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I am not able to understand the differences between std::string and std::wstring. I know wstring supports wide characters such as Unicode characters. I have got the following questions:
When should I use std::wstring over std::string?
Can std::string hold the entire ASCII character set, including the special characters?
Is std::wstring supported by all popular C++ compilers?
What is exactly a "wide character"?
string? wstring?
std::string is a basic_string templated on a char, and std::wstring on a wchar_t.
char vs. wchar_t
char is supposed to hold a character, usually an 8-bit character.
wchar_t is supposed to hold a wide character, and then, things get tricky:
On Linux, a wchar_t is 4 bytes, while on Windows, it's 2 bytes.
What about Unicode, then?
The problem is that neither char nor wchar_t is directly tied to unicode.
On Linux?
Let's take a Linux OS: My Ubuntu system is already unicode aware. When I work with a char string, it is natively encoded in UTF-8 (i.e. Unicode string of chars). The following code:
#include <cstring>
#include <iostream>
int main()
{
const char text[] = "olé";
std::cout << "sizeof(char) : " << sizeof(char) << "\n";
std::cout << "text : " << text << "\n";
std::cout << "sizeof(text) : " << sizeof(text) << "\n";
std::cout << "strlen(text) : " << strlen(text) << "\n";
std::cout << "text(ordinals) :";
for(size_t i = 0, iMax = strlen(text); i < iMax; ++i)
{
unsigned char c = static_cast<unsigned_char>(text[i]);
std::cout << " " << static_cast<unsigned int>(c);
}
std::cout << "\n\n";
// - - -
const wchar_t wtext[] = L"olé" ;
std::cout << "sizeof(wchar_t) : " << sizeof(wchar_t) << "\n";
//std::cout << "wtext : " << wtext << "\n"; <- error
std::cout << "wtext : UNABLE TO CONVERT NATIVELY." << "\n";
std::wcout << L"wtext : " << wtext << "\n";
std::cout << "sizeof(wtext) : " << sizeof(wtext) << "\n";
std::cout << "wcslen(wtext) : " << wcslen(wtext) << "\n";
std::cout << "wtext(ordinals) :";
for(size_t i = 0, iMax = wcslen(wtext); i < iMax; ++i)
{
unsigned short wc = static_cast<unsigned short>(wtext[i]);
std::cout << " " << static_cast<unsigned int>(wc);
}
std::cout << "\n\n";
}
outputs the following text:
sizeof(char) : 1
text : olé
sizeof(text) : 5
strlen(text) : 4
text(ordinals) : 111 108 195 169
sizeof(wchar_t) : 4
wtext : UNABLE TO CONVERT NATIVELY.
wtext : ol�
sizeof(wtext) : 16
wcslen(wtext) : 3
wtext(ordinals) : 111 108 233
You'll see the "olé" text in char is really constructed by four chars: 110, 108, 195 and 169 (not counting the trailing zero). (I'll let you study the wchar_t code as an exercise)
So, when working with a char on Linux, you should usually end up using Unicode without even knowing it. And as std::string works with char, so std::string is already unicode-ready.
Note that std::string, like the C string API, will consider the "olé" string to have 4 characters, not three. So you should be cautious when truncating/playing with unicode chars because some combination of chars is forbidden in UTF-8.
On Windows?
On Windows, this is a bit different. Win32 had to support a lot of application working with char and on different charsets/codepages produced in all the world, before the advent of Unicode.
So their solution was an interesting one: If an application works with char, then the char strings are encoded/printed/shown on GUI labels using the local charset/codepage on the machine, which could not be UTF-8 for a long time. For example, "olé" would be "olé" in a French-localized Windows, but would be something different on an cyrillic-localized Windows ("olй" if you use Windows-1251). Thus, "historical apps" will usually still work the same old way.
For Unicode based applications, Windows uses wchar_t, which is 2-bytes wide, and is encoded in UTF-16, which is Unicode encoded on 2-bytes characters (or at the very least, UCS-2, which just lacks surrogate-pairs and thus characters outside the BMP (>= 64K)).
