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Re: is "x *= ++f * ++f" a valid statement ?

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

> On 7/22/24 13:51, testuseri2p wrote:
>
>> I'd say in simple words, if you alter a variable multiple times in
>> one statement, you get UB.
>
> The correct (and admittedly more complicated) statement of the
> relevant rule is:

> "If a side effect on a memory location (6.7.1) is unsequenced
> relative to either another side effect on the same memory location
> or a value computation using the value of any object in the same
> memory location, and they are not potentially concurrent (6.9.2),
> the behavior is undefined."
>
> The biggest difference between the exact rule and what you said is
> that two different updates to a variable may occur in the same
> statement, so long as they are sequenced relative to each other.
> Sub-expressions of an expression are sequenced before evaluation of
> the expression itself.  In general, the sub-expressions of a
> expression are unsequenced, but there several exceptions: ||, &&,
> ?:, the comma operator.

Don't forget << (and also >>?).

> A minor detail is that a variable must be declared, whereas memory
> locations can, for instance, be part of allocated memory for which
> no declaration exists - it is still undefined behavior to write code
> that applies unsequence side-effects to such memory locations.

The original statement most likely meant "variable" as a stand-in
for "object".

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is "x *= ++f * ++f" a valid statement ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-23 16:14 +0200
  Re: is "x *= ++f * ++f" a valid statement ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2024-06-18 18:53 -0700
    Re: is "x *= ++f * ++f" a valid statement ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-19 17:40 +0200
    Re: is "x *= ++f * ++f" a valid statement ? PLO olcott <polcott333@gmail.com> - 2024-06-21 16:55 -0500
      Re: is "x *= ++f * ++f" a valid statement ? PLO Richard Damon <richard@damon-family.org> - 2024-06-21 18:10 -0400
        Re: is "x *= ++f * ++f" a valid statement ? PLO olcott <polcott333@gmail.com> - 2024-06-21 18:06 -0500
          Re: is "x *= ++f * ++f" a valid statement ? PLO Richard Damon <richard@damon-family.org> - 2024-06-21 20:14 -0400
          Re: is "x *= ++f * ++f" a valid statement ? PLO Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-21 17:35 -0700
            Re: is "x *= ++f * ++f" a valid statement ? PLO olcott <polcott333@gmail.com> - 2024-06-21 22:58 -0500
              Re: is "x *= ++f * ++f" a valid statement ? PLO Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-21 23:18 -0700
                Re: is "x *= ++f * ++f" a valid statement ? PLO olcott <polcott333@gmail.com> - 2024-06-22 07:38 -0500
                Re: is "x *= ++f * ++f" a valid statement ? PLO Richard Damon <richard@damon-family.org> - 2024-06-22 09:45 -0400
                Re: is "x *= ++f * ++f" a valid statement ? PLO olcott <polcott333@gmail.com> - 2024-06-22 09:13 -0500
                Re: is "x *= ++f * ++f" a valid statement ? PLO Richard Damon <richard@damon-family.org> - 2024-06-22 10:23 -0400
                Re: is "x *= ++f * ++f" a valid statement ? PLO Mikko <mikko.levanto@iki.fi> - 2024-06-23 11:48 +0300
                Re: is "x *= ++f * ++f" a valid statement ? PLO Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-22 17:54 -0700
          Re: is "x *= ++f * ++f" a valid statement ? PLO James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-06-21 23:42 -0400
            Re: is "x *= ++f * ++f" a valid statement ? PLO olcott <polcott333@gmail.com> - 2024-06-21 23:02 -0500
              Re: is "x *= ++f * ++f" a valid statement ? PLO David Brown <david.brown@hesbynett.no> - 2024-06-22 13:09 +0200
                Re: is "x *= ++f * ++f" a valid statement ? PLO olcott <polcott333@gmail.com> - 2024-06-22 07:40 -0500
