Re: Is 'extern' necessary?

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: Is 'extern' necessary?
Date	2017-02-14 21:35 +0100
Organization	A noiseless patient Spider
Message-ID	<o7vpif$kgm$1@dont-email.me> (permalink)
References	(10 earlier) <o7uqci$bg$1@dont-email.me> <o7ut4a$9gu$1@dont-email.me> <2e2f9023-8486-4956-bce2-03c1d3204a18@googlegroups.com> <o7v1u0$sfa$1@dont-email.me> <1aa5c741-fa95-4c30-8994-9324af270c6e@googlegroups.com>

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On 14/02/17 16:24, supercat@casperkitty.com wrote:
> On Tuesday, February 14, 2017 at 7:51:49 AM UTC-6, David Brown wrote:
>> I suppose its main purpose is documentary, like identifier names - it
>> tells the user that these pointers should be distinct and will be
>> treated that way in the function body.  It could also be used for static
>> error checking - the complier could issue a warning or error if it could
>> see that the restricted pointers overlap.
>
> In what cases could a compiler meaningfully offer such warnings without being
> able to see into the function in question?  If it can see into the function in
> question, the existence or absence of "restrict" in the declaration would be
> irrelevant.  Since "restrict" does have a documentary purpose similar to names,
> it may be helpful for an implementation which includes names to include the
> "restrict" as well, but if its purpose is solely documentary I see no reason
> to include it in a prototype whose purpose is solely functional.
>

If you have:

extern void foo(int * restrict a, int * restrict b);

and

void bar(int * c) {
	foo(c, c);
}

then the compiler would know there is something bad going on, and could 
warn about it.  It would only work in a few cases - the compiler has no 
way of knowing if "foo(c, c + 1)" is valid or not.

