Re: Meta-C question about header order

From	Ian Collins <ian-news@hotmail.com>
Newsgroups	comp.lang.c
Subject	Re: Meta-C question about header order
Date	2014-04-13 17:21 +1200
Message-ID	<bqul5uFb55dU6@mid.individual.net> (permalink)
References	<bqtj0hF60hpU1@mid.individual.net> <CNh2v.39400$Wy2.31318@en-nntp-16.dc1.easynews.com> <20140412201155.452@kylheku.com> <bquhvdFb55dU5@mid.individual.net> <20140412214930.120@kylheku.com>

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Kaz Kylheku wrote:
> On 2014-04-13, Ian Collins <ian-news@hotmail.com> wrote:
>> Kaz Kylheku wrote:
>>> On 2014-04-12, Richard Damon <Richard@Damon-Family.org> wrote:
>>>> On 4/12/14, 3:37 PM, Jens Schweikhardt wrote:
>>>>> 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).
>>>>>
>>>>
>>>> A rule that says that a header can NOT include other headers, even if it
>>>> depends on the contents of that header is, in my mind, totally broken.
>>>
>>> I used to think so fresh out of school.
>>>
>>> But actually, this style is superior because leads to much cleaner code
>>> organization and faster compilation. It keeps everything "tight".
>>
>> The faster compilation argument is a non-starter these days.
>
> Personal preference.
>
> Even if the recompile is fast thanks to the hardware, I would still rather wait
> 5 seconds for a recompile than 8 seconds.

My lost point was that in practice where the includes are included makes 
no real difference to the build time.

> The faster the machines get, the less I tolerate response and turnaround time.

I must admit I do miss being able to do crosswords during builds :)

>>> I chose this approach in the TXR project, and am very pleased with it.
>>> I understand now why some people recommend it.
>>>
>>> The compiler diagnostics are simpler. None of this:
>>>
>>> "Syntax error in line 32 of X
>>> included from line 42 of Y,
>>> included from line 15 of Z ..."
>>>
>>> Also, the dependencies are easy to understand. If you look at the
>>> list of #include directives at the top of a .c file, those are
>>> the files which, if they are touched, will trigger a re-compile
>>> of this file. And no others!
>>
>> And?
>
> And, I like it; I think it is beautiful to have an explicit view of the
> dependencies laid out in the code.
>
> Another benefit: no ugly #ifndef SYMBOL / #define SYMBOL ... #endif crap
> in all the header files! Just a comment block and the definitions!

Yes, but if there are platform or other outside dependencies which 
govern which headers a particular configuration requires, they have to 
be written out in each source file.  If code were write once, change 
never this wouldn't be a problem.  But it isn't (except for perl, which 
we all know is a write only language).

>>> It's easy to generate a dependency makefile. If we have a foo.c
>>> with these contents:
>>>
>>>     #include <stdio.h>
>>>     #include "a.h"
>>>     #include "b.h"
>>>     #include "foo.h"
>>>
>>> then the dependency rule is precisely this:
>>>
>>>     foo.o: foo.c a.h b.h foo.h
>>
>> A decent make will do this for you.
>
> I don't know of any make that generates dependencies. Compilers do (e.g gcc -MM).
>
> This is nicer.

OK, "the build system" will do this for you!

>> So would you rather include and maintain all of the headers (and
>> accompanying platform specific conditional include spaghetti) a
>> particular library uses in every source file, or just include the
>> library's public header?  All of that crud is the encapsulation referred
>> to here.
>
> When we divide the program into libraries, we are adding a level to the
> organizational hirarchy. So it would be too pigheaded not to allow the
> permitted #include level to also increase by one level.
>
> The library does encapsulate; as a user of the library, I don't care
> about how it is divided into modules.
>
> Of course a library is a unit, and it should ideally provide one simple header
> (or one for each major feature area).

No argument there then.

-- 
Ian Collins

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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