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Re: Style question: Declaration of globals in header file

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Steve Keller <keller@no.invalid> writes:

> James Kuyper <jameskuyper@verizon.net> writes:
>
>> Therefore, the "file scope declaration of that identifier ... with an
>> initializer ..." described in 6.9.2p2 qualifies as an external
>> definition, despite the fact that the translation unit it's in contains
>> no actual definition for that identifier, just tentative ones.
>
> OK, thanks for this explanation and also the explanation of Ben.  Now,
> I get a clearer understanding of these details.
>
> And I will use extern for declarations in header files in the future.
>
> Until now I thought tentative definition are there to allow easier
> definition of objects with external linkage (i.e. only one definition
> in a header file to be included several times).  Since that is not
> allowed, I now wonder what the purpose of tentative definitions is.
> I don't see much use of having them in *one* translation unit.

I suspect the it's just the clash of history with pragmatics.  All the
old C compilers merged duplicate definitions so that what later came to
be called tentative were sometimes used as you describe.  But when
standardising the language the committee will have had to decide whether
to /require/ that an implementation be able to do this.  I suspect there
were reports of linkers that could not ensure this behaviour so it was
left undefined.

-- 
Ben.

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Style question: Declaration of globals in header file Steve Keller <keller@no.invalid> - 2017-06-06 19:33 +0200
  Re: Style question: Declaration of globals in header file "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-06 14:21 -0400
    Re: Style question: Declaration of globals in header file Steve Keller <keller@no.invalid> - 2017-06-12 11:07 +0200
      Re: Style question: Declaration of globals in header file bartc <bc@freeuk.com> - 2017-06-12 11:03 +0100
      Re: Style question: Declaration of globals in header file Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-12 11:40 +0100
      Re: Style question: Declaration of globals in header file James Kuyper <jameskuyper@verizon.net> - 2017-06-12 07:33 -0400
        Re: Style question: Declaration of globals in header file Steve Keller <keller@no.invalid> - 2017-06-12 18:00 +0200
          Re: Style question: Declaration of globals in header file "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-12 12:11 -0400
            Re: Style question: Declaration of globals in header file Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-12 17:27 +0100
          Re: Style question: Declaration of globals in header file Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-12 17:18 +0100
          Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-06-12 09:44 -0700
      Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-06-12 07:55 -0700
        Re: Style question: Declaration of globals in header file Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-12 16:51 +0100
  Re: Style question: Declaration of globals in header file Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-06 19:21 +0100
  Re: Style question: Declaration of globals in header file Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-06-06 19:54 +0000
  Re: Style question: Declaration of globals in header file Andrey Tarasevich <andreytarasevich@hotmail.com> - 2017-06-06 18:37 -0700
    Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-06-07 07:54 -0700
      Re: Style question: Declaration of globals in header file David Brown <david.brown@hesbynett.no> - 2017-06-07 17:23 +0200
        Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-06-07 11:10 -0700
          Re: Style question: Declaration of globals in header file David Brown <david.brown@hesbynett.no> - 2017-06-07 22:13 +0200
            Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-06-07 14:57 -0700
              Re: Style question: Declaration of globals in header file David Brown <david.brown@hesbynett.no> - 2017-06-08 00:05 +0200
              Re: Style question: Declaration of globals in header file bartc <bc@freeuk.com> - 2017-06-07 23:19 +0100
                Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-06-07 16:16 -0700
              Re: Style question: Declaration of globals in header file Ian Collins <ian-news@hotmail.com> - 2017-06-08 12:56 +1200
                Re: Style question: Declaration of globals in header file David Brown <david.brown@hesbynett.no> - 2017-06-08 08:51 +0200
                Re: Style question: Declaration of globals in header file David Thompson <dave.thompson2@verizon.net> - 2017-07-09 22:43 -0400
                Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-07-10 08:46 -0700
                Re: Style question: Declaration of globals in header file Robert Wessel <robertwessel2@yahoo.com> - 2017-07-10 21:00 -0500
                Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-07-10 21:08 -0700
                Re: Style question: Declaration of globals in header file Robert Wessel <robertwessel2@yahoo.com> - 2017-07-11 01:18 -0500
                Re: Style question: Declaration of globals in header file bartc <bc@freeuk.com> - 2017-06-08 10:10 +0100
                Re: Style question: Declaration of globals in header file raltbos@xs4all.nl (Richard Bos) - 2017-06-17 18:08 +0000
            Re: Style question: Declaration of globals in header file "Patrick.Schluter" <Patrick.Schluter@free.fr> - 2017-06-10 08:36 +0200
    Re: Style question: Declaration of globals in header file Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-09 10:09 -0700
      Re: Style question: Declaration of globals in header file supercat@casperkitty.com - 2017-06-09 12:17 -0700
  Re: Style question: Declaration of globals in header file Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-09 09:52 -0700

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