Visual Studio 中（基于字符的）STL（流）容器的编译错误

这基本上是同一个问题[SO]：C2491：'std :: numpunct :: id'：不允许定义dllimport静态数据成员[关闭]，但考虑以下事实：

• （在我看来）这是一个完全有效的问题（根据[SO]：如何创建一个最小的、完整的、可验证的示例），真不知道为什么有些用户有种想关闭它的冲动
• 标记为解决方案的答案提供了修复错误的指南（一般而言），但是不适用就目前的情况而言，当然，没有解决它,

请不要关闭它或将其标记为重复项（至少，在没有仔细阅读和理解它的情况下）。

main.cpp:

#include <sstream>


//#define THROW_C2491
#if defined(THROW_C2491)
typedef int CharType;
#else
typedef char CharType;
#endif


int main() {
    std::basic_stringstream<CharType> stream;
    CharType c = 0x41;
    stream << c;
    return 0;
}

代码稍作修改（简化），编译失败if THROW_C2491被定义为：

xlocnum(294): error C2491: 'std::numpunct<_Elem>::id': definition of dllimport static data member not allowed

Output:

E:\Work\Dev\StackOverflow\q048716223>"c:\Install\x86\Microsoft\Visual Studio Community\2015\vc\vcvarsall.bat" amd64

E:\Work\Dev\StackOverflow\q048716223>
E:\Work\Dev\StackOverflow\q048716223>"c:\Install\x86\Microsoft\Visual Studio Community\2015\vc\bin\amd64\cl.exe" /GS /W3 /Zc:wchar_t /ZI /Gm /Od /Zc:inline /fp:precise /D "_DEBUG" /D "_CONSOLE" /D "_UNICODE" /D "UNICODE" /errorReport:prompt /WX- /Zc:forScope /RTC1 /Gd /MDd /EHsc /nologo -c "src\main.cpp"
main.cpp

E:\Work\Dev\StackOverflow\q048716223>echo %errorlevel%
0

E:\Work\Dev\StackOverflow\q048716223>
E:\Work\Dev\StackOverflow\q048716223>"c:\Install\x86\Microsoft\Visual Studio Community\2015\vc\bin\amd64\cl.exe" /GS /W3 /Zc:wchar_t /ZI /Gm /Od /Zc:inline /fp:precise /D "_DEBUG" /D "_CONSOLE" /D "_UNICODE" /D "UNICODE" /errorReport:prompt /WX- /Zc:forScope /RTC1 /Gd /MDd /EHsc /nologo -c "src\main.cpp" /D "THROW_C2491"
main.cpp
c:\install\x86\microsoft\visual studio community\2015\vc\include\xlocnum(294): warning C4273: 'id': inconsistent dll linkage
c:\install\x86\microsoft\visual studio community\2015\vc\include\xlocnum(120): note: see previous definition of 'public: static std::locale::id std::numpunct<int>::id'
c:\install\x86\microsoft\visual studio community\2015\vc\include\xlocnum(120): note: while compiling class template static data member 'std::locale::id std::numpunct<_Elem>::id'
        with
        [
            _Elem=CharType
        ]
c:\install\x86\microsoft\visual studio community\2015\vc\include\xlocnum(1261): note: see reference to function template instantiation 'const _Facet &std::use_facet<std::numpunct<_Elem>>(const std::locale &)' being compiled
        with
        [
            _Facet=std::numpunct<CharType>,
            _Elem=CharType
        ]
c:\install\x86\microsoft\visual studio community\2015\vc\include\xlocnum(1255): note: while compiling class template member function 'std::ostreambuf_iterator<_Elem,_Traits> std::num_put<_Elem,std::ostreambuf_iterator<_Elem,_Traits>>::do_put(_OutIt,std::ios_base &,_Elem,bool) const'
        with
        [
            _Elem=CharType,
            _Traits=std::char_traits<CharType>,
            _OutIt=std::ostreambuf_iterator<CharType,std::char_traits<CharType>>
        ]
c:\install\x86\microsoft\visual studio community\2015\vc\include\ostream(305): note: see reference to class template instantiation 'std::num_put<_Elem,std::ostreambuf_iterator<_Elem,_Traits>>' being compiled
        with
        [
            _Elem=CharType,
            _Traits=std::char_traits<CharType>
        ]
c:\install\x86\microsoft\visual studio community\2015\vc\include\ostream(291): note: while compiling class template member function 'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(int)'
        with
        [
            _Elem=CharType,
            _Traits=std::char_traits<CharType>
        ]
e:\work\dev\stackoverflow\q048716223\src\main.cpp(16): note: see reference to function template instantiation 'std::basic_ostream<_Elem,_Traits> &std::basic_ostream<_Elem,_Traits>::operator <<(int)' being compiled
        with
        [
            _Elem=CharType,
            _Traits=std::char_traits<CharType>
        ]
c:\install\x86\microsoft\visual studio community\2015\vc\include\istream(939): note: see reference to class template instantiation 'std::basic_ostream<_Elem,_Traits>' being compiled
        with
        [
            _Elem=CharType,
            _Traits=std::char_traits<CharType>
        ]
c:\install\x86\microsoft\visual studio community\2015\vc\include\sstream(574): note: see reference to class template instantiation 'std::basic_iostream<_Elem,_Traits>' being compiled
        with
        [
            _Elem=CharType,
            _Traits=std::char_traits<CharType>
        ]
e:\work\dev\stackoverflow\q048716223\src\main.cpp(14): note: see reference to class template instantiation 'std::basic_stringstream<CharType,std::char_traits<_Elem>,std::allocator<_Elem>>' being compiled
        with
        [
            _Elem=CharType
        ]
c:\install\x86\microsoft\visual studio community\2015\vc\include\xlocnum(294): error C2491: 'std::numpunct<_Elem>::id': definition of dllimport static data member not allowed
        with
        [
            _Elem=CharType
        ]

