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Groups > comp.lang.c > #105776
| Newsgroups | comp.lang.c |
|---|---|
| Date | 2017-03-10 15:37 -0800 |
| References | <b0f99f2b-09a3-4510-89dd-c3511fba3321@googlegroups.com> <ln37ekhnzz.fsf@kst-u.example.com> <6efb4ec5-8a50-4ecd-95ac-3328682a7a03@googlegroups.com> <1c6010ab-c0e6-468b-8b9d-94cbe2aa4ac8@googlegroups.com> <r5c6cch9bq72g8tk64sl9di7lp67ucm66h@4ax.com> |
| Message-ID | <3fb4148c-8b5b-468c-8399-e5a5fc8575ee@googlegroups.com> (permalink) |
| Subject | Re: va_start without the first argument? |
| From | Thiago Adams <thiago.adams@gmail.com> |
On Friday, March 10, 2017 at 8:13:50 PM UTC-3, robert...@yahoo.com wrote:
> On Fri, 10 Mar 2017 14:53:02 -0800 (PST), Thiago Adams
> wrote:
>
> >On Friday, March 10, 2017 at 7:36:37 PM UTC-3, Thiago Adams wrote:
> >> On Friday, March 10, 2017 at 5:32:05 PM UTC-3, Keith Thompson wrote:
> >> > Thiago Adams writes:
> >> > > Is it possible to create a var args function without the
> >> > > first argument? (firstArgument in va_start)
> >> > >
> >> > > void F(...)
> >> >
> >> > No. The va_start macro requires the name of the last non-variadic
> >> > parameter, and syntax of a parameter-type-list requires at least one
> >> > parameter-declaration (N1570 6.7.6).
> >> >
> >> > [...]
> >>
> >>
> >> How it works?
> >> How does it knows the alignment/padding between the arguments?
> >>
> >
> >I opened the definition of va_list etc from Visual C++ 2017 includes:
> >
> >typedef char* va_list;
> >
> >
> >#define _ADDRESSOF(v) (&(v))
> >
> >#define _INTSIZEOF(n) ((sizeof(n) + sizeof(int) - 1) & ~(sizeof(int) - 1))
> >
> >#define __crt_va_start_a(ap, v) ((void)(ap = (va_list)_ADDRESSOF(v) + _INTSIZEOF(v)))
> >
> >#define __crt_va_arg(ap, t) (*(t*)((ap += _INTSIZEOF(t)) - _INTSIZEOF(t)))
> >
> >
> >#define __crt_va_end(ap) ((void)(ap = (va_list)0))
> >
> >The macro _INTSIZEOF has some tricks I don't understand.
>
>
> None of what you found in the MSVC headers actually means anything to
> you. *How* va_args is implemented is entirely implementation
> dependent, and the above may not even work on the next patch level of
> MSVC. *Some* implementation *is* required, but the innards are secret
> magic. That being said, I suspect a fair number of implementations
> are quite similar.
>
> As for what _INTSIZEOF is doing, it's computing the alignment (on the
> stack), or effective size, of a parameter on the stack. Basically it
> computes (ceil(sizeof(type)/sizeof(int))*sizeof(int)). IOW, it rounds
> the size up to the next whole numbers of ints. Which corresponds to
> how this implementation lays out parameters on the stack. And again,
> that happens to work for this *one* implementation, at *this* moment.
I am trying to understand to create va_list on heap.
(not working at this moment)
#include <stdarg.h>
#include <stdlib.h>
#include <stdio.h>
void F2(const char* fmt, va_list vl)
{
int i = va_arg(vl, int);
double d = va_arg(vl, double);
printf("i = %d, d = %lf\n", i, d);
}
void F(const char* fmt, ...)
{
va_list vl;
va_start(vl, fmt);
F2(fmt, vl);
va_end(vl);
}
va_list Heap(int i, double d)
{
//not working
void* pv = malloc(sizeof(int) + sizeof(double));
va_list * p = (va_list *)pv;
//*(int*)p = i;
//p += _INTSIZEOF(i);
va_arg(p, int) = i; //walk next
//*(double*)p = d;
//p += _INTSIZEOF(d);
va_arg(p, double) = d; //walk next
return pv;
}
int main()
{
F("", 1, 2.0);
F2("", Heap(1, 2.0));
return 0;
}
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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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