Re: Q: Local variables initialization shortcut.

From	"BartC" <bc@freeuk.com>
Newsgroups	comp.lang.c
Subject	Re: Q: Local variables initialization shortcut.
Date	2012-06-02 16:17 +0100
Organization	A noiseless patient Spider
Message-ID	<jqdaq0$v02$1@dont-email.me> (permalink)
References	(4 earlier) <0ecf3c52-be95-4a37-a6f0-42469d378f1e@m3g2000vbl.googlegroups.com> <a2uj5rFvv1U1@mid.uni-berlin.de> <0e159ddf-1c62-4bc2-bb70-a8369dec0c00@a16g2000vby.googlegroups.com> <jqd6od$6s7$1@dont-email.me> <7ff937d6-bd95-4235-9378-06f92d6f6d40@fr28g2000vbb.googlegroups.com>

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"Jean-Christophe" <5.d@free.fr> wrote in message
news:7ff937d6-bd95-4235-9378-06f92d6f6d40@fr28g2000vbb.googlegroups.com...
> On Jun 2, 4:08 pm, "BartC" :

> Output :
>
> &a = 4221624
> &b = 4221632
> &x = 4221640
> &y = 4221641
> &z = 4221642

I tried it on four x86-32 compilers, and get the following (I've added an
extra term to highlight the differences):

&a = 4202528 0
&b = 4202544 16
&x = 4202552 -4
&y = 4202540 -12
&z = 4202536 -4

&a = 4214968 0
&b = 4214984 16
&x = 4214992 -7
&y = 4214977 -15
&z = 4214976 -1

&a = 4244000 0
&b = 4244008 8
&x = 4245044 1037
&y = 4245045 1
&z = 4245046 1

&a = 4231444 0
&b = 4231452 8
&x = 4231464 8
&y = 4231460 -4
&z = 4231468 8

The following was from a non-C compiler (although it's possible that some C
compiler could return this too):

&a = 1638040 0
&b = 1638028 -12
&x = 1638039 11
&y = 1638038 -1
&z = 1638037 -1

>> You'll probably find the addresses are all mixed up.
>> Even when *all* variables are doubles, you won't know
>> which have the lowest and highest addresses.
>
> :o)

While in the C examples, 'a' had the lower address, I don't see how this can
guaranteed (and you might expect it to have higher address, if allocated
first and the stack frame growing downwards). And in general you can't know
what order variables might be allocated in (perhaps in declaration order,
perhaps in alphabetical order, but it can be anything). Or some might not 
exist in memory at all.

