如何在C ++中创建Unicode txt文件

Question

There are four kind of encoding options when creating a .txt file in Windows.

• ANSI
• UNICODE(litte endian)
• UNICODE(big endian)
• UTF-8

C standard library supports this option, by using FILE .

FILE* file;
file = _wfopen(L"test.txt", L"wt+,ccs=UTF-16LE");

It has been working great, but I found there is no parameter for this in std::ofstream .

wofstream myfile;
myfile.open("example.txt", ?????????);

So, I want to know how to create files like this in C++. Is there any solution for this in C++ STL?

Answer 1

Starting with C++11, the standard C++ library allows to generate UTF16 text files with the following steps:

• build a locale using the C++11 class std::codecvt_utf16 - you can specify endianness in constructor
• open a file using a std::wofstream in which you will write unicode text
• just imbue the locale into the wide stream and start writing, optionnaly starting with a Byte Order Mark character (U+FEFF)

Here is an example adapted from the page referenced by @HansPassant in its comment:

// codecvt_utf16: writing unicode string as UTF-16
#include <iostream>
#include <locale>
#include <string>
#include <codecvt>
#include <fstream>

int main ()
{
  std::wstring str ( { 0xa8, 0xa9 });

  std::locale loc (std::locale(), new std::codecvt_utf16<wchar_t>);
  std::basic_ofstream<wchar_t> ofs ("test.txt");
  ofs.imbue(loc);

  std::cout << "Writing to file (UTF-16)... ";
  ofs << (wchar_t) 0xfeff; // BOM
  ofs << str;
  std::cout << "done!\n";

  return 0;
}

You get an utf16 file starting with a little endian BOM and containing èé

(hexadecimal dump:

$ od -xc test.txt
0000000      fffe    a800    a900
         376 377  \0 250  \0 251

)

Answer 2

There is no "C STL". STL stands for Standard Template Library. C does not have templates. You may be referring to the C standard library and C++ standard library.

The C standard library has no functions for "creating unicode" or converting text to or from unicode. There is no _wfopen in the C standard libray. You're using a function from the Microsoft C Run-Time Library.

The C++ library does have an API to convert between (UTF-8 and UTF-16) and (UTF-8 and UTF-32) and (system native wide and system native multibyte) encodings: http://en.cppreference.com/w/cpp/locale/codecvt

There is hardly any other support for unicode in the standard library. You must take care that the string that you're writing is in the encoding that you want it to be and you must explicitly write a BOM if you need to.