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Re: A portable stack in C

From "BartC" <bc@freeuk.com>
Newsgroups comp.lang.c
Subject Re: A portable stack in C
Date 2011-11-15 18:45 +0000
Organization A noiseless patient Spider
Message-ID <j9uc14$7nn$1@dont-email.me> (permalink)
References (2 earlier) <j9t7gd$45e$1@speranza.aioe.org> <j9tdlo$669$1@dont-email.me> <j9temn$o6u$1@speranza.aioe.org> <0.ef2e570d4fa8ea6e44a0.20111115114550GMT.871ut9vcb5.fsf@bsb.me.uk> <j9tk3s$7bl$1@speranza.aioe.org>

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"jacob navia" <jacob@spamsink.net> wrote in message
news:j9tk3s$7bl$1@speranza.aioe.org...
> Le 15/11/11 12:45, Ben Bacarisse a écrit :
>> jacob navia<jacob@spamsink.net>  writes:
>> <snip>
>>> Conceptually ANY pointer is an index in a big array called "memory"
>>> (or RAM if you like).
>>
>> C pointers don't fit this concept.  They have a type which contributes
>> to the result of operations like *p, sizeof *p and p + 1.
>>
>
> The *p operation is just
> 1) Read the value of the pointer
> 2) Index the memory
> 3) read that position.
>
> This is just memory[p] (assuming non segmented memory)


Yes, you can throw away everything in C, and just have a gigantic static
array of bytes 'memory'.

But superimposing ordinary variables, arrays, and structs on top of that is
fiddly.

However, even supposing that was done, that's not sufficient, because each
function invocation will have it's own local byte-array for local variables. 
Now, this array can presumably also be located a space somewhere in the 
global array, but then, so what?

I'm not sure where you're going with this. You know have control over the
size and range of pointers, by using indexes (although if memory[] is the
same size as the machine's memory, the width of your index will be the same
as the width of your pointers), but you've thrown away half of C too, and
programming becomes next to impossible.

Maybe this is how it's all done at a low-level, but I don't think it's what
that poster had in mind.

> In general, what I want to emphasize is the equivalence between array
> indices and pointers.

Array accesses usually involve two elements: the array, and the index. And
the array itself will be a pointer (that is, if you forget the nonsense
about a giant byte-array).

While pointer accesses usually involve one element, the pointer value, with
an optional offset.

And if you have this:

 int A;

and want to pass a pointer to A to some function, how exactly would you turn
that into an index, without rewriting your entire application in a
stripped-down, low-level version of C?