Applications using char are said "multibyte" (because each glyph is composed of one or more chars), while applications using wchar_t are said "widechar" (because each glyph is composed of one or two wchar_t. See MultiByteToWideChar and WideCharToMultiByte Win32 conversion API for more info.
Thus, if you work on Windows, you badly want to use wchar_t (unless you use a framework hiding that, like GTK or QT...). The fact is that behind the scenes, Windows works with wchar_t strings, so even historical applications will have their char strings converted in wchar_t when using API like SetWindowText() (low level API function to set the label on a Win32 GUI).
Memory issues?
UTF-32 is 4 bytes per characters, so there is no much to add, if only that a UTF-8 text and UTF-16 text will always use less or the same amount of memory than an UTF-32 text (and usually less).
If there is a memory issue, then you should know than for most western languages, UTF-8 text will use less memory than the same UTF-16 one.
Still, for other languages (chinese, japanese, etc.), the memory used will be either the same, or slightly larger for UTF-8 than for UTF-16.
All in all, UTF-16 will mostly use 2 and occassionally 4 bytes per characters (unless you're dealing with some kind of esoteric language glyphs (Klingon? Elvish?), while UTF-8 will spend from 1 to 4 bytes.
See https://en.wikipedia.org/wiki/UTF-8#Compared_to_UTF-16 for more info.
Conclusion
When I should use std::wstring over std::string?
On Linux? Almost never (§).
On Windows? Almost always (§).
On cross-platform code? Depends on your toolkit...
(§) : unless you use a toolkit/framework saying otherwise
Can std::string hold all the ASCII character set including special characters?
Notice: A std::string is suitable for holding a 'binary' buffer, where a std::wstring is not!
On Linux? Yes.
On Windows? Only special characters available for the current locale of the Windows user.
Edit (After a comment from Johann Gerell):
a std::string will be enough to handle all char-based strings (each char being a number from 0 to 255). But:
ASCII is supposed to go from 0 to 127. Higher chars are NOT ASCII.
a char from 0 to 127 will be held correctly
a char from 128 to 255 will have a signification depending on your encoding (unicode, non-unicode, etc.), but it will be able to hold all Unicode glyphs as long as they are encoded in UTF-8.
Is std::wstring supported by almost all popular C++ compilers?
Mostly, with the exception of GCC based compilers that are ported to Windows.
It works on my g++ 4.3.2 (under Linux), and I used Unicode API on Win32 since Visual C++ 6.
What is exactly a wide character?
On C/C++, it's a character type written wchar_t which is larger than the simple char character type. It is supposed to be used to put inside characters whose indices (like Unicode glyphs) are larger than 255 (or 127, depending...).
I recommend avoiding std::wstring on Windows or elsewhere, except when required by the interface, or anywhere near Windows API calls and respective encoding conversions as a syntactic sugar.
My view is summarized in http://utf8everywhere.org of which I am a co-author.
Unless your application is API-call-centric, e.g. mainly UI application, the suggestion is to store Unicode strings in std::string and encoded in UTF-8, performing conversion near API calls. The benefits outlined in the article outweigh the apparent annoyance of conversion, especially in complex applications. This is doubly so for multi-platform and library development.
And now, answering your questions:
A few weak reasons. It exists for historical reasons, where widechars were believed to be the proper way of supporting Unicode. It is now used to interface APIs that prefer UTF-16 strings. I use them only in the direct vicinity of such API calls.
This has nothing to do with std::string. It can hold whatever encoding you put in it. The only question is how You treat its content. My recommendation is UTF-8, so it will be able to hold all Unicode characters correctly. It's a common practice on Linux, but I think Windows programs should do it also.
No.
Wide character is a confusing name. In the early days of Unicode, there was a belief that a character can be encoded in two bytes, hence the name. Today, it stands for "any part of the character that is two bytes long". UTF-16 is seen as a sequence of such byte pairs (aka Wide characters). A character in UTF-16 takes either one or two pairs.
So, every reader here now should have a clear understanding about the facts, the situation. If not, then you must read paercebal's outstandingly comprehensive answer [btw: thanks!].
My pragmatical conclusion is shockingly simple: all that C++ (and STL) "character encoding" stuff is substantially broken and useless. Blame it on Microsoft or not, that will not help anyway.
