AW: A: a new bug to old plain C

> -----Ursprüngliche Nachricht-----
> Von: Gcc-help <[email protected]> Im Auftrag von
> Jonathan Wakely via Gcc-help
> Gesendet: Freitag, 21. November 2025 12:47
> An: Chris S <[email protected]>
> Cc: Александр Поваляев <[email protected]>; gcc-help <gcc-
> [email protected]>
> Betreff: Re: A: a new bug to old plain C
> 
> On Fri, 21 Nov 2025 at 03:25, Chris S via Gcc-help <[email protected]>
> wrote:
> >
> > You're applying two consts to the same thing, so it's an error.
> 
> No, that's not happening here.
> 
> The explanation is
> https://isocpp.org/wiki/faq/const-correctness#constptrptr-conversion
> 
> >
> > "Const int" and "int const" are the same (look up East vs West const),
> > but "const int const" is an error.  Declaring a pointer to that
> > invalid type declaration is still invalid.
> >
> > On Thu, Nov 20, 2025, 5:27 PM Александр Поваляев via Gcc-help <
> > [email protected]> wrote:
> >
> > > struct zzz {
> > > unsigned x, y;
> > > };
> > >
> > > void square(struct zzz ** arr_of_ptr, unsigned count) {
> > >
> > > *// The first "const" produce an error (not a warning) within some
> > > GCC toolchains, for example ARM GCC trunk (linux), see goldbolt.org
> > > <http://goldbolt.org>*
> > > struct zzz const * const * const end_of_arr = arr_of_ptr + count;
> > >
> > > *// Without the first const "struct zzz * const * const end_of_arr =
> > > arr_of_ptr + count;" it works fine!!!*
> > >
> > > }
> > >
> > > Respectfully,
> > > Aleksandr G Povaliaev.
> > >

Consider:

char const * foo1(char * x) {
    char const * y = x;
    *x = 'a';
    return y;
}

char const ** foo2(char ** x) {
    char const ** y = x;
    **x = 'a';
    return y;
}

typedef char * cp;
cp const * foo3(cp * x) {
    cp const * y = x;
    **x = 'a';
    return y;
}

All three should compile fine, but one does not. 
It is not consistent.