Re: Program to sort three integers

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From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: Program to sort three integers
Date	Fri, 06 Nov 2015 12:52:41 -0800
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Bartc <bc@freeuk.com> writes:
> On 06/11/2015 19:36, Keith Thompson wrote:
>> void sort2(int *x, int *y) {
>>      if (*x > *y) {
>>          const int old_x = *x;
>>          *x = *y;
>>          *y = old_x;
>>      }
>> }
>
> I'd question the benefit of using 'const' here. Actually I found it 
> distracted from the code (the out-of-sequence declaration, which also 
> renders the first assignment out of alignment, doesn't help).

Noted.

> A variable has value stored it it, then that value is used just once, 
> two lines later, and the function returns. What would happen without the 
> const?

One thing that *could* happen is that if I mixed up the assignments and
assigned a new value to old_x, the compiler would catch it for me.

I like to define things as const *unless* I'm going to be modifying
them.  If I follow that consistently, then an object defined without
const stands out and implies that I'm going to want to modify it.

I understand not everyone follows that convention.

> And why not also write:
>
>   void sort2(int * const x, int * const y) ?

Good question.  If I were to be 100% consistent then yes, I'd define
the parameters as const.  There are several reasons I don't bother,
none of them really good.  One is that I like to keep parameter
declarations in function declarations and definitions consistent,
and the const is meaningless in a declaration.  Another is that I
stumble briefly over the ordering of "*" and "const", so omitting
"const" makes it a little easier to read.

(As I've probably mentioned too many times, in my dream language objects
would be read-only by default, and you'd have to add a keyword if you
want to be able to change them after initialization.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

Program to sort three integers Alla _ <modelling.data@gmail.com> - 2015-11-06 08:20 -0800
  Re: Program to sort three integers Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-06 11:32 -0500
    Re: Program to sort three integers Alla _ <modelling.data@gmail.com> - 2015-11-07 00:20 -0800
      Re: Program to sort three integers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-07 11:04 +0000
  Re: Program to sort three integers "Osmium" <r124c4u102@comcast.net> - 2015-11-06 10:34 -0600
  Re: Program to sort three integers "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-06 08:37 -0800
    Re: Program to sort three integers supercat@casperkitty.com - 2015-11-06 10:36 -0800
      Re: Program to sort three integers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-06 19:17 +0000
        Re: Program to sort three integers supercat@casperkitty.com - 2015-11-06 11:30 -0800
        Re: Program to sort three integers Alla _ <modelling.data@gmail.com> - 2015-11-07 01:01 -0800
      Re: Program to sort three integers "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-06 11:48 -0800
        Re: Program to sort three integers David Brown <david.brown@hesbynett.no> - 2015-11-06 23:15 +0100
          Re: Program to sort three integers "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-06 14:39 -0800
          Re: Program to sort three integers Keith Thompson <kst-u@mib.org> - 2015-11-06 15:57 -0800
      Re: Program to sort three integers Nick Bowler <nbowler@draconx.ca> - 2015-11-06 22:33 +0000
  Re: Program to sort three integers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-06 16:39 +0000
    Re: Program to sort three integers Alla _ <modelling.data@gmail.com> - 2015-11-07 00:22 -0800
  Re: Program to sort three integers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-06 16:45 +0000
    Re: Program to sort three integers "Bill Davy" <Bill@SynectixLtd.com> - 2015-11-06 18:30 +0000
    Re: Program to sort three integers Keith Thompson <kst-u@mib.org> - 2015-11-06 11:36 -0800
      Re: Program to sort three integers Bartc <bc@freeuk.com> - 2015-11-06 19:50 +0000
        Re: Program to sort three integers Keith Thompson <kst-u@mib.org> - 2015-11-06 12:52 -0800
          Re: Program to sort three integers Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-09 13:36 +0000
            Re: Program to sort three integers David Brown <david.brown@hesbynett.no> - 2015-11-09 15:41 +0100
          Re: Program to sort three integers raltbos@xs4all.nl (Richard Bos) - 2015-11-10 16:56 +0000
            Re: Program to sort three integers Keith Thompson <kst-u@mib.org> - 2015-11-10 09:11 -0800
            Re: Program to sort three integers supercat@casperkitty.com - 2015-11-10 09:15 -0800
            Re: Program to sort three integers Les Cargill <lcargill99@comcast.com> - 2015-11-10 19:37 -0600
      Re: Program to sort three integers asetofsymbols@gmail.com - 2015-11-06 11:52 -0800
        Re: Program to sort three integers Bartc <bc@freeuk.com> - 2015-11-06 20:01 +0000
          Re: Program to sort three integers asetofsymbols@gmail.com - 2015-11-06 12:21 -0800
          Re: Program to sort three integers "Osmium" <r124c4u102@comcast.net> - 2015-11-06 14:23 -0600
      Re: Program to sort three integers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-06 20:58 +0000
      Re: Program to sort three integers Mark Storkamp <mstorkamp@yahoo.com> - 2015-11-06 16:04 -0600
        Re: Program to sort three integers Mark Storkamp <mstorkamp@yahoo.com> - 2015-11-06 16:08 -0600
          Re: Program to sort three integers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-06 22:49 +0000
            Re: Program to sort three integers Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-10 16:04 -0800
              Re: Program to sort three integers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-11 21:51 +0000
          Re: Program to sort three integers bartekltg <bartekltg@gmail.com> - 2015-11-11 23:50 +0100
        Re: Program to sort three integers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-06 22:52 +0000
          Re: Program to sort three integers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-07 01:17 +0000
      Re: Program to sort three integers Alla _ <modelling.data@gmail.com> - 2015-11-07 01:24 -0800
        Re: Program to sort three integers Chad <cdalten@gmail.com> - 2015-11-07 02:04 -0800
    Re: Program to sort three integers Alla _ <modelling.data@gmail.com> - 2015-11-07 00:57 -0800
  Re: Program to sort three integers Barry Schwarz <schwarzb@dqel.com> - 2015-11-06 10:14 -0800
    Re: Program to sort three integers Richard Heathfield <rjh@cpax.org.uk> - 2015-11-06 18:27 +0000
  Re: Program to sort three integers Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-06 11:22 -0800
    Re: Program to sort three integers Alla _ <modelling.data@gmail.com> - 2015-11-07 01:15 -0800
  Re: Program to sort three integers Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-07 00:57 -0800
  Re: Program to sort three integers bartekltg <bartekltg@gmail.com> - 2015-11-10 02:07 +0100

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