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Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding

From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c++
Subject Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding
Date 2019-11-28 12:51 -0800
Organization A noiseless patient Spider
Message-ID <86pnhbafn8.fsf@linuxsc.com> (permalink)
References (5 earlier) <qr7v3c$lvv$1@dont-email.me> <lnsgmgxq5r.fsf@kst-u.example.com> <qr88ln$4ck$1@dont-email.me> <qr902l$bdp$1@dont-email.me> <qr908i$bdp$2@dont-email.me>

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James Kuyper <jameskuyper@alumni.caltech.edu> writes:

> On 11/22/19 10:49 AM, James Kuyper wrote:
>
>> On 11/22/19 4:10 AM, David Brown wrote:
>>
>>> On 22/11/2019 09:37, Keith Thompson wrote:
>>
>> ...
>>
>>>> Or an array wrapped in a struct to allow assignment.  (An array of 4
>>>> uint8_t elements is guaranteed to be 32 bits, but a struct containing
>>>> such an array is not -- but it's a nearly safe assumption that there
>>>> will be no padding between the elements or at the end.)
>>>
>>> While it is true in theory that a struct can have extra padding at the
>>> end (beyond what is needed for an array of the struct to have proper
>>> alignment for all members), are there any compilers that have done so in
>>> practice?
>>
>> I can't name names, but my understanding is that there have been (and
>> might still be) implementations where all struct types have the same
>> alignment requirement as the most strictly aligned type supported by
>> that implementation.  If that alignment requirement is greater than the
>> requirements of any of the member types, that will sometimes require
>> padding at the end of the struct.
>
> I said that wrong.  Unless all members of the struct have the maximum
> alignment requirement, it's possible that such an implementation would
> have to put padding at the end.

Don't you mean, unless the last member of a struct has the
maximum alignment requirement, it's possible such an
implementation would have to put padding at the end.

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Thread

[QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-20 19:55 +0100
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-20 20:12 +0100
    Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-20 22:33 -0800
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-20 20:22 +0100
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-11-20 19:34 +0000
    Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-21 00:54 +0100
      Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Öö Tiib <ootiib@hot.ee> - 2019-11-20 16:27 -0800
      Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Manfred <invalid@add.invalid> - 2019-11-21 01:48 +0100
        Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-21 04:09 +0100
      Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-20 17:44 -0800
        Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-21 04:14 +0100
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-20 22:03 +0100
    Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-21 01:00 +0100
      Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-21 13:22 +0100
        Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-21 11:30 -0800
          Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-21 22:54 +0100
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Paavo Helde <myfirstname@osa.pri.ee> - 2019-11-20 23:28 +0200
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-20 15:48 -0800
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Reinhardt Behm <rbehm@hushmail.com> - 2019-11-21 10:33 +0800
    Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-21 13:25 +0100
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-20 22:32 -0800
    Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-20 22:43 -0800
      Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-21 12:53 +0100
        Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Paavo Helde <myfirstname@osa.pri.ee> - 2019-11-21 18:20 +0200
          Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-21 18:07 +0100
          Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-11-21 17:34 +0000
          Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Christian Gollwitzer <auriocus@gmx.de> - 2019-11-22 07:26 +0100
            Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-22 00:37 -0800
              Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 10:10 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Öö Tiib <ootiib@hot.ee> - 2019-11-22 02:23 -0800
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 12:38 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Manfred <noname@add.invalid> - 2019-11-22 17:13 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 18:48 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-22 10:49 -0500
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-22 10:52 -0500
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-28 12:51 -0800
              Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-22 11:20 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-22 10:00 -0800
            Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 09:37 +0100
              Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Öö Tiib <ootiib@hot.ee> - 2019-11-22 01:37 -0800
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 11:40 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Öö Tiib <ootiib@hot.ee> - 2019-11-22 04:55 -0800
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 15:18 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Öö Tiib <ootiib@hot.ee> - 2019-11-22 07:23 -0800
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 16:34 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding scott@slp53.sl.home (Scott Lurndal) - 2019-11-22 15:16 +0000
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Öö Tiib <ootiib@hot.ee> - 2019-11-23 05:11 -0800
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-22 10:56 -0500
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Öö Tiib <ootiib@hot.ee> - 2019-11-23 07:03 -0800
              Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-22 11:31 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 12:23 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-22 13:14 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding David Brown <david.brown@hesbynett.no> - 2019-11-22 15:04 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-22 19:35 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-22 14:11 -0500
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-23 00:25 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-22 23:56 -0500
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-23 11:12 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Paavo Helde <myfirstname@osa.pri.ee> - 2019-11-23 14:51 +0200
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-25 11:45 -0500
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-22 22:04 -0800
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-23 11:26 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-23 12:27 -0800
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-24 00:54 +0100
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Keith Thompson <kst-u@mib.org> - 2019-11-23 17:06 -0800
                Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Soviet_Mario <SovietMario@CCCP.MIR> - 2019-11-24 12:10 +0100
  Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-28 13:21 -0800

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