将utf16写入二进制模式的文件

时间:2008-10-16 07:17:40

标签: c++ unicode utf-16

我正在尝试用二进制模式的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Firefox中打开test.txt,编码设置为UTF16,它将显示为:

您好

有人能告诉我为什么会这样吗?

修改

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?

6 个答案:

答案 0 :(得分:14)

这里我们讨论一下使用很少的语言环境属性。 如果您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。

N.B。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);
   }
};

答案 1 :(得分:6)

我怀疑你的环境中sizeof(wchar_t)是4 - 即它写出了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,您需要应用正确的编码,因为代理对开始发挥作用。

答案 2 :(得分:6)

如果您使用C++11标准,那就很容易了(因为还有很多额外的包含,例如"utf8"可以永远解决这个问题)。

但是如果你想使用旧标准的多平台代码,你可以使用这种方法来编写流:

  1. Read the article about UTF converter for streams
  2. 从上面的来源
  3. 向您的项目添加stxutif.h
  4. 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();
    
  5. 然后将文件打开为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...
    

答案 3 :(得分:2)

在使用wofstream的窗口和上面定义的utf16 facet失败时,wofstream会将值为0A的所有字节转换为2字节0D 0A,这与您如何传递0A字节无关,'\ x0A',L'\ x0A',L'\ x000A','\ n',L'\ n'和std :: endl都给出相同的结果。 在Windows上,您必须在二进制模式下使用ofstream(而不是wofsteam)打开文件,并像在原始帖子中一样编写输出。

答案 4 :(得分:1)

提供的Utf16Facetgcc中没有用于大字符串,这是适用于我的版本...这样文件将保存在UTF-16LE中。对于UTF-16BE,只需转换do_indo_out中的分配,例如to[0] = from[1]to[1] = from[0]

#include <locale>
#include <bits/codecvt.h>


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
   {

       for(;from < from_end;from += 2,++to)
       {
           if(to<=to_limit){
               (*to)                               = L'\0';

               reinterpret_cast<char*>(to)[0]  = from[0];
               reinterpret_cast<char*>(to)[1]  = from[1];

               from_next   = from;
               to_next     = to;
           }
       }

       return((to != to_limit)?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);++from, to += 2)
       {
           if(to <= to_limit){

               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);
   }
};

答案 5 :(得分:0)

您应该在十六进制编辑器中查看输出文件,例如WinHex,这样您就可以看到实际的位和字节,以验证输出实际上是UTF-16。将它发布在这里,让我们知道结果。这将告诉我们是否要归咎于Firefox或你的C ++程序。

但它让我觉得你的C ++程序很有效,Firefox并没有正确地解释你的UTF-16。 UTF-16为每个字符调用两个字节。但是Firefox打印的字符数量应该是它应该的两倍,因此它可能会尝试将您的字符串解释为UTF-8或ASCII,每个字符通常只有1个字节。

当你说“编码设置为UTF16的Firefox”是什么意思?我对这项工作表示怀疑。