I need a code in C++ to convert a string given in wchar_t* to a UTF-16 string. It must work both on Windows and Linux. I've looked through a lot of web-pages during the search, but the subject still is not clear to me.
As I understand I need to:
Call setlocale with LC_TYPE and UTF-16 encoding.
Use wcstombs to convert wchar_t to UTF-16 string.
Call setlocale to restore previous locale.
Do you know the way I can convert wchar_t* to UTF-16 in a portable way (Windows and Linux)?
There is no single cross-platform method for doing this in C++03 (not without a library). This is in part because wchar_t is itself not the same thing across platforms. Under Windows, wchar_t is a 16-bit value, while on other platforms it is often a 32-bit value. So you would need two different codepaths to do it.
C++11's std::codecvt_utf16 should work, I think.
std::codecvt_utf16 is a std::codecvt facet which encapsulates conversion between a UTF-16 encoded byte string and UCS2 or UCS4 character string (depending on the type of Elem).
See this: http://en.cppreference.com/w/cpp/locale/codecvt_utf16
You can assume that wchar_t is utf-32 in the non-Windows world. It is true on Linux and Mac OS X and most *nix systems (there are very few exceptions to that, and on systems you will probably never touch :-)
And wchar_t is utf-16 on Windows. So on Windows the conversion function can just do a memcpy :-)
On everything else, the conversion is algorithmic, and pretty simple. So there is no need of fancy support from 3rd party libraries.
Here is the basic algorithm: http://unicode.org/faq/utf_bom.html#utf16-3
And you can probably find find a dozen different implementations if you don't want to write your own :-)
The problem is with wchar_t being rather underspecified. You could use GNU libiconv to do what you want. It accepts special encoding name "wchar_t" as both source and target encoding. That way it will be portable to both Windows and Linux and elsewhere where you can provide libiconv.
The g++ compiler appears to support wcstombs?
Related
I have a question:
Some libraries use WCHAR as the text parameter and others use CHAR (as UTF-8): I need to know when to use WCHAR or CHAR when I write my own library.
Use char and treat it as UTF-8. There are a great many reasons for this; this website summarises it much better than I can:
http://utf8everywhere.org/
It recommends converting from wchar_t to char (UTF-16 to UTF-8) as soon as you receive it from any library, and converting back when you need to pass strings to it. So to answer your question, always use char except at the point that an API requires you to pass or receive wchar_t.
WCHAR (or wchar_t on Visual C++ compiler) is used for Unicode UTF-16 strings.
This is the "native" string encoding used by Win32 APIs.
CHAR (or char) can be used for several other string formats: ANSI, MBCS, UTF-8.
Since UTF-16 is the native encoding of Win32 APIs, you may want to use WCHAR (and better a proper string class based on it, like std::wstring) at the Win32 API boundary, inside your app.
And you can use UTF-8 (so, CHAR/char and std::string) to exchange your Unicode text outside your application boundary. For example: UTF-8 is widely used on the Internet, and when you exchange UTF-8 text between different platforms you don't have the problem of endianness (instead with UTF-16 you have to consider both the UTF-16BE big-endian and the UTF-16LE little-endian cases).
You can convert between UTF-16 and UTF-8 using the WideCharToMultiByte() and MultiByteToWideChar() Win32 APIs. These are pure-C APIs, and these can be conveniently wrapped in C++ code, using string classes instead of raw character pointers, and exceptions instead of raw error codes. You can find an example of that here.
The right question is not which type to use, but what should be your contract with your library users. Both char and wchar_t can mean more than one thing.
The right answer to me, is use char and consider everything utf-8 encoded, as utf8everywhere.org suggests. This will also make it easier to write cross-platform libraries.
Make sure you make correct use of strings though. Some APIs like fopen(), would accept a char* string and treat it differently (not as UTF-8) when compiled on Windows. If Unicode is important to you (and it probably is, when you are dealing with strings), be sure to handle your strings correctly. A good example can be seen in boost::locale. I also recommend using boost::nowide on Windows to get strings handled correctly inside your library.
In Windows we stick to WCHARS. std::wstring. Mainly because if you don't you end up having to convert because calling Windows functions.
