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Re: error in code

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Tim Rentsch <txr@alumni.caltech.edu> writes:
> Keith Thompson <kst-u@mib.org> writes:
>> Tim Rentsch <txr@alumni.caltech.edu> writes:
>>> pacman@kosh.dhis.org (Alan Curry) writes:
>> [...]
>>>> I also think it's a syntax error, but take a look at this more subtle case:
>>>>
>>>>   int i=1, j=2;
>>>>
>>>>   int main(void)
>>>>   {
>>>>     int a[] = i, j;
>>>>   }
>>>>
>>>> It's invalid because the array initializer doesn't have braces. But that's
>>>> not a requirement of the grammar. In n1256.pdf, the clause that it violates
>>>> is 6.7.8.16, under the heading of "Semantics", not "Constraints".
>>>>
>>>> And it can be made valid by putting braces around just the i, which makes a
>>>> single-element a[] and a local j shadowing the global j:
>>>>     int a[] = {i}, j;
>>>> or by putting braces around both, making a 2-element a[]:
>>>>     int a[] = {i, j};
>>>>
>>>> A compiler that accepts the form without braces must be choosing one of those
>>>> interpretations. Which one?
>>>
>>> If no diagnostic message is issued, the first one.
>>
>> How do you arrive at that conclusion?
>
> Because if 'j' is part of the initializer for 'a[]' rather than a
> separate declarator there is a syntax violation.
>
>> If no diagnostic message is issued, the compiler is non-conforming.
>
> Did you miss Alan Curry's comment?  The missing braces around {i}
> is only undefined behavior, not a constraint violation, and there
> is no syntax violation.

You're right.

And I think I see some sloppy wording in 6.7.8.16p13:

    The initializer for a structure or union object that has
    automatic storage duration shall be either an initializer list
    as described below, or a single expression that has compatible
    structure or union type. In the latter case, the initial value of
    the object, including unnamed members, is that of the expression.

But an initializer-list doesn't include the '{' and '}' delimiters.
For example, given
    struct foo obj = { 10, 20 };
the initializer-list is ``10, 20'', *not* ``{ 10, 20 }''.  p13 seems
to be referring to ``{ 10, 20 }'' as an "initializer list".

> I should acknowledge that the UB here actually does grant
> sufficient freedom to permit the second interpretation.  However,
> any implementation that knowingly provides an extension to omit
> the braces for array initializers would be rather perverse in
> making that choice, going as does against the grain of the
> syntactic analysis necessary to avoid a diagnostic.

Which makes me wonder why the standard didn't just make it a
constraint violation.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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error in code "Bill Cunningham" <nospam@nspam.invalid> - 2011-05-28 15:28 -0400
  Re: error in code pozz <pozzugno@gmail.com> - 2011-05-28 21:49 +0200
    Re: error in code "Bill Cunningham" <nospam@nspam.invalid> - 2011-05-28 16:12 -0400
      Re: error in code Shao Miller <sha0.miller@gmail.com> - 2011-05-28 15:33 -0500
        Re: error in code "Bill Cunningham" <nospam@nspam.invalid> - 2011-05-28 17:12 -0400
          Re: error in code Geoff <geoff@invalid.invalid> - 2011-05-28 14:26 -0700
          Re: error in code Shao Miller <sha0.miller@gmail.com> - 2011-05-28 16:29 -0500
          Re: error in code Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-05-28 17:26 -0600
      Re: error in code Geoff <geoff@invalid.invalid> - 2011-05-28 14:20 -0700
        Re: error in code "Bill Cunningham" <nospam@nspam.invalid> - 2011-05-29 02:16 -0400
      Re: error in code Lew Pitcher <lpitcher@teksavvy.com> - 2011-05-28 16:35 -0400
        Re: error in code "Bill Cunningham" <nospam@nspam.invalid> - 2011-05-29 15:50 -0400
        Re: error in code Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-05-29 20:39 -0600
  Re: error in code Geoff <geoff@invalid.invalid> - 2011-05-28 13:46 -0700
  Re: error in code Nobody <nobody@nowhere.com> - 2011-05-28 23:06 +0100
    Re: error in code Ian Collins <ian-news@hotmail.com> - 2011-05-29 10:10 +1200
  Re: error in code Ian Collins <ian-news@hotmail.com> - 2011-05-29 10:09 +1200
  Re: error in code Angel <angel+news@spamcop.net> - 2011-05-28 22:28 +0000
    Re: error in code Ian Collins <ian-news@hotmail.com> - 2011-05-29 10:37 +1200
      Re: error in code Angel <angel+news@spamcop.net> - 2011-05-28 22:45 +0000
        Re: error in code Ian Collins <ian-news@hotmail.com> - 2011-05-29 10:48 +1200
          Re: error in code Angel <angel+news@spamcop.net> - 2011-05-28 22:56 +0000
            Re: error in code Seebs <usenet-nospam@seebs.net> - 2011-05-29 00:38 +0000
        Re: error in code "Morris Keesan" <mkeesan@post.harvard.edu> - 2011-05-28 23:11 -0400
  Re: error in code Keith Thompson <kst-u@mib.org> - 2011-05-28 15:54 -0700
  Re: error in code Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-05-28 17:23 -0600
  Re: error in code jacob navia <jacob@spamsink.net> - 2011-05-29 19:30 +0200
    Re: error in code Geoff <geoff@invalid.invalid> - 2011-05-29 18:14 -0700
      Re: error in code Keith Thompson <kst-u@mib.org> - 2011-05-29 18:50 -0700
        Re: error in code Geoff <geoff@invalid.invalid> - 2011-05-29 19:10 -0700
          Re: error in code Seebs <usenet-nospam@seebs.net> - 2011-05-30 02:54 +0000
            Re: error in code Geoff <geoff@invalid.invalid> - 2011-05-29 20:35 -0700
              Re: error in code Seebs <usenet-nospam@seebs.net> - 2011-05-30 06:15 +0000
      Re: error in code jacob navia <jacob@spamsink.net> - 2011-05-30 08:46 +0200
        Re: error in code Geoff <geoff@invalid.invalid> - 2011-05-30 18:50 -0700
          Re: error in code Keith Thompson <kst-u@mib.org> - 2011-05-31 10:49 -0700
    Re: error in code Peter Nilsson <airia@acay.com.au> - 2011-05-29 21:04 -0700
      Re: error in code jacob navia <jacob@spamsink.net> - 2011-05-30 08:44 +0200
      Re: error in code Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-31 01:35 -0700
        Re: error in code pacman@kosh.dhis.org (Alan Curry) - 2011-05-31 23:36 +0000
          Re: error in code Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-01 03:01 -0700
            Re: error in code Keith Thompson <kst-u@mib.org> - 2011-06-01 08:08 -0700
              Re: error in code Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-01 12:50 -0700
                Re: error in code Keith Thompson <kst-u@mib.org> - 2011-06-01 13:26 -0700
                Re: error in code Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-02 18:10 -0700
                Re: error in code jacob navia <jacob@spamsink.net> - 2011-06-03 11:55 +0200
                Re: error in code Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-03 19:37 -0700
                Re: error in code jacob navia <jacob@spamsink.net> - 2011-06-04 08:13 +0200
      Re: error in code Nisse Engström <news.NOSPAM.idf0Z@luden.se> - 2011-06-01 09:02 +0200

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