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From: Ike Naar <ike@sdf.org>
Newsgroups: comp.lang.c
Subject: Re: question about linker
Date: Fri, 29 Nov 2024 12:06:14 -0000 (UTC)
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On 2024-11-29, Bart <bc@freeuk.com> wrote:
> These are similar examples:
>
>      int * const z1;
>      int const * z2;
>
>      z1=0;          // invalid
>      z2=0;          // valid
>
> [snip]
>
> Both 'const' in my new examples are the the right-most one! Yet one 
> makes the immediate storage const and one doesn't. I guess then that 
> it's the right-most possible 'const' if it were to be used. In my 
> example,  that would follow the '*'.


The order in which '*' and 'const' appear matters.
With

    int * const z1;

the const applies to z1 because it appears immediately before 'z1'.
z1 is a const pointer to int.
(hint: read the declaration out loud from right to left).

    *z1 = 0; /* valid */
    z1 = 0; /* invalid, z1 is readonly */


With

    int const * z2;

the const applies to *z2 because it appears immediately before '* z2'.
*z2 is a const int, z2 is a pointer to const int.
(again, read the declaration out loud from right to left).

    *z2 = 0; /* invalid, *z2 is readonly */
    z2 = 0; /* valid */


With

    int const * const z3;

the leftmost const applies to *z3 and the rightmost const applies to z3.
z3 is a const pointer to const int.

    *z3 = 0; /* invalid, *z3 is readonly */
    z3 = 0; /* invalid, z3 is readonly */