Re: Is there any place to talk about language features?

Newsgroups	comp.lang.c
Date	2016-10-03 14:34 -0700
References	(19 earlier) <5def853b-2418-4f89-a7ad-3ea77b66b654@googlegroups.com> <e5e8kuFq0riU1@mid.individual.net> <47b562a1-78e4-4c20-86e5-e980954ab436@googlegroups.com> <e5fpdnF716rU1@mid.individual.net> <6f007f5a-7bc1-48d8-aa2b-549fa09e583c@googlegroups.com>
Message-ID	<14aa2ff2-32cd-4261-bba7-102426072c67@googlegroups.com> (permalink)
Subject	Re: Is there any place to talk about language features?
From	supercat@casperkitty.com

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On Monday, October 3, 2016 at 3:12:12 PM UTC-5, Malcolm McLean wrote:
> The special cases aren't really special cases. The creator of a
> resource either destroys it or passes it up. If all he does is
> create an intialise the resource, the natural way to pass back up 
> is by returning a pointer. But if we pass a double pointer which 
> he then fills, we are not changing anything significant.

Unfortunately, there is no type in Standard C that can serve as a "pointer
to a pointer to a structure of arbitrary type".  In the days prior to
aggressive type-based aliasing, many implementations would allow a void**
to be used--with suitable typecasts--for such a purpose, but Standard C
does not provide any reasonable equivalent.  While a pattern like:

    myResource *rsrc;
    actionIndirectlyCreatingResource(&rsrc, procToCreateResource);

is better than

    myResource *rsrc;
    rsrc = actionIndirectlyCreatingResource(procToCreateResource);

at handling situations where the function might fail after the resource is
created (if the action that creates the resource populates the pointer when
the resource reaches a state requiring cleanup, outer code will be able to
tell which things need cleanup even if an intermediate-level function fails).
Unfortunately, while the latter pattern works just fine even if the action
creating the resource doesn't know what type it is (the outer function can
simply return a void*) the former pattern would require either that the
client code use type void* to hold pointers to objects whose type the client
code knows, or that the client code create a temporary void*, copy its pointer
to that, pass the address of the temporary, and then copy the void* back to
its real pointer (which would cause the resource to be lost if something
fails and causes a longjmp() after the resource has been created).