My solution, after in-depth investigation, much frustration and the consequential experiences is the following:
accept, that you have to be responsible on your own for the encoding and conversion stuff (and you will see that much of it is rather trivial)
use std::string for any UTF-8 encoded strings (just a typedef std::string UTF8String)
accept that such an UTF8String object is just a dumb, but cheap container. Do never ever access and/or manipulate characters in it directly (no search, replace, and so on). You could, but you really just really, really do not want to waste your time writing text manipulation algorithms for multi-byte strings! Even if other people already did such stupid things, don't do that! Let it be! (Well, there are scenarios where it makes sense... just use the ICU library for those).
use std::wstring for UCS-2 encoded strings (typedef std::wstring UCS2String) - this is a compromise, and a concession to the mess that the WIN32 API introduced). UCS-2 is sufficient for most of us (more on that later...).
use UCS2String instances whenever a character-by-character access is required (read, manipulate, and so on). Any character-based processing should be done in a NON-multibyte-representation. It is simple, fast, easy.
add two utility functions to convert back & forth between UTF-8 and UCS-2:
UCS2String ConvertToUCS2( const UTF8String &str );
UTF8String ConvertToUTF8( const UCS2String &str );
The conversions are straightforward, google should help here ...
That's it. Use UTF8String wherever memory is precious and for all UTF-8 I/O. Use UCS2String wherever the string must be parsed and/or manipulated. You can convert between those two representations any time.
Alternatives & Improvements
conversions from & to single-byte character encodings (e.g. ISO-8859-1) can be realized with help of plain translation tables, e.g. const wchar_t tt_iso88951[256] = {0,1,2,...}; and appropriate code for conversion to & from UCS2.
if UCS-2 is not sufficient, than switch to UCS-4 (typedef std::basic_string<uint32_t> UCS2String)
ICU or other unicode libraries?
For advanced stuff.
When you want to have wide characters stored in your string. wide depends on the implementation. Visual C++ defaults to 16 bit if i remember correctly, while GCC defaults depending on the target. It's 32 bits long here. Please note wchar_t (wide character type) has nothing to do with unicode. It's merely guaranteed that it can store all the members of the largest character set that the implementation supports by its locales, and at least as long as char. You can store unicode strings fine into std::string using the utf-8 encoding too. But it won't understand the meaning of unicode code points. So str.size() won't give you the amount of logical characters in your string, but merely the amount of char or wchar_t elements stored in that string/wstring. For that reason, the gtk/glib C++ wrapper folks have developed a Glib::ustring class that can handle utf-8.
If your wchar_t is 32 bits long, then you can use utf-32 as an unicode encoding, and you can store and handle unicode strings using a fixed (utf-32 is fixed length) encoding. This means your wstring's s.size() function will then return the right amount of wchar_t elements and logical characters.
Yes, char is always at least 8 bit long, which means it can store all ASCII values.
Yes, all major compilers support it.
I frequently use std::string to hold utf-8 characters without any problems at all. I heartily recommend doing this when interfacing with API's which use utf-8 as the native string type as well.
For example, I use utf-8 when interfacing my code with the Tcl interpreter.
The major caveat is the length of the std::string, is no longer the number of characters in the string.
A good question!
I think DATA ENCODING (sometimes a CHARSET also involved) is a MEMORY EXPRESSION MECHANISM in order to save data to a file or transfer data via a network, so I answer this question as:
1. When should I use std::wstring over std::string?
If the programming platform or API function is a single-byte one, and we want to process or parse some Unicode data, e.g read from Windows'.REG file or network 2-byte stream, we should declare std::wstring variable to easily process them. e.g.: wstring ws=L"中国a"(6 octets memory: 0x4E2D 0x56FD 0x0061), we can use ws[0] to get character '中' and ws[1] to get character '国' and ws[2] to get character 'a', etc.
2. Can std::string hold the entire ASCII character set, including the special characters?
Yes. But notice: American ASCII, means each 0x00~0xFF octet stands for one character, including printable text such as "123abc&*_&" and you said special one, mostly print it as a '.' avoid confusing editors or terminals. And some other countries extend their own "ASCII" charset, e.g. Chinese, use 2 octets to stand for one character.
