C 统一码 : How do I apply C11 standard amendment DR488 fix to C11 standard function c16rtomb()?

Question

问题:

如函数的 C 引用页所述，c16rtomb，来自 CPPReference ，在注释部分下:

In C11 as published, unlike mbrtoc16, which converts variable-width multibyte (such as UTF-8) to variable-width 16-bit (such as UTF-16) encoding, this function can only convert single-unit 16-bit encoding, meaning it cannot convert UTF-16 to UTF-8 despite that being the original intent of this function. This was corrected by the post-C11 defect report DR488.

在这段话的下方，C 引用页面提供了一个示例源代码，上面有以下句子:

Note: this example assumes the fix for the defect report 488 is applied.

这句话暗示有一种方法可以采用 DR488 并以某种方式将修复程序“应用”到 C11 标准函数 c16rtomb。

我想知道如何为 GCC 应用修复程序。因为在我看来，从 v141 开始，该修复程序已应用于 Visual Studio 2017 Visual C++。

在 GCC 中看到的行为，在 GDB 中调试代码时，与在 DR488 中发现的一致，如下所示:

Section 7.28.1 describes the function c16rtomb(). In particular, it states "When c16 is not a valid wide character, an encoding error occurs". "wide character" is defined in section 3.7.3 as "value representable by an object of type wchar_t, capable of representing any character in the current locale". This wording seems to imply that, e.g. for the common cases (e.g, an implementation that defines __STDC_UTF_16__ and a program that uses an UTF-8 locale), c16rtomb() will return -1 when it encounters a character that is encoded as multiple char16_t (for UTF-16 a wide character can be encoded as a surrogate pair consisting of two char16_t). In particular, c16rtomb() will not be able to process strings generated by mbrtoc16().

粗体文字是所描述的行为。

源代码:

#include <stdio.h>
#include <uchar.h>

#define __STD_UTF_16__

int main() {
    char16_t* ptr_string = (char16_t*) u"我是誰";

    //C++ disallows variable-length arrays. 
    //GCC uses GNUC++, which has a C++ extension for variable length arrays.
    //It is not a truly standard feature in C++ pedantic mode at all.
    //https://stackoverflow.com/questions/40633344/variable-length-arrays-in-c14
    char buffer[64];
    char* bufferOut = buffer;

    //Must zero this object before attempting to use mbstate_t at all.
    mbstate_t multiByteState = {};

    //c16 = 16-bit Characters or char16_t typed characters
    //r = representation
    //tomb = to Multi-Byte Strings
    while (*ptr_string) {
        char16_t character = *ptr_string;
        size_t size = c16rtomb(bufferOut, character, &multiByteState);
        if (size == (size_t) -1)
            break;
        bufferOut += size;
        ptr_string++;
    }

    size_t bufferOutSize = bufferOut - buffer;
    printf("Size: %zu - ", bufferOutSize);
    for (int i = 0; i < bufferOutSize; i++) {
        printf("%#x ", +(unsigned char) buffer[i]);
    }

    //This statement is used to set a breakpoint. It does not do anything else.
    int debug = 0;
    return 0;
}

Visual Studio 的输出:

Size: 9 - 0xe6 0x88 0x91 0xe6 0x98 0xaf 0xe8 0xaa 0xb0

GCC 的输出:

Size: 0 -

Answer 1

在 Linux 中，您应该可以通过调用 setlocale(LC_ALL, "en_US.utf8");

来解决这个问题

关于 ideone 的示例

此函数将执行以下操作，如 Microsoft documentation 中所述:

Convert a UTF-16 wide character into a multibyte character in the current locale.

POSIX 文档类似。 __STD_UTF_16__ 在这两个编译器中似乎都没有效果。它应该指定源的编码，应该是 UTF16。它没有指定目的地的编码。

Windows 文档似乎更不一致，因为它似乎暗示 setlocale 是必需的或转换为 ANSI 代码页是一个选项