Thread

Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 09:35 -0700
  Re: Is there any place to talk about language features? Keith Thompson <kst-u@mib.org> - 2016-09-28 09:39 -0700
    Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 09:46 -0700
      Re: Is there any place to talk about language features? Richard Heathfield <rjh@cpax.org.uk> - 2016-09-28 17:53 +0100
      Re: Is there any place to talk about language features? David Brown <david.brown@hesbynett.no> - 2016-09-28 21:21 +0200
      Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-09-28 20:36 +0100
        Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 13:55 -0700
          Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 14:02 -0700
          Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-09-29 10:03 +1300
            Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 14:13 -0700
              Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-09-29 10:22 +1300
                Re: Is there any place to talk about language features? Robert Latest <boblatest@yahoo.com> - 2016-10-03 08:47 +0000
                Re: Is there any place to talk about language features? James Kuyper <jameskuyper@verizon.net> - 2016-10-03 07:44 -0400
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-03 04:56 -0700
                Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-10-03 13:18 +0100
                Re: Is there any place to talk about language features? BGB <cr88192@hotmail.com> - 2016-10-03 12:43 -0500
                Re: Is there any place to talk about language features? Ike Naar <ike@iceland.freeshell.org> - 2016-10-03 21:43 +0000
                Re: Is there any place to talk about language features? John Gordon <gordon@panix.com> - 2016-10-03 22:28 +0000
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-10-03 04:51 -0700
                Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-10-03 13:10 +0100
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-03 05:48 -0700
                Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-10-03 14:03 +0100
                Re: Is there any place to talk about language features? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-03 14:24 +0100
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-03 07:07 -0700
                Re: Is there any place to talk about language features? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-03 19:16 +0100
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-03 07:16 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-03 07:45 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-03 07:57 -0700
                Re: Is there any place to talk about language features? James Kuyper <jameskuyper@verizon.net> - 2016-10-03 08:21 -0400
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-10-03 05:31 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-03 06:43 -0700
                Re: Is there any place to talk about language features? David Brown <david.brown@hesbynett.no> - 2016-10-03 15:08 +0200
              Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 14:22 -0700
                Re: Is there any place to talk about language features? Keith Thompson <kst-u@mib.org> - 2016-09-28 15:16 -0700
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 16:08 -0700
                Re: Is there any place to talk about language features? Keith Thompson <kst-u@mib.org> - 2016-09-28 16:57 -0700
          Re: Is there any place to talk about language features? Keith Thompson <kst-u@mib.org> - 2016-09-28 14:19 -0700
            Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 14:50 -0700
              Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 17:03 -0700
              Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-09-29 01:08 +0100
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-28 17:33 -0700
                Re: Is there any place to talk about language features? Melzzzzz <Melzzzzz@zzzzz.com> - 2016-09-29 01:02 +0000
                Re: Is there any place to talk about language features? BGB <cr88192@hotmail.com> - 2016-09-29 01:39 -0500
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-29 00:48 -0700
                Re: Is there any place to talk about language features? BGB <cr88192@hotmail.com> - 2016-09-29 11:59 -0500
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-01 08:09 +1300
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-30 12:14 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-01 09:07 +1300
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-30 13:53 -0700
                Re: Is there any place to talk about language features? Gareth Owen <gwowen@gmail.com> - 2016-09-30 22:13 +0100
                Re: Is there any place to talk about language features? raltbos@xs4all.nl (Richard Bos) - 2016-10-01 09:36 +0000
                Re: Is there any place to talk about language features? Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-01 13:04 -0400
                Re: Is there any place to talk about language features? "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-09-30 14:20 -0700
                Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-09-30 22:30 +0100
                Re: Is there any place to talk about language features? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2016-10-02 07:30 +0000
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-01 01:51 -0700
                Re: Is there any place to talk about language features? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-01 10:31 +0100
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-01 23:22 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-01 06:15 -0700
                Re: Is there any place to talk about language features? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-01 15:28 +0100
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-01 10:07 -0700
                Re: Is there any place to talk about language features? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-01 19:52 +0100
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-02 20:38 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-02 03:37 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-03 08:35 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-02 15:17 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-03 18:29 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-03 01:09 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-04 08:21 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-03 13:12 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-03 14:34 -0700
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-04 00:47 -0700
                Re: Is there any place to talk about language features? Ike Naar <ike@iceland.freeshell.org> - 2016-10-04 07:49 +0000
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-04 07:50 -0700
                Re: Is there any place to talk about language features? Keith Thompson <kst-u@mib.org> - 2016-10-04 08:57 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-04 10:42 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-05 15:47 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-04 20:58 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-05 18:14 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-05 02:15 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-05 22:44 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-05 03:12 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-06 15:38 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-05 19:50 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-06 16:25 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-05 21:19 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-06 18:11 +1300
                Re: Is there any place to talk about language features? Gareth Owen <gwowen@gmail.com> - 2016-10-06 06:38 +0100
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-06 00:36 -0700
                Re: Is there any place to talk about language features? gwowen <gwowen@gmail.com> - 2016-10-06 07:33 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-06 09:00 -0700
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-07 00:32 -0700
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-10-07 05:05 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-07 08:13 -0700
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-07 00:20 -0700
                Re: Is there any place to talk about language features? Gareth Owen <gwowen@gmail.com> - 2016-10-07 17:01 +0100
                Re: Is there any place to talk about language features? Les Cargill <lcargill99@comcast.com> - 2016-10-05 12:45 -0500
                Re: Is there any place to talk about language features? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-05 11:12 +0100
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-05 03:15 -0700
                Re: Is there any place to talk about language features? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-05 14:41 +0100
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-05 08:01 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-05 08:41 -0700
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-05 10:29 -0700
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-10-05 12:29 -0700
                Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-10-05 11:08 +0100
                Re: Is there any place to talk about language features? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-05 14:35 +0100
                Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-10-05 18:15 +0100
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-05 10:38 -0700
                Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-10-05 19:14 +0100
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-05 11:56 -0700
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-10-05 11:57 -0700
                Re: Is there any place to talk about language features? Keith Thompson <kst-u@mib.org> - 2016-10-05 12:18 -0700
                Re: Is there any place to talk about language features? David Brown <david.brown@hesbynett.no> - 2016-10-05 21:49 +0200
                Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-10-05 13:07 -0700
                Re: Is there any place to talk about language features? "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-05 16:23 -0400
                Re: Is there any place to talk about language features? David Brown <david.brown@hesbynett.no> - 2016-10-06 14:26 +0200
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-05 13:56 -0700
                Re: Is there any place to talk about language features? BartC <bc@freeuk.com> - 2016-10-06 14:17 +0100
                Re: Is there any place to talk about language features? David Brown <david.brown@hesbynett.no> - 2016-10-06 15:53 +0200
                Re: Is there any place to talk about language features? Keith Thompson <kst-u@mib.org> - 2016-10-06 09:12 -0700
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-06 11:28 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-06 15:31 +1300
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-06 15:32 +1300
                Re: Is there any place to talk about language features? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-05 19:43 -0700
                Re: Is there any place to talk about language features? Ian Collins <ian-news@hotmail.com> - 2016-10-06 16:05 +1300
                Re: Is there any place to talk about language features? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2016-10-02 07:24 +0000
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-09-30 16:17 -0700
                Re: Is there any place to talk about language features? raltbos@xs4all.nl (Richard Bos) - 2016-10-01 09:39 +0000
                Re: Is there any place to talk about language features? supercat@casperkitty.com - 2016-10-01 14:11 -0700
            Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-29 07:47 -0700
            Re: Is there any place to talk about language features? Thiago Adams <thiago.adams@gmail.com> - 2016-09-29 10:25 -0700
  Re: Is there any place to talk about language features? "James R. Kuyper" <jameskuyper@verizon.net> - 2016-09-28 12:59 -0400
    Re: Is there any place to talk about language features? Richard Heathfield <rjh@cpax.org.uk> - 2016-09-28 18:30 +0100
      Re: Is there any place to talk about language features? Keith Thompson <kst-u@mib.org> - 2016-09-28 12:10 -0700
    Re: Is there any place to talk about language features? James Harris <james.harris.1@gmail.com> - 2016-09-28 20:20 +0100

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