Groups | Search | Server Info | Login | Register

Groups > comp.lang.c > #397323

Re: gcc and 'include'

Show all headers | View raw

On Tue, 31 Mar 2026 00:26:09 -0700
Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:

> Michael S <already5chosen@yahoo.com> writes:
> 
> > On Mon, 30 Mar 2026 08:19:52 -0700
> > Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
> >  
> >> Michael S <already5chosen@yahoo.com> writes:
> >>  
> >>> On Fri, 27 Mar 2026 09:03:23 -0700
> >>> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
> >>>  
> >>>> Michael S <already5chosen@yahoo.com> writes:
> >>>>  
> >>>>> On Thu, 26 Mar 2026 19:08:16 -0700
> >>>>> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
> >>>>>  
> >>>>>> Michael S <already5chosen@yahoo.com> writes:
> >>>>>>  
> >>>>>>> On Thu, 26 Mar 2026 22:36:59 +0000
> >>>>>>> Bart <bc@freeuk.com> wrote:
> >>>>>>>  
> >>>>>>>> Take this program:
> >>>>>>>>
> >>>>>>>>    #include <stdlib.h>
> >>>>>>>>
> >>>>>>>>    inline int F(){return rand();}
> >>>>>>>>
> >>>>>>>>    int main(void) {
> >>>>>>>>        return F();
> >>>>>>>>    }
> >>>>>>>>
> >>>>>>>> This compiles fine with gcc using -O1 -O2 -O3.
> >>>>>>>>
> >>>>>>>> But compile without optimising, and it fails to link as it
> >>>>>>>> can't find a function 'F'.
> >>>>>>>>
> >>>>>>>> Is it supposed to behave like that?  I assume no discrete
> >>>>>>>> function F is being generated because of the 'inline'
> >>>>>>>> attribute, but you'd think it would ignore that if
> >>>>>>>> inlining wasn't enabled.
> >>>>>>>>
> >>>>>>>> [...]  
> >>>>>>>
> >>>>>>> Sounds like a bug introduced during transition to c99/gnu99
> >>>>>>> front end.
> >>>>>>> With gcc4.x,  which defaults to gnu89 it still works.
> >>>>>>> Also works with the latest gcc -std=gnu89
> >>>>>>> But there is no hope that gcc maintaines will ever admit that
> >>>>>>> it is a bug.  
> >>>>>>
> >>>>>> It isn't a bug.  The C standard allows this behavior.  
> >>>>>
> >>>>> So, by C standard, there is no situation in which 'inline'
> >>>>> with no addition qualifuers like 'static' or 'extern' can be
> >>>>> used with predictabe outcome?  
> >>>>

<<<<<<<<<<<<<<<<<<
> >>>> That depends on just how you mean the question.  If we have this
> >>>> source file
> >>>>
> >>>>     inline int
> >>>>     F(){
> >>>>         return 0;
> >>>>     }
> >>>>
> >>>>     int
> >>>>     main(void){
> >>>>         return F();
> >>>>     }
> >>>>
> >>>> then we might get an undefined reference for F().  However if we
> >>>> expand that source file just slightly, to
> >>>>
> >>>>     inline int
> >>>>     F(){
> >>>>         return 0;
> >>>>     }
> >>>>
> >>>>     int
> >>>>     main(void){
> >>>>         return F();
> >>>>     }
> >>>>
> >>>>     int F();
> >>>>
> >>>> then the program has well-defined behavior.  This result obtains
> >>>> because the function F() now has a declaration that is
> >>>> (implicitly) external, and without specifying 'inline', in
> >>>> addition to the original inline definition.  
> >>>

<<<<<<<<<<<<<<<<<<


> >>> It is indeed well-defined.  But well-defined behavior does not
> >>> match the most probable intention of programmer, which is to
> >>> create a body of F() in case that it was not actually inlined and
> >>> to *not* create it otherwise.  
> >>
> >> I simply disagree.  The behavior you describe is what people expect
> >> for static inline functions.  It doesn't make sense that they would
> >> expect the same thing for non-static inline functions, if they had
> >> taken some time to think about it.
> >>  
> >>> For something like MSVC it does not matter, because by default it
> >>> does not link unused functions into executive.  But something like
> >>> gcc by default links everything in.  
> >>
> >> That depends on what you mean by "by default".  gcc does not
> >> produce an actual function body for any optimization level
> >> above -O0.  Surely the most common practice these days is to
> >> enable some optimization level above -O0.  
> >
> > In the comment above I was talking specifically about that:
> > https://godbolt.org/z/4TazP4sq1  
> 
> I don't know what you were expecting me to learn by looking at
> that page.  As far as I can tell it adds no information beyond
> what has already been presented.
> 

The page shows that when, according to your suggestion, source code is
modified to make it well-defined then body of F() is generated
regardless of optimization level. As you likely expected. 
It was a point of suggested modification, was not it?

> Also I'm surprised that you didn't say anything in reaction to the
> first paragraph of my comments.  No conclusion, just surprised.

What do you consider 1st paragraph?
My reading was that lines between <<<<<<<<<<<<<<<<<< marks were meant to
be read together, as a single item.

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar

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

csiph-web