3.Is std::wstring supported by all popular C++ compilers?
Maybe, or mostly. I have used: VC++6 and GCC 3.3, YES
4. What is exactly a "wide character"?
a wide character mostly indicates using 2 octets or 4 octets to hold all countries' characters. 2 octet UCS2 is a representative sample, and further e.g. English 'a', its memory is 2 octet of 0x0061(vs in ASCII 'a's memory is 1 octet 0x61)
When you want to store 'wide' (Unicode) characters.
Yes: 255 of them (excluding 0).
Yes.
Here's an introductory article: http://www.joelonsoftware.com/articles/Unicode.html
There are some very good answers here, but I think there are a couple of things I can add regarding Windows/Visual Studio. Tis is based on my experience with VS2015. On Linux, basically the answer is to use UTF-8 encoded std::string everywhere. On Windows/VS it gets more complex. Here is why. Windows expects strings stored using chars to be encoded using the locale codepage. This is almost always the ASCII character set followed by 128 other special characters depending on your location. Let me just state that this in not just when using the Windows API, there are three other major places where these strings interact with standard C++. These are string literals, output to std::cout using << and passing a filename to std::fstream.
I will be up front here that I am a programmer, not a language specialist. I appreciate that USC2 and UTF-16 are not the same, but for my purposes they are close enough to be interchangeable and I use them as such here. I'm not actually sure which Windows uses, but I generally don't need to know either. I've stated UCS2 in this answer, so sorry in advance if I upset anyone with my ignorance of this matter and I'm happy to change it if I have things wrong.
String literals
If you enter string literals that contain only characters that can be represented by your codepage then VS stores them in your file with 1 byte per character encoding based on your codepage. Note that if you change your codepage or give your source to another developer using a different code page then I think (but haven't tested) that the character will end up different. If you run your code on a computer using a different code page then I'm not sure if the character will change too.
If you enter any string literals that cannot be represented by your codepage then VS will ask you to save the file as Unicode. The file will then be encoded as UTF-8. This means that all Non ASCII characters (including those which are on your codepage) will be represented by 2 or more bytes. This means if you give your source to someone else the source will look the same. However, before passing the source to the compiler, VS converts the UTF-8 encoded text to code page encoded text and any characters missing from the code page are replaced with ?.
The only way to guarantee correctly representing a Unicode string literal in VS is to precede the string literal with an L making it a wide string literal. In this case VS will convert the UTF-8 encoded text from the file into UCS2. You then need to pass this string literal into a std::wstring constructor or you need to convert it to utf-8 and put it in a std::string. Or if you want you can use the Windows API functions to encode it using your code page to put it in a std::string, but then you may as well have not used a wide string literal.
std::cout
When outputting to the console using << you can only use std::string, not std::wstring and the text must be encoded using your locale codepage. If you have a std::wstring then you must convert it using one of the Windows API functions and any characters not on your codepage get replaced by ? (maybe you can change the character, I can't remember).
std::fstream filenames
Windows OS uses UCS2/UTF-16 for its filenames so whatever your codepage, you can have files with any Unicode character. But this means that to access or create files with characters not on your codepage you must use std::wstring. There is no other way. This is a Microsoft specific extension to std::fstream so probably won't compile on other systems. If you use std::string then you can only utilise filenames that only include characters on your codepage.
Your options
If you are just working on Linux then you probably didn't get this far. Just use UTF-8 std::string everywhere.
If you are just working on Windows just use UCS2 std::wstring everywhere. Some purists may say use UTF8 then convert when needed, but why bother with the hassle.
If you are cross platform then it's a mess to be frank. If you try to use UTF-8 everywhere on Windows then you need to be really careful with your string literals and output to the console. You can easily corrupt your strings there. If you use std::wstring everywhere on Linux then you may not have access to the wide version of std::fstream, so you have to do the conversion, but there is no risk of corruption. So personally I think this is a better option. Many would disagree, but I'm not alone - it's the path taken by wxWidgets for example.
