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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107735] Inconsistent error messages for std::array out of
 bound
Date: Thu, 17 Nov 2022 22:24:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107735

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I wonder if this is because doing=20
constexpr const int *v1 =3D &array[3];

is valid and well defined.

Even clang gives two different error messages:
<source>:3:21: error: constexpr variable 'v1' must be initialized by a cons=
tant
expression
constexpr const int v1 =3D array[3];
                    ^    ~~~~~~~~
<source>:3:26: note: read of dereferenced one-past-the-end pointer is not
allowed in a constant expression
constexpr const int v1 =3D array[3];
                         ^
<source>:4:15: error: constexpr variable 'v2' must be initialized by a cons=
tant
expression
constexpr int v2 =3D array[4];
              ^    ~~~~~~~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/13.0.0/../../.=
./../include/c++/13.0.0/array:213:9:
note: cannot refer to element 4 of array of 3 elements in a constant expres=
sion
        return _M_elems[__n];
               ^
<source>:4:20: note: in call to '&array->operator[](4)'
constexpr int v2 =3D array[4];
                   ^
---- CUT ----
I do think clang's note of one-past-the-end gives more of a hint of why the
error message is different though.

And I do think GCC could add that note.=