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Groups > comp.lang.c > #103653
| From | Les Cargill <lcargill99@comcast.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Is 'extern' necessary? |
| Date | 2017-02-10 19:24 -0600 |
| Organization | A noiseless patient Spider |
| Message-ID | <o7lor7$8rf$1@dont-email.me> (permalink) |
| References | <o7ksei$n0$1@dont-email.me> |
BartC wrote: > I've been trying to find out what the point of 'extern' is. > > Usually, if you declare: > > int abc; > > at filespec in modules A and B, then you end up with one copy of 'abc' > shared across both modules. It doesn't matter which of A or B is abc's > 'home' module. > > If one of them uses 'extern', then it's the same. But it fails when both > use 'extern'. > > Unless one (or both) modules has a second declaration with just 'int > abc;'; that seems to have the effect of cancelling 'extern'. So it must > be doing something, but what? > > When abc is initialised, then this is fine too (unless you initialise > the declaration with 'extern'), but now only one module can initialise > it; initialising both causes link errors. > > It seems that most of the time you can get by without 'extern'. So when > is it necessary? > IMO, as a nod to those who follow you, it is always necessary. A good toolchain ( again, IMO ) should think you've had an unintentional name collision and throw an error. -- Les Cargill
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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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