1200
        Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-13 05:02 +0000
          Re: Meta-C question about header order Ian Collins <ian-news@hotmail.com> - 2014-04-13 17:21 +1200
            Re: Meta-C question about header order Ken Brody <kenbrody@spamcop.net> - 2014-04-15 10:59 -0400
            Re: Meta-C question about header order Ken Brody <kenbrody@spamcop.net> - 2014-04-15 11:02 -0400
          Re: Meta-C question about header order Ken Brody <kenbrody@spamcop.net> - 2014-04-15 10:59 -0400
            Re: Meta-C question about header order Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-15 08:26 -0700
            Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-15 15:56 +0000
      Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-13 11:34 +0000
      Re: Meta-C question about header order Richard Damon <Richard@Damon-Family.org> - 2014-04-13 15:04 -0400
      Re: Meta-C question about header order Ken Brody <kenbrody@spamcop.net> - 2014-04-15 10:52 -0400
  Re: Meta-C question about header order Ian Collins <ian-news@hotmail.com> - 2014-04-13 11:09 +1200
    Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-13 11:47 +0000
      Re: Meta-C question about header order Ian Collins <ian-news@hotmail.com> - 2014-04-14 08:54 +1200
        Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-13 21:37 +0000
          Re: Meta-C question about header order Ian Collins <ian-news@hotmail.com> - 2014-04-14 09:49 +1200
        Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-14 19:17 +0000
          Re: Meta-C question about header order Ian Collins <ian-news@hotmail.com> - 2014-04-15 10:24 +1200
            Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-16 19:58 +0000
          Re: Meta-C question about header order Richard Damon <Richard@Damon-Family.org> - 2014-04-14 21:45 -0400
  Re: Meta-C question about header order luser- -droog <luser.droog@gmail.com> - 2014-04-12 16:48 -0700
    Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-13 11:52 +0000
  Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-13 01:04 +0000
  Re: Meta-C question about header order "BartC" <bc@freeuk.com> - 2014-04-13 10:15 +0100
    Re: Meta-C question about header order Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-13 04:06 -0700
    Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-13 12:01 +0000
      Re: Meta-C question about header order "BartC" <bc@freeuk.com> - 2014-04-13 13:46 +0100
        Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-13 13:58 +0000
  Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-13 11:29 +0000
    Re: Meta-C question about header order Martin Shobe <martin.shobe@yahoo.com> - 2014-04-13 08:48 -0500
      Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-13 14:25 +0000
        Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-13 15:02 +0000
        Re: Meta-C question about header order Martin Shobe <martin.shobe@yahoo.com> - 2014-04-13 21:45 -0500
          Re: Meta-C question about header order Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-14 01:16 -0700
            Re: Meta-C question about header order "BartC" <bc@freeuk.com> - 2014-04-14 10:16 +0100
            Re: Meta-C question about header order Richard Damon <Richard@Damon-Family.org> - 2014-04-14 21:33 -0400
          Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-14 16:25 +0000
            Re: Meta-C question about header order Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-14 09:47 -0700
            Re: Meta-C question about header order Martin Shobe <martin.shobe@yahoo.com> - 2014-04-14 13:29 -0500
              Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-14 19:31 +0000
                Re: Meta-C question about header order Les Cargill <lcargill99@comcast.com> - 2014-04-14 20:03 -0500
                Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-15 01:04 +0000
              Re: Meta-C question about header order Keith Thompson <kst-u@mib.org> - 2014-04-14 15:15 -0700
            Re: Meta-C question about header order Richard Damon <Richard@Damon-Family.org> - 2014-04-14 22:01 -0400
            Re: Meta-C question about header order "BartC" <bc@freeuk.com> - 2014-04-15 09:51 +0100
              Re: Meta-C question about header order Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-15 06:01 -0700
                Re: Meta-C question about header order "BartC" <bc@freeuk.com> - 2014-04-15 14:29 +0100
                Re: Meta-C question about header order Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-15 10:38 -0700
                Re: Meta-C question about header order Kaz Kylheku <kaz@kylheku.com> - 2014-04-15 18:27 +0000
                Re: Meta-C question about header order Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-15 12:45 -0700
                Re: Meta-C question about header order ralph <nt_consulting@yahoo.com> - 2014-04-15 22:02 -0500
          Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-14 17:44 +0000
  Re: Meta-C question about header order Tim Rentsch <txr@alumni.caltech.edu> - 2014-04-19 01:25 -0700
    Re: Meta-C question about header order Richard Damon <Richard@Damon-Family.org> - 2014-04-19 10:30 -0400
      Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-23 19:47 +0000
        Re: Meta-C question about header order James Kuyper <jameskuyper@verizon.net> - 2014-04-23 15:53 -0400
      Re: Meta-C question about header order Tim Rentsch <txr@alumni.caltech.edu> - 2014-06-10 09:25 -0700
    Re: Meta-C question about header order Jens Schweikhardt <usenet@schweikhardt.net> - 2014-04-23 19:27 +0000
      Re: Meta-C question about header order Tim Rentsch <txr@alumni.caltech.edu> - 2014-06-10 09:40 -0700

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