                Re: is "x *= ++f * ++f" a valid statement ? PLO Richard Damon <richard@damon-family.org> - 2024-06-22 09:56 -0400
                Re: is "x *= ++f * ++f" a valid statement ? PLO "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-22 12:14 -0700
                Re: is "x *= ++f * ++f" a valid statement ? PLO David Brown <david.brown@hesbynett.no> - 2024-06-22 16:52 +0200
                Re: is "x *= ++f * ++f" a valid statement ? PLO olcott <polcott333@gmail.com> - 2024-06-22 11:27 -0500
                Re: is "x *= ++f * ++f" a valid statement ? PLO Richard Damon <richard@damon-family.org> - 2024-06-22 13:20 -0400
                Re: is "x *= ++f * ++f" a valid statement ? PLO Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-22 17:55 -0700
                Re: is "x *= ++f * ++f" a valid statement ? PLO David Brown <david.brown@hesbynett.no> - 2024-06-23 14:46 +0200
              Re: is "x *= ++f * ++f" a valid statement ? PLO James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-06-22 15:48 -0400
  Re: is "x *= ++f * ++f" a valid statement ? Richard Damon <richard@damon-family.org> - 2024-06-18 22:27 -0400
  Re: is "x *= ++f * ++f" a valid statement ? olcott <polcott333@gmail.com> - 2024-06-22 21:51 -0500
    Re: is "x *= ++f * ++f" a valid statement ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-22 21:51 -0700
    Re: is "x *= ++f * ++f" a valid statement ? Richard Damon <richard@damon-family.org> - 2024-06-23 07:32 -0400
      Re: is "x *= ++f * ++f" a valid statement ? olcott <polcott333@gmail.com> - 2024-06-23 07:59 -0500
        Re: is "x *= ++f * ++f" a valid statement ? Richard Damon <richard@damon-family.org> - 2024-06-23 14:25 -0400
          Re: is "x *= ++f * ++f" a valid statement ? olcott <polcott333@gmail.com> - 2024-06-23 14:18 -0500
            Re: is "x *= ++f * ++f" a valid statement ? Richard Damon <richard@damon-family.org> - 2024-06-23 16:23 -0400
              Re: is "x *= ++f * ++f" a valid statement ? David Brown <david.brown@hesbynett.no> - 2024-06-24 09:11 +0200
  Re: is "x *= ++f * ++f" a valid statement ? what@tf.com (testuseri2p) - 2024-07-22 17:51 +0000
    Re: is "x *= ++f * ++f" a valid statement ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-07-22 14:58 -0700
    Re: is "x *= ++f * ++f" a valid statement ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-07-22 21:57 -0400
      Re: is "x *= ++f * ++f" a valid statement ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-07-22 20:40 -0700
        Re: is "x *= ++f * ++f" a valid statement ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-07-23 10:15 -0400
        Re: is "x *= ++f * ++f" a valid statement ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-07-23 07:28 -0700
          Re: is "x *= ++f * ++f" a valid statement ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-07-23 14:42 -0700
            Re: is "x *= ++f * ++f" a valid statement ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-07-23 15:05 -0700
              Re: is "x *= ++f * ++f" a valid statement ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 06:22 -0700
                Re: is "x *= ++f * ++f" a valid statement ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-08-11 14:09 -0700
            Re: is "x *= ++f * ++f" a valid statement ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-08-11 06:11 -0700
              Re: is "x *= ++f * ++f" a valid statement ? Chris Ahlstrom <OFeem1987@teleworm.us> - 2024-08-11 09:25 -0400
              Re: is "x *= ++f * ++f" a valid statement ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-08-11 14:17 -0400
      Re: is "x *= ++f * ++f" a valid statement ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-07-23 07:32 -0700
    Re: is "x *= ++f * ++f" a valid statement ? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2024-07-22 19:53 -0700
    Re: is "x *= ++f * ++f" a valid statement ? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-07-23 10:01 -0400

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