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Re: 80386 C compiler

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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> Kaz Kylheku <643-408-1753@kylheku.com> writes:
>
>> On 2024-11-25, Rosario19 <Ros@invalid.invalid> wrote:
>>
>>> On Mon, 25 Nov 2024 18:23:58 -0000 (UTC), Kaz Kylheku  wrote:
>>>
>>>> void fn(int a)
>>>> {
>>>>   int x[3] = { foo(), bar(), a }; /* not in C90 */
>>>
>>> is in the above foo() called before bar()?
>>
>> No, you cannot rely on that.  Maybe it's fixed in a more recent standard,
>> but C99 (which I happen to have open in a PDF reader tab) stated that
>> "The order in which any side effects occur among the initialization list
>> expressions is unspecified.".  This implies that there is no sequence
>> point between any two initializing expressions, which means we don't
>> know whose expression's function call takes place first.
>
> N3096 (C23 draft) has :
> """
> The evaluations of the initialization list expressions are
> indeterminately sequenced with respect to one another and thus the order
> in which any side effects occur is unspecified.
> """
>
> C23 is more explicit (redundant?) than C99, which doesn't mention the
> lack of a sequence point.  (C11 dropped sequence points, replacing them
> with "sequenced before", "sequenced after", and "unsequenced", basically
> a new way of describing the same semantics.)
>
> Given:
>
>     int n = 42;
>     int a[] = { n++, n++ };
>
> C99 could imply that the value of a is merely unspecified, either {
> 42, 43 } or { 43, 42 }.  Though it can almost certainly be inferred
> from other parts of the C99 standard that there is no sequence
> point between the two evaluations of n++ (I haven't taken the time
> to check).

Under C99 rules, I believe this initializer has undefined
behavior, because of more than one modification of an object
without an intervening sequence point.

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80386 C compiler "Paul Edwards" <mutazilah@gmail.com> - 2024-11-24 22:00 +0800
  Re: 80386 C compiler fir <profesor.fir@gmail.com> - 2024-11-24 18:51 +0100
    Re: 80386 C compiler fir <profesor.fir@gmail.com> - 2024-11-24 18:58 +0100
      Re: 80386 C compiler "Paul Edwards" <mutazilah@gmail.com> - 2024-11-25 08:00 +0800
    Re: 80386 C compiler Bart <bc@freeuk.com> - 2024-11-24 18:00 +0000
      Re: 80386 C compiler BGB <cr88192@gmail.com> - 2024-11-24 17:46 -0600
        Re: 80386 C compiler "Paul Edwards" <mutazilah@gmail.com> - 2024-11-25 08:15 +0800
  Re: 80386 C compiler Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-11-24 19:52 +0100
    Re: 80386 C compiler "Paul Edwards" <mutazilah@gmail.com> - 2024-11-25 07:46 +0800
      Re: 80386 C compiler Kaz Kylheku <643-408-1753@kylheku.com> - 2024-11-25 18:23 +0000
        Re: 80386 C compiler Rosario19 <Ros@invalid.invalid> - 2024-11-25 22:14 +0100
          Re: 80386 C compiler Kaz Kylheku <643-408-1753@kylheku.com> - 2024-11-26 17:59 +0000
            Re: 80386 C compiler Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-26 13:05 -0800
              Re: 80386 C compiler "Paul Edwards" <mutazilah@gmail.com> - 2024-11-27 05:30 +0800
                Re: 80386 C compiler Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-26 14:27 -0800
                Re: 80386 C compiler "Paul Edwards" <mutazilah@gmail.com> - 2024-11-27 13:23 +0800
                Re: 80386 C compiler Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-26 21:59 -0800
                Re: 80386 C compiler "Paul Edwards" <mutazilah@gmail.com> - 2024-11-27 21:50 +0800
              Re: 80386 C compiler Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-11-27 16:45 -0800
            Re: 80386 C compiler David Brown <david.brown@hesbynett.no> - 2024-11-27 11:00 +0100
              Re: 80386 C compiler Kaz Kylheku <643-408-1753@kylheku.com> - 2024-11-27 19:42 +0000
                Re: 80386 C compiler James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-27 14:59 -0500
                Re: 80386 C compiler Kaz Kylheku <643-408-1753@kylheku.com> - 2024-11-27 21:52 +0000
                Re: 80386 C compiler James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-27 18:07 -0500
                Re: 80386 C compiler Kaz Kylheku <643-408-1753@kylheku.com> - 2024-11-30 01:30 +0000
                Re: 80386 C compiler Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-11-29 21:00 -0800
                Re: 80386 C compiler James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-11-30 09:00 -0500
                Re: 80386 C compiler David Brown <david.brown@hesbynett.no> - 2024-11-28 09:12 +0100
            Re: 80386 C compiler Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-11-27 19:26 -0800
            Re: 80386 C compiler Rosario19 <Ros@invalid.invalid> - 2024-11-30 16:41 +0100
        Re: 80386 C compiler "Paul Edwards" <mutazilah@gmail.com> - 2024-11-26 10:48 +0800
  Re: 80386 C compiler Lynn McGuire <lynnmcguire5@gmail.com> - 2024-11-25 15:55 -0600
    Re: 80386 C compiler Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-25 14:10 -0800
      Re: 80386 C compiler Lynn McGuire <lynnmcguire5@gmail.com> - 2024-11-25 18:32 -0600
        Re: 80386 C compiler Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-11-25 16:49 -0800
          Re: 80386 C compiler BGB <cr88192@gmail.com> - 2024-11-26 13:22 -0600

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