I have a feeling that trying to use utf8 internally simply because of http://utf8everywhere.org/ is gonna bite us in the bum later on down the line.
It is best recommended that, when developing a Windows application, resort to TCHARs. The good thing about TCHARs is that they can be either regular chars or wchars, depending whether the unicode setting is set or not. Once you resort to TCHARs, you make sure that all string manipulations that you use also start with the _t prefix (e.g. _tcslen for length of string). That way you will know that your code will work both in Unicode and ASCII environments.
I want to develope an application in Linux. I want to use wstring beacuse my application should supports unicode and I don't want to use UTF-8 strings.
In Windows OS, using wstring is easy. beacuse any ANSI API has a unicode form. for example there are two CreateProcess API, first API is CreateProcessA and second API is CreateProcessW.
wstring app = L"C:\\test.exe";
CreateProcess
(
app.c_str(), // EASY!
....
);
But it seems working with wstring in Linux is complicated! for example there is an API in Linux called parport_open (It just an example).
and I don't know how to send my wstring to this API (or APIs like parport_open that accept a string parameter).
wstring name = L"myname";
parport_open
(
0, // or a valid number. It is not important in this question.
name.c_str(), // Error: because type of this parameter is char* not wchat_t*
....
);
My question is how can I use wstring(s) in Linux APIs?
Note: I don't want to use UTF-8 strings.
Thanks
Linux APIs (on recent kernels and with correct locale setting) on almost every distribution use UTF-8 strings by default1. You too should use them inside your code. Resistance is futile.
The wchar_t (and thus wstring) on Windows were convenient only when Unicode was limited to 65536 characters (i.e. wchar_t were used for UCS-2), now that the 16-bit Windows wchar_t are used for UTF-16 the advantage of 1 wchar_t=1 Unicode character is long gone, so you have the same disadvantages of using UTF-8. Nowadays IMHO the Linux approach is the most correct. (Another answer of mine on UTF-16 and why Windows and Java use it)
By the way, both string and wstring aren't encoding-aware, so you can't reliably use any of these two to manipulate Unicode code points. I heard that wxString from the wxWidgets toolkit handles UTF-8 nicely, but I never did extensive research about it.
actually, as pointed out below, the kernel aims to be encoding-agnostic, i.e. it treats the strings as opaque sequences of (NUL-terminated?) bytes (and that's why encodings that use "larger" character types like UTF-16 cannot be used). On the other hand, wherever actual string manipulation is done, the current locale setting is used, and by default on almost any modern Linux distribution it is set to UTF-8 (which is a reasonable default to me).
I don't want to use UTF-8 strings.
Well, you will need to overcome that reluctance, at least when calling the APIs. Linux uses single byte string encodings, invariably UTF-8. Clearly you should use a single byte string type since you obviously can't pass wide characters to a function that expects char*. Use string rather than wstring.
I'm currently taking care of an application that uses std::string and char for string operations - which is fine on linux, since Linux is agnostic to Unicode (or so it seems; I don't really know, so please correct me if I'm telling stories here). This current style naturally leads to this kind of function/class declarations:
std::string doSomethingFunkyWith(const std::string& thisdata)
{
/* .... */
}
However, if thisdata contains unicode characters, it will be displayed wrongly on windows, since std::string can't hold unicode characters on Windows.
So I thought up this concept:
namespace MyApplication {
#ifdef UNICODE
typedef std::wstring string_type;
typedef wchar_t char_type;
#else
typedef std::string string_type;
typedef char char_type;
#endif
/* ... */
string_type doSomethingFunkyWith(const string_type& thisdata)
{
/* ... */
}
}
Is this a good concept to go with to support Unicode on windows?
My current toolchain consists of gcc/clang on Linux, and wine+MinGW for Windows support (crosstesting also happens via wine), if that matters.
Multiplatform issues comes from the fact that there are many encodings, and a wrong encoding pick will lead to encóding Ãssues. Once you tackle that problem, you should be able to use std::wstring on all your program.
