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？
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：
stxutif.h
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();
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Utf16Facet在gcc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_in和do_out中的分配，例如to[0] = from[1]和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。