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Groups > comp.arch.embedded > #10635

Re: Getting started with AVR and C

From James Kuyper <jameskuyper@verizon.net>
Newsgroups comp.arch.embedded, comp.lang.c
Subject Re: Getting started with AVR and C
Date 2012-11-29 09:07 -0500
Organization A noiseless patient Spider
Message-ID <k97q71$hn3$1@dont-email.me> (permalink)
References (6 earlier) <JaGdnWuCkdH4wyvNnZ2dnUVZ_oOdnZ2d@web-ster.com> <k960mf$ghq$1@speranza.aioe.org> <TN6dnaDoIqIhMCvNnZ2dnUVZ8v-dnZ2d@lyse.net> <k96he8$m87$1@speranza.aioe.org> <OdWdnXwRtuUQvSrNnZ2dnUVZ8uSdnZ2d@lyse.net>

Cross-posted to 2 groups.

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On 11/29/2012 03:37 AM, David Brown wrote:
...
> Default "int" promotions are done first for each operand.  They are 
> promoted to "signed int", "unsigned int", "signed long int" or "unsigned 
> long int" (and "long long" for newer C standards), stopping at the first 
> type that covers the entire range.  In practice, this means anything 
> smaller than an "int" will get promoted to a "signed int".

Not quite. The integer conversions never change anything to any type
other than 'int' or 'unsigned int'.

"If an int can represent all values of the original type (as restricted
by the width, for a bit-field), the value is converted to an int;
otherwise, it is converted to an unsigned int. These are called the
integer promotions.58) All other types are unchanged by the integer
promotions." (6.3.1.1p2) The first use of "integer promotions" in that
clause is italicized, which is an ISO convention indicating that the
sentence containing that phrase serves as the definition of the phrase.

..
>> Now it gets interesting. When were the int_32_t and int_16_t added to C?
>>
> 
> The types were officially added with C99, but they existed in practice 
> before that as "long int" and "short int" on most compilers (some 
> targets don't support 16-bit types, and thus have "short int" as 32-bit 
> and no int16_t.  And the standards allow compilers with a "short" of 
> 64-bit or more, in which case neither "int32_t" nor "int16_t" would 
> exist - but I have never heard of such a beast).

I've heard of machines with 32-bit short, but not 64-bit. Note that
while int32_t and int16_t could not be provided by <stdint.h> for such a
compiler, int_least32_t and int_fast32_t (and similarly for 16) must be.

>> Seems to me that compilers only claiming a version of the standard
>> before they were added wouldn't have to use the same rules.
> 
> The rules haven't changed (again, sorry for my mistaken post). ...

Yes they have. In C99 and later, <stdint.h> and <inttypes.h> are
standard headers, and if #included, the identifiers they define must
meet certain well-specified requirements. In C90, there were no such
standard headers, no guarantees on what a header file with that name
would contain if you successfully #included it, and no corresponding
restrictions on how user code could use those identifiers after
#including those header files.

> ... Types
> such as "int32_t" are just typedef's for "normal" C types.

That depends upon what you mean by 'normal'. The C99 standard
distinguishes between standard and extended integer types. The standard
integer types have names specified by the C standard; extended types are
implementation-defined, and may have other names. There are many
standard typedefs that are required to have either arithmetic or integer
type; but there are none that are restricted to standard integer types.
Would you consider __extended_integer_type to be a "normal" C type?

...
> The "int128_t" here is either a typedef for an existing C type (which 
> could include "long long int" in C99), in which case it would have to 
> support all integral operations, or it is purely a compiler extension, 
> in which case it is non-standard.

No, supporting int128_t would not be a non-standard extension, it's just
providing an optional feature of standard C. The key difference is that
if an implementation chooses to support an optional feature, it must
support it in precisely the manner specified by the standard for that
feature; extensions give an implementation a lot more freedom. In C2011,
there's a lot of optional features.

