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Groups > comp.lang.c > #150062
| From | "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Offsetof with array elements |
| Date | 2020-02-16 16:03 -0800 |
| Organization | Aioe.org NNTP Server |
| Message-ID | <r2cl93$1pgc$1@gioia.aioe.org> (permalink) |
| References | <r1udrq$hoe$1@dont-email.me> |
On 2/11/2020 6:31 AM, David Brown wrote:
> #include <stddef.h>
>
> struct S {
> int a[10];
> };
>
> int test(int i) {
> return offsetof(struct S, a[i]);
> }
>
>
> Is this allowed in standard C? It works in most compilers I tried (even
> in the most pedantic modes I checked on gcc), but failed in one embedded
> compiler. According to the standard, "offsetof" expands to "an integer
> constant expression", and "&s.a[i]" must evaluate to an address constant
> (where "s" is an object of type "struct S").
>
> So by my reading, the standard C does not require the expression in
> "test" to be valid, and allows a conforming compiler to reject it.
> Equally, it does not require a diagnostic, and allows a conforming
> compiler to accept it without complaint.
>
Don't know exactly why, but this reminds me of the following macro that
can determine the alignment of a type:
#define RALLOC_ALIGN_OF(mp_type) \
offsetof( \
struct { \
char pad_RALLOC_ALIGN_OF; \
mp_type type_RALLOC_ALIGN_OF; \
}, \
type_RALLOC_ALIGN_OF \
)
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Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-11 15:31 +0100
Re: Offsetof with array elements Guillaume <message@bottle.org> - 2020-02-11 16:08 +0100
Re: Offsetof with array elements James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-11 08:32 -0800
Re: Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-11 18:46 +0100
Re: Offsetof with array elements Manfred <noname@add.invalid> - 2020-02-11 19:24 +0100
Re: Offsetof with array elements Manfred <noname@add.invalid> - 2020-02-11 19:36 +0100
Re: Offsetof with array elements James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-11 22:50 -0500
Re: Offsetof with array elements Manfred <noname@add.invalid> - 2020-02-12 13:53 +0100
Re: Offsetof with array elements Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-02-18 01:43 -0800
Re: Offsetof with array elements Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-02-18 01:39 -0800
Re: Offsetof with array elements Bart <bc@freeuk.com> - 2020-02-11 16:56 +0000
Re: Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-11 18:49 +0100
Re: Offsetof with array elements Bonita Montero <Bonita.Montero@gmail.com> - 2020-02-11 21:00 +0100
Re: Offsetof with array elements Bart <bc@freeuk.com> - 2020-02-11 20:13 +0000
Re: Offsetof with array elements Bonita Montero <Bonita.Montero@gmail.com> - 2020-02-11 21:24 +0100
Re: Offsetof with array elements Bart <bc@freeuk.com> - 2020-02-11 20:33 +0000
Re: Offsetof with array elements Bonita Montero <Bonita.Montero@gmail.com> - 2020-02-11 21:39 +0100
Re: Offsetof with array elements Bart <bc@freeuk.com> - 2020-02-11 20:48 +0000
Re: Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-12 10:56 +0100
Re: Offsetof with array elements Bonita Montero <Bonita.Montero@gmail.com> - 2020-02-12 14:07 +0100
Re: Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-12 15:24 +0100
Re: Offsetof with array elements Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-12 10:39 +0000
Re: Offsetof with array elements Bonita Montero <Bonita.Montero@gmail.com> - 2020-02-12 14:08 +0100
Re: Offsetof with array elements James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-12 05:29 -0800
Re: Offsetof with array elements James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-12 11:45 -0800
Re: Offsetof with array elements Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-12 17:50 +0000
Re: Offsetof with array elements Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-02-16 02:41 -0800
Re: Offsetof with array elements Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-16 11:18 +0000
Re: Offsetof with array elements already5chosen@yahoo.com - 2020-02-13 02:42 -0800
Re: Offsetof with array elements James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-14 00:20 -0500
Re: Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-14 08:24 +0100
Re: Offsetof with array elements already5chosen@yahoo.com - 2020-02-14 03:59 -0800
Re: Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-14 15:25 +0100
Re: Offsetof with array elements already5chosen@yahoo.com - 2020-02-16 03:15 -0800
Re: Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-16 14:09 +0100
Re: Offsetof with array elements already5chosen@yahoo.com - 2020-02-16 06:36 -0800
Re: Offsetof with array elements James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-15 08:18 -0500
Re: Offsetof with array elements David Brown <david.brown@hesbynett.no> - 2020-02-15 15:49 +0100
Re: Offsetof with array elements fir <profesor.fir@gmail.com> - 2020-02-12 04:40 -0800
Re: Offsetof with array elements "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-02-16 16:03 -0800
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