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| From | Noob <root@127.0.0.1> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Generic read/write function - casting vs union |
| Date | 2016-09-22 12:36 +0200 |
| Organization | A noiseless patient Spider |
| Message-ID | <ns0c7q$49a$1@dont-email.me> (permalink) |
| References | <ns08ge$o5v$1@dont-email.me> <ns0ah9$uhd$1@dont-email.me> |
On 22/09/2016 12:07, Richard Heathfield wrote:
> On 22/09/16 10:33, Noob wrote:
>
>> As you can see, I had to cast away the constness of the write buffer,
>> because my generic function does change buf, only in the read case.
>> But I think there is no undefined behavior, because I do not modify
>> the const buf. Is that correct?
>
> Yes. Beware, however, of the name access(), as it is a common extension.
> (In fact, I'm pretty sure it's in POSIX.)
The actual name is raw_access. (In any case, thanks for pointing it out.)
>> Something I didn't mention is that the access function actually
>> updates buf in the EPILOG.
>>
>> buf->in += len;
>>
>> Is it *100%* guaranteed that incrementing buf->in is strictly
>> equivalent to incrementing buf->out ?
>
> You can't do pointer arithmetic on void *. :-)
Right. Assume union buf { u8 *in; const u8 *out; }; instead
(with a suitable definition for u8 in scope).
> But you can assign to an unsigned char *, and increment that instead.
And it is 100% safe, because u8 * and const u8 * are "compatible" ?
Regards.
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Generic read/write function - casting vs union Noob <root@127.0.0.1> - 2016-09-22 11:33 +0200
Re: Generic read/write function - casting vs union Richard Heathfield <rjh@cpax.org.uk> - 2016-09-22 11:07 +0100
Re: Generic read/write function - casting vs union Noob <root@127.0.0.1> - 2016-09-22 12:36 +0200
Re: Generic read/write function - casting vs union Richard Heathfield <rjh@cpax.org.uk> - 2016-09-22 14:07 +0100
Re: Generic read/write function - casting vs union Keith Thompson <kst-u@mib.org> - 2016-09-22 11:48 -0700
Re: Generic read/write function - casting vs union raltbos@xs4all.nl (Richard Bos) - 2016-09-23 19:42 +0000
Re: Generic read/write function - casting vs union BartC <bc@freeuk.com> - 2016-09-22 13:11 +0100
Re: Generic read/write function - casting vs union Noob <root@127.0.0.1> - 2016-09-22 14:46 +0200
Re: Generic read/write function - casting vs union David Brown <david.brown@hesbynett.no> - 2016-09-22 15:10 +0200
Re: Generic read/write function - casting vs union Noob <root@127.0.0.1> - 2016-09-22 15:36 +0200
Re: Generic read/write function - casting vs union Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-22 19:28 -0700
Re: Generic read/write function - casting vs union David Brown <david.brown@hesbynett.no> - 2016-09-23 09:59 +0200
Re: Generic read/write function - casting vs union Barry Schwarz <schwarzb@dqel.com> - 2016-09-22 20:11 -0700
Re: Generic read/write function - casting vs union Richard Damon <Richard@Damon-Family.org> - 2016-09-23 11:13 -0400
Re: Generic read/write function - casting vs union Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-22 08:35 -0700
Re: Generic read/write function - casting vs union Noob <root@127.0.0.1> - 2016-09-25 23:17 +0200
Re: Generic read/write function - casting vs union Noob <root@127.0.0.1> - 2016-09-26 14:54 +0200
Re: Generic read/write function - casting vs union boon <root@localhost.localdomain> - 2016-09-26 19:47 +0200
Re: Generic read/write function - casting vs union Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-26 19:23 +0100
Re: Generic read/write function - casting vs union Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-27 13:10 -0700
Re: Generic read/write function - casting vs union David Thompson <dave.thompson2@verizon.net> - 2016-10-16 18:08 -0400
Re: Generic read/write function - casting vs union Anton Shepelev <anton.txt@gmail.com> - 2016-10-17 23:40 +0300
Re: Generic read/write function - casting vs union albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2016-12-11 15:20 +0100
Re: Generic read/write function - casting vs union supercat@casperkitty.com - 2016-12-11 09:38 -0800
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