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

Groups > comp.lang.c > #145742

Re: Question about use (and non-use) of "extern"

Show all headers | View raw

Lew Pitcher <lew.pitcher@digitalfreehold.ca> writes:

> David Brown wrote:
<cut>
>> Yes.  The C language does not allow such multiple definitions,
>
> Perhaps I'm misreading the C standard, but I believe that the C standard 
> explicitly disagrees with your assertion.
>
> In the C11 standard (the n1570 document), Section 6.2.2 (Linkages of 
> Identifiers) paragraph 5 states "If the declaration of an identifier for an 
> object has file scope and no storage-class specifier, its linkage is 
> external." Thus, the standard requires that C treat the "global variable" 
> (sic) in question as if it were declared "extern".
>
> Additionally, in paragraph 2 of that section, the standard states "In the 
> set of translation units and libraries that constitutes an entire program, 
> each declaration of a particular identifier with external linkage denotes 
> the same object or function." So, all identically-named "global variables" 
> (sic) that appear with external linkage in other modules reference the same 
> object.
>
> If anything, the prohibition you refer to resides outside the language, in 
> the definition of, and tools that support, object module linking.

6.9 p5:

  An /external definition/ is an external declaration that is also a
  definition of a function (other than an inline definition) or an
  object. If an identifier declared with external linkage is used in an
  expression (other than as part of the operand of a sizeof or _Alignof
  operator whose result is an integer constant), somewhere in the entire
  program there shall be exactly one external definition for the
  identifier; otherwise, there shall be no more than one.

-- 
Ben.

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

Thread

Question about use (and non-use) of "extern" gazelle@shell.xmission.com (Kenny McCormack) - 2019-08-20 13:11 +0000
  Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-08-20 16:09 +0200
  Re: Question about use (and non-use) of "extern" Bart <bc@freeuk.com> - 2019-08-20 16:41 +0100
    Re: Question about use (and non-use) of "extern" Bart <bc@freeuk.com> - 2019-08-20 16:47 +0100
    Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-08-20 19:27 +0200
      Re: Question about use (and non-use) of "extern" Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2019-08-20 13:54 -0400
        Re: Question about use (and non-use) of "extern" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-08-21 02:09 +0100
        Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-08-21 10:54 +0200
      Re: Question about use (and non-use) of "extern" Bart <bc@freeuk.com> - 2019-08-21 00:41 +0100
        Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-08-21 10:58 +0200
  Re: Question about use (and non-use) of "extern" richard@cogsci.ed.ac.uk (Richard Tobin) - 2019-08-20 16:10 +0000
    Re: Question about use (and non-use) of "extern" Siri Cruise <chine.bleu@yahoo.com> - 2019-08-20 16:23 -0700
  Re: Question about use (and non-use) of "extern" already5chosen@yahoo.com - 2019-08-21 06:50 -0700
    Re: Question about use (and non-use) of "extern" gazelle@shell.xmission.com (Kenny McCormack) - 2019-08-22 20:20 +0000
      Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-08-23 00:25 +0200
      Re: Question about use (and non-use) of "extern" Bart <bc@freeuk.com> - 2019-08-23 01:35 +0100
        Re: Question about use (and non-use) of "extern" gazelle@shell.xmission.com (Kenny McCormack) - 2019-08-23 03:40 +0000
          Re: Question about use (and non-use) of "extern" Bart <bc@freeuk.com> - 2019-08-23 11:09 +0100
        Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-08-23 08:16 +0200
      Re: Question about use (and non-use) of "extern" scott@slp53.sl.home (Scott Lurndal) - 2019-08-23 15:02 +0000
        Re: Question about use (and non-use) of "extern" Bart <bc@freeuk.com> - 2019-08-23 17:06 +0100
          Re: Question about use (and non-use) of "extern" gazelle@shell.xmission.com (Kenny McCormack) - 2019-08-23 18:40 +0000
          Re: Question about use (and non-use) of "extern" scott@slp53.sl.home (Scott Lurndal) - 2019-08-23 20:38 +0000
            Re: Question about use (and non-use) of "extern" Richard Damon <Richard@Damon-Family.org> - 2019-08-23 17:55 -0400
              Richard Damon weighs in... (Was: Question about use (and non-use) of "extern") gazelle@shell.xmission.com (Kenny McCormack) - 2019-08-23 23:50 +0000
  Re: Question about use (and non-use) of "extern" Andrey Tarasevich <andreytarasevich@hotmail.com> - 2019-08-27 15:03 -0700
    Re: Question about use (and non-use) of "extern" Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-09-03 05:57 -0700
      Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-09-03 15:45 +0200
        Re: Question about use (and non-use) of "extern" Keith Thompson <kst-u@mib.org> - 2019-09-03 11:13 -0700
          Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-09-04 12:11 +0200
            Re: Question about use (and non-use) of "extern" James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-09-04 08:18 -0400
          Re: Question about use (and non-use) of "extern" Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-09-06 02:25 -0700
            Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-09-06 11:45 +0200
          Re: Question about use (and non-use) of "extern" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-09-06 21:15 +0100
        Re: Question about use (and non-use) of "extern" James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-09-03 21:10 -0400
          Re: Question about use (and non-use) of "extern" David Brown <david.brown@hesbynett.no> - 2019-09-04 12:21 +0200
      Re: Question about use (and non-use) of "extern" Andrey Tarasevich <andreytarasevich@hotmail.com> - 2019-09-04 12:04 -0700
        Re: Question about use (and non-use) of "extern" James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-09-04 15:29 -0400
        Re: Question about use (and non-use) of "extern" Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-09-06 02:46 -0700
  Re: Question about use (and non-use) of "extern" Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-05 10:01 +0200
    Re: Question about use (and non-use) of "extern" Andrey Tarasevich <andreytarasevich@hotmail.com> - 2019-09-05 10:43 -0700
      Re: Question about use (and non-use) of "extern" Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-06 20:24 +0200

csiph-web