Re: Generic read/write function - casting vs union

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: Generic read/write function - casting vs union
Date	2016-09-22 11:48 -0700
Organization	None to speak of
Message-ID	<lnr38bvkh8.fsf@kst-u.example.com> (permalink)
References	<ns08ge$o5v$1@dont-email.me> <ns0ah9$uhd$1@dont-email.me>

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Richard Heathfield <rjh@cpax.org.uk> writes:
> On 22/09/16 10:33, Noob wrote:
[...]
>> 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 *. :-)
>
> But you can assign to an unsigned char *, and increment that instead.

Note that gcc permits pointer arithmetic on void* as an extension.
I don't recommend using that extension, but be aware that gcc will
not warn about such pointer arithmetic by default.  You can use
-pedantic or -pedantic-errors to disable the warning and get the
required diagnostics.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

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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