Thread

Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-10 17:16 +0000
  Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-10 09:33 -0800
    Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-10 18:41 +0000
      Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-10 12:09 -0800
        Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-10 20:29 +0000
          Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-10 13:26 -0800
            Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-10 22:56 +0000
              Re: Is 'extern' necessary? jameskuyper@verizon.net - 2017-02-10 20:19 -0800
                Re: Is 'extern' necessary? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-11 09:53 -0500
              Re: Is 'extern' necessary? Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-13 05:19 -0800
      Re: Is 'extern' necessary? jameskuyper@verizon.net - 2017-02-10 12:09 -0800
        Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-10 20:50 +0000
          Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-10 13:09 -0800
          Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-10 13:33 -0800
          Re: Is 'extern' necessary? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-10 23:23 +0000
            Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-10 23:35 +0000
              Re: Is 'extern' necessary? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-11 00:34 +0000
            Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-13 12:41 +0100
              Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-13 13:14 +0000
                Re: Is 'extern' necessary? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-13 14:05 +0000
                Re: Is 'extern' necessary? jameskuyper@verizon.net - 2017-02-13 07:49 -0800
          Re: Is 'extern' necessary? jameskuyper@verizon.net - 2017-02-10 19:33 -0800
            Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-11 09:41 -0800
              Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-11 10:19 -0800
                Re: Is 'extern' necessary? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-11 13:39 -0500
                Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-12 10:10 -0800
      Re: Is 'extern' necessary? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-02-10 14:59 -0800
      Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-13 12:33 +0100
  Re: Is 'extern' necessary? Siri Cruise <chine.bleu@yahoo.com> - 2017-02-10 09:35 -0800
    Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-10 12:12 -0800
  Re: Is 'extern' necessary? jameskuyper@verizon.net - 2017-02-10 10:38 -0800
  Re: Is 'extern' necessary? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-10 21:10 +0000
    Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-10 13:25 -0800
  Re: Is 'extern' necessary? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-02-10 14:53 -0800
    Re: Is 'extern' necessary? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-02-10 15:06 -0800
    Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-10 23:24 +0000
      Re: Is 'extern' necessary? Ian Collins <ian-news@hotmail.com> - 2017-02-11 12:34 +1300
        Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-13 13:14 +0100
          Re: Is 'extern' necessary? GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-13 13:44 +0100
            Re: Is 'extern' necessary? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-13 14:13 +0000
            Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-13 15:16 +0100
              Re: Is 'extern' necessary? GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-13 17:24 +0100
                Re: Is 'extern' necessary? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-13 14:24 -0500
                Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-13 23:29 +0100
            Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-13 11:06 -0800
            Re: Is 'extern' necessary? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-02-13 11:15 -0800
          Re: Is 'extern' necessary? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-13 11:48 -0500
            Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-13 09:03 -0800
            Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-13 23:37 +0100
      Re: Is 'extern' necessary? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-02-10 15:40 -0800
      Re: Is 'extern' necessary? Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-13 05:09 -0800
        Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-13 13:46 +0000
          Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-13 09:52 -0800
            Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-13 19:19 +0000
              Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-13 11:34 -0800
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-13 20:13 +0000
              Re: Is 'extern' necessary? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-02-13 13:11 -0800
              Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-14 00:33 +0100
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-14 01:02 +0000
                Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-14 09:28 +0100
                Re: Is 'extern' necessary? Robert Wessel <robertwessel2@yahoo.com> - 2017-02-14 03:31 -0600
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-14 11:42 +0000
                Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-14 13:29 +0100
                Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-14 05:16 -0800
                Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-14 14:51 +0100
                Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-14 07:24 -0800
                Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-14 21:35 +0100
                Re: Is 'extern' necessary? James Kuyper <jameskuyper@verizon.net> - 2017-02-14 15:53 -0500
                Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-15 09:31 +0100
                Re: Is 'extern' necessary? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-15 11:36 -0500
                Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-15 09:12 -0800
                Re: Is 'extern' necessary? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-15 12:58 -0500
                Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-15 10:01 -0800
                Re: Is 'extern' necessary? jameskuyper@verizon.net - 2017-02-15 10:55 -0800
                Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-15 11:42 -0800
                Re: Is 'extern' necessary? jameskuyper@verizon.net - 2017-02-15 12:28 -0800
                Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-15 13:58 -0800
                Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-14 08:54 -0800
                Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-14 08:51 -0800
                Re: Is 'extern' necessary? Richard Heathfield <rjh@cpax.org.uk> - 2017-02-14 17:32 +0000
                Re: Is 'extern' necessary? Gareth Owen <gwowen@gmail.com> - 2017-02-14 17:45 +0000
                Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-14 21:38 +0100
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-14 23:26 +0000
                Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-14 16:33 -0800
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-15 00:47 +0000
                Re: Is 'extern' necessary? Jean-Marc Bourguet <jm@bourguet.org> - 2017-02-14 18:17 +0100
                Re: Is 'extern' necessary? Keith Thompson <kst-u@mib.org> - 2017-02-14 09:47 -0800
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-14 18:36 +0000
                Re: Is 'extern' necessary? jameskuyper@verizon.net - 2017-02-14 11:20 -0800
                Re: Is 'extern' necessary? supercat@casperkitty.com - 2017-02-14 11:42 -0800
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-14 20:22 +0000
                Re: Is 'extern' necessary? Robert Wessel <robertwessel2@yahoo.com> - 2017-02-14 17:58 -0600
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-15 01:29 +0000
                Re: Is 'extern' necessary? Robert Wessel <robertwessel2@yahoo.com> - 2017-02-16 05:02 -0600
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-16 11:38 +0000
                Re: Is 'extern' necessary? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-16 14:37 +0000
                Re: Is 'extern' necessary? BartC <bc@freeuk.com> - 2017-02-16 15:43 +0000
                Re: Is 'extern' necessary? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-16 16:08 +0000
                Re: Is 'extern' necessary? GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-16 18:42 +0100
                Re: Is 'extern' necessary? David Brown <david.brown@hesbynett.no> - 2017-02-15 09:47 +0100
                Re: Is 'extern' necessary? Robert Wessel <robertwessel2@yahoo.com> - 2017-02-16 05:05 -0600
          Re: Is 'extern' necessary? Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-15 16:53 -0800
    Re: Is 'extern' necessary? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-10 23:55 +0000
  Re: Is 'extern' necessary? Les Cargill <lcargill99@comcast.com> - 2017-02-10 19:24 -0600
  Re: Is 'extern' necessary? void <nathan.gothier@gmail.com> - 2017-02-11 03:17 -0800

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