Re: C scope and struct definitions

From	pacman@kosh.dhis.org (Alan Curry)
Newsgroups	comp.lang.c
Subject	Re: C scope and struct definitions
Date	2012-06-26 20:08 +0000
Organization	Aioe.org NNTP Server
Message-ID	<jsd4qv$bap$1@speranza.aioe.org> (permalink)
References	<mYGdnXsGt41dNnnSnZ2dnUVZ_u-dnZ2d@bestweb.net> <lny5nd78em.fsf@nuthaus.mib.org> <js698k$7rm$1@speranza.aioe.org> <Nv6dnf0QUclO4HXSnZ2dnUVZ_vadnZ2d@bestweb.net>

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In article <Nv6dnf0QUclO4HXSnZ2dnUVZ_vadnZ2d@bestweb.net>,
Kenneth Brody  <kenbrody@spamcop.net> wrote:
>On 6/24/2012 1:40 AM, Alan Curry wrote:
>> In article <lny5nd78em.fsf@nuthaus.mib.org>,
>> Keith Thompson  <kst-u@mib.org> wrote:
>>> pacman@kosh.dhis.org (Alan Curry) writes:
>[...]
>>>> Variable scopes make sense because the object named by the variable doesn't
>>>> exist until the function is called. A type isn't an object.
>>>
>>> Are you conflating scope and lifetime?
>>
>> Are you seriously saying they aren't (or shouldn't be) closely tied together?
>
>I don't think they are tied together at all.
>
>I was going to say that the exception would be that a lifetime can't extend 
>beyond a scope, but then thought of:
>
>     void foo(void)
>         {
>         static struct bar { ... } foobar;
>         ...
>         }
>
>Can you give an example where scope and lifetime are (or "should") be 
>closely tied together?

Scope is the boundary of a variable's existence at compile time. Lifetime is
the boundary of a variable's existence at runtime. They're basically the same
thing in different dimensions (temporal at runtime, spatial at compile time).

And for local variables, they both default to the block enclosing the
declaration. At compile time, the variable can be referenced (i.e. its name
can be used) while that block is being parsed. At runtime, the variable can
be referenced (i.e. its value can be loaded from memory) while that block is
active.

static locals break that nice symmetry between compile time and runtime, in
the same way as the localized type definitions we've been talking about. And
they are inessential for the same reason: if you pull foobar out of the
function and give it a unique name, everything works exactly the same.

This is not an attack, a proposal, or a demand for anyone to stop using
"static". I know that's how things get interpreted by the more aggressive
posters here. So calm down everybody, not everything has to be a fight. I
have lots of local static variables in my own code. They don't feel as weird
to me as local types for some reason I can't explain.

Between nested functions, static local variables, and locally-scoped struct
definitions, the only one whose absence couldn't be easily worked around is
the one that's actually absent.

-- 
Alan Curry

Thread

C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-22 13:30 -0400
  Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-22 14:02 -0400
    Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-22 22:40 +0000
      Re: C scope and struct definitions Ben Pfaff <blp@cs.stanford.edu> - 2012-06-22 15:47 -0700
      Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-22 20:32 -0400
        Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-23 22:06 +0000
          Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 16:18 -0700
            Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-25 10:19 -0400
              Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-25 11:51 -0700
          Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 19:54 -0400
            Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 00:56 +0000
              Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 21:48 -0400
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 06:03 +0000
                Re: C scope and struct definitions nick_keighley_nospam@hotmail.com - 2012-06-25 00:05 -0700
              Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 19:25 -0700
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 05:40 +0000
                Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-24 10:47 +0200
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-24 11:00 -0700
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-25 03:53 +0000
                Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-25 01:14 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-24 22:38 -0700
                Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:03 -0400
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 20:08 +0000
                Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-26 23:21 +0200
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 21:47 +0000
                Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 18:05 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-26 16:45 -0700
                Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-27 08:26 +0200
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 00:01 -0700
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-27 06:57 -0400
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-27 15:00 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 14:48 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 16:14 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-29 09:36 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 16:27 -0700
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:03 -0700
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:11 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 15:53 -0700
                Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 17:59 -0400
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 22:18 +0000
                Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 18:33 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-26 17:22 -0700
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 00:03 -0700
                Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-27 14:13 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:15 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-29 09:43 -0700
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-29 11:59 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-01 18:32 -0700
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-27 20:59 +0000
                Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-28 16:42 -0400
            Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-23 20:57 -0400
              Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 22:11 -0400
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-23 22:51 -0400
                Re: C scope and struct definitions Nick Bowler <nbowler@draconx.ca> - 2012-06-25 17:31 +0000
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-25 14:46 -0400
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-25 14:43 -0700
                Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-26 13:44 +0200
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 20:07 -0700
              Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-24 10:56 +0200
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-24 08:29 -0400
              Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-24 10:26 -0700
          Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 10:50 -0400
      Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-24 09:23 -0700
        Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:17 -0400
          Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-25 14:22 -0700
  Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:11 -0400

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