为什么在使用 wprintf 时将 ©（版权符号）替换为 (C)？

Question

当我尝试使用 printf 或 write 打印版权符号 © 时，效果很好：

#include <stdio.h>

int main(void)
{
    printf("©\n");
}

#include <unistd.h>

int main(void)
{
    write(1, "©\n", 3);
}

输出：

©

但是当我尝试用 wprintf 打印它时，我得到 (C):

#include <stdio.h>
#include <wchar.h>

int main(void)
{
    wprintf(L"©\n");
}

输出：

(C)

当我添加对 setlocale 的调用时它已修复，但是：

#include <stdio.h>
#include <wchar.h>
#include <locale.h>

int main(void)
{
    setlocale(LC_ALL, "");
    wprintf(L"©\n");
}

输出：

©

为什么会出现原始行为，为什么在我调用 setlocale 时它会修复？此外，这种转换发生在哪里？我怎样才能使 setlocale 之后的行为成为默认值？

编译命令：

gcc test.c

locale:

LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

echo $LC_CTYPE:

uname -a:

Linux penguin 4.19.79-07511-ge32b3719f26b #1 SMP PREEMPT Mon Nov 18 17:41:41 PST 2019 x86_64 GNU/Linux

file test.c（所有示例都相同）：

test.c: C source, UTF-8 Unicode text

gcc --version:

gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

/lib/x86_64-linux-gnu/libc-2.24.so（glibc版本）：

GNU C Library (Debian GLIBC 2.24-11+deb9u4) stable release version 2.24, by Roland McGrath et al.
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 6.3.0 20170516.
Available extensions:
        crypt add-on version 2.1 by Michael Glad and others
        GNU Libidn by Simon Josefsson
        Native POSIX Threads Library by Ulrich Drepper et al
        BIND-8.2.3-T5B
libc ABIs: UNIQUE IFUNC
For bug reporting instructions, please see:
<http://www.debian.org/Bugs/>.

cat /etc/debian_version:

9.12

Answer 1

新进程不会自动继承调用进程的语言环境。

程序第一次启动时是C语言环境。 man page for setlocale(3) 表示如下：

On startup of the main program, the portable "C" locale is selected as default. A program may be made portable to all locales by calling:
setlocale(LC_ALL, "");
...

The locale "C" or "POSIX" is a portable locale; its LC_CTYPE part corresponds to the 7-bit ASCII character set.

因此，如输出所示，任何多字节/非 ASCII 字符都将转换为一个或多个 ASCII 字符。

区域设置如下：

setlocale(LC_ALL, "");

LC_ALL 标志指定更改所有与语言环境相关的变量。 locale 为空字符串表示根据相关环境变量设置locale。完成后，您应该会看到 shell 语言环境的字符。

#include <stdio.h>
#include <wchar.h>
#include <locale.h>

int main()
{
    char *before = setlocale(LC_ALL, NULL);
    setlocale(LC_ALL, "");
    char *after = setlocale(LC_ALL, NULL);

    wprintf(L"before locale: %s\n", before);
    wprintf(L"after locale: %s\n", after);
    wprintf(L"©\n");
    wprintf(L"\u00A9\n");
    return 0;
}

输出：

before locale: C
after locale: en_US.utf8
©
©

为什么在使用 wprintf 时将 ©（版权符号）替换为 (C)？

Why is © (the copyright symbol) replaced with (C) when using wprintf?

c

printf

widechar