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Groups > comp.lang.c > #104390

Re: modifying local const variable run time

From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: modifying local const variable run time
Date 2017-02-22 09:50 -0800
Organization None to speak of
Message-ID <lnshn6jesv.fsf@kst-u.example.com> (permalink)
References (1 earlier) <20170222160611.91c1f3085d6c9e3571a68156@gmail.com> <3cba5f3c-735a-45b7-87f2-d03dd8a18720@googlegroups.com> <20170222173450.4fe314b3c852b242bb2dc35a@gmail.com> <ln1suqkul5.fsf@kst-u.example.com> <20170222183223.a4daa256d17cc9bfcc04d4b9@gmail.com>

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GOTHIER Nathan <nathan.gothier@gmail.com> writes:
> On Wed, 22 Feb 2017 09:23:50 -0800
> Keith Thompson <kst-u@mib.org> wrote:
>
>> "const" means read-only.
>
> Should we assume that this keyword only provide warnings on assignments with
> zero optimization?

I'm not sure what that means.  The "const" keyword does not specify
any kind of optimization.  It imposes constraints on code that code
that refers to const-qualified objects and types.  A compiler can
take advantage of those constraints for purposes of optimization,
but is not required to do so.  In many cases, a compiler can perform
exactly the same optimizations without the "const" keyword, if it's
able to infer the same information.

Personally, I use "const" mostly to make code clearer, so it's
obvious at a glance to a human reader that a given object won't
be modified, and so that the compiler can diagnose any incorrect
attempt to modify it.  If a compiler can use that information to
generate faster code, so much the better.

-- 
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"

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Thread

modifying local const variable run time rahul.dev.agg@gmail.com - 2017-02-22 06:39 -0800
  Re: modifying local const variable run time GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-22 16:06 +0100
    Re: modifying local const variable run time rahul.dev.agg@gmail.com - 2017-02-22 07:26 -0800
      Re: modifying local const variable run time David Brown <david.brown@hesbynett.no> - 2017-02-22 16:31 +0100
        Re: modifying local const variable run time rahul.dev.agg@gmail.com - 2017-02-22 07:43 -0800
          Re: modifying local const variable run time Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-22 16:06 +0000
      Re: modifying local const variable run time James Kuyper <jameskuyper@verizon.net> - 2017-02-22 11:13 -0500
      Re: modifying local const variable run time supercat@casperkitty.com - 2017-02-22 08:34 -0800
        Re: modifying local const variable run time David Brown <david.brown@hesbynett.no> - 2017-02-22 23:03 +0100
      Re: modifying local const variable run time GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-22 17:34 +0100
        Re: modifying local const variable run time Robert Wessel <robertwessel2@yahoo.com> - 2017-02-22 10:52 -0600
          Re: modifying local const variable run time GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-22 17:52 +0100
            Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 09:33 -0800
            Re: modifying local const variable run time James Kuyper <jameskuyper@verizon.net> - 2017-02-22 15:50 -0500
              Re: modifying local const variable run time supercat@casperkitty.com - 2017-02-22 13:13 -0800
                Re: modifying local const variable run time Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-22 21:55 +0000
                Re: modifying local const variable run time supercat@casperkitty.com - 2017-02-22 14:43 -0800
        Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 09:23 -0800
          Re: modifying local const variable run time GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-02-22 18:32 +0100
            Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 09:50 -0800
              Re: modifying local const variable run time David Brown <david.brown@hesbynett.no> - 2017-02-22 23:07 +0100
                Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 15:20 -0800
                Re: modifying local const variable run time David Brown <david.brown@hesbynett.no> - 2017-02-23 09:50 +0100
  Re: modifying local const variable run time James Kuyper <jameskuyper@verizon.net> - 2017-02-22 10:16 -0500
  Re: modifying local const variable run time Keith Thompson <kst-u@mib.org> - 2017-02-22 09:17 -0800

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