c++ 无法让“wcout”打印 unicode，并让“cout”正常工作

Question

无法让“wcout”在多个代码页中打印 unicode 字符串，同时让“cout”继续工作

请帮我让这 3 行代码一起工作。

std::wcout<<"abc "<<L'\u240d'<<" defg "<<L'א'<<" hijk"<<std::endl;
std::cout<<"hello world from cout! \n";
std::wcout<<"hello world from wcout! \n";

输出：

abc hello world from cout!

我试过了：

#include <io.h> 
#include <fcntl.h>
_setmode(_fileno(stdout), _O_U8TEXT);

问题： “wcout”失败

试过了：

std::locale mylocale("");
std::wcout.imbue(mylocale);

和：

SetConsoleOutputCP(1251);

和

setlocale(LC_ALL, "");

和

SetConsoleCP(CP_UTF8)

没有任何效果

Answer 1

C++ 说：

[C++11: 27.4.1/3]: 在相应的宽字符流和窄字符流上混合操作遵循与在FILEs 上混合此类操作相同的语义，如 ISO C 标准的修正 1 中所指定。

而the referenced document 说：

流的定义已更改为包含文本流和二进制流的方向概念。在流与文件关联之后，但在对流执行任何操作之前，流是没有方向的。如果将宽字符输入或输出函数应用于没有方向的流，则流将变为宽方向。同样，如果将字节输入或输出操作应用于具有方向的流，则流将变为面向字节的。此后，只有fwide() 或freopen() 函数可以改变流的方向。

字节输入/输出函数不应应用于面向宽的流，宽字符输入/输出函数不应应用于面向字节的流。

根据我的解释，这意味着，简而言之，不要混用 std::cout 和 std::wcout。

Answer 2

在wcout 或wcin 可以工作之前，Microsoft 需要对_setmode() 进行一些非标准设置。这个例子在样板文件上相当繁重，所以不是很清楚，但它可以在 clang++、g++ 和 MSVC++ 上运行：

#include <iostream>
#include <locale>
#include <locale.h>
#include <stdlib.h>

#ifndef MS_STDLIB_BUGS // Allow overriding the autodetection.
/* The Microsoft C and C++ runtime libraries that ship with Visual Studio, as
 * of 2017, have a bug that neither stdio, iostreams or wide iostreams can
 * handle Unicode input or output.  Windows needs some non-standard magic to
 * work around that.  This includes programs compiled with MinGW and Clang
 * for the win32 and win64 targets.
 */
#  if ( _MSC_VER || __MINGW32__ || __MSVCRT__ )
    /* This code is being compiled either on MS Visual C++, or MinGW, or
     * clang++ in compatibility mode for either, or is being linked to the
     * msvcrt.dll runtime.
     */
#    define MS_STDLIB_BUGS 1
#  else
#    define MS_STDLIB_BUGS 0
#  endif
#endif

#if MS_STDLIB_BUGS
#  include <io.h>
#  include <fcntl.h>
#endif

#if !HAS_APP17_FILESYSTEM && !HAS_TS_FILESYSTEM && __has_include(<filesystem>)
#  include <filesystem> /* MSVC has this header, but not the standard API. */
#  if __cpp_lib_filesystem >= 201703
#    define HAS_CPP17_FILESYSTEM 1
#  endif
#endif

#if !HAS_CPP17_FILESYSTEM && __has_include(<experimental/filesystem>)
#  include <experimental/filesystem>
/* Microsoft screws this one up, too, by not defining the feature-test
 * macro specified by the standard.
 */
#  if __cpp_lib_experimental_filesystem >= 201406 || MS_STDLIB_BUGS
#    define HAS_TS_FILESYSTEM 1
/* With g++6, this requires -lstdc++fs, AFTER this source file on the
 * command line.
 */
#  endif
#endif

#if HAS_CPP17_FILESYSTEM
  using std::filesystem::absolute;
  using std::filesystem::current_path;
  using std::filesystem::directory_entry;
  using std::filesystem::directory_iterator;
  using std::filesystem::is_directory;
  using std::filesystem::exists;
  using std::filesystem::path;
#elif HAS_TS_FILESYSTEM
  using std::experimental::filesystem::absolute;
  using std::experimental::filesystem::current_path;
  using std::experimental::filesystem::directory_entry;
  using std::experimental::filesystem::directory_iterator;
  using std::experimental::filesystem::is_directory;
  using std::experimental::filesystem::exists;
  using std::experimental::filesystem::path;
#else
#  error "This library has neither <filesystem> nor <experimental/filesystem>."
#endif

void init_locale(void)
// Does magic so that wcout can work.
{
#if MS_STDLIB_BUGS
  // Windows needs a little non-standard magic.
  constexpr char cp_utf16le[] = ".1200"; // UTF-16 little-endian locale.
  setlocale( LC_ALL, cp_utf16le );
  _setmode( _fileno(stdout), _O_WTEXT );
  /* Repeat for _fileno(stdin), if needed. */
#else
  // The correct locale name may vary by OS, e.g., "en_US.utf8".
  constexpr char locale_name[] = "";
  setlocale( LC_ALL, locale_name );
  std::locale::global(std::locale(locale_name));
  std::wcin.imbue(std::locale())
  std::wcout.imbue(std::locale());
#endif
}

using std::endl;

int main( const int argc, const char * const argv[] )
{
  init_locale();

  const path cwd = (argc > 1) ? absolute(path( argv[1], std::locale() ))
                              : absolute(current_path());

  if (exists(cwd)) {
    std::wcout << cwd.wstring() << endl;
  } else {
    std::wcerr << "Path does not exist.\n";
    return EXIT_FAILURE;
  }

  if (is_directory(cwd)) {
    for ( const directory_entry &f : directory_iterator(cwd) )
      std::wcout << f.path().filename().wstring() << endl;
  }

  return EXIT_SUCCESS;
}

这可能比实际需要的复杂得多：std::filesystem 自 2018 年起不受支持，但 <experimental/filesystem> 永远不会被删除。

这是一个简化版本，其中仅包含使 wcout 工作的样板：

#include <iostream>
#include <locale>
#include <locale.h>

#ifndef MS_STDLIB_BUGS
#  if ( _MSC_VER || __MINGW32__ || __MSVCRT__ )
#    define MS_STDLIB_BUGS 1
#  else
#    define MS_STDLIB_BUGS 0
#  endif
#endif

#if MS_STDLIB_BUGS
#  include <io.h>
#  include <fcntl.h>
#endif

void init_locale(void)
{
#if MS_STDLIB_BUGS
  constexpr char cp_utf16le[] = ".1200";
  setlocale( LC_ALL, cp_utf16le );
  _setmode( _fileno(stdout), _O_WTEXT );
#else
  // The correct locale name may vary by OS, e.g., "en_US.utf8".
  constexpr char locale_name[] = "";
  setlocale( LC_ALL, locale_name );
  std::locale::global(std::locale(locale_name));
  std::wcin.imbue(std::locale())
  std::wcout.imbue(std::locale());
#endif
}

Answer 3

这是因为 Unicode 在代码页中无法表示，导致 wcout 失败。

std::wcout<<"abc "<<L'\u240d'<<" defg "<<L'א'<<" hijk"<<std::endl;
if(std::wcout.fail()){
    std::cout<<"\nConversion didn't succeed\n";
    std::wcout << "This statement has no effect on the console";
    std::wcout.clear();
    std::wcout<<"hello world from wcout! \n";
}
std::cout<<"hello world from cout! \n";
std::wcout<<"hello world from wcout again! \n";