带有char16_t或char32_t的Visual Studio C ++ 2015 std :: codecvt [英] Visual Studio C++ 2015 std::codecvt with char16_t or char32_t

问题描述

此代码在VS2013下可以正常编译：

This code compiled OK under VS2013:

std::string Unicode::utf16_to_utf8(std::u16string utf16_string)
{
    std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> convert;
    return convert.to_bytes(utf16_string);
}

现在有了VS2015，我得到：

Now with VS2015 I get:

1>unicode.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static class std::locale::id std::codecvt<char16_t,char,struct _Mbstatet>::id" (__imp_?id@?$codecvt@_SDU_Mbstatet@@@std@@2V0locale@2@A)

推荐答案

旧问题，但供以后参考：这是Visual Studio 2015中的已知错误，如最新文章（2016年1月7日）中的< a href = https://social.msdn.microsoft.com/Forums/en-US/8f40dcd8-c67f-4eba-9134-a19b9178e481/vs-2015-rc-linker-stdcodecvt-error?forum=vcgeneral rel = noreferrer> MSDN Social的该线程。

Old question, but for future reference: this is a known bug in Visual Studio 2015, as explained in the latest post (January 7th 2016) in this thread of MSDN Social.

您的示例的解决方法如下所示（为简单起见，我将您的方法实现为自由函数）：

The workaround for your example looks like this (I implemented your method as a free function for simplicity):

#include <codecvt>
#include <locale>
#include <string>
#include <iostream>

#if _MSC_VER >= 1900

std::string utf16_to_utf8(std::u16string utf16_string)
{
    std::wstring_convert<std::codecvt_utf8_utf16<int16_t>, int16_t> convert;
    auto p = reinterpret_cast<const int16_t *>(utf16_string.data());
    return convert.to_bytes(p, p + utf16_string.size());
}

#else

std::string utf16_to_utf8(std::u16string utf16_string)
{
    std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> convert;
    return convert.to_bytes(utf16_string);
}

#endif

int main()
{
    std::cout << utf16_to_utf8(u"Élémentaire, mon cher Watson!") << std::endl;

    return 0;
}

希望该问题将在以后的版本中得到解决，否则 #if 条件将需要优化。
更新：不，在VS 2017中未解决。因此，我将预处理器的条件更新为> = 1900 （最初是 == 1900 ）。

Hopefully, the problem will be fixed in future releases, otherwise the #if condition will need refining. UPDATE: nope, not fixed in VS 2017. Therefore, I've updated the preprocessor conditional to >= 1900 (initially was == 1900).

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