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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Tue, 10 May 2022 14:27:12 +0100
Message-ID: <CAH6eHdRFxHYe_sAQgvswX+Owpzhw_bh0MNsD++o9bVc-OePR9Q@mail.gmail.com>
Subject: Re: -Wformat and u8""
To: Andreas Schwab <schwab@linux-m68k.org>
Cc: Florian Weimer via Gcc <gcc@gcc.gnu.org>,
 Florian Weimer <fweimer@redhat.com>, Ulrich Drepper <drepper@redhat.com>
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On Mon, 9 May 2022 at 11:09, Andreas Schwab wrote:
>
> On Mai 09 2022, Florian Weimer via Gcc wrote:
>
> > * Ulrich Drepper via Gcc:
> >
> >> t.cc: In function =E2=80=98int main()=E2=80=99:
> >> t.cc:5:24: warning: format string is not an array of type =E2=80=98cha=
r=E2=80=99 [-Wformat=3D]
> >>     5 |   printf((const char*) u8"test %d\n", 1);
> >>       |                        ^~~~~~~~~~~~~
> >
> > This is not an aliasing violation because of the exception for char,
> > right?  So the warning does not even highlight theoretical undefined
> > behavior.
> >
> > On the other hand, that cast is still quite ugly.  All string-related
> > functions in the C library currently need it.  It might obscure real
> > type errors.  Isn't this a problem with char8_t?
>
> In C++20, u8 literals have a distinct type, which is an incompatible
> change from C++17.

And the recommended way to deal with it is to use a cast as Ulrich did.