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Re: Smaller C

From "James Harris" <james.harris.1@gmail.com>
Newsgroups alt.os.development
Subject Re: Smaller C
Date 2015-09-18 14:48 +0100
Organization A noiseless patient Spider
Message-ID <mth4jo$bja$1@dont-email.me> (permalink)
References (16 earlier) <mt3d77$boq$1@dont-email.me> <op.x4wfnyq1yfako5@localhost> <mt4dpo$6es$1@dont-email.me> <mt6dtq$dcc$1@dont-email.me> <op.x4zj4l2myfako5@localhost>

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"Rod Pemberton" <boo@fasdfrewar.cdm> wrote in message 
news:op.x4zj4l2myfako5@localhost...
> On Mon, 14 Sep 2015 08:19:54 -0400, James Harris 
> <james.harris.1@gmail.com> wrote:
>
>> "James Harris" <james.harris.1@gmail.com> wrote in message
>> news:mt4dpo$6es$1@dont-email.me...
>>> "Rod Pemberton" <boo@fasdfrewar.cdm> wrote in message
>>> news:op.x4wfnyq1yfako5@localhost...
>>>> On Sun, 13 Sep 2015 04:49:27 -0400, James Harris
>>>> <james.harris.1@gmail.com> wrote:
>
>> Those standards docs are very much NOT easy to read.
>
> See, there is no real point in rejecting H&S as an authorative source.
> That was meant to be funny, but is a half-truth.  You really only
> need the specifications for determining the validity of rather
> rare situations.  Even then, most people have problems understanding
> what is truly meant by them due to the abstractions used.  So, is
> there a valid reason to go through the pain?  H&S went through that
> for you.  In this case, you're asking your "savior", i.e., H&S, to
> be perfect.
>
> ;-)

You have a point. The rules for static vs extern vs no qualifier are 
very fiddly and the standard writes them in such a way that every word 
matters. For example, from C89 draft: "If the declaration of an 
identifier for a function has no storage-class specifier, its linkage is 
determined exactly as if it were declared with the storage-class 
specifier extern . If the declaration of an identifier for an object has 
file scope and no storage-class specifier, its linkage is external." But 
"extern" and "its linkage is external" don't necessarily mean the same 
thing.

In the previous case where we discussed H&S, i.e. in connection with the 
switch statement, I found an online copy of their book and it seemed to 
me that they had come across what they thought of were two different 
forms (and were surprised at what they had found) so listed them without 
realising how C worked.

I don't know but it seems here that they may have done the same thing 
and heard of or come across another form of declaration and so included 
it in their book but not understood it. (Unlike the switch statement, 
however, in this case I don't blame them!)

Nevertheless, the standard does seem to allow for an identifier to be 
declared with both internal and external linkage without the compiler 
objecting, which is worrying. If an identifier is so declared the C89 
standard just says that the behaviour is undefined.

>> The choices, then:
>> 1) pay for the services of a top legal team to work out the answer or 
>> 2)
>> try to work out the answer myself ... then pay for the services of a 
>> top
>> psychiatric team to help me recover.
>
> LOL.
>
> You seemed to be doing really good understanding them, even though
> I usually disagree with some of your conclusions. (Ditto Alexei.)

Thanks. I have even written up a grid to try to separate out all of the 
meanings. The problem, then, is to write that in a concise form that is 
easier to understand than the standard's legalese.

>> Believe it or not the answer seems to depend on the *order* in which 
>> the
>> declarations appear - but only sometimes.
>
> It makes no real difference to me, as I've almost never used 'static'.
> Until you (or Alexei) can convince me otherwise, it's a moot point
> from my perspective.

The interesting thing, to me, is that C's extern keyword does not mean 
that an object or function should be external! Instead, extern is almost 
a tentative external, i.e. make this external unless you got a better 
offer elsewhere. I didn't know any of that. My guess is that it was 
designed so that a header can have the term extern in it and still be 
#included in the one file where the same identifier is declared and 
defined.

But it gets weirder in that extern will copy the attributes of something 
already in scope. For example, if you declared X as static and then 
extern C would treat it as static. But if you declared it as extern and 
then static then you would get undefined behaviour. That suggests that 
we are supposed to define external objects *before* #including headers 
that refer to them. Again, not something I knew or have ever considered.