The usual workflow is:
raw_input_data = read_raw_data()
input_encoding = "???" // What is your file or terminal encoding?
unicode_data = convert_to_unicode(raw_input_data, input_encoding)
// Do something with the unicode_data, store in some var, etc.
output_encoding = "???" // Is your terminal output encoding the same as your input?
raw_output_data = convert_from_unicode(unicode_data, output_encoding)
print_raw_data(raw_data)
Most Unicode issues comes from wrongly detecting the values of input_encoding and output_encoding. On a modern Linux distribution this is usually UTF-8. On Windows YMMV.
Standard C++ don't know about encodings, you should use some library like ICU to do the conversion.
How you store a string within your application is entirely up to you -- after all, nobody would know as long as the strings stay within your application. The problem starts when you try to read or write strings from the outside world (console, files, sockets etc.) and this is where the OS matters.
Linux isn't exactly "agnostic" to Unicode -- it does recognize Unicode but the standard library functions assume UTF-8 encoding, so Unicode strings fit into standard char arrays. Windows, on the other hand, uses UTF-16 encoding, so you need a wchar_t array to represent 16-bit characters.
The typedefs you proposed should work fine, but keep in mind that this alone doesn't make your code portable. As an example, if you want to store text in files in a portable manner, you should choose one encoding and stick to it across all platforms -- this could require converting between encodings on certain platforms.
Linux does support Unicode, it simply uses UTF-8. Probably a better way to make your system portable would be to make use of International Components for Unicode and treat all std::string objects as containing UTF-8 characters, and convert them to UTF-16 as needed when invoking Windows functions. It almost always makes sense to use UTF-8 over UTF-16, as UTF-8 uses less space for some of the most commonly used characters (e.g. English*) and more space for less frequent characters, whereas UTF-16 wastes space equally for all characters, no matter how frequently they are used.
While you can use your typedefs, this will mean that you have to write two copies of every single function that has to deal with strings. I think it would be more efficient to simply do all internal computations in UTF-8 and simply translate that to/from UTF-16 if necessary when inputting/outputting as needed.
*For HTML, XML, and JSON that use English as part of the encoding (e.g. "<html>, <body>, etc.) regardless of the language of the values, this can still be a win for foreign languages.
The problem for Linux and using Unicode is that all the IO and most system functions use UTF-8 and the wide character type is 32 bit. Then there is interfacing to Java and other programs which requires UTF-16.
As a suggestion for Unicode support, see the OpenRTL library at http://code.google.com/p/openrtl which supports all UTF-8, UTF-16 and UTF-32 on windows, Linux, Osx and Ios. The Unicode support is not just the character types, but also Unicode collation, normalization, case folding, title casing and about 64 different Unicode character properties per full unsigned 32 bit character.
The OpenRTL code is ready now to support char8_t, char16_t and char32_t for the new C++ standards as well, allthough the same character types are supported using macros for existing C and C++ compilers. I think for Unicode and strings processing that it might be what you want for your library.
The point is that if you use OpenRTL, you can build the system using the OpenRTL "char_t" type. This supports the notion that your entire library can be built in either UTF8, UTF16 or UTF32 mode, even on Linux, because OpenRTL is already handling all the interfacing to a lot of system functions like files and io stuff. It has its own print_f functions for example.
By default the char_t is mapping to the wide character type. So on windows it is 32 bit and on Linux it is 32 bit. But you can make it also make it 8 bit everywhere for example. Also it has the support to do fast UTF decoding inside loops using macros.
So instead of ifdeffing between wchar_t and char, you can build everything using char_t and OpenRTL takes care of the rest.
At my company we have a cross platform(Linux & Windows) library that contains our own extension of the STL std::string, this class provides all sort of functionality on top of the string; split, format, to/from base64, etc. Recently we were given the requirement of making this string unicode "friendly" basically it needs to support characters from Chinese, Japanese, Arabic, etc. After initial research this seems fine on the Linux side since every thing is inherently UTF-8, however I am having trouble with the Windows side; is there a trick to getting the STL std::string to work as UTF-8 on windows? Is it even possible? Is there a better way? Ideally we would keep ourselves based on the std::string since that is what the string class is based on in Linux.
Thank you,
There are several misconceptions in your question.
Neither C++ nor the STL deal with encodings.
std::string is essentially a string of bytes, not characters. So you should have no problem stuffing UTF-8 encoded Unicode into it. However, keep in mind that all string functions also work on bytes, so myString.length() will give you the number of bytes, not the number of characters.
