std :: u32string转换为/从std :: string和std :: u16string [英] std::u32string conversion to/from std::string and std::u16string

问题描述

我需要在UTF-8，UTF-16和UTF-32之间转换不同的API /模块，因为我知道有选择使用C ++ 11上午看新的字符串类型。

看起来像我可以使用 string ， u16string 和 u32string 用于UTF-8，UTF-16和UTF-32。我还发现 codecvt_utf8 和 codecvt_utf16 看起来能够在 char 或 char16_t 和 char32_t ，看起来像一个更高级别 wstring_convert ，但只显示与字节/ std :: string ，而不是大量的文档。

我想用UTF-16↔UTF-32和UTF-8↔UTF-32的情况下使用 wstring_convert 我只是真的发现了UTF-8到UTF-16的例子，我甚至不确定将在Linux上正确的 wchar_t 通常被认为是UTF-32 ...或做更复杂的事情与那些codecvt的事情直接？

或者这只是还没有真正在一个可用的状态，我应该坚持我自己现有的小程序使用8，16和32位无符号整数？

解决方案

如果您阅读CppReference.com上的，以便于在各种UTF之间进行转换。尽管它的名字，它不仅限于 std :: wstring ，它实际上与任何 std :: basic_string 类型（ std :: string ， std :: wstring 和 std :: uXXstring

类模板std :: wstring_convert执行字节字符串 std :: string 和宽字符串 std :: basic_string< Elem> ，使用单个代码转换facet Codecvt。 std :: wstring_convert假定转换构面的所有权，并且不能使用由区域设置管理的构面。 适合与std :: wstring_convert一起使用的标准方面包括用于UTF-8 / UCS2和UTF-8 / UCS4转换的std :: codecvt_utf8，以及用于UTF-8 / UTF-16转换的std :: codecvt_utf8_utf16 。

例如：

  typedef std :: string u8string; 
 
 u8string To_UTF8（const std :: u16string& s）
 {
 std :: wstring_convert< std :: codecvt_utf8_utf16< char16_t>，char16_t>转换
 return conv.to_bytes（s）; 
} 
 
 u8string To_UTF8（const std :: u32string& s）
 {
 std :: wstring_convert< std :: codecvt_utf8< char32_t>，char32_t>转换
 return conv.to_bytes（s）; 
} 
 
 std :: u16string To_UTF16（const u8string& s）
 {
 std :: wstring_convert< std :: codecvt_utf8_utf16< char16_t>，char16_t>转换
 return conv.from_bytes（s）; 
} 
 
 std :: u16string To_UTF16（const std :: u32string& s）
 {
 std :: wstring_convert< std :: codecvt_utf16< char32_t& char32_t>转换
 std :: string bytes = conv.to_bytes（s）; 
 return std :: u16string（reinterpret_cast< const char16_t *>（bytes.c_str（）），bytes.length（）/ sizeof（char16_t））; 
} 
 
 std :: u32string To_UTF32（const u8string& s）
 {
 std :: wstring_convert< codecvt_utf8< char32_t>，char32_t>转换
 return conv.from_bytes（s）; 
} 
 
 std :: u32string To_UTF32（const std :: u16string& s）
 {
 const char16_t * pData = s.c_str 
 std :: wstring_convert< std :: codecvt_utf16< char32_t>，char32_t>转换
 return conv.from_bytes（reinterpret_cast< const char *>（pData），reinterpret_cast< const char *>（pData + s.length（）））; 
} 
  




I need to convert between UTF-8, UTF-16 and UTF-32 for different API's/modules and since I know have the option to use C++11 am looking at the new string types.

It looks like I can use string, u16string and u32string for UTF-8, UTF-16 and UTF-32. I also found codecvt_utf8 and codecvt_utf16 which look to be able to do a conversion between char or char16_t and char32_t and what looks like a higher level wstring_convert but that only appears to work with bytes/std::string and not a great deal of documentation.

Am I meant to use a wstring_convert somehow for the UTF-16 ↔ UTF-32 and UTF-8 ↔ UTF-32 case? I only really found examples for UTF-8 to UTF-16, which I am not even sure will be correct on Linux where wchar_t is normally considered UTF-32... Or do something more complex with those codecvt things directly?

Or is this just still not really in a usable state and I should stick with my own existing small routines using 8, 16 and 32bit unsigned integers?

解决方案

If you read the documentation at CppReference.com for wstring_convert, codecvt_utf8, codecvt_utf16, and codecvt_utf8_utf16, the pages include a table that tells you exactly what you can use for the various UTF conversions.

And yes, you would use std::wstring_convert to facilitate the conversion between the various UTFs. Despite its name, it is not limited to just std::wstring, it actually operates with any std::basic_string type (which std::string, std::wstring, and std::uXXstring are all based on).

Class template std::wstring_convert performs conversions between byte string std::string and wide string std::basic_string<Elem>, using an individual code conversion facet Codecvt. std::wstring_convert assumes ownership of the conversion facet, and cannot use a facet managed by a locale. The standard facets suitable for use with std::wstring_convert are std::codecvt_utf8 for UTF-8/UCS2 and UTF-8/UCS4 conversions and std::codecvt_utf8_utf16 for UTF-8/UTF-16 conversions.

For example:

typedef std::string u8string;

u8string To_UTF8(const std::u16string &s)
{
    std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> conv;
    return conv.to_bytes(s);
}

u8string To_UTF8(const std::u32string &s)
{
    std::wstring_convert<std::codecvt_utf8<char32_t>, char32_t> conv;
    return conv.to_bytes(s);
}

std::u16string To_UTF16(const u8string &s)
{
    std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> conv;
    return conv.from_bytes(s);
}

std::u16string To_UTF16(const std::u32string &s)
{
    std::wstring_convert<std::codecvt_utf16<char32_t>, char32_t> conv;
    std::string bytes = conv.to_bytes(s);
    return std::u16string(reinterpret_cast<const char16_t*>(bytes.c_str()), bytes.length()/sizeof(char16_t));
}

std::u32string To_UTF32(const u8string &s)
{
    std::wstring_convert<codecvt_utf8<char32_t>, char32_t> conv;
    return conv.from_bytes(s);
}

std::u32string To_UTF32(const std::u16string &s)
{
    const char16_t *pData = s.c_str();
    std::wstring_convert<std::codecvt_utf16<char32_t>, char32_t> conv;
    return conv.from_bytes(reinterpret_cast<const char*>(pData), reinterpret_cast<const char*>(pData+s.length()));
}

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