>> One good thing is that the standard seems to have been very 
>> consistent
>> between c89 and c2011.
>
> Amazing.  That must be a first ...
>
>> To test the understanding I came to I made up some examples and ran 
>> them
>> through GCC. Fortunately it agreed with me!
>
> :-)
>
> It's likely the standard behavior, then, although I'd only rank that
> at about 98% certainty.

Agreed, and that is probably generous. I was just glad to get something 
to agree.

...

>> If someone else wants to try to explain the above feel free.
>> Either way, I will get back to it later.
>
> Sorry, I'm definately not interested.  Don't fault me.  I'm human! 
> :-)

No worries. Though, as above, this has turned into something related 
more to extern than to static, and to how to pull in header files.

James

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Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-07-11 20:39 -0700
  Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-12 04:24 -0400
    Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-07-12 03:17 -0700
      Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-13 03:28 -0400
    Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-07-12 19:12 +0100
      Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-07-12 17:09 -0700
      Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-07-13 11:10 +0100
        Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-13 23:13 -0400
          Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-07-14 09:08 +0100
            Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-15 02:23 -0400
  Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-08-15 02:12 -0700
    Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-06 15:54 -0700
      Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-07 12:19 -0700
        Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-07 13:30 -0700
          Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-09 19:38 -0700
            Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-09 19:49 -0700
            Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-09 20:58 -0700
            Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-10 01:45 -0700
              Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-10 10:45 -0700
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-10 23:20 -0700
                Re: Smaller C "wolfgang kern" <nowhere@never.at> - 2015-09-11 09:26 +0200
                Re: Smaller C "wolfgang kern" <nowhere@never.at> - 2015-09-11 09:50 +0200
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-11 00:58 -0700
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-11 17:38 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-11 23:39 +0100
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-11 19:39 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-12 11:22 +0100
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-12 02:21 -0700
                Re: Smaller C "wolfgang kern" <nowhere@never.at> - 2015-09-12 21:53 +0200
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 03:37 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-13 09:49 +0100
                Re: Smaller C "wolfgang kern" <nowhere@never.at> - 2015-09-13 12:58 +0200
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 07:32 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-13 19:05 +0100
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-14 13:19 +0100
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-15 00:01 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-18 14:48 +0100
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-26 16:23 -0400
                Re: Smaller C James Harris <james.harris.1@gmail.com> - 2015-09-27 00:23 +0100
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-26 16:37 -0700
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-27 10:17 -0400
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-27 10:24 -0400
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-27 10:46 -0400
                Re: Smaller C James Harris <james.harris.1@gmail.com> - 2016-01-16 16:14 +0000
                Re: Smaller C Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-01-23 13:20 -0500
                Re: Smaller C James Harris <james.harris.1@gmail.com> - 2016-01-27 13:52 +0000
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-27 10:28 -0400
                Re: Smaller C James Harris <james.harris.1@gmail.com> - 2016-01-16 16:31 +0000
                Re: Smaller C Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-01-23 13:20 -0500
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-18 16:21 +0100
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-20 17:25 -0700
                Re: Smaller C "wolfgang kern" <nowhere@never.at> - 2015-09-13 12:43 +0200
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-13 09:21 +0100
                Re: Smaller C "wolfgang kern" <nowhere@never.at> - 2015-09-13 13:02 +0200
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-13 19:09 +0100
                Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-11 13:32 -0700
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-11 18:51 -0400
                Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-11 18:16 -0700
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-12 02:36 -0700
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-12 11:56 +0100
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 03:45 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-13 10:28 +0100
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-13 02:53 -0700
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 11:17 -0400
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-13 16:54 -0700
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 21:39 -0400
                Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-13 20:31 -0700
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 09:03 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-13 19:48 +0100
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 21:33 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-14 23:17 +0100
                Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-20 17:37 -0400
                Re: Smaller C "James Harris" <james.harris.1@gmail.com> - 2015-09-20 23:46 +0100
  Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-11 21:37 -0700
    Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-11 22:29 -0700
      Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-12 03:25 -0700
        Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-12 11:18 -0700
          Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-12 11:39 -0700
          Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 03:47 -0400
            Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 11:31 -0400
          Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-13 02:00 -0700
            Re: Smaller C "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-09-13 11:31 -0400
            Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-13 09:15 -0700
    Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-12 02:45 -0700
      Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-12 10:55 -0700
  Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-15 19:23 -0700
    Re: Smaller C "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-09-16 03:03 -0700
      Re: Smaller C "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-09-16 10:17 -0700

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