Linux is not inherently UTF-8. Most distributions nowadays default to UTF-8, but it should not be relied upon.
Yes - by being more aware of locales and encodings.
Windows has two function calls for everything that requires text, a FoobarA() and a FoobarW(). The *W() functions take UTF-16 encoded strings, the *A() takes strings in the current codepage. However, Windows doesn't support a UTF-8 code page, so you can't directly use it in that sense with the *A() functions, nor would you want to depend on that being set by users. If you want "Unicode" in Windows, use the Unicode-capable (*W) functions. There are tutorials out there, Googling "Unicode Windows tutorial" should get you some.
If you are storing UTF-8 data in a std::string, then before you pass it off to Windows, convert it to UTF-16 (Windows provides functions for doing such), and then pass it to Windows.
Many of these problems arise from C/C++ being generally encoding-agnostic. char isn't really a character, it's just an integral type. Even using char arrays to store UTF-8 data can get you into trouble if you need to access individual code units, as char's signed-ness is left undefined by the standards. A statement like str[x] < 0x80 to check for multiple-byte characters can quickly introduce a bug. (That statement is always true if char is signed.) A UTF-8 code unit is an unsigned integral type with a range of 0-255. That maps to the C type of uint8_t exactly, although unsigned char works as well. Ideally then, I'd make a UTF-8 string an array of uint8_ts, but due to old APIs, this is rarely done.
Some people have recommended wchar_t, claiming it to be "A Unicode character type" or something like that. Again, here the standard is just as agnostic as before, as C is meant to work anywhere, and anywhere might not be using Unicode. Thus, wchar_t is no more Unicode than char. The standard states:
which is an integer type whose range of values can represent distinct codes for all members of the largest extended character set specified among the supported locales
In Linux, a wchat_t represents a UTF-32 code unit / code point. It is thus 4 bytes. However, in Windows, it's a UTF-16 code unit, and is only 2 bytes. (Which, I would have said does not conform to the above, since 2-bytes cannot represent all of Unicode, but that's the way it works.) This size difference, and difference in data encoding, clearly puts a strain on portability. The Unicode standard itself recommends against wchar_t if you need portability. (§5.2)
The end lesson: I find it easiest to store all my data in some well-declared format. (Typically UTF-8, usually in std::string's, but I'd really like something better.) The important thing here is not the UTF-8 part, but rather, I know that my strings are UTF-8. If I'm passing them to some other API, I must also know that that API expects UTF-8 strings. If it doesn't, then I must convert them. (Thus, if I speak to Window's API, I must convert strings to UTF-16 first.) A UTF-8 text string is an "orange", and a "latin1" text string is an "apple". A char array that doesn't know what encoding it is in is a recipe for disaster.
Putting UTF-8 code points into an std::string should be fine regardless of platform. The problem on Windows is that almost nothing else expects or works with UTF-8 -- it expects and works with UTF-16 instead. You can switch to an std::wstring which will store UTF-16 (at least on most Windows compilers) or you can write other routines that will accept UTF-8 (probably by converting to UTF-16, and then passing through to the OS).
Have you looked at std::wstring? It's a version of std::basic_string for wchar_t rather than the char that std::string uses.
No, there is no way to make Windows treat "narrow" strings as UTF-8.
Here is what works best for me in this situation (cross-platform application that has Windows and Linux builds).
Use std::string in cross-platform portion of the code. Assume that it always contains UTF-8 strings.
In Windows portion of the code, use "wide" versions of Windows API explicitly, i.e. write e.g. CreateFileW instead of CreateFile. This allows to avoid dependency on build system configuration.
In the platfrom abstraction layer, convert between UTF-8 and UTF-16 where needed (MultiByteToWideChar/WideCharToMultiByte).
Other approaches that I tried but don't like much:
typedef std::basic_string<TCHAR> tstring; then use tstring in the business code. Wrappers/overloads can be made to streamline conversion between std::string and std::tstring, but it still adds a lot of pain.
Use std::wstring everywhere. Does not help much since wchar_t is 16 bit on Windows, so you either have to restrict yourself to BMP or go to a lot of complications to make the code dealing with Unicode cross-platform. In the latter case, all benefits over UTF-8 evaporate.
