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Groups > comp.lang.c > #103629
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Is 'extern' necessary? |
| Date | 2017-02-10 13:33 -0800 |
| Organization | None to speak of |
| Message-ID | <lnshnlvih7.fsf@kst-u.example.com> (permalink) |
| References | <o7ksei$n0$1@dont-email.me> <lnd1eqvtl6.fsf@kst-u.example.com> <o7l1ci$l0t$1@dont-email.me> <4920b63e-c9ac-4ddb-96f4-5c45257f6689@googlegroups.com> <o7l8uh$jip$1@dont-email.me> |
BartC <bc@freeuk.com> writes:
> On 10/02/2017 20:09, jameskuyper@verizon.net wrote:
>> On Friday, February 10, 2017 at 1:41:10 PM UTC-5, Bart wrote:
>>> On 10/02/2017 17:33, Keith Thompson wrote:
>>>> BartC <bc@freeuk.com> writes:
>>>>> I've been trying to find out what the point of 'extern' is.
>>>>
>>>> N1570 6.9.2, tentative definitions.
>>>
>>> It mentions 'external definition'. What does that mean?
>>
>> Go up one level. Section 6.9 is titled "External definitions", 6.9p1
>> defines what an external declaration is, and 6.9p5 defines an
>> external definition as an external declaration that is also a
>> definition, referring back to 6.7p5 for the definition of
>> "definition".
>>
>>> Presumably it can't mean a definition with 'extern', because if I write:
>>>
>>> extern int abc = 100;
>>
>> In 6.9, "external" means "outside of any function" (6.9p4), whereas
>> in most other parts of the standard it refers to "external linkage".
>
> I remember that from a previous discussion. It comes up in K&R2 1.10
> (p31): "An external variable... must be defined outside of any function.
> ...The variable must also be declared in each function that wants to
> access it...". And it goes on to suggest using an explicit 'extern'
> statement.
>
> I think that's just ramped up the confusion by a magnitude or so!
That appears to be some unfortunate wording in K&R2. It implies (and
the example shows) that the variables need to be declared *inside* each
function that refers to them. In fact, the declaration merely needs to
be visible.
Note that the idea of header files has not yet been introduced at that
point.
[...]
--
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"
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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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