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

Groups > alt.os.development > #8816

Re: Smaller C

From "James Harris" <james.harris.1@gmail.com>
Newsgroups alt.os.development
Subject Re: Smaller C
Date 2015-09-18 16:21 +0100
Organization A noiseless patient Spider
Message-ID <mtha30$2le$1@dont-email.me> (permalink)
References (17 earlier) <op.x4v4snbyyfako5@localhost> <mt3d77$boq$1@dont-email.me> <op.x4wfnyq1yfako5@localhost> <mt4dpo$6es$1@dont-email.me> <mt6dtq$dcc$1@dont-email.me>

Show all headers | View raw

"James Harris" <james.harris.1@gmail.com> wrote in message 
news:mt6dtq$dcc$1@dont-email.me...

...

>  int X1; /* External linkage */
>  extern int X1; /* Copies the above */
>
>  extern int X2; /* External linkage */
>  int X2; /* External linkage */
>
>  static int X3; /* Internal linkage */
>  int X3; /* External linkage - conflict */
>
>  static int X4; /* Internal linkage */
>  extern int X4; /* Copies the above */
>
>  extern int X5; /* External linkage */
>  static int X5; /* Internal linkage - conflict */
>
> Verified. GCC complained about X3 and X5 only.
>
>
>  void F1(void); /* == extern void F(void); */
>  extern void F1(void); /* Copies the above */
>
>  extern void F2(void);
>  void F2(void); /* == extern void F(void); */
>
>  static void F3(void); /* Internal linkage */
>  void F3(void); /* == extern ...; copies the above */
>
>  static void F4(void);
>  extern void F4(void); /* Copies the above */
>
>  void F5(void); /* == extern .... External linkage */
>  static void F5(void); /* Internal linkage - conflict */
>
>  extern void F6(void); /* External linkage */
>  static void F6(void); /* Internal linkage - conflict */
>
> Verified. GCC complained about F5 and F6 only.
>
>
> If someone else wants to try to explain the above feel free. Either 
> way, I will get back to it later.

Based on <http://port70.net/~nsz/c/c89/c89-draft.html C89 draft. Section 
3.1.2.2
Linkages of identifiers> here is my attempt to explain the rules as 
simply as possible. I have included the nomenclature of the standard but 
added other descriptions which I feel are easier to understand. Feel 
free to disagree with the new descriptions if they reflect a poor 
understanding but I have called them

  external linkage --> "public"
  internal linkage --> "private to a translation unit"
  no linkage --> "private to a function"

In the standard other identifiers have no linkage but here we are just 
looking at objects defined within functions.

I think the terms "public" and "private" are easier to understand but I 
have written both below.



"extern"

* If "extern" is applied to a second or subsequent declaration of an 
object or a function then use the linkage of the first declaration.

* If "extern" is applied to the first declaration of an object or a 
function then the object or function has external linkage (i.e. is 
public).


"static"

* Within a function a "static" object has no linkage (i.e. is private to 
that function).

* At file level "static" gives the object or function internal linkage 
(i.e. makes it private to that translation unit).


unqualified

* Within a function an unqualified object has no linkage (i.e. is 
private to that function).

* At file level an unqualified *object* is given external linkage (i.e. 
is public) whereas an unqualified *function* is treated as if it was 
qualified as "extern". See above.



In other words: "extern" is the copying qualification. It will copy the 
linkage of a previous declaration if one is in scope or, if the name is 
new, will declare it as external. "static" always means what it says. 
For unqualfied names see the detail above.

If the above is right then why is it so complicated? Any suggestions?

James

Back to alt.os.development | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

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

csiph-web