The only size-named types that a conforming implementation of <stdint.h>
must provide are [u]int_leastN_t, and [u]int_fastN_t for N = 8, 16, 32,
and 64. For all other values of N, and for [u]intN_t for all values of
N, the typedefs are optional. You can determine precisely which of the
optional <stdint.h> types are supported by #ifdef of the corresponding
*_MAX macro. If that macro is #defined, you can use the corresponding
type in full confidence that it behaves precisely as specified by the
standard.
-- 
James Kuyper

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Thread

Getting started with AVR and C Robert Roland <fake@ddress.no> - 2012-11-24 17:41 +0100
  Re: Getting started with AVR and C hamilton <hamilton@nothere.com> - 2012-11-24 09:55 -0700
    Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-25 10:39 +0100
  Re: Getting started with AVR and C Rene <a@b.c> - 2012-11-24 18:03 +0100
    Re: Getting started with AVR and C Rene <a@b.c> - 2012-12-10 13:21 +0100
      Re: Getting started with AVR and C Christopher Head <chead@is.invalid> - 2012-12-10 18:33 -0800
        Re: Getting started with AVR and C Rene <a@b.c> - 2012-12-11 12:34 +0100
  Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.please> - 2012-11-24 12:44 -0600
  Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-24 11:12 -0800
  Re: Getting started with AVR and C mike <ham789@netzero.net> - 2012-11-24 11:28 -0800
    Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-24 11:42 -0800
      Re: Getting started with AVR and C mike <ham789@netzero.net> - 2012-11-25 07:01 -0800
    Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-25 20:14 +0100
  Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-25 03:18 +0700
  Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-25 04:18 +0700
    Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-11-24 17:09 -0500
    Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-24 22:12 +0000
      Re: Getting started with AVR and C Dave Nadler <drn@nadler.com> - 2012-11-24 21:01 -0800
        statement / expression contexts in C Ivan Shmakov <oneingray@gmail.com> - 2012-11-28 12:54 +0700
      Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-28 13:37 +0700
        Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-28 14:49 +0000
        Re: Getting started with AVR and C Frank Miles <fpm@u.washington.edu> - 2012-11-28 17:53 +0000
          Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-28 18:05 +0000
            Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 12:56 -0600
              Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-28 21:45 +0000
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 15:55 -0600
                Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-29 01:35 +0100
                Re: Getting started with AVR and C Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-11-29 01:47 +0100
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 09:24 +0100
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 01:18 +0000
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 20:07 -0600
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:23 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 11:01 -0500
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 19:19 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 14:32 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 11:44 -0800
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 21:23 +0000
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 18:15 -0800
                Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-30 09:26 -0800
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 13:22 -0800
                Re: Getting started with AVR and C me@linnix.info-for.us - 2012-11-30 14:10 -0800
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 15:16 -0800
                Re: Getting started with AVR and C Mel Wilson <mwilson@the-wire.com> - 2012-11-30 17:36 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-30 15:18 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-01 10:08 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 00:45 -0800
                Re: Getting started with AVR and C Ed Beroset <beroset@mindspring.com> - 2012-12-01 08:00 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 13:22 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-01 17:33 -0800
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-01 17:43 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-02 14:13 -0800
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-04 20:34 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-04 18:25 -0800
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-05 07:55 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:11 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-05 07:52 -0800
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-05 11:02 -0500
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 21:28 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:21 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 23:05 +0200
                Re: Getting started with AVR and C Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2012-12-05 23:22 +0200
                Re: Getting started with AVR and C Niklas Holsti <niklas.holsti@tidorum.invalid> - 2012-12-06 00:00 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 12:17 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-05 23:10 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 15:25 -0800
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-06 07:15 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 21:52 -0800
                Re: Getting started with AVR and C Lanarcam <lanarcam1@yahoo.fr> - 2012-12-06 20:59 +0100
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-06 12:38 -0800
                Re: Getting started with AVR and C George Neuner <gneuner2@comcast.net> - 2012-12-06 20:39 -0500
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-06 22:31 -0500
                Re: Getting started with AVR and C Mel Wilson <mwilson@the-wire.com> - 2012-12-05 16:32 -0500
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 15:25 -0800
                Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-05 17:04 -0800
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-12-05 22:01 -0800
                Re: Getting started with AVR and C Ian Malcolm <See.My.Sig.for.email@totally.invalid> - 2012-12-06 14:05 +0000
                Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-06 10:28 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-06 16:58 -0800
                Re: Getting started with AVR and C Mark Borgerson <mborgerson@comcast.net> - 2012-12-06 07:34 -0800
                Re: Getting started with AVR and C Walter Banks <walter@bytecraft.com> - 2012-12-06 10:55 -0500
                Re: Getting started with AVR and C Rich Webb <bbew.ar@mapson.nozirev.ten> - 2012-12-06 11:11 -0500
                Re: Getting started with AVR and C Rocky <RobertGush@gmail.com> - 2012-12-06 21:38 -0800
                Re: Getting started with AVR and C dp <dp@tgi-sci.com> - 2012-12-07 03:49 -0800
                Re: Getting started with AVR and C Robert Wessel <robertwessel2@yahoo.com> - 2012-12-01 02:58 -0600
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-01 17:28 +0200
                Re: Getting started with AVR and C Robert Wessel <robertwessel2@yahoo.com> - 2012-12-01 11:55 -0600
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-11-29 22:17 +0200
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 12:36 -0800
                Re: Getting started with AVR and C Stephen Sprunk <stephen@sprunk.org> - 2012-11-29 16:22 -0600
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 18:36 -0800
                Re: Getting started with AVR and C "Boudewijn Dijkstra" <sp4mtr4p.boudewijn@indes.com> - 2012-12-11 10:53 +0100
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-12-11 14:53 +0000
                Unicode Ivan Shmakov <oneingray@gmail.com> - 2012-12-14 23:25 +0700
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-15 14:30 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-15 12:24 -0800
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-15 18:02 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-15 15:45 -0800
                Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-16 22:55 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-16 23:20 -0800
                Re: Getting started with AVR and C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:27 +0200
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-12-17 11:17 +0000
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 14:07 +0000
                Re: Getting started with AVR and C Nobody <nobody@nowhere.com> - 2012-12-16 03:28 +0000
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-16 10:40 +0200
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 02:31 +0000
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 03:36 +0000
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 03:55 +0000
                Re: Getting started with AVR and C Christopher Head <chead@is.invalid> - 2012-11-28 23:24 -0800
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 09:37 +0100
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 11:31 +0000
                Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 13:44 +0100
                Re: Getting started with AVR and C Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-11-29 13:22 +0100
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 13:32 +0000
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 11:28 -0800
                Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 13:20 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 09:07 -0500
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 09:17 -0500
                Re: Getting started with AVR and C pete <pfiland@mindspring.com> - 2012-11-29 18:25 -0500
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 22:46 -0500
                Re: Getting started with AVR and C lawrence.jones@siemens.com - 2012-11-30 11:47 -0500
                Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 11:38 -0800
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 15:21 -0500
              Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-28 22:26 +0000
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 17:32 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 19:02 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 18:29 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 23:39 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.please> - 2012-11-29 00:59 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 07:57 -0500
                Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-29 13:02 -0600
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:19 +0000
                Re: Getting started with AVR and C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-11-29 12:03 +0200
                Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 11:39 +0000
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 08:04 -0500
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:17 +0000
              Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 19:19 -0600
                Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 23:44 -0500
          Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 13:15 -0500
            Re: Getting started with AVR and C Arlet Ottens <usenet+5@c-scape.nl> - 2012-11-28 19:17 +0100
              Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 19:30 -0600
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:29 +0000
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-11-29 16:36 +0000
                Re: Getting started with AVR and C upsidedown@downunder.com - 2012-11-29 22:40 +0200
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 13:55 -0800
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 22:06 +0000
                Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 14:22 -0800
                Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 21:59 +0000
                Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-11-30 08:29 +0000
    Re: Getting started with AVR and C Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-11-25 05:41 -0800
    Re: Getting started with AVR and C Rosario1903 <Rosario@invalid.invalid> - 2012-11-27 10:21 +0100
  Re: Getting started with AVR and C dbr@kbrx.com - 2012-11-24 21:49 +0000
    Re: Getting started with AVR and C MK <mk@nospam.co.uk> - 2012-11-25 12:24 +0000
      Re: Getting started with AVR and C Ian Malcolm <See.My.Sig.for.email@totally.invalid> - 2012-11-26 00:08 +0000

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