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Re: va_start without the first argument?

From Ike Naar <ike@iceland.freeshell.org>
Newsgroups comp.lang.c
Subject Re: va_start without the first argument?
Date 2017-03-15 21:55 +0000
Organization A noiseless patient Spider
Message-ID <slrn3vfsocje8a.ffd.ike@iceland.freeshell.org> (permalink)
References (10 earlier) <oa8p90$n6q$1@dont-email.me> <lnh92vkf22.fsf@kst-u.example.com> <UcVxA.62280$Bp6.51791@fx36.iad> <ln4lyvk8ql.fsf@kst-u.example.com> <931c4a06-8f14-4c60-8a41-f34b36d07563@googlegroups.com>

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On 2017-03-14, supercat@casperkitty.com <supercat@casperkitty.com> wrote:
> On Tuesday, March 14, 2017 at 1:34:55 PM UTC-5, Keith Thompson wrote:
>> Why?  In both David's version and mine, the reference to x in
>> the macro definition is already parenthesized.  The fact that the
>> parentheses are for a function call (or macro invocation?) rather
>> than grouping doesn't matter as far as operator precedence is
>> concerned.  Similarly, if a macro definition uses an argument as
>> an array index, it's already surrounded by [] so it doesn't need
>> additional ().
>
> If bar is a function-like macro which is supposed to accept a single value,
> there are corner cases in which
>
>     #define foo(x) bar(x)
>
> may fail but adding extra parentheses around x would make it work.  One
> might question whether any sane person would write client-side code that
> would break the above definition of foo(x), or whether one should try
> to defend against client-side programmers that are crazy enough to do so,
> but adding parentheses will guard against such things.
>
> BTW, a sample corner case where the parentheses are necessary:
>
>     #define triangles(x) (int const[]){1,3,6,10}[x]
>
>     #define mac1(x) x
>     #define mac2(x) mac1(x)
>
>     int test99()
>     {
>       return mac2(triangles(3));
>     }
>
> The above will fail compilation, but changing the mac2 definition to
>
>     #define mac2(x) mac1(x)
>
> will fix it.

What's the difference between

    #define mac2(x) mac1(x)

and

    #define mac2(x) mac1(x)

?

