Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: no stack |
| Date | 2015-03-25 10:57 -0700 |
| Organization | None to speak of |
| Message-ID | <87384tq7t6.fsf@kst-u.example.com> (permalink) |
| References | <347790b0-5f11-4008-b254-5b5d5229a387@googlegroups.com> <f00ddc97-5d80-49ab-b0cf-1a04801b9a5e@googlegroups.com> <87egoery65.fsf@kst-u.example.com> <metqrr$o19$1@dont-email.me> |
David Brown <david.brown@hesbynett.no> writes:
> On 24/03/15 20:30, Keith Thompson wrote:
[...]
>> Quibble: Scope and lifetime are two distinct things. Scope is a region
>> of program text in which an identifier is visible; lifetime is a
>> duration during program execution in which an object exists.
>>
>> For local variables with automatic storage duration, the distinction can
>> *almost* be ignored; you can think of both scope and lifetime as
>> extending to the closing }. But (a) the lifetime of a local object
>> begins at the beginning of the enclosing block, not at its declaration
>> (there are contrived cases where you can access the object within its
>> lifetime but outside its scope),
>
> I am curious here - can you give an example of a legal way to access an
> object within its lifetime and outside its scope, other than by passing
> its address to an outside function (the function is not within the scope
> of the local data, but it is run while the scope is still "active" in
> the calling function)? I don't imagine such contrived cases would be
> useful in practice, but I can't think of any myself - so I wonder what
> you are thinking of here.
#include <stdio.h>
#include <stdbool.h>
int main(void) {
bool first_time = true;
TOP:;
int *ptr;
if (!first_time) printf("*ptr = %d\n", *ptr);
int i = 42;
ptr = &i;
if (first_time) {
first_time = false;
goto TOP;
}
}
The lifetime of `i` begins on entry to the block that makes up the body
of `main`, and ends on reaching the closing `}`. The scope of `i`
extends from its declaration to the closing `}`. The printf call is
outside the scope of `i`, so it can't refer to `i` by name -- but the
object `i` exists and it can access that object via `ptr`, which was
previously set to point to `i`.
(You could try to do something similar with a loop, but the lifetime of
`i` would be restricted to the body of the loop, and `*ptr` would refer
to a different object on the second iteration -- though it would
probably "work".)
--
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"
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
no stack fir <profesor.fir@gmail.com> - 2015-03-22 02:09 -0700
Re: no stack wssimms@gmail.com - 2015-03-22 02:52 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 03:04 -0700
Re: no stack Richard Heathfield <rjh@cpax.org.uk> - 2015-03-22 13:15 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 07:37 -0700
Re: no stack Lőrinczy Zsigmond <nospam@for.me> - 2015-03-22 11:10 +0100
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 03:30 -0700
Re: no stack jacob navia <jacob@jacob.remcomp.fr> - 2015-03-22 11:15 +0100
Re: no stack jacob navia <jacob@jacob.remcomp.fr> - 2015-03-22 11:23 +0100
Re: no stack jacob navia <jacob@jacob.remcomp.fr> - 2015-03-22 11:24 +0100
Re: no stack jacob navia <jacob@jacob.remcomp.fr> - 2015-03-22 11:41 +0100
Re: no stack Keith Thompson <kst-u@mib.org> - 2015-03-22 12:18 -0700
Re: no stack Melzzzzz <mel@zzzzz.com> - 2015-03-22 20:25 +0100
Re: no stack Stephen Sprunk <stephen@sprunk.org> - 2015-03-23 12:17 -0500
Re: no stack James Kuyper <jameskuyper@verizon.net> - 2015-03-23 13:22 -0400
Re: no stack Bartc <bc@freeuk.com> - 2015-03-22 11:13 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 04:29 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 04:33 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 04:39 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 04:46 -0700
Re: no stack Bartc <bc@freeuk.com> - 2015-03-22 12:16 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 05:25 -0700
Re: no stack Bartc <bc@freeuk.com> - 2015-03-22 12:59 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 07:15 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-22 15:39 +0100
Re: no stack Bartc <bc@freeuk.com> - 2015-03-22 19:47 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-23 02:18 -0700
Re: no stack Bartc <bc@freeuk.com> - 2015-03-23 11:21 +0000
Re: no stack Richard Heathfield <rjh@cpax.org.uk> - 2015-03-23 11:35 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-23 07:07 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-23 07:28 -0700
Re: no stack Bartc <bc@freeuk.com> - 2015-03-23 14:56 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-23 08:13 -0700
Re: no stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-22 13:01 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-23 13:14 +0100
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 05:30 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-22 14:15 +0100
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 04:49 -0700
Re: no stack Melzzzzz <mel@zzzzz.com> - 2015-03-22 12:37 +0100
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 05:06 -0700
Re: no stack Melzzzzz <mel@zzzzz.com> - 2015-03-22 13:23 +0100
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 05:48 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 08:51 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-23 07:39 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-23 07:54 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-22 14:45 +0100
Re: no stack Richard Heathfield <rjh@cpax.org.uk> - 2015-03-22 14:20 +0000
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-22 15:43 +0100
Re: no stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-22 13:09 -0700
Re: no stack Bartc <bc@freeuk.com> - 2015-03-22 20:38 +0000
Re: no stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-22 13:54 -0700
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-23 02:08 -0700
Re: no stack Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-03-23 12:07 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-23 07:13 -0700
Re: no stack Kaz Kylheku <kaz@kylheku.com> - 2015-03-22 20:59 +0000
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 07:35 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-22 16:27 +0100
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-22 05:10 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-22 13:56 +0100
Re: no stack John Bode <jfbode1029@gmail.com> - 2015-03-24 09:01 -0700
Re: no stack Keith Thompson <kst-u@mib.org> - 2015-03-24 12:30 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-25 09:16 +0100
Re: no stack Tim Rentsch <txr@alumni.caltech.edu> - 2015-03-25 09:00 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-25 17:33 +0100
Re: no stack James Kuyper <jameskuyper@verizon.net> - 2015-03-25 13:35 -0400
Re: no stack Tim Rentsch <txr@alumni.caltech.edu> - 2015-03-25 16:22 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-26 08:54 +0100
Re: no stack Keith Thompson <kst-u@mib.org> - 2015-03-26 08:48 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-26 23:00 +0100
Re: no stack Tim Rentsch <txr@alumni.caltech.edu> - 2015-03-28 09:15 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-28 18:17 +0100
Re: no stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-28 12:36 -0700
Re: no stack Richard Damon <Richard@Damon-Family.org> - 2015-03-28 17:33 -0400
Re: no stack Tim Rentsch <txr@alumni.caltech.edu> - 2015-03-30 08:04 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-04-07 00:39 +0200
Re: no stack fir <profesor.fir@gmail.com> - 2015-03-26 01:21 -0700
Re: no stack Keith Thompson <kst-u@mib.org> - 2015-03-25 10:57 -0700
Re: no stack David Brown <david.brown@hesbynett.no> - 2015-03-25 21:55 +0100
csiph-web