Re: Never use strncpy!

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c++
Subject	Re: Never use strncpy!
Date	2022-09-21 23:14 +0200
Organization	A noiseless patient Spider
Message-ID	<tgfus6$1tinp$1@dont-email.me> (permalink)
References	<tgenin$qc3$1@gioia.aioe.org> <tgf39h$1qua1$1@dont-email.me> <tgf3l1$1qu51$3@dont-email.me> <tgfh5a$1s7n1$1@dont-email.me> <tgfhrv$1s8i7$1@dont-email.me>

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On 21/09/2022 19:33, Bonita Montero wrote:
> Am 21.09.2022 um 19:20 schrieb David Brown:
>> On 21/09/2022 15:30, Bonita Montero wrote:
>>> Am 21.09.2022 um 15:24 schrieb David Brown:
>>>
>>>> Several of the str* functions in the C standard library are 
>>>> downright silly.  There are surprising inconsistencies (strncat 
>>>> guarantees a null-terminated result, strncpy does not), mostly 
>>>> useless return values, and missing functions (no strnlen).  There 
>>>> are no volatile versions which could be used to ensure that 
>>>> something like an "memset" to wipe memory would actually be run. ...
>>>
>>> volatile ist mostly deprecated. 
>>
>> Volatile is not deprecated at all. Overly complex expressions 
>> involving volatile were deprecated in C++20 as their semantics were 
>> unclear.
> 
> The semantics of volatile has been reduced with C++20:
> https://en.cppreference.com/w/cpp/language/cv

No, the page there says - as I said - that some uses of volatile in 
complex expressions were deprecated in C++20.

> 
>>> atomics are used most of the time
>>> where you used volatiles before. 
>>
>> Complete nonsense.  Volatile accesses and atomics are different 
>> things, for different purposes.
> 
> Before C++11 volatile were partitially used where today you use atomics.

If you used "volatile" thinking you got the effects of atomic access, 
you were wrong.  Prior to C++11 (and C11), C and C++ did not have any 
concept of multiple threads - they did not have any need of "atomic" 
accesses in the language.  People who write OS's and similar low-level 
code needed to implement atomics for the system, and "volatile" was 
/part/ of those implementations.  People writing code for such OS's and 
using atomics, used the OS's functions, classes, and macros.

If you use "volatile" when you mean "atomic", your code is wrong.  If 
you use "atomic" when you mean "volatile", your code will probably work 
but will be much less efficient.  "volatile atomic" is an extremely 
common combination.

> But the whole semantics were platform-specific. F.e. there's a mode of
> MSVC where volatile reads have acquire semantics and volatile writes
> have release semantics.
> 

The details of volatile accesses are implementation-dependent, by 
necessity.  And an implementation is allowed to make them stronger - 
though doing so is going to be inefficient and encourage misconceptions 
and unwarranted assumptions.

>> Following a memcpy() or memset() with a memory barrier (a relaxed 
>> order full fence) is certainly a possibility.  But such fences can be 
>> a lot more expensive than using volatile writes.
> 
> volatile writes can't be substituted with fences.
> 

A fence implies a memory barrier - writes that are logically part of the 
source code must be completed before the barrier completes.  That is 
part of why you have fences.

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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