E:\Work\Dev\StackOverflow\q048716223>echo %errorlevel%
2

Notes:

• 一切都是VStudio 2015

开始笔记:

• 我在用VStudio 社区 2015 (v14.0.25431.01更新3）。版本在这里很重要，因为标准头文件可能会因版本而异（并且行号可能不同）
• Created [MSDN]：Visual Studio 中 STL（流）容器的编译错误

方法:

1. 快速（浅层）调查

   On VStudio IDE double click, on the 2^nd note in the Output window (after attempting to compile the file), and from there repeated RClicks on relevant macros, and from the context menu choosing Go To Definition (F12):

   • xlocnum (#120)：（注释是原始文件/行的一部分）

     __PURE_APPDOMAIN_GLOBAL _CRTIMP2_PURE static locale::id id; // unique facet id
     

   • yvals.h：（#494）:

          #define _CRTIMP2_PURE _CRTIMP2
     

   • crtdefs.h (#29+):

     #ifndef _CRTIMP2
         #if defined CRTDLL2 && defined _CRTBLD
             #define _CRTIMP2 __declspec(dllexport)
         #else
             #if defined _DLL && !defined _STATIC_CPPLIB
                 #define _CRTIMP2 __declspec(dllimport)  // @TODO - cfati: line #34: Here is the definition
             #else
                 #define _CRTIMP2
             #endif
         #endif
     #endif
     

   正如所见，__declspec(dllimport)定义在第 #34 行。重复该过程_DLL宏，没有结果。发现于[MSDN]：预定义宏:

   _DLL定义为 1，当/MD or /MDd（多线程 DLL）编译器选项已设置。否则，未定义。

   我想到了两种可能的方法（都导致了成功的构建）：

   • Use static的版本显像管运行时 ([MSDN]：/MD、/MT、/LD（使用运行时库））。我不认为这是一个可行的选择，特别是当该项目包括.dlls（确实如此）：坏事可能会发生（例如[SO]：在 MSVC 2013 上链接到 protobuf 3 时出错，甚至更糟糕的情况可能会在运行时发生）
   • 手动#undef _DLL (in main.cpp, before any #include）。这是一个蹩脚的解决方法（gainarie）。它构建得很好，但是篡改这些东西可能（并且很可能会）触发未定义的行为在运行时

   这两个选项都不是完全令人满意，因此：
   

2. 更深入一点

   试图进一步简化事情（main.cpp):

   #include <sstream>
   
   
   //typedef unsigned short CharType;  // wchar_t  unsigned short
   #define CharType unsigned short
   
   
   int main() {
       std::basic_stringstream<CharType> stream;
       CharType c = 0x41;
       stream << c;
       return 0;
   }
   

   Notes:

   • 已更换typedef by #define（消除新类型定义的复杂性）
   • 切换到unsigned short这是wchar_t的定义 (/Zc:wchar_t-）以避免任何可能的字体大小 / 结盟差异

   
   “编译”上面的代码[MSDN]：/E（预处理到标准输出） and [MSDN]：/EP（在没有 #line 指令的情况下预处理到标准输出）（以便警告/错误仅引用当前文件中的行号）：

   • 生成的预处理文件（使用上面的每个标志）：~1MB+ (~56.5k lines)
   • 文件中唯一的区别是#define (wchar_t vs. unsigned short）在最后的某个地方
   • 编译这些文件（令人震惊:)）产生了相同的结果：wchar_t一个编译时unsigned short因同样的错误而失败
   • Added some #pragma message statements (yes, they are handled by the preprocessor, but still) in the file that fails (before each warning/note), noticed some difference between the 2 #defines, but so far unable to figure out why ¹
   • While browsing the generated file(s), noticed a template<> struct char_traits<char32_t> definition, so I gave it a try, and it worked (at least the current program compiled) ¹ (and, as expected sizeof(char32_t) is 4). Then, found [MSDN]: char, wchar_t, char16_t, char32_t

   
   Notes:

   • 虽然这解决了我的current问题（仍然不知道为什么），将不得不试一试end goal
   • ¹ Although I looked over the file, I didn't see any template definitions targeting only the "privileged" types (e.g. I didn't see anything that would differentiate wchar_t, signed char or char32_t from unsigned short for example), so I don't know (yet) why it works for some types but not for others. This is an open topic, whenever I'll get new updates, I will share them

底线:

As 经验地发现，在使用时允许使用以下类型char based STL容器:

• char
• unsigned char
• signed char
• wchar_t
• char16_t
• char32_t
• unsigned short (/Zc:wchar_t- only )

最后的注释:

• 我将合并任何有用的东西（例如comments）在答案中

@EDIT0:

• 基于 @IgorTandetnik 的回答[MSDN]：Visual Studio 中 STL（流）容器的编译错误，尽管仍然有一点雾气：

  • unsigned char and signed char
  • 之间的区别static and dynamic C++ RTLib

  
  我将接受这个作为答案。