Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.std.c > #1570

Re: When is the complete type of an external definition known?

Show all headers | View raw

Wojtek Lerch <wojtek_l@yahoo.ca> writes:
> On 19-Aug-12 10:22 PM, Keith Thompson wrote:
>> Vlad from Moscow <vlad.moscow@mail.ru> writes:
>>> понедельник, 20 августа 2012 г., 1:56:49 UTC+4 пользователь Ike Naar написал:
>>>> On 2012-08-19, Vlad from Moscow <vlad.moscow@mail.ru> wrote:
>> [...]
>>>>    static int a[];
>>>>
>>>> violates 6.9.2 p3:
>>>>
>>>> "If the declaration of an identifier for an object is a tentative
>>>> definition and has internal linkage, the declared type shall not be
>>>> an incomplete type."
>>
>> ... (more precisely a constraint violation).
>
> Actually that paragraph is in a Semantics section, not in a Constraints 
> section.  It's plain undefined behaviour without a promise of a diagnostic.
>
> Out of curiosity, does anybody know the reason for this restriction?  It 
> sounds like a useful thing to be able to do.  (And I have to admit that 
> did it more than once, before I knew about this.)  Is it because 
> different compilers used to interpret it differently back in the day, 
> and the standard didn't want to break them?  The Rationale doesn't seem 
> to mention "tentative" at all.

And assuming the restriction is necessary, why isn't it a constraint?
Is it difficult for a compiler to detect a violation?

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

Back to comp.std.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

When is the complete type of an external definition known? Vlad from Moscow <vlad.moscow@mail.ru> - 2012-08-19 13:40 -0700
  Re: When is the complete type of an external definition known? Keith Thompson <kst-u@mib.org> - 2012-08-19 14:06 -0700
    Re: When is the complete type of an external definition known? Vlad from Moscow <vlad.moscow@mail.ru> - 2012-08-19 14:30 -0700
      Re: When is the complete type of an external definition known? Ike Naar <ike@iceland.freeshell.org> - 2012-08-19 21:56 +0000
        Re: When is the complete type of an external definition known? Vlad from Moscow <vlad.moscow@mail.ru> - 2012-08-19 16:42 -0700
          Re: When is the complete type of an external definition known? Keith Thompson <kst-u@mib.org> - 2012-08-19 19:22 -0700
            Re: When is the complete type of an external definition known? Wojtek Lerch <wojtek_l@yahoo.ca> - 2012-08-20 10:57 -0400
              Re: When is the complete type of an external definition known? Keith Thompson <kst-u@mib.org> - 2012-08-20 13:01 -0700
                Re: When is the complete type of an external definition known? Wojtek Lerch <wojtek_l@yahoo.ca> - 2012-08-20 16:58 -0400
              Re: When is the complete type of an external definition known? pacman@kosh.dhis.org (Alan Curry) - 2012-08-21 00:44 +0000
          Re: When is the complete type of an external definition known? Ike Naar <ike@sverige.freeshell.org> - 2012-08-20 05:57 +0000
            Re: When is the complete type of an external definition known? Vlad from Moscow <vlad.moscow@mail.ru> - 2012-08-20 03:22 -0700
              Re: When is the complete type of an external definition known? Ike Naar <ike@sverige.freeshell.org> - 2012-08-20 12:27 +0000
                Re: When is the complete type of an external definition known? Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-20 17:04 +0200
                Re: When is the complete type of an external definition known? Ike Naar <ike@iceland.freeshell.org> - 2012-08-20 16:35 +0000
                Re: When is the complete type of an external definition known? Jens Gustedt <jens.gustedt@loria.fr> - 2012-08-20 20:43 +0200
          Re: When is the complete type of an external definition known? James Kuyper <jameskuyper@verizon.net> - 2012-08-20 08:46 -0400
  Re: When is the complete type of an external definition known? Vlad from Moscow <vlad.moscow@mail.ru> - 2012-08-19 14:24 -0700
  Re: When is the complete type of an external definition known? "Ersek, Laszlo" <lacos@caesar.elte.hu> - 2012-08-19 23:36 +0200
    Re: When is the complete type of an external definition known? Vlad from Moscow <vlad.moscow@mail.ru> - 2012-08-19 14:46 -0700

csiph-web