将utf16写入二进制模式的文件

Question

我试图用二进制模式的ofstream写一个wstring文件,但我觉得我做错了.这就是我尝试过的:

ofstream outFile("test.txt", std::ios::out | std::ios::binary);
wstring hello = L"hello";
outFile.write((char *) hello.c_str(), hello.length() * sizeof(wchar_t));
outFile.close();

在例如Firefox中打开test.txt,编码设置为UTF16,它将显示为:

你好

谁能告诉我为什么会这样？

编辑:

在十六进制编辑器中打开文件我得到:

FF FE 68 00 00 00 65 00 00 00 6C 00 00 00 6C 00 00 00 6F 00 00 00 

看起来我出于某种原因在每个角色之间得到两个额外的字节？

Answer 1

在这里,我们遇到了很少使用的语言环境属性.如果将字符串输出为字符串(而不是原始数据),则可以使区域设置自动进行适当的转换.

注意:此代码未考虑wchar_t字符的edianness.

#include <locale>
#include <fstream>
#include <iostream>
// See Below for the facet
#include "UTF16Facet.h"

int main(int argc,char* argv[])
{
   // construct a custom unicode facet and add it to a local.
   UTF16Facet *unicodeFacet = new UTF16Facet();
   const std::locale unicodeLocale(std::cout.getloc(), unicodeFacet);

   // Create a stream and imbue it with the facet
   std::wofstream   saveFile;
   saveFile.imbue(unicodeLocale);


   // Now the stream is imbued we can open it.
   // NB If you open the file stream first. Any attempt to imbue it with a local will silently fail.
   saveFile.open("output.uni");
   saveFile << L"This is my Data\n";


   return(0);
}    

文件:UTF16Facet.h

 #include <locale>

class UTF16Facet: public std::codecvt<wchar_t,char,std::char_traits<wchar_t>::state_type>
{
   typedef std::codecvt<wchar_t,char,std::char_traits<wchar_t>::state_type> MyType;
   typedef MyType::state_type          state_type;
   typedef MyType::result              result;


   /* This function deals with converting data from the input stream into the internal stream.*/
   /*
    * from, from_end:  Points to the beginning and end of the input that we are converting 'from'.
    * to,   to_limit:  Points to where we are writing the conversion 'to'
    * from_next:       When the function exits this should have been updated to point at the next location
    *                  to read from. (ie the first unconverted input character)
    * to_next:         When the function exits this should have been updated to point at the next location
    *                  to write to.
    *
    * status:          This indicates the status of the conversion.
    *                  possible values are:
    *                  error:      An error occurred the bad file bit will be set.
    *                  ok:         Everything went to plan
    *                  partial:    Not enough input data was supplied to complete any conversion.
    *                  nonconv:    no conversion was done.
    */
   virtual result  do_in(state_type &s,
                           const char  *from,const char *from_end,const char* &from_next,
                           wchar_t     *to,  wchar_t    *to_limit,wchar_t*    &to_next) const
   {
       // Loop over both the input and output array/
       for(;(from < from_end) && (to < to_limit);from += 2,++to)
       {
           /*Input the Data*/
           /* As the input 16 bits may not fill the wchar_t object
            * Initialise it so that zero out all its bit's. This
            * is important on systems with 32bit wchar_t objects.
            */
           (*to)                               = L'\0';

           /* Next read the data from the input stream into
            * wchar_t object. Remember that we need to copy
            * into the bottom 16 bits no matter what size the
            * the wchar_t object is.
            */
           reinterpret_cast<char*>(to)[0]  = from[0];
           reinterpret_cast<char*>(to)[1]  = from[1];
       }
       from_next   = from;
       to_next     = to;

       return((from > from_end)?partial:ok);
   }



   /* This function deals with converting data from the internal stream to a C/C++ file stream.*/
   /*
    * from, from_end:  Points to the beginning and end of the input that we are converting 'from'.
    * to,   to_limit:  Points to where we are writing the conversion 'to'
    * from_next:       When the function exits this should have been updated to point at the next location
    *                  to read from. (ie the first unconverted input character)
    * to_next:         When the function exits this should have been updated to point at the next location
    *                  to write to.
    *
    * status:          This indicates the status of the conversion.
    *                  possible values are:
    *                  error:      An error occurred the bad file bit will be set.
    *                  ok:         Everything went to plan
    *                  partial:    Not enough input data was supplied to complete any conversion.
    *                  nonconv:    no conversion was done.
    */
   virtual result do_out(state_type &state,
                           const wchar_t *from, const wchar_t *from_end, const wchar_t* &from_next,
                           char          *to,   char          *to_limit, char*          &to_next) const
   {
       for(;(from < from_end) && (to < to_limit);++from,to += 2)
       {
           /* Output the Data */
           /* NB I am assuming the characters are encoded as UTF-16.
            * This means they are 16 bits inside a wchar_t object.
            * As the size of wchar_t varies between platforms I need
            * to take this into consideration and only take the bottom
            * 16 bits of each wchar_t object.
            */
           to[0]     = reinterpret_cast<const char*>(from)[0];
           to[1]     = reinterpret_cast<const char*>(from)[1];

       }
       from_next   = from;
       to_next     = to;

       return((to > to_limit)?partial:ok);
   }
};

Answer 2

我怀疑你的环境中sizeof(wchar_t)是4 - 即它写出UTF-32/UCS-4而不是UTF-16.这肯定是十六进制转储的样子.

这很容易测试(只需打印出sizeof(wchar_t)),但我很确定这是正在发生的事情.

要从UTF-32 wstring转换为UTF-16,您需要应用适当的编码,因为代理对开始发挥作用.

Answer 3

如果你使用C++11标准就很容易(因为还有很多额外的包含"utf8"可以永远解决这个问题).

但是,如果要使用旧标准的多平台代码,可以使用此方法使用流写入:

1. 阅读有关流的UTF转换器的文章
2. stxutif.h从上面的来源添加到您的项目

3. 以ANSI模式打开文件并将BOM添加到文件的开头,如下所示:

   std::ofstream fs;
   fs.open(filepath, std::ios::out|std::ios::binary);
   
   unsigned char smarker[3];
   smarker[0] = 0xEF;
   smarker[1] = 0xBB;
   smarker[2] = 0xBF;
   
   fs << smarker;
   fs.close();
   

4. 然后打开文件UTF并在那里写下您的内容:

   std::wofstream fs;
   fs.open(filepath, std::ios::out|std::ios::app);
   
   std::locale utf8_locale(std::locale(), new utf8cvt<false>);
   fs.imbue(utf8_locale); 
   
   fs << .. // Write anything you want...