Another option could be to typedef unicodestring as std::string on Linux and std::wstring on Windows, and have a macro called UNI() which prefixes L on Windows and nothing on Linux, then the code
#include <fstream>
#include <string>
#include <iostream>
#include <Windows.h>
#ifdef _WIN32
typedef std::wstring unicodestring;
#define UNI(text) L ## text
std::string formatForConsole(const unicodestring &str)
{
std::string result;
//Call WideCharToMultiByte to do the conversion
return result;
}
#else
typedef std::string unicodestring;
#define UNI(text) text
std::string formatForConsole(const unicodestring &str)
{
return str;
}
#endif
int main()
{
unicodestring fileName(UNI("fileName"));
std::ofstream fout;
fout.open(fileName);
std::cout << formatForConsole(fileName) << std::endl;
return 0;
}
would be fine on either platform I think.
Answers
So To answer your questions
1) If you are programming for Windows, then all the time, if cross platform then maybe all the time, unless you want to deal with possible corruption issues on Windows or write some code with platform specific #ifdefs to work around the differences, if just using Linux then never.
2)Yes. In addition on Linux you can use it for all Unicode too. On Windows you can only use it for all unicode if you choose to manually encode using UTF-8. But the Windows API and standard C++ classes will expect the std::string to be encoded using the locale codepage. This includes all ASCII plus another 128 characters which change depending on the codepage your computer is setup to use.
3)I believe so, but if not then it is just a simple typedef of a 'std::basic_string' using wchar_t instead of char
4)A wide character is a character type which is bigger than the 1 byte standard char type. On Windows it is 2 bytes, on Linux it is 4 bytes.
Applications that are not satisfied with only 256 different characters have the options of either using wide characters (more than 8 bits) or a variable-length encoding (a multibyte encoding in C++ terminology) such as UTF-8. Wide characters generally require more space than a variable-length encoding, but are faster to process. Multi-language applications that process large amounts of text usually use wide characters when processing the text, but convert it to UTF-8 when storing it to disk.
The only difference between a string and a wstring is the data type of the characters they store. A string stores chars whose size is guaranteed to be at least 8 bits, so you can use strings for processing e.g. ASCII, ISO-8859-15, or UTF-8 text. The standard says nothing about the character set or encoding.
Practically every compiler uses a character set whose first 128 characters correspond with ASCII. This is also the case with compilers that use UTF-8 encoding. The important thing to be aware of when using strings in UTF-8 or some other variable-length encoding, is that the indices and lengths are measured in bytes, not characters.
The data type of a wstring is wchar_t, whose size is not defined in the standard, except that it has to be at least as large as a char, usually 16 bits or 32 bits. wstring can be used for processing text in the implementation defined wide-character encoding. Because the encoding is not defined in the standard, it is not straightforward to convert between strings and wstrings. One cannot assume wstrings to have a fixed-length encoding either.
If you don't need multi-language support, you might be fine with using only regular strings. On the other hand, if you're writing a graphical application, it is often the case that the API supports only wide characters. Then you probably want to use the same wide characters when processing the text. Keep in mind that UTF-16 is a variable-length encoding, meaning that you cannot assume length() to return the number of characters. If the API uses a fixed-length encoding, such as UCS-2, processing becomes easy. Converting between wide characters and UTF-8 is difficult to do in a portable way, but then again, your user interface API probably supports the conversion.
when you want to use Unicode strings and not just ascii, helpful for internationalisation
yes, but it doesn't play well with 0
not aware of any that don't
wide character is the compiler specific way of handling the fixed length representation of a unicode character, for MSVC it is a 2 byte character, for gcc I understand it is 4 bytes. and a +1 for http://www.joelonsoftware.com/articles/Unicode.html
If you keep portability for string, you can use tstring, tchar. It is widely used technique from long ago. In this sample, I use self-defined TCHAR, but you can find out tchar.h implementation for linux on internet.
This idea means that wstring/wchar_t/UTF-16 is used on windows and string/char/utf-8(or ASCII..) is used on Linux.
In the sample below, the searching of english/japanese multibyte mixed string works well on both windows/linux platforms.
