Re: Q: Local variables initialization shortcut.

From	jt@toerring.de (Jens Thoms Toerring)
Newsgroups	comp.lang.c
Subject	Re: Q: Local variables initialization shortcut.
Date	2012-06-02 22:15 +0000
Organization	Freie Universitaet Berlin
Message-ID	<a2vhkiFl0bU2@mid.uni-berlin.de> (permalink)
References	(4 earlier) <0e159ddf-1c62-4bc2-bb70-a8369dec0c00@a16g2000vby.googlegroups.com> <a2v1eeFru9U1@mid.uni-berlin.de> <9c25c022-dab8-4e7e-ba8f-1227a6b34023@b1g2000vbb.googlegroups.com> <a2ve8uFl0bU1@mid.uni-berlin.de> <jqe15h$90d$1@dont-email.me>

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Eric Sosman <esosman@ieee-dot-org.invalid> wrote:
> On 6/2/2012 5:18 PM, Jens Thoms Toerring wrote:
> > [...] Learning assembler before C has
> > for sure its advantages, e.g. pointers, which seem to con-
> > fuse quite a number of people at first, are something ob-
> > vious etc. [...]

>      A bad effect of learning assembly languages before C is
> that one is tempted to think "Pointers?  Oh, I get it: They're
> just addresses, and I already know about addresses."

>      What's wrong with thinking "Pointers are addresses?"  Here's
> an illustration: In an assembly setting you might be told that
> the R1 register holds an address and be asked to test whether the
> value R1 points to is zero.  Are you ready to write the test?  No,
> you need to ask "What kind of value does R1 point at?  A single
> byte, a two-byte integer, an eight-byte floating-point number, or
> what?"

>      You never need to ask such questions in C, because a pointer
> is not a bare address: It is an address *and a type*.  If you're
> told that the variable R1 points somewhere and you're asked to
> test whether the pointee is zero, you're all set: The type of R1
> is known, hence the type it points at is known, and you have all
> the information you need: `if (*R1 == 0)', and you're off to the
> races (if R1 points to something that's not comparable to zero
> the compiler will complain -- but in that case the "test for zero"
> question made no sense in the first place).

>      It seems to me from some of the rather peculiar subtractions
> he's attempted that Jean-Christophe may harbor this very confusion
> between typed pointers and assembly-style "bare" addresses.

Yes, that could be one of things I had to unlearn the hard
way... C makes a lot of things much more simple and safer,
but it can take some time to learn what they are, how they
work and then to appreciate them in the end;-) To be honest,
for about the first 5 years of using C I was blissfully igno-
rant of a lot of potential problems in the code I wrote - I
was programming on an architecture were I knew the assembler,
I had studied how the linker works in detail etc. and there
were no real surprises - everything seemed to fit quite nicely
and I considered myself to be a quite competent programmer. And
then came the day when I had to port one of my programs to a
different architecture - you can guess the rest of the story...
After a lot of pain (and quite a bit of deflation of my self-
esteem;-) I started to learn that C isn't assembler in dis-
guise - and lurking in comp.lang.c for some of time hope-
fully helped to cure some of the worst of my stupid mis-
understandings;-)
                           Regards, Jens
-- 
  \   Jens Thoms Toerring  ___      jt@toerring.de
   \__________________________      http://toerring.de

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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