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va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-10 11:57 -0800
  Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-10 12:04 -0800
  Re: va_start without the first argument? Keith Thompson <kst-u@mib.org> - 2017-03-10 12:32 -0800
    Re: va_start without the first argument? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-03-10 15:51 -0500
    Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-10 14:36 -0800
      Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-10 14:53 -0800
        Re: va_start without the first argument? Robert Wessel <robertwessel2@yahoo.com> - 2017-03-10 17:14 -0600
          Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-10 15:37 -0800
            Re: va_start without the first argument? Robert Wessel <robertwessel2@yahoo.com> - 2017-03-10 23:12 -0600
              Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 10:29 -0700
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 11:31 -0700
                Re: va_start without the first argument? scott@slp53.sl.home (Scott Lurndal) - 2017-03-13 18:40 +0000
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 12:31 -0700
            Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-11 19:53 +0100
              Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-11 19:05 +0000
                Re: va_start without the first argument? Keith Thompson <kst-u@mib.org> - 2017-03-11 11:56 -0800
              Re: va_start without the first argument? antispam@math.uni.wroc.pl - 2017-03-12 05:41 +0000
              Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-12 13:52 +0100
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-12 14:40 +0000
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-12 18:13 +0100
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-12 18:04 +0000
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-12 21:04 +0100
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-12 21:02 +0000
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-12 22:40 +0100
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-12 15:51 -0700
                Re: va_start without the first argument? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-03-12 16:52 -0700
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-13 00:56 +0100
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-13 09:17 -0700
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-13 17:54 +0000
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-13 22:12 +0100
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-13 22:48 +0000
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-14 13:46 +0100
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-14 13:37 +0000
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-14 15:24 +0100
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-14 08:25 -0700
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-14 17:02 +0100
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-14 09:45 -0700
                Re: va_start without the first argument? Keith Thompson <kst-u@mib.org> - 2017-03-14 09:15 -0700
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-14 10:02 -0700
                Re: va_start without the first argument? jt@toerring.de (Jens Thoms Toerring) - 2017-03-14 20:32 +0000
                Re: va_start without the first argument? raltbos@xs4all.nl (Richard Bos) - 2017-03-14 07:44 +0000
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-14 13:38 +0100
                Re: va_start without the first argument? Keith Thompson <kst-u@mib.org> - 2017-03-14 08:57 -0700
                Re: va_start without the first argument? Keith Thompson <kst-u@mib.org> - 2017-03-13 11:21 -0700
                Re: va_start without the first argument? scott@slp53.sl.home (Scott Lurndal) - 2017-03-13 18:33 +0000
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-13 22:08 +0100
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-13 15:23 -0700
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-14 13:58 +0100
                Re: va_start without the first argument? Keith Thompson <kst-u@mib.org> - 2017-03-14 09:18 -0700
                Re: va_start without the first argument? scott@slp53.sl.home (Scott Lurndal) - 2017-03-14 16:52 +0000
                Re: va_start without the first argument? Keith Thompson <kst-u@mib.org> - 2017-03-14 11:34 -0700
                Re: va_start without the first argument? scott@slp53.sl.home (Scott Lurndal) - 2017-03-14 18:54 +0000
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-14 13:30 -0700
                Re: va_start without the first argument? Ike Naar <ike@iceland.freeshell.org> - 2017-03-15 21:55 +0000
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-15 15:16 -0700
                Re: va_start without the first argument? Philip Lantz <prl@canterey.us> - 2017-03-23 21:04 -0700
                Re: va_start without the first argument? David Brown <david.brown@hesbynett.no> - 2017-03-14 21:48 +0100
                Re: va_start without the first argument? scott@slp53.sl.home (Scott Lurndal) - 2017-03-14 14:01 +0000
                Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-14 07:42 -0700
                Re: va_start without the first argument? scott@slp53.sl.home (Scott Lurndal) - 2017-03-14 12:38 +0000
                Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-13 01:11 +0100
                Re: va_start without the first argument? Ian Collins <ian-news@hotmail.com> - 2017-03-13 15:43 +1300
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-13 10:36 +0000
                Re: va_start without the first argument? Ian Collins <ian-news@hotmail.com> - 2017-03-14 07:33 +1300
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-13 19:00 +0000
                Re: va_start without the first argument? Ian Collins <ian-news@hotmail.com> - 2017-03-14 08:05 +1300
                Re: va_start without the first argument? BartC <bc@freeuk.com> - 2017-03-13 23:10 +0000
                Re: va_start without the first argument? Ian Collins <ian-news@hotmail.com> - 2017-03-14 17:38 +1300
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-14 05:48 -0700
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 12:12 -0700
                Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-12 19:39 +0100
  Re: va_start without the first argument? jt@toerring.de (Jens Thoms Toerring) - 2017-03-10 20:49 +0000
    Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-10 14:41 -0800
      Re: va_start without the first argument? John Bode <jfbode1029@gmail.com> - 2017-03-10 16:05 -0800
        Re: va_start without the first argument? jacob navia <jacob@jacob.remcomp.fr> - 2017-03-11 21:47 +0100
          Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-11 13:07 -0800
            Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-11 22:24 +0100
              Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 05:44 -0700
                Re: va_start without the first argument? Jerry Stuckle <jstucklex@attglobal.net> - 2017-03-13 08:59 -0400
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 06:17 -0700
                Re: va_start without the first argument? Jerry Stuckle <jstucklex@attglobal.net> - 2017-03-13 13:27 -0400
                Re: va_start without the first argument? Jerry Stuckle <jstucklex@attglobal.net> - 2017-03-13 13:30 -0400
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 11:00 -0700
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 10:34 -0700
          Re: va_start without the first argument? antispam@math.uni.wroc.pl - 2017-03-12 06:00 +0000
          Re: va_start without the first argument? gordonb.gas5o@burditt.org (Gordon Burditt) - 2017-03-17 09:46 -0500
            Re: va_start without the first argument? supercat@casperkitty.com - 2017-03-17 09:07 -0700
        Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 05:39 -0700
          Re: va_start without the first argument? John Bode <jfbode1029@gmail.com> - 2017-03-13 11:40 -0700
            Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 12:01 -0700
              Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-13 23:17 +0100
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 16:15 -0700
                Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-14 00:26 +0100
                Re: va_start without the first argument? kikiins@gmail.com - 2017-03-13 16:51 -0700
                Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-14 01:12 +0100
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 18:24 -0700
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-13 18:57 -0700
                Re: va_start without the first argument? raltbos@xs4all.nl (Richard Bos) - 2017-03-14 07:59 +0000
                Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-14 06:45 -0700
                Re: va_start without the first argument? Robert Wessel <robertwessel2@yahoo.com> - 2017-03-13 18:20 -0500
                Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-14 00:31 +0100
    Re: va_start without the first argument? raltbos@xs4all.nl (Richard Bos) - 2017-03-13 16:51 +0000
  Re: va_start without the first argument? jacobnavia <jacob@jacob.remcomp.fr> - 2017-03-11 19:29 +0100
  Re: va_start without the first argument? Siri Cruise <chine.bleu@yahoo.com> - 2017-03-11 12:12 -0800
  Re: va_start without the first argument? luser droog <luser.droog@gmail.com> - 2017-03-13 05:37 -0700
    Re: va_start without the first argument? luser droog <luser.droog@gmail.com> - 2017-03-15 11:45 -0700
      Re: va_start without the first argument? Thiago Adams <thiago.adams@gmail.com> - 2017-03-15 13:39 -0700

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