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Re: gcc and 'include'

From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c
Subject Re: gcc and 'include'
Date 2026-03-30 00:41 -0700
Organization A noiseless patient Spider
Message-ID <86y0j9228t.fsf@linuxsc.com> (permalink)
References <10q4ceb$38i2d$1@dont-email.me> <10q7pgg$bju3$1@dont-email.me> <86fr5k2yyg.fsf@linuxsc.com> <10qcbqr$1vvfo$1@dont-email.me>

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Andrey Tarasevich <noone@noone.net> writes:

> On Sat 3/28/2026 12:30 AM, Tim Rentsch wrote:
>
>>> So, you have to choose a site for the out-of-line definition - one and
>>> only one translation unit, in which you have to declare your function
>>> as `extern inline`. This translation unit will host the out-of-line
>>> "body" for the function.  Since in your case you have only one
>>> translation unit, you can do it as
>>>
>>>    inline int F(){return rand();}
>>>    extern inline int F(); /* <- emits an out-of-line definition */
>>
>> Note that both 'extern' and 'inline' here can be dispensed with
>> on the declaration.  Rather than 'extern inline int F();' it
>> suffices to say
>>
>>      int F();
>>
>> to force the compiler to produce a real function body with
>> a linker-visible symbol.  And doing that doesn't interfere
>> with the function being an inline function.
>
> Yes, I see that any kind of `extern` declaration for this function
> (including the implicit `extern`) causes the compiler to emit the
> non-inline definition for the corresponding TU, i.e. any of
>
>   int F();
>   extern int F();
>   extern inline int F();
>
> lead to the same effect.
>
> Personally, if following this approach (i.e. add a re-declaration to
> one .c file), I'd probably stick to `extern inline` version just to
> express the intent better:  to make it clear that this declaration was
> placed there specifically for that purpose - to emit a non-inline body
> for an inline function.

I wouldn't want to advise you on how to write your own code, however
to me this choice seems rather backwards.  I follow the same rule
for functions that I do for variables - 'extern' for declarations to
mean defined somewhere else, and without 'extern' for definitions to
mean defined here (or at least in this compilation unit).  My habit
for 'static' functions is to give a foward declaration (of course
with 'static') near the start of the file, and to not use either
'static' or 'extern' on the actual definition.  Following this rule
lets me change the linkage from internal to external by changing
only one place (the factoring principle, later to be called "Don't
Repeat Yourself").  My preference would be to follow the same rule
for 'static' variables, but unfortunately the C standard doesn't
allow that, which strikes me as a shortsighted decision, but oh
well.

> Otherwise, it would like like an ordinary
> function declaration sitting in the middle of the file for no apparent
> reason.  (Of course, one can also write a comment stating the purpose.)

Right.  I would add to that that if there is one inline external
function then there is likely more than one, and the definitions for
all those functions could be put together, right at the end of the
source file, in which case it would be more obvious what they were
doing (or that only one comment would be needed for all).

> P.S. As it has already been mentioned somewhere in the thread, there
> an alternative, header-only approach:  just use the preprocessor to
> alter the header file definition in one chosen TU
>
>   #ifdef MAKE_BODY_
>     extern
>   #endif /* MAKE_BODY_ */
>   inline int F() { /* whatever */ }

Ugh.  This idea is one of those appropriately described as "too
clever by half".  The downsides greatly outweigh the upsides.

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Thread

gcc and 'include' Bart <bc@freeuk.com> - 2026-03-26 22:36 +0000
  Re: gcc and 'include' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-26 16:12 -0700
    Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-27 10:55 +0000
      Re: gcc and 'include' David Brown <david.brown@hesbynett.no> - 2026-03-27 13:49 +0100
      Re: gcc and 'include' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-27 10:51 -0700
      Re: gcc and 'include' Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-03-27 21:27 +0000
        Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-27 22:05 +0000
          Re: gcc and 'include' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-27 17:03 -0700
          Re: gcc and 'include' Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-03-28 05:10 +0100
          Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-28 20:37 +0300
            Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-28 18:33 +0000
              Re: gcc and 'include' antispam@fricas.org (Waldek Hebisch) - 2026-03-29 00:53 +0000
                Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-29 22:37 +0100
                Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-30 05:33 -0700
                Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-30 14:42 +0100
                Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-30 16:53 +0300
                Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-30 18:11 +0100
                Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-30 08:27 -0700
                Re: gcc and 'include' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-30 11:54 -0700
                Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-30 21:54 +0100
                Re: gcc and 'include' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-30 18:07 -0700
                Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-31 11:39 +0100
                Re: gcc and 'include' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-31 13:56 -0700
                Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-06 20:56 -0700
                Re: gcc and 'include' Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-04-06 23:12 -0700
                Re: gcc and 'include' James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-03-30 21:06 -0400
              Re: gcc and 'include' David Brown <david.brown@hesbynett.no> - 2026-03-29 11:24 +0200
                Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-29 12:44 +0100
                Re: gcc and 'include' David Brown <david.brown@hesbynett.no> - 2026-03-31 15:57 +0200
            Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-30 07:20 -0700
          Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-30 05:07 -0700
  Re: gcc and 'include' Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-03-27 00:25 +0000
    Re: gcc and 'include' Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-03-30 07:13 +0000
      Re: gcc and 'include' Andrey Tarasevich <noone@noone.net> - 2026-03-30 07:54 -0700
        Re: gcc and 'include' Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-03-31 01:46 +0000
          Re: gcc and 'include' antispam@fricas.org (Waldek Hebisch) - 2026-03-31 05:28 +0000
  Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-27 04:10 +0300
    Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-26 19:08 -0700
      Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-27 16:47 +0300
        Re: gcc and 'include' David Brown <david.brown@hesbynett.no> - 2026-03-27 16:43 +0100
        Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-27 09:03 -0700
          Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-29 11:46 +0300
            Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-30 08:19 -0700
              Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-30 20:08 +0300
                Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-31 00:26 -0700
                Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-31 11:27 +0300
                Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-07 09:45 -0700
        Re: gcc and 'include' Andrey Tarasevich <noone@noone.net> - 2026-03-28 10:25 -0700
          Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-29 10:37 +0300
            Re: gcc and 'include' David Brown <david.brown@hesbynett.no> - 2026-03-29 11:30 +0200
            Re: gcc and 'include' Andrey Tarasevich <noone@noone.net> - 2026-03-29 07:22 -0700
            Re: gcc and 'include' James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-03-29 13:56 -0400
              Re: gcc and 'include' Michael S <already5chosen@yahoo.com> - 2026-03-29 21:39 +0300
                Re: gcc and 'include' James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-03-29 20:08 -0400
                Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-30 01:58 +0100
                Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-30 07:59 -0700
  Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-26 19:06 -0700
  Re: gcc and 'include' Bart <bc@freeuk.com> - 2026-03-27 16:20 +0000
    Re: gcc and 'include' David Brown <david.brown@hesbynett.no> - 2026-03-27 18:07 +0100
    Re: gcc and 'include' James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-03-28 18:48 -0400
  Re: gcc and 'include' Andrey Tarasevich <noone@noone.net> - 2026-03-27 22:38 -0700
    Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-28 00:30 -0700
      Re: gcc and 'include' Andrey Tarasevich <noone@noone.net> - 2026-03-29 16:15 -0700
        Re: gcc and 'include' Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-30 00:41 -0700

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