如何在带有std库的Linux上从utf-16转换为utf-32? [英] How to convert from utf-16 to utf-32 on Linux with std library?

问题描述

在MSVC上，将utf-16转换为utf-32很容易-使用C11的 codecvt_utf16 语言环境方面.但是在GCC(gcc(Debian 4.7.2-5)4.7.2)中，似乎尚未实现此新功能.有没有一种方法可以在没有iconv的Linux上执行这种转换(最好使用std库的转换工具)?

On MSVC converting utf-16 to utf-32 is easy - with C11's codecvt_utf16 locale facet. But in GCC (gcc (Debian 4.7.2-5) 4.7.2) seemingly this new feature hasn't been implemented yet. Is there a way to perform such conversion on Linux without iconv (preferrably using conversion tools of std library)?

推荐答案

将UTF-16解码为UTF-32非常简单.

Decoding UTF-16 into UTF-32 is extremely easy.

您可能希望在编译时检测正在使用的libc版本，如果检测到损坏的libc(没有所需的功能)，请部署转换例程.

You may want to detect at compile time the libc version you're using, and deploy your conversion routine if you detect a broken libc (without the functions you need).

输入:

• 指向源UTF-16数据的指针(char16_t *，ushort *，-为方便起见UTF16 *);
• 它的大小；
• 指向UTF-32数据的指针(char32_t *，uint *-为方便起见，UTF32 *).

• a pointer to the source UTF-16 data (char16_t *, ushort *, -- for convenience UTF16 *);
• its size;
• a pointer to the UTF-32 data (char32_t *, uint * -- for convenience UTF32 *).

代码如下:

void convert_utf16_to_utf32(const UTF16 *input, 
                            size_t input_size, 
                            UTF32 *output) 
{
    const UTF16 * const end = input + input_size;
    while (input < end) {
        const UTF16 uc = *input++;
        if (!is_surrogate(uc)) {
            *output++ = uc; 
        } else {
            if (is_high_surrogate(uc) && input < end && is_low_surrogate(*input))
                *output++ = surrogate_to_utf32(uc, *input++);
            else
                // ERROR
        }
    }
}

剩下的是错误处理.您可能想在流中插入U+FFFD¹并继续进行，或者只是纾困，这完全取决于您.辅助功能很简单:

Error handling is left. You might want to insert a U+FFFD¹ into the stream and keep on going, or just bail out, really up to you. The auxiliary functions are trivial:

int is_surrogate(UTF16 uc) { return (uc - 0xd800u) < 2048u; }
int is_high_surrogate(UTF16 uc) { return (uc & 0xfffffc00) == 0xd800; }
int is_low_surrogate(UTF16 uc) { return (uc & 0xfffffc00) == 0xdc00; }

UTF32 surrogate_to_utf32(UTF16 high, UTF16 low) { 
    return (high << 10) + low - 0x35fdc00; 
}

---

¹Cf. Unicode:

---

¹ Cf. Unicode:

• §3.9 Unicode编码形式(使用U + FFFD的最佳实践)
• 第5.22节"U + FFFD替换最佳实践"

²另外请考虑!is_surrogate(uc)分支是迄今为止最常见的分支(如果第二个分支则是非错误路径)，则可能要使用__builtin_expect或类似的方法对其进行优化.

² Also consider that the !is_surrogate(uc) branch is by far the most common (as well the non-error path in the second if), you might want to optimize that with __builtin_expect or similar.

这篇关于如何在带有std库的Linux上从utf-16转换为utf-32?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！