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

From	Ian Collins <ian-news@hotmail.com>
Newsgroups	comp.lang.c
Subject	Re: Is there any place to talk about language features?
Date	2016-10-01 23:22 +1300
Message-ID	<e59h3bFkp66U1@mid.individual.net> (permalink)
References	(9 earlier) <nshp7i$722$1@news.albasani.net> <nsicve$s6j$1@news.albasani.net> <3e7e20c2-c69d-4777-a98a-b7d212f546c9@googlegroups.com> <e57rk4Fa94uU1@mid.individual.net> <c7787c1f-f39c-499f-8d93-1caa13d4c005@googlegroups.com>

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On 10/ 1/16 09:51 PM, Malcolm McLean wrote:
> On Friday, September 30, 2016 at 8:10:05 PM UTC+1, Ian Collins wrote:
>> On 09/29/16 08:48 PM, Malcolm McLean wrote
>>>>
>>> The problem as I see it with C++ is that each new feature creates
>>> difficulties or hard to answer questions, which necessitate another
>>> feature.
>>> For example how is a constructor to fail? The answer is to throw
>>> an exception. Then how is the stack to be unwound? By calling
>>> implicit destructors. But how do you make sure that your object
>>> is in a  destructible state? By allowing memberwise initialisation
>>> before the constructor is actually executed. How do you make sure
>>> that the members can be initialised? With default constructors.
>>> But how do allow the default constructor to fail? It can't, you
>>> should make it "no throw".
>>>
>>> And so it goes on. Feature after feature, which in C you just
>>> don't need because we simply don't create opaque structures on
>>> the stack. We return a pointer to the object on the heap, and
>>> if the constructor fails, it is null. You lose the ability to
>>> construct on the stack (though you can always rewrite if
>>> necessary) and, a bit more annoyingly, you lose automatic
>>> destruction. But construction on the stack is a real benefit only
>>> for tiny, trivial structures which in C wouldn't usually be
>>> opaque anyway. So the only real loss is automatic destruction.
>>
>> Which, given a problem such as "Resource X must be freed once all uses
>> of it end".  Such a problem is trivial to manage in C++ and far from
>> trivial in C.
>>
>> It all comes down to where the complexity required to manage a task
>> lies: in user code in C or in the language in C++.
>>
> In C we can use this pattern.
>
> a) Variables may not be declared in block scope, only function scope.
> (only really matters for pointer and handles, but make it all).
> b) Every pointer or handle is initialised to null.
> c) There is a label called "out_of_memory" (for a "Malcolm function,
> which can only fail on out of memory conditions and for no other
> reason) or "error_exit" (for a "Malcolm procedure" which does IO
> and can experience IO failure).
> d) out_of_memory or error_exit is jumped to on memory allocation
> or IO failure.
> e) code the error label destroys all resources, which will be null
> if not intialised.
> f) In the usual situation of an failure also meaning a failure in
> caller, an error return must be passed up. So normally if the function
> return a pointer it returns null, otherwise it returns -1 for
> out-of memory, or a lower negative for IO errors.
>
>
> Simple rules, not very complex or hard to follow.

Simple but fallible rules for simple use cases of simple resources. 
Life gets way more interesting when those simple things become a little 
more complicated.

> The only real point of difficulty is that when allocating a structure
> which itself contains pointers to be allocated, those pointers must
> immediately be set to null so the destructor logic doesn't free
> wild pointers.

You overlook the fact that many if not most resource allocation and 
release happens in different parts of a programme.

-- 
Ian

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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