Re: Never use strncpy!

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c++
Subject	Re: Never use strncpy!
Date	2022-09-24 16:22 +0200
Organization	A noiseless patient Spider
Message-ID	<tgn3ri$309ud$1@dont-email.me> (permalink)
References	(8 earlier) <tghbql$23qfo$1@dont-email.me> <tgk4vu$2gu8f$1@dont-email.me> <tgk6er$2h1tg$1@dont-email.me> <tgkc46$2hhg9$1@dont-email.me> <tgkeah$2hnjc$1@dont-email.me>

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On 23/09/2022 16:03, Bonita Montero wrote:
> Am 23.09.2022 um 15:25 schrieb David Brown:
>> On 23/09/2022 13:49, Bonita Montero wrote:
>>> Am 23.09.2022 um 13:23 schrieb David Brown:
>>>
>>>> The key point of an atomic access, above all else, is that it is an 
>>>> all-or-nothing access.  If one thread writes to an atomic object, 
>>>> and another thread reads it, then the reading thread will see either 
>>>> the complete old data or the complete new data.
>>>
>>> Although it is possible no one actually uses atomics for non-native
>>> types. And for native types what I said holds true against volatiles.
>>>
>>
>> No.
> 
> If you use non-native types with atomics they use STM, and that's
> really slow. That's while no one uses atomic for non-native types.

There are a number of ways to implement atomics that are larger than a 
single bus operation can handle, or that involve multiple bus 
operations.  Different processor types have different solutions, and 
some are optimised or limited to particular setups (such as single 
writer, single processor, etc.).  Some processors can handle atomic 
accesses for sizes that are bigger than native C/C++ types (such as 
128-bit accesses).  Some cannot handle atomic writes for the bigger 
native types.

And non-aligned accesses might be supported for volatile accesses, while 
not being atomic.

In summary - you are making so many assumptions it is easiest just to 
say you are wrong.

> 
>>
>>>> "Atomic" does not have those semantics.  The compiler can combine 
>>>> two relaxed atomic writes to one.
>>>
>>> Cite the standard.
>>>
>>
>> "As if" rule.
>>
>>>> In the C standards (I refer to them as they are simpler and clearer 
>>>> than the C++ standards, but the memory model is the same) say that 
>>>> an "atomic_thread_fence(memory_order_relaxed)" has no effect.  This 
>>>> is rather different from a memory barrier, which requires 
>>>> compiler-specific extensions and which can be viewed roughly as a 
>>>> kind of "cache flush" in which the "cache" is the processor 
>>>> registers along with any information the compiler knows about any 
>>>> objects.
>>>
>>> That's pettifogging since no one uses fences which actually won't work.
>>>
>>
>> They /do/ work - they just do what they are supposed to do, not what 
>> you think they should do.
> 
> No, they have actually no effect.
> 

Perhaps some of your misconceptions are valid within your limited little 
world of x86 programming on Windows with MSVC.  There is a wider world 
out there, and even if you never enter it, please stop making posts in a 
general C++ newsgroup full of invalid assumptions that only applies to 
such a limited subset of C++.

