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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Types in C |
| Date | 2011-05-23 13:03 -0700 |
| Organization | None to speak of |
| Message-ID | <ln1uzp2nh5.fsf@nuthaus.mib.org> (permalink) |
| References | (3 earlier) <lnvcx1xw6m.fsf@nuthaus.mib.org> <slrnitl4c6.o5q.usenet-nospam@guild.seebs.net> <ireaa0$92r$1@speranza.aioe.org> <lnaaed2pwu.fsf@nuthaus.mib.org> <slrnitldk4.tio.usenet-nospam@guild.seebs.net> |
Seebs <usenet-nospam@seebs.net> writes:
> On 2011-05-23, Keith Thompson <kst-u@mib.org> wrote:
>> Just a quibble: size_t may be exactly the same type as unsigned long,
>> since a typedef merely creates an alias for an existing type, not
>> a new and distinct type. plain char and signed char (for example)
>> are distinct in a way that size_t and unsigned long (for example)
>> are not.
>
> True. Although, possibly confusingly, there are places where it seems
> that the thing a typedef creates is itself then called "a type". The
> wording is a bit fuzzy.
(Didn't we already have this discussion?)
> We all know what we mean, I think. You could say it several ways:
>
> Typedef does not actually create types; instead, it creates
> names which refer to existing types.
That's my preference.
> Typedef creates types, but those types are identical to existing
> types and can be used interchangably with them.
I dislike that description.
Given:
typedef unsigned int word;
there is only one *type* being considered; it has two *names*, "unsigned
int" and "word". "unsigned int" is not itself a type; it's a sequence
of keywords that is the *name* of a type.
And using the idea of "identical types" makes it difficult to discuss
the difference between the relationship of size_t vs. unsigned int
(same type) and the relationship of char vs. signed char (identical
but distinct types).
> These appear to me to be essentially equivalent. I tend to think of
> the created name as being "a type" because my map has "type" connecting
> to "the mapping from a name to a representation and storage thing", but
> of course this isn't quite right, because of the plain char and (either
> signed or unsigned char) equivalence; it's the same representation and
> such as one of them, but it's not the same type as either.
>
> I'm aware this isn't quite how it works, but consider this point you
> made:
>
>> Of course size_t should be thought of as something that's quite
>> distinct from any predefined integer type, but the thing that's
>> distinct is something other than a C type. (IMHO this is a weakness
>> of C's type system.)
>
> Yes.
And the "thing that's distinct", I now realize, is simply the *name*.
> I would love to know how much code would ACTUALLY break if typedef
> created "types". Such that, say:
> typedef int a;
> typedef int b;
> a foo;
> b *bar = &foo;
> was a constraint violation.
>
> My guess is it would work well.
My guess is that it would break a lot of code. It would be a good
thing, IMHO, if size_t were distinct from any predefined type (which
would break only code that deserves to be broken).
> And that's why I tend to treat C *as if* that were true, because the only
> code which I regard as "broken" which isn't broken according to the C type
> system is generally bad code, and it prevents me from doing stupid things
> as much.
Typedefs are used in different ways. Sometimes a typedef creates a name
for a type, when the type being named may vary from one system to
another, or from one version of the program to another (size_t, word).
And sometimes a typedef just creates a name for a type because you don't
like the existing name, but the type being named will never change.
Some examples of the latter:
typedef unsigned long ulong; /* I don't do this myself */
typedef unsigned char byte;
typedef struct node {
struct node *next;
int data;
} node;
Note that if "struct node" and "node" were two distinct types, this
wouldn't work.
I would have liked to see one mechanism that creates a new name for a
type, and another that creates a new distinct type with the same
characteristics as an existing type. (Ada has this, "subtype"
vs. "derived type".)
