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Message-ID: <20201130145126.GO534@brightrain.aerifal.cx>
Date: Mon, 30 Nov 2020 09:51:26 -0500
From: Rich Felker <dalias@...c.org>
To: Dong Brett <brett.browning.dong@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: Question on C++ locale
On Mon, Nov 30, 2020 at 06:41:33PM +0800, Dong Brett wrote:
> Hi all,
>
> I am troubleshooting a locale related issue of our C++ software when building with musl. With some efforts I narrowed our problem down to the inability of setting a UTF-8 locale in C++ standard library.
>
> The following C code prints UTF-8 characters correctly:
> #include <ncurses.h>
> #include <langinfo.h>
> #include <locale.h>
>
> int main()
> {
> setlocale(LC_ALL, "");
> initscr();
> printw("LC_ALL: %s\n", setlocale(LC_ALL, NULL));
> printw("CODESET: %s\n", nl_langinfo(CODESET));
> printw("Hello, world!\n");
> printw("你好，世界!\n");
> refresh();
> getch();
> endwin();
> return 0;
> }
>
> Giving the output of
> LC_ALL: C.UTF-8;C;C;C;C;C
> CODESET: UTF-8
> Hello, world!
> 你好，世界!
>
> However, the following C++ code does not work (our software uses std::locale in C++ standard library for locale related stuff):
> #include <langinfo.h>
> #include <locale.h>
> #include <locale>
> using namespace std;
> int main()
> {
> std::locale::global(locale(""));
> initscr();
> printw("LC_ALL: %s\n", setlocale(LC_ALL, NULL));
> printw("C++ locale: %s\n", locale().name().c_str());
> printw("CODESET: %s\n", nl_langinfo(CODESET));
> printw("Hello, world!\n");
> printw("你好，世界!\n");
> refresh();
> getch();
> endwin();
> return 0;
> }
>
> Giving a corrupted output:
> LC_ALL: C
> C++ locale: C
> CODESET: ASCII
> Hello, world!
> 你好?~L?~V?~U~L!
>
> Seems only ASCII C locale is available in C++. If I run the above C++ code with LANG="C.UTF-8", an exception is thrown and the program is aborted:
> terminate called after throwing an instance of 'std::runtime_error'
> what(): locale::facet::_S_create_c_locale name not valid
> Aborted
>
> I also tried LANG="UTF-8”, LANG="en_US.UTF-8" but none of those
> works. Only LANG="C" could make the program run but then only ASCII
> characters are supported.
>
> My question is that is there a way to make locale in C++ standard
> library work with musl? Or had I done anything wrong with it?
Thanks for raising this. Indeed you've uncovered a (pile of) bug(s) in
libstdc++, but they don't seem to be relevant to your usage with
ncurses. Being a C library, not a C++ one, curses behavior depends on
the locale as set through the C/POSIX mechanisms, setlocale and/or
newlocale/uselocale. You shouldn't be using C++'s locale framework for
this. Any program using ncurses should start with either
setlocale(LC_ALL,"") or setlocale(LC_CTYPE,"") (depending on whether
you want the behavior of the other categories).
I'll try to figure out what we need to do to get this fixed in
libstdc++. Since it's never been reported before, I suspect just very
few programs are using the C++ locale API so hopefully at least the
problem is low-impact.
Rich
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