Thread

Never use strncpy! Juha Nieminen <nospam@thanks.invalid> - 2022-09-21 10:04 +0000
  Re: Never use strncpy! "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-09-21 15:06 +0200
  Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-21 15:24 +0200
    Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-21 15:30 +0200
      Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-21 19:20 +0200
        Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-21 19:33 +0200
          Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-21 23:14 +0200
            Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-22 04:40 +0200
              Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-22 08:56 +0200
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-22 12:02 +0200
                Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-23 13:23 +0200
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-23 13:49 +0200
                Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-23 15:25 +0200
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-23 16:03 +0200
                Re: Never use strncpy! scott@slp53.sl.home (Scott Lurndal) - 2022-09-23 14:34 +0000
                Re: Never use strncpy! Michael S <already5chosen@yahoo.com> - 2022-09-23 08:19 -0700
                Re: Never use strncpy! scott@slp53.sl.home (Scott Lurndal) - 2022-09-23 17:57 +0000
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-23 18:36 +0200
                Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-24 16:22 +0200
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-24 16:25 +0200
                Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-24 17:09 +0200
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-24 17:14 +0200
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-09-26 17:34 -0700
                Re: Never use strncpy! Juha Nieminen <nospam@thanks.invalid> - 2022-09-26 07:53 +0000
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-26 10:21 +0200
                Re: Never use strncpy! Juha Nieminen <nospam@thanks.invalid> - 2022-09-26 08:34 +0000
                Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-26 13:39 +0200
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-09-26 17:47 -0700
                Re: Never use strncpy! scott@slp53.sl.home (Scott Lurndal) - 2022-09-27 14:17 +0000
                Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-27 18:07 +0200
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-09-27 12:42 -0700
                Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-28 09:32 +0200
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-09-28 13:34 -0700
                Re: Never use strncpy! scott@slp53.sl.home (Scott Lurndal) - 2022-09-28 21:11 +0000
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-01 06:26 +0200
                Re: Never use strncpy! scott@slp53.sl.home (Scott Lurndal) - 2022-10-01 17:01 +0000
                Re: Never use strncpy! Michael S <already5chosen@yahoo.com> - 2022-10-02 15:32 -0700
                Re: Never use strncpy! scott@slp53.sl.home (Scott Lurndal) - 2022-10-03 14:01 +0000
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-03 13:49 -0700
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-02 12:46 -0700
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-03 04:14 +0200
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-02 19:43 -0700
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-02 19:48 -0700
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-03 04:53 +0200
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-02 19:58 -0700
                Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-10-03 08:27 +0200
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-03 13:49 -0700
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-04 10:53 -0700
                Re: Never use strncpy! "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-10-02 12:44 -0700
            Re: Never use strncpy! Juha Nieminen <nospam@thanks.invalid> - 2022-09-22 05:59 +0000
              Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-22 09:32 +0200
    Re: Never use strncpy! Muttley@dastardlyhq.com - 2022-09-21 15:42 +0000
      Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-21 18:10 +0200
        Re: Never use strncpy! Muttley@dastardlyhq.com - 2022-09-21 16:19 +0000
          Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-21 18:27 +0200
            Re: Never use strncpy! Muttley@dastardlyhq.com - 2022-09-23 14:47 +0000
      Re: Never use strncpy! scott@slp53.sl.home (Scott Lurndal) - 2022-09-21 16:12 +0000
    Re: Never use strncpy! Philipp Klaus Krause <pkk@spth.de> - 2022-09-23 19:52 +0200
      Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-24 16:25 +0200
  Re: Never use strncpy! scott@slp53.sl.home (Scott Lurndal) - 2022-09-21 14:00 +0000
    Re: Never use strncpy! Juha Nieminen <nospam@thanks.invalid> - 2022-09-22 06:03 +0000
      Re: Never use strncpy! Philipp Klaus Krause <pkk@spth.de> - 2022-09-23 19:50 +0200
        Re: Never use strncpy! Juha Nieminen <nospam@thanks.invalid> - 2022-09-26 07:54 +0000
  Re: Never use strncpy! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-09-21 15:56 +0100
  Re: Never use strncpy! Muttley@dastardlyhq.com - 2022-09-21 15:36 +0000
  Re: Never use strncpy! Frederick Virchanza Gotham <cauldwell.thomas@gmail.com> - 2022-09-21 08:59 -0700
  Re: Never use strncpy! Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-09-21 13:23 -0700
    Re: Never use strncpy! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-09-21 21:49 +0100
      Re: Never use strncpy! Richard Damon <Richard@Damon-Family.org> - 2022-09-21 19:18 -0400
        Re: Never use strncpy! Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-09-22 00:39 +0100
          Re: Never use strncpy! Richard Damon <Richard@Damon-Family.org> - 2022-09-21 20:45 -0400
            Re: Never use strncpy! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-09-21 18:00 -0700
          Re: Never use strncpy! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-09-21 17:55 -0700
        Re: Never use strncpy! Juha Nieminen <nospam@thanks.invalid> - 2022-09-22 06:09 +0000
          Re: Never use strncpy! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-09-22 11:44 -0700
          Re: Never use strncpy! Richard Damon <Richard@Damon-Family.org> - 2022-09-22 23:33 -0400
      Re: Never use strncpy! Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-09-22 19:00 -0700
        Re: Never use strncpy! Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-09-22 19:04 -0700
          Re: Never use strncpy! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-09-22 22:49 -0700
    Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-24 11:38 +0200
      Re: Never use strncpy! Muttley@dastardlyhq.com - 2022-09-24 09:43 +0000
        Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-24 11:59 +0200
      Re: Never use strncpy! Richard Damon <Richard@Damon-Family.org> - 2022-09-24 06:27 -0400
        Re: Never use strncpy! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-09-24 11:53 -0700
          Re: Never use strncpy! Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-24 20:58 +0200
  Re: Never use strncpy! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-09-21 16:01 -0700
    Re: Never use strncpy! David Brown <david.brown@hesbynett.no> - 2022-09-22 09:37 +0200
    Re: Never use strncpy! Manfred <noname@add.invalid> - 2022-10-01 01:24 +0200
      Re: Never use strncpy! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-09-30 16:43 -0700
  Re: Never use strncpy! Lynn McGuire <lynnmcguire5@gmail.com> - 2022-09-22 21:03 -0500

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