Re: Pointers, constant values

From	James Kuyper <jameskuyper@verizon.net>
Newsgroups	comp.lang.c
Subject	Re: Pointers, constant values
Date	2015-10-16 14:22 -0400
Organization	A noiseless patient Spider
Message-ID	<mvrf63$gun$1@dont-email.me> (permalink)
References	<5b2ab074-7644-4798-9b90-a3ae47e1f2b8@googlegroups.com> <mvrcaa$5rr$1@dont-email.me>

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On 10/16/2015 01:37 PM, Les Cargill wrote:
> Alla _ wrote:
>> Hello!
>>
> <snip>
>>
>> Does int * const array_end = array + n; mean that the pointer
>> array_end has a constant value of array[0] + n, or that it will not
>> be able to change the value of (array + n)?
>>
> 
> So these are modestly different:
> 
> int const array_end *       = array + n;
> int const array_end * const = array + n;
> int       array_end * const = array + n;

The syntax specified for pointer declarators is

T * type-qualifier-listopt D

Where T is the type pointed at, and D is another declarator. A pointer
declaration cannot end with either the '*' or a type-qualifier like
'const'. array_end is in the wrong location in every one of those
declarations. In each case, it should be moved just before the '=':

    int const *       array_end1 = array + n;
    int const * const array_end2 = array + n;
    int       * const array_end2 = array + n;

> One means "the pointer cannot be changed."
> The other means "the thing being pointed to cannot be changed."
> 
> I never remember which is which and have to look it up
> every time :) Or put a line of code in ( to be
> removed quickly ) to test it.

If you move the type specifier ('int') all the way to the left, there's
a simple rule that works for many object declarations (it gets a little
more complicated when functions and pointers to functions are involved):

If you move all qualifier as far left as they can go without moving them
past a  '*', then the thing that appears to the right of any given
sequence of qualifiers is, after removing any other qualifiers that it
itself contains, a model of an expression that refers to the thing
qualified by those qualifiers.

Thus, the first 'const' says that *array_end1 is const-qualified. The
second 'const' applies to '* const array_end2', from which you should
remove the other 'const', so it says that *array_end2 is const
qualified. The third 'const' say that array_end2 is itself
const-qualified, just as the fourth 'const' says that array_end3 is
const qualified.
-- 
James Kuyper

Thread

Pointers, constant values Alla _ <modelling.data@gmail.com> - 2015-10-16 00:49 -0700
  Re: Pointers, constant values Philip Lantz <prl@canterey.us> - 2015-10-16 01:49 -0700
  Re: Pointers, constant values James Kuyper <jameskuyper@verizon.net> - 2015-10-16 09:41 -0400
    Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 08:55 -0700
  Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 08:25 -0700
    Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 09:11 -0700
      Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 12:06 -0700
        Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 12:55 -0700
    Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 17:49 +0100
      Re: Pointers, constant values Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-10-16 13:23 -0400
        Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 19:34 +0100
          Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 12:05 -0700
        Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 12:18 -0700
      Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 12:13 -0700
        Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 20:33 +0100
          Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 13:01 -0700
            Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 21:09 +0100
              Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 13:41 -0700
          Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 21:07 +0100
            Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 21:20 +0100
              Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 22:02 +0100
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 22:21 +0100
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 14:39 -0700
                Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 15:26 -0700
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 15:44 -0700
                Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 16:58 -0700
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 17:28 -0700
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 22:50 +0100
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 15:14 -0700
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-17 01:23 +0100
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-17 19:39 +0100
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-17 22:42 +0100
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 00:31 +0100
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-18 02:11 +0100
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 11:59 +0100
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-18 12:12 +0100
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-18 12:28 +0100
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 23:16 +0100
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-18 23:34 +0100
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 01:45 +0100
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-19 11:51 +0100
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 12:55 +0100
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-19 13:51 +0100
                Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-19 06:02 -0700
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-19 07:02 -0700
                Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-19 15:39 +0100
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-19 08:54 -0700
                Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-19 09:14 -0700
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-19 10:21 -0700
                Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-19 12:57 -0700
                Re: Pointers, constant values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-19 21:20 +0000
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-20 20:50 -0700
                Re: Pointers, constant values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-21 04:58 +0000
                Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-19 08:40 -0700
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 20:17 +0100
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-17 16:44 -0700
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 11:52 +0100
                Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-18 05:15 -0700
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 21:54 +0100
                Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-18 16:09 -0700
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-18 07:55 -0700
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 21:47 +0100
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-18 15:37 -0700
                Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 00:10 +0100
                Re: Pointers, constant values supercat@casperkitty.com - 2015-10-18 19:04 -0700
        Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 21:13 +0100
      Re: Pointers, constant values Ian Collins <ian-news@hotmail.com> - 2015-10-17 11:27 +1300
        Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-17 00:56 +0100
  Re: Pointers, constant values Les Cargill <lcargill99@comcast.com> - 2015-10-16 12:37 -0500
    Re: Pointers, constant values James Kuyper <jameskuyper@verizon.net> - 2015-10-16 14:22 -0400
  Re: Pointers, constant values Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-16 18:57 +0000
    Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 20:40 +0100
      Re: Pointers, constant values Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-16 20:46 +0000
        Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 14:24 -0700
          Re: Pointers, constant values Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-19 12:43 +0000
  Re: Pointers, constant values Siri Cruz <chine.bleu@yahoo.com> - 2015-10-16 13:20 -0700
    Re: Pointers, constant values supercat@casperkitty.com - 2015-10-17 13:59 -0700

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