-- 
Bartc

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Thread

A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-14 17:54 +0100
  Re: A portable stack in C Barry Schwarz <schwarzb@dqel.com> - 2011-11-14 20:55 -0800
    Re: A portable stack in C jacob navia <jacob@spamsink.net> - 2011-11-15 09:22 +0100
      Re: A portable stack in C Ike Naar <ike@iceland.freeshell.org> - 2011-11-15 09:00 +0000
        Re: A portable stack in C jacob navia <jacob@spamsink.net> - 2011-11-15 11:26 +0100
      Re: A portable stack in C "BartC" <bc@freeuk.com> - 2011-11-15 10:05 +0000
        Re: A portable stack in C jacob navia <jacob@spamsink.net> - 2011-11-15 11:25 +0100
          Re: A portable stack in C "BartC" <bc@freeuk.com> - 2011-11-15 11:08 +0000
          Re: A portable stack in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-15 11:45 +0000
            Re: A portable stack in C jacob navia <jacob@spamsink.net> - 2011-11-15 12:57 +0100
              Re: A portable stack in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-15 12:39 +0000
                Re: A portable stack in C jacob navia <jacob@spamsink.net> - 2011-11-15 14:26 +0100
                Re: A portable stack in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-15 15:31 +0000
                Re: A portable stack in C Keith Thompson <kst-u@mib.org> - 2011-11-15 12:53 -0800
                Re: A portable stack in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-15 21:15 +0000
                Re: A portable stack in C Keith Thompson <kst-u@mib.org> - 2011-11-15 14:29 -0800
                Re: A portable stack in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-15 22:59 +0000
                Re: A portable stack in C James Kuyper <jameskuyper@verizon.net> - 2011-11-15 17:30 -0500
                Re: A portable stack in C Willem <willem@toad.stack.nl> - 2011-11-15 22:33 +0000
                Re: A portable stack in C Keith Thompson <kst-u@mib.org> - 2011-11-15 15:07 -0800
                Re: A portable stack in C Seebs <usenet-nospam@seebs.net> - 2011-11-15 22:37 +0000
                Re: A portable stack in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-15 23:01 +0000
              Re: A portable stack in C "BartC" <bc@freeuk.com> - 2011-11-15 18:45 +0000
            Re: A portable stack in C Keith Thompson <kst-u@mib.org> - 2011-11-15 12:41 -0800
          Re: A portable stack in C Richard Damon <news.x.richarddamon@xoxy.net> - 2011-11-15 23:07 -0500
            Re: A portable stack in C Keith Thompson <kst-u@mib.org> - 2011-11-15 20:18 -0800
            Re: A portable stack in C Robert Wessel <robertwessel2@yahoo.com> - 2011-11-15 22:53 -0600
              Re: A portable stack in C "BartC" <bc@freeuk.com> - 2011-11-16 12:00 +0000
                Re: A portable stack in C falk@rahul.net (Edward A. Falk) - 2011-11-16 16:08 +0000
              Re: A portable stack in C David Thompson <dave.thompson2@verizon.net> - 2012-01-19 02:41 -0500
      Re: A portable stack in C Thomas David Rivers <rivers@dignus.com> - 2011-11-15 11:21 -0500
      Re: A portable stack in C Barry Schwarz <schwarzb@dqel.com> - 2011-11-15 17:53 -0800
    Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-15 19:21 +0100
      Re: A portable stack in C Barry Schwarz <schwarzb@dqel.com> - 2011-11-15 17:53 -0800
        Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-18 08:13 +0100
  Re: A portable stack in C Rui Maciel <rui.maciel@gmail.com> - 2011-11-15 10:14 +0000
    Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-15 19:20 +0100
  Re: A portable stack in C Acid Washed China Blue Jeans <chine.bleu@yahoo.com> - 2011-11-15 08:13 -0800
  Re: A portable stack in C Kaz Kylheku <kaz@kylheku.com> - 2011-11-15 16:27 +0000
    Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-15 19:21 +0100
    Re: A portable stack in C Keith Thompson <kst-u@mib.org> - 2011-11-15 13:19 -0800
  Re: A portable stack in C blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-11-17 15:45 +0000
    Re: A portable stack in C John Gordon <gordon@panix.com> - 2011-11-17 15:56 +0000
    Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-17 18:02 +0100
      Re: A portable stack in C "BartC" <bc@freeuk.com> - 2011-11-17 17:35 +0000
        Re: A portable stack in C Vincenzo Mercuri <vincenzo.mercuri@yahoo.it> - 2011-11-17 18:45 +0100
        Re: A portable stack in C Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-18 00:27 -0800
          Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-18 10:40 +0100
            Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-20 07:22 +0100
            Re: A portable stack in C Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-21 00:38 -0800
              Re: A portable stack in C "Jo" <none@none.none> - 2011-11-21 03:44 -0600
                Re: A portable stack in C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-21 13:00 +0200
                Re: A portable stack in C "Jo" <none@none.none> - 2011-11-21 06:07 -0600
              Re: A portable stack in C "Jo" <none@none.none> - 2011-11-21 03:50 -0600
              Re: A portable stack in C "Jo" <none@none.none> - 2011-11-21 07:48 -0600
              Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-21 20:11 +0100
          Re: A portable stack in C "BartC" <bc@freeuk.com> - 2011-11-18 12:47 +0000
          Re: A portable stack in C "Jo" <none@none.none> - 2011-11-18 23:31 -0600
      Re: A portable stack in C blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-11-18 14:45 +0000
        Re: A portable stack in C James Kuyper <jameskuyper@verizon.net> - 2011-11-18 10:14 -0500
        Re: A portable stack in C Keith Thompson <kst-u@mib.org> - 2011-11-18 12:20 -0800
          Re: A portable stack in C blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-11-19 17:23 +0000
            Re: A portable stack in C Seebs <usenet-nospam@seebs.net> - 2011-11-19 18:49 +0000
              Re: A portable stack in C "Jo" <none@none.none> - 2011-11-19 22:41 -0600
              Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-20 07:27 +0100
                Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-21 20:12 +0100
            Re: A portable stack in C "io_x" <a@b.c.invalid> - 2011-11-20 07:50 +0100
          Re: A portable stack in C "Jo" <none@none.none> - 2011-11-21 01:24 -0600
            Re: A portable stack in C Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-21 05:22 -0800
              Re: A portable stack in C "Jo" <none@none.none> - 2011-11-22 03:31 -0600
  Re: A portable stack in C 88888 Dihedral <dihedral88888@googlemail.com> - 2011-11-21 06:38 -0800

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