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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Array sizes and const |
| Date | 2012-06-03 13:51 -0700 |
| Organization | None to speak of |
| Message-ID | <lny5o4dsqr.fsf@nuthaus.mib.org> (permalink) |
| References | <jqdtou$koe$1@dont-email.me> <lnmx4lfk8a.fsf@nuthaus.mib.org> <jqe303$id9$1@dont-email.me> <jqfe45$q7d$1@dont-email.me> |
"BartC" <bc@freeuk.com> writes:
[...]
> But, who care's about that; what I want to know is why, at some point
> during the last forty years, didn't someone just add a feature like:
>
> constant int d = 4000;
>
> and it means exactly that: d is a synonym for the literal d. It has a
> precise type, and follows normal scoping rules. You also can't use it
> as an lvalue so it is guaranteed to have that value. It can also be
> used to initialise fixed size arrays, and does not to be written in
> capitals.
>
> It's a five-minute job to add to the language (exaggerating a little,
> but it is pretty trivial to implement). Instead we have a series of
> unsatisfactory alternatives: #define, const (which doesn't work, or
> works but you unintentionally end up with a VLA), and enum{}, which
> you described as a 'trick'...
In fact someone did do that: Bjarne Stroustrup, when he was designing
C++.
Except that he didn't introduce a new keyword; he just tweaked the
semantics of "const".
In C++, if you declare
const some_type x = init_expr;
x becomes a constant expression *if* some_type is arithmetic *and*
init_expr is a constant expression. Otherwise, it has pretty much the
same meaning it has in C. (I probably haven't gotten that 100% right,
but that's the general idea.)
So, for example, in C++ (which doesn't have VLAs) you can have this:
{
const int array_size = 20;
int arr[arr_size];
}
but not this:
{
const int array_size = rand() % 20 + 1;
int arr[arr_size]; // invalid
}
I don't think it would have been terribly difficult for C to adopt this
feature, and I think it would have been a good idea. Maybe for C202x.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Will write code for food.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Array sizes and const Les Cargill <lcargill99@comcast.com> - 2012-06-02 15:43 -0500
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-03 08:56 +1200
Re: Array sizes and const Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-02 16:59 -0400
Re: Array sizes and const Les Cargill <lcargill99@comcast.com> - 2012-06-02 16:35 -0500
Re: Array sizes and const jgk@panix.com (Joe keane) - 2012-06-08 20:05 +0000
Re: Array sizes and const jgk@panix.com (Joe keane) - 2012-06-09 21:36 +0000
Re: Array sizes and const Les Cargill <lcargill99@comcast.com> - 2012-06-02 16:43 -0500
Re: Array sizes and const Keith Thompson <kst-u@mib.org> - 2012-06-02 14:59 -0700
Re: Array sizes and const Les Cargill <lcargill99@comcast.com> - 2012-06-02 17:12 -0500
Re: Array sizes and const Keith Thompson <kst-u@mib.org> - 2012-06-02 18:27 -0700
Re: Array sizes and const Les Cargill <lcargill99@comcast.com> - 2012-06-02 22:27 -0500
Re: Array sizes and const "BartC" <bc@freeuk.com> - 2012-06-03 11:24 +0100
Re: Array sizes and const Keith Thompson <kst-u@mib.org> - 2012-06-03 13:51 -0700
Re: Array sizes and const "BartC" <bc@freeuk.com> - 2012-06-04 12:20 +0100
Re: Array sizes and const Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-04 13:54 +0200
Re: Array sizes and const Keith Thompson <kst-u@mib.org> - 2012-06-04 14:32 -0700
Re: Array sizes and const Nobody <nobody@nowhere.com> - 2012-06-02 23:50 +0100
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-03 10:53 +1200
Re: Array sizes and const Nobody <nobody@nowhere.com> - 2012-06-03 14:35 +0100
Re: Array sizes and const James Kuyper <jameskuyper@verizon.net> - 2012-06-02 21:11 -0400
Re: Array sizes and const Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-06-03 07:39 -0700
Re: Array sizes and const James Kuyper <jameskuyper@verizon.net> - 2012-06-03 16:03 -0400
Re: Array sizes and const Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-03 21:49 +0100
Re: Array sizes and const Keith Thompson <kst-u@mib.org> - 2012-06-03 14:49 -0700
Re: Array sizes and const Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-06-03 15:02 -0700
Re: Array sizes and const Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-04 01:21 +0100
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-04 09:08 +1200
Re: Array sizes and const Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-06-03 15:08 -0700
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-04 10:37 +1200
Re: Array sizes and const "BartC" <bc@freeuk.com> - 2012-06-03 23:47 +0100
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-04 10:55 +1200
Re: Array sizes and const Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-06-03 16:04 -0700
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-04 11:14 +1200
Re: Array sizes and const "BartC" <bc@freeuk.com> - 2012-06-04 00:23 +0100
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-04 11:30 +1200
Re: Array sizes and const "BartC" <bc@freeuk.com> - 2012-06-04 00:52 +0100
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-04 12:04 +1200
Re: Array sizes and const Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-04 01:39 +0100
Re: Array sizes and const Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-06-04 02:35 -0700
Re: Array sizes and const Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-06-04 01:33 +0100
Re: Array sizes and const Ian Collins <ian-news@hotmail.com> - 2012-06-04 12:35 +1200
Re: Array sizes and const pacman@kosh.dhis.org (Alan Curry) - 2012-06-04 21:28 +0000
Re: Array sizes and const James Kuyper <jameskuyper@verizon.net> - 2012-06-04 12:08 -0400
Re: Array sizes and const jgk@panix.com (Joe keane) - 2012-06-04 22:49 +0000
Re: Array sizes and const David Brown <david.brown@hesbynett.no> - 2012-06-03 15:46 -0500
Re: Array sizes and const Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-08 02:08 -0700
Re: Array sizes and const Les Cargill <lcargill99@comcast.com> - 2012-06-08 06:45 -0500
Re: Array sizes and const Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-08 10:49 -0700
Re: Array sizes and const Les Cargill <lcargill99@comcast.com> - 2012-06-08 18:05 -0500
Re: Array sizes and const Keith Thompson <kst-u@mib.org> - 2012-06-08 13:31 -0700
Re: Array sizes and const Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-08 20:30 -0700
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