-- 
Bartc

Thread

Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 02:49 -0700
  Re: Q: Local variables initialization shortcut. China Blue Max <chine.bleu@yahoo.com> - 2012-06-02 03:03 -0700
    Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 03:17 -0700
  Re: Q: Local variables initialization shortcut. jacob navia <jacob@spamsink.net> - 2012-06-02 12:06 +0200
    Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 03:25 -0700
      Re: Q: Local variables initialization shortcut. James Kuyper <jameskuyper@verizon.net> - 2012-06-02 10:59 -0400
        Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 13:02 -0700
          Re: Q: Local variables initialization shortcut. Keith Thompson <kst-u@mib.org> - 2012-06-02 14:51 -0700
  Re: Q: Local variables initialization shortcut. Ian Collins <ian-news@hotmail.com> - 2012-06-02 22:10 +1200
  Re: Q: Local variables initialization shortcut. jt@toerring.de (Jens Thoms Toerring) - 2012-06-02 10:31 +0000
    Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 03:59 -0700
      Re: Q: Local variables initialization shortcut. jt@toerring.de (Jens Thoms Toerring) - 2012-06-02 11:55 +0000
        Re: Q: Local variables initialization shortcut. pete <pfiland@mindspring.com> - 2012-06-02 08:15 -0400
        Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 05:37 -0700
          Re: Q: Local variables initialization shortcut. jt@toerring.de (Jens Thoms Toerring) - 2012-06-02 13:35 +0000
            Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 06:47 -0700
              Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 15:08 +0100
                Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 07:37 -0700
                Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 16:17 +0100
                Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 19:02 +0100
              Re: Q: Local variables initialization shortcut. jt@toerring.de (Jens Thoms Toerring) - 2012-06-02 17:39 +0000
                Re: Q: Local variables initialization shortcut. Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-02 15:27 -0400
                Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 12:58 -0700
                Re: Q: Local variables initialization shortcut. Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-02 16:15 -0400
                Re: Q: Local variables initialization shortcut. David Brown <david.brown@hesbynett.no> - 2012-06-03 15:27 -0500
                Re: Q: Local variables initialization shortcut. Noob <root@localhost> - 2012-06-05 09:12 +0200
                Re: Q: Local variables initialization shortcut. David Brown <david@westcontrol.removethisbit.com> - 2012-06-05 09:21 +0200
                Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 12:53 -0700
                Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 21:16 +0100
                Re: Q: Local variables initialization shortcut. jt@toerring.de (Jens Thoms Toerring) - 2012-06-02 21:18 +0000
                Re: Q: Local variables initialization shortcut. Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-02 17:38 -0400
                Re: Q: Local variables initialization shortcut. jt@toerring.de (Jens Thoms Toerring) - 2012-06-02 22:15 +0000
                Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-03 00:51 -0700
                Re: Q: Local variables initialization shortcut. Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-06-03 11:46 -0700
                Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-03 00:13 -0700
                Re: Q: Local variables initialization shortcut. Keith Thompson <kst-u@mib.org> - 2012-06-02 14:50 -0700
                Re: Q: Local variables initialization shortcut. David Brown <david.brown@hesbynett.no> - 2012-06-03 15:34 -0500
          Re: Q: Local variables initialization shortcut. David Brown <david.brown@hesbynett.no> - 2012-06-03 15:25 -0500
        Re: Q: Local variables initialization shortcut. Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-02 08:46 -0400
        Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 05:46 -0700
          Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 05:53 -0700
            Re: Q: Local variables initialization shortcut. Ike Naar <ike@sverige.freeshell.org> - 2012-06-02 17:08 +0000
            Re: Q: Local variables initialization shortcut. "io_x" <a@b.c.invalid> - 2012-06-03 10:33 +0200
              Re: Q: Local variables initialization shortcut. "io_x" <a@b.c.invalid> - 2012-06-03 11:32 +0200
      Re: Q: Local variables initialization shortcut. pete <pfiland@mindspring.com> - 2012-06-02 08:03 -0400
        Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 05:18 -0700
    Re: Q: Local variables initialization shortcut. "io_x" <a@b.c.invalid> - 2012-06-03 10:32 +0200
  Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 11:45 +0100
    Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 04:17 -0700
      Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 12:40 +0100
        Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 12:51 +0100
        Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 04:57 -0700
          Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 14:00 +0100
            Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 06:12 -0700
              Re: Q: Local variables initialization shortcut. Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-02 09:58 -0400
                Re: Q: Local variables initialization shortcut. David Brown <david.brown@hesbynett.no> - 2012-06-03 15:41 -0500
              Re: Q: Local variables initialization shortcut. Robert Wessel <robertwessel2@yahoo.com> - 2012-06-02 11:45 -0500
  Re: Q: Local variables initialization shortcut. Noob <root@localhost> - 2012-06-02 16:05 +0200
    Re: Q: Local variables initialization shortcut. Jean-Christophe <5.d@free.fr> - 2012-06-02 07:48 -0700
      Re: Q: Local variables initialization shortcut. "BartC" <bc@freeuk.com> - 2012-06-02 18:31 +0100
      Re: Q: Local variables initialization shortcut. jt@toerring.de (Jens Thoms Toerring) - 2012-06-02 17:50 +0000

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