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Re: How to compile several C files

From Richard Heathfield <rjh@cpax.org.uk>
Newsgroups comp.lang.c
Subject Re: How to compile several C files
Date 2017-02-08 12:11 +0000
Organization Fix this later
Message-ID <o7f1q1$m6q$1@dont-email.me> (permalink)
References (3 earlier) <137458b9-1471-27ef-8c1e-8d9e781f315f@verizon.net> <5b6f9245-8bdf-4365-8a73-201c192f6980@googlegroups.com> <o7cvk5$hmt$1@dont-email.me> <8760klby18.fsf@bsb.me.uk> <o7erj0$1ob$1@dont-email.me>

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On 08/02/17 10:25, David Brown wrote:
> On 07/02/17 20:28, Ben Bacarisse wrote:
>> Richard Heathfield <rjh@cpax.org.uk> writes:
>> <snip>
>>
>>> RULE ONE: DO NOT USE FILE SCOPE OBJECTS!

(or rather, don't identify objects at file scope!)

> There is a big distinction between objects defined at file scope with
> "static", and those defined at file scope /without/ "static".  The
> lifetime is the same, the scope of the identifier is the same, but the
> linkage is different.

True. With internal linkage, the mess is limited to one translation 
unit. With external linkage, it could be anywhere.

> File static data can often be extremely useful.  It lets you have
> controlled access to the data from a known set of functions (those in
> the same file), without having lots of pointers passed around as
> function parameters.  It is somewhat like having a singleton class in
> C++, with the static data being the data members, static functions being
> private methods, and non-static functions being public methods.

I always wondered about static data in C++ classes. The whole point of a 
class is that each object knows all it needs to know about *itself*. A 
static object in a C++ class has just one value that is shared across 
all objects of that class.

A friend of mine, who was a student at the time, once tried to explain 
to me why it was a good idea. "Imagine a 'Student' class," he said. (I 
suspect it was a familiar example to him at the time!) He explained that 
it would be very useful for there to be a static member called, say, 
NumStudents, which would record how many students there actually are, so 
that every Student object would always know how many Student objects exist.

"You're a student, right?"

He acknowledged the fact.

"Exactly how many students are there at your university?"

"How should I know? Oh, I see."

> "globals" usually (IME) refers to file scope data that is /not/ static,
> and thus has external linkage and can be access from other files.  That
> is when you need to be very wary - any other files can access the data
> so you have lost that control.  Global data like this is often viewed as
> "evil", and that's not a bad first approximation.  It can be useful when
> used correctly - but you need to be very careful.

Yes. Sometimes one has no choice - one arrives on a project to find that 
they /already/ have a zillion such identifiers, and there isn't the time 
or the budget to fix the problem (although there always seems to be 
plenty of time and budget to fix the second-generation problems that 
ensue!).

I /have/ defined a file scope non-const with external linkage in real 
world code. Once ever, I think. It was very, very evil, but for that 
particular project it was still the lesser of two evils. The alternative 
was to add an extra parameter to every single function in the library, 
and that included rewriting qsort() and bsearch() to support comparison 
functions with three parameters.

