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Re: Q: Local variables initialization shortcut.

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Jean-Christophe <5.d@free.fr> writes:
> On 2 juin, 19:39, j...@toerring.de (Jens Thoms Toerring) wrote:
>
>> (...) BTW, I jut noticed something funny:
>> the output of this program
>> #include <stdio.h>
>> double a, b;
>> int main( void )
>> {   double c, d;
>>     printf( "global diff: %td\n", ( char * ) &a - ( char * ) &b );
>>     printf( "local diff:  %td\n", ( char * ) &c - ( char * ) &d );
>>     return 0;
>> }
>> is
>> global diff: 8
>> local diff:  -8
>
> I understand that : the address allocation for global
> variables increases from the starting address,
> while for local variables allocated on the stack
> the stack pointer is decreased for each new variable.

Global variables are allocated wherever the &^*%$ the implementation
decides to allocate them.

Local variables are allocated wherever the &^*%$ the implementation
decides to allocate them.

You should not make *any* assumptions about what any particular
implementation does.

Well, that might not *quite* be true, but it's very rare that it would
make any sense to make such assumptions.  The result will be code that
can break badly when compiled on a different system, with a different
version of the same compiler, with the same compiler and different
optimization options, or with exactly the same options during a
different phase of the Moon.

You seem to have started with a certain set of assumptions based on the
behavior of one particular implementation, and are now trying to
understand systems that behave differently.  You're likely to have
better luck by trying to understand just what the language does and does
not guarantee, and then understanding individual implementations in
terms of the choice they make within the limits imposed by the standard.

Don't worry about how variables are allocated; instead, write code that
will work regardless of how they're allocated.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
    Will write code for food.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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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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