Use ATL/WTL/MFC CString in the platfrom-specific portion; use std::string in cross-platfrom portion. This is actually a variant of what I recommend above. CString is in many aspects superior to std::string (in my opinion). But it introduces an additional dependency and thus not always acceptable or convenient.
If you want to avoid headache, don't use the STL string types at all. C++ knows nothing about Unicode or encodings, so to be portable, it's better to use a library that is tailored for Unicode support, e.g. the ICU library. ICU uses UTF-16 strings by default, so no conversion is required, and supports conversions to many other important encodings like UTF-8. Also try to use cross-platform libraries like Boost.Filesystem for things like path manipulations (boost::wpath). Avoid std::string and std::fstream.
In the Windows API and C runtime library, char* parameters are interpreted as being encoded in the "ANSI" code page. The problem is that UTF-8 isn't supported as an ANSI code page, which I find incredibly annoying.
I'm in a similar situation, being in the middle of porting software from Windows to Linux while also making it Unicode-aware. The approach we've taken for this is:
Use UTF-8 as the default encoding for strings.
In Windows-specific code, always call the "W" version of functions, converting string arguments between UTF-8 and UTF-16 as necessary.
This is also the approach Poco has taken.
It really platform dependant, Unicode is headache. Depends on which compiler you use. For older ones from MS (VS2010 or older), you would need use API described in MSDN
for VS2015
std::string _old = u8"D:\\Folder\\This \xe2\x80\x93 by ABC.txt"s;
according to their docs. I can't check that one.
for mingw, gcc, etc.
std::string _old = u8"D:\\Folder\\This \xe2\x80\x93 by ABC.txt";
std::cout << _old.data();
output contains proper file name...
You should consider using QString and QByteArray, it has good unicode support
The history of Encoding Schemes / multiple Operating Systems and Endian-nes have led to a mess in terms of encoding all forms of string data (--i.e., all alphabets); for this reason protocol buffers only deals with ASCII or UTF-8 in its string types, and I can't see any polymorphic overloads that accept the C++ wstring. The question then is how is one expected to get a UTF-16 string into a protocol buffer ?
Presumably I need to keep the data as a wstring in my application code and then perform a UTF-8 conversion before I stuff it into (or extract from) the message. What is the simplest - Windows/Linux portable way to do this (A single function call from a well-supported library would make my day) ?
Data will originate from various web-servers (Linux and windows) and will eventually ends up in SQL Server (and possibly other end points).
-- edit 1--
Mark Wilkins suggestion seems to fit the bill, perhaps someone who has experience with the library can post a code snippet -- from wstring to UTF-8 -- so that I can gauge how easy it will be.
-- edit 2 --
sth's suggestion even more so. I will investigate boost serialization further.
The Boost Serialization library contains a UTF-8 codecvt facet that you can use to convert unicode to UTF-8 and back. There even is an example in the documentation doing exactly that.
Take a look at UTF8-CPP:
// converts a utf-8 encoded std::string s to utf-16 wstring ws
utf8to16(s.begin(), s.end(), back_inserter(ws));
It may be overkill, but the ICU libraries will do everything you need and you can use them on both Windows and Linux.
However, if you are only wanting conversion, then under Windows, a simple call to MultiByteToWideChar and WideCharToMultiByte can do the conversion between UTF-8 and
UTF-16. For example:
// utf-8 to utf-16
MultiByteToWideChar( CP_UTF8, 0, myUtf8String, -1,
myUtf16Buf, lengthOfUtf16Buf );
With Linux, libidn might do what you need. It can convert between UTF-8 and UCS, which I think is equivalent to UTF-32 at some level. For example:
// utf-8 to UCS
ucsStr = stringprep_utf8_to_ucs4( "asdf", 4, &items );
However, in Linux I think you might be best simply working with UTF-8. Unless you have an existing library for UTF-16, I am not sure there is a compelling reason to use it in Linux.
On Linux it's trivial: each wchar_t is one Unicode codepoint, and with trivial bitops you can find the corresponding UTF-8 byte(s). On Windows it isn't much harder, as there is an API for it: WideCharToMultiByte(CP_UTF8, 0, input.c_str(), input.size(), &out[0], out.size(), 0,0);