<snip>

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within

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Thread

How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 06:10 -0800
  Re: How to compile several C files Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-02-07 07:02 -0800
  Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-07 16:03 +0100
  Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-07 15:06 +0000
    Re: How to compile several C files BartC <bc@freeuk.com> - 2017-02-07 15:14 +0000
      Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-07 16:02 +0000
    Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-07 15:42 +0000
      Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-07 16:19 +0000
        Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-07 16:40 +0000
          Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-07 17:16 +0000
            Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 10:19 +0100
        Re: How to compile several C files "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-07 11:51 -0500
      Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 08:26 -0800
        Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-07 16:42 +0000
          Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 10:14 -0800
          Re: How to compile several C files vitale.alla@gmail.com - 2017-02-16 09:49 -0800
      Re: How to compile several C files Ian Collins <ian-news@hotmail.com> - 2017-02-08 17:35 +1300
        Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 10:28 +0100
          Re: How to compile several C files Ian Collins <ian-news@hotmail.com> - 2017-02-08 22:43 +1300
            Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 11:29 +0100
      Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 10:14 +0100
  Re: How to compile several C files James Kuyper <jameskuyper@verizon.net> - 2017-02-07 10:07 -0500
    Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 07:56 -0800
      Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 08:24 -0800
        Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-07 16:44 +0000
          Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 08:54 -0800
            Re: How to compile several C files "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-07 12:20 -0500
              Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 10:05 -0800
                Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-07 18:27 +0000
                Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-07 18:40 +0000
                Re: How to compile several C files Keith Thompson <kst-u@mib.org> - 2017-02-07 12:22 -0800
                Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 10:33 +0100
                Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-08 10:25 -0800
      Re: How to compile several C files Keith Thompson <kst-u@mib.org> - 2017-02-07 08:58 -0800
      Re: How to compile several C files "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-07 12:07 -0500
        Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 09:14 -0800
          Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-07 17:21 +0000
            Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 10:14 -0800
            Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 10:28 -0800
              Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-07 18:43 +0000
                Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 10:55 -0800
            Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-07 19:28 +0000
              Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-07 19:51 +0000
              Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 11:25 +0100
                Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-08 12:11 +0000
                Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 14:58 +0100
                Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-08 14:23 +0000
                Re: How to compile several C files supercat@casperkitty.com - 2017-02-08 07:48 -0800
                Re: How to compile several C files Richard Heathfield <rjh@cpax.org.uk> - 2017-02-08 16:09 +0000
                Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 17:23 +0100
                Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 15:01 +0000
                Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 17:22 +0100
                Re: How to compile several C files Keith Thompson <kst-u@mib.org> - 2017-02-08 09:27 -0800
                Re: How to compile several C files supercat@casperkitty.com - 2017-02-08 09:51 -0800
                Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 21:06 +0000
                Re: How to compile several C files supercat@casperkitty.com - 2017-02-08 13:20 -0800
                Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 21:40 +0000
                Re: How to compile several C files supercat@casperkitty.com - 2017-02-08 13:49 -0800
                Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 23:09 +0000
                Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 23:25 +0100
                Re: How to compile several C files supercat@casperkitty.com - 2017-02-08 15:17 -0800
                Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-09 01:17 +0100
                Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 23:19 +0100
                Re: How to compile several C files Keith Thompson <kst-u@mib.org> - 2017-02-08 16:44 -0800
                Re: How to compile several C files Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-08 22:32 -0800
                Re: How to compile several C files Robert Wessel <robertwessel2@yahoo.com> - 2017-02-09 04:03 -0600
                Re: How to compile several C files Ian Collins <ian-news@hotmail.com> - 2017-02-10 07:52 +1300
                Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 12:12 +0000
                Re: How to compile several C files BartC <bc@freeuk.com> - 2017-02-08 13:09 +0000
                Re: How to compile several C files Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-02-08 05:14 -0800
                Re: How to compile several C files Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-08 15:32 +0000
                Re: How to compile several C files David Brown <david.brown@hesbynett.no> - 2017-02-08 15:09 +0100
        Re: How to compile several C files Keith Thompson <kst-u@mib.org> - 2017-02-07 09:22 -0800
          Re: How to compile several C files Gareth Owen <gwowen@gmail.com> - 2017-02-07 18:29 +0000
            Re: How to compile several C files bart4858@gmail.com - 2017-02-07 11:05 -0800
            Re: How to compile several C files Keith Thompson <kst-u@mib.org> - 2017-02-07 12:26 -0800
  Re: How to compile several C files Barry Schwarz <schwarzb@dqel.com> - 2017-02-07 08:34 -0800
    Re: How to compile several C files Alla _ <modelling.data@gmail.com> - 2017-02-07 08:57 -0800
      Re: How to compile several C files "James R. Kuyper" <jameskuyper@verizon.net> - 2017-02-07 12:29 -0500
      Re: How to compile several C files Manfred <noname@invalid.add> - 2017-02-07 19:02 +0100

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