On the other hand, C does have a mechanism for creating new types, the
"struct" keyword.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Types in C jacob navia <jacob@spamsink.net> - 2011-05-22 21:29 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-22 12:48 -0700
Re: Types in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-05-22 23:03 +0100
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-23 10:35 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-23 08:40 -0700
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 17:19 +0000
Re: Types in C John Gordon <gordon@panix.com> - 2011-05-23 17:54 +0000
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-23 11:33 -0700
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-23 11:44 -0700
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 19:08 +0000
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-23 20:50 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-23 12:11 -0700
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 19:45 +0000
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-23 13:03 -0700
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-23 22:25 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-23 14:38 -0700
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-23 23:45 +0200
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 22:02 +0000
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-24 00:10 +0200
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-23 22:12 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-23 13:27 -0700
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-23 22:33 +0200
Re: Types in C Martin Ambuhl <mambuhl@earthlink.net> - 2011-05-24 03:17 -0400
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-24 10:55 +0200
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 09:29 +1200
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-23 23:42 +0200
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 09:51 +1200
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-24 00:04 +0200
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 10:57 +1200
Re: Types in C David Thompson <dave.thompson2@verizon.net> - 2011-06-01 16:33 -0400
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-23 19:33 -0500
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-24 08:27 -0700
Re: Types in C Tim Rentsch <txr@alumni.caltech.edu> - 2011-05-31 00:40 -0700
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-31 11:32 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-31 11:30 -0700
Re: Types in C Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-01 01:23 -0700
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 16:51 -0400
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 09:25 +1200
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-23 23:40 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-24 08:36 -0700
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 17:53 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 22:24 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 19:23 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 23:57 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 21:22 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-24 03:46 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 00:24 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-24 04:44 +0000
Re: Types in C pete <pfiland@mindspring.com> - 2011-05-24 07:46 -0400
Re: Types in C James Kuyper <jameskuyper@verizon.net> - 2011-05-24 07:48 -0400
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 10:35 +1200
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 22:38 +0000
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 10:53 +1200
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 23:17 +0000
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 11:24 +1200
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 23:39 +0000
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-24 11:23 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-24 08:46 -0700
Re: Types in C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-05-24 09:14 -0700
Re: Types in C Michael Press <rubrum@pacbell.net> - 2011-05-28 21:50 -0700
Re: Types in C "io_x" <a@b.c.invalid> - 2011-06-07 19:50 +0200
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 19:33 -0400
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 12:03 +1200
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 21:27 -0400
Re: Types in C Ian Collins <ian-news@hotmail.com> - 2011-05-24 13:47 +1200
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 23:45 -0400
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-24 00:07 -0700
Re: Types in C James Kuyper <jameskuyper@verizon.net> - 2011-05-24 08:05 -0400
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-23 19:54 -0500
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 21:03 -0400
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-23 22:12 -0500
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 00:03 -0400
Re: Types in C pete <pfiland@mindspring.com> - 2011-05-24 00:19 -0400
Re: Types in C pete <pfiland@mindspring.com> - 2011-05-24 00:20 -0400
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-24 00:46 -0500
Re: Types in C pete <pfiland@mindspring.com> - 2011-05-24 07:36 -0400
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 10:58 -0400
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-24 09:40 -0700
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 21:36 -0400
Re: Types in C David Thompson <dave.thompson2@verizon.net> - 2011-06-01 16:33 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-24 16:50 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 21:10 -0400
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-24 18:19 -0700
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 21:42 -0400
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-24 23:47 -0500
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-25 10:13 -0400
Re: Types in C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-05-24 22:19 -0600
Re: Types in C Dr Nick <3-nospam@temporary-address.org.uk> - 2011-05-25 07:04 +0100
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-25 08:53 -0700
Re: Types in C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-05-25 10:11 -0600
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-24 09:02 -0700
Re: Types in C James Kuyper <jameskuyper@verizon.net> - 2011-05-24 07:37 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 22:02 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 18:15 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 22:25 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 19:39 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-23 23:57 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 21:10 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-24 01:58 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-23 23:56 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-24 04:32 +0000
Re: Types in C "BartC" <bc@freeuk.com> - 2011-05-25 01:29 +0100
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-23 22:20 -0500
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-23 22:42 -0500
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 00:07 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-24 04:44 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 10:24 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-24 16:50 +0000
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 21:16 -0400
Re: Types in C Seebs <usenet-nospam@seebs.net> - 2011-05-25 03:36 +0000
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-24 01:26 -0500
Re: Types in C Uncle Steve <stevet810@gmail.com> - 2011-05-24 11:04 -0400
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-24 09:06 -0700
Re: Types in C David Thompson <dave.thompson2@verizon.net> - 2011-06-01 16:33 -0400
Re: Types in C Marcin Grzegorczyk <mgrzegor@poczta.onet.pl> - 2011-05-30 22:42 +0200
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-30 17:45 -0500
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-05-31 08:47 -0700
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-31 13:54 -0400
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-05-31 00:16 +0200
Re: Types in C Shao Miller <sha0.miller@gmail.com> - 2011-05-30 18:30 -0500
Re: Types in C Marcin Grzegorczyk <mgrzegor@poczta.onet.pl> - 2011-06-02 22:44 +0200
Re: Types in C jacob navia <jacob@spamsink.net> - 2011-06-02 22:49 +0200
Re: Types in C Keith Thompson <kst-u@mib.org> - 2011-06-02 15:26 -0700
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