#include <locale.h>
#include <stdio.h>
#include <algorithm>
#include <string>
using namespace std;
#ifdef _WIN32
#include <tchar.h>
#else
#define _TCHAR char
#define _T
#define _tprintf printf
#endif
#define tstring basic_string<_TCHAR>
int main() {
setlocale(LC_ALL, "");
tstring s = _T("abcあいうえおxyz");
auto pos = s.find(_T("え"));
auto r = s.substr(pos);
_tprintf(_T("r=%s\n"), r.c_str());
}
1) As mentioned by Greg, wstring is helpful for internationalization, that's when you will be releasing your product in languages other than english
4) Check this out for wide character
http://en.wikipedia.org/wiki/Wide_character
When should you NOT use wide-characters?
When you're writing code before the year 1990.
Obviously, I'm being flip, but really, it's the 21st century now. 127 characters have long since ceased to be sufficient. Yes, you can use UTF8, but why bother with the headaches?
Hello everybody and good afternoon. So I'm still new-ish to this scene but have quite the ambition for it and I've been trying to learn as much as i can. i consider myself to be adept in c++ but I've always programming DOS programs and recently I've broadened my horizons to the Windows API.... with that being said, I've noticed that Windows API is greatly intertwined with UNI-CODE while DOS used ANSI.. so i know that ANSI uses 8-bit character codes and UNI-CODE uses 16-bit.. so my questions are:
1) why is this important.. is it more specific or able to hold more information since its 16 bits verses 8? i mean i know that there are some characters that ANSI does not support that UNI-CODE does but is that it??
2) What's the difference between TCHAR and WCHAR and is it just the 16 bit version of char? if WCHAR is wide char then whats TCHAR?
3)I understand that LPWSTR is long pointer to wide string but when would you use this and why? is it just a windows thing? and isn't a long pointer automatically 16 bits? Does that mean a regular pointer is 8 bits? if so why would you need the extra bits?
4)Next why would you need wstring and would you need to use wchar and tchar with it for certain functions? i.e.
wstring myStr;
TCHAR myChar;
if (myStr.find(myChar) != string::npos) { krmormrm }
or does it matter..
char myChar;
if (myStr.find(myChar) != string::npos) { jnrnikvnr }
5) Last but not least, i had trouble displaying WCHAR and wstring or even int without a conversion.. for instance (i figured it out sort of) i did:
WCHAR myChar = '1';
int i = 2;
wstring myString;
ofstream File1("myFile.txt");
if (File1.is_open())
{
File1 << (char)myChar; //if i didn't typecast it to char it displayed 49 instead of 1;
File1 << (WCHAR)i; //if i didn't typecast it to WCHAR(like to char instead)it displays symbols
WCHAR temp;
copy(myString.begin(), myString.end(), temp);
File1 << (char)temp;
}
ok so i had a little problem with the wstring and copy. what i did in my real program (this was just a quick rescript) was took 9 WCHAR variables... used wstringstream to load them all into its variable(wss) and then into myString(my wstring variable)... so to make sure they all loaded correctly i copied it into a WCHAR temp to send it to file1 so i could physically see what loaded into it but for some reason it loaded the variables i wanted AND extra variables i didnt want and ive gone over the code multiple times and found nothing wrong.. so i got rid of the copy function and displayed each variable individually with a for loop like:
for (int i = 0; i < 81; i++)
{
File1 << "Box " << (WCHAR)i << ": " << (char)BoxNum[i] << "\n";
}
and i concluded everything held the correct values... just fyi i was inputting the values into a text box and retrieving the text and storing it in individual variables.. the text boxes are lined up 9 by 9... so there's 9 in a row and 9 in a column... and then i used the variables from the boxes in the first row and put it in myString so i could just use the string.find() function to check for numbers in that row instead of box by box.. my problem was displaying this wstring...... ANYWAYS lol sorry just trying to provide as much info as possible, maybe someone can solve that problem for me as well.
8 bit character encoding only allows 256 different characters, minus a lot of control characters. That's enough for English, but when you want to cover other European languages, like those containing strange characters like ößé or ø, this is simply not enough. Sure, you could use different codepages which place different characters on the higher 128 codepoints of an 8bit encoding, but what if you need to mix multiple languages in the same string? And what about languages like Chinese which have far more than 256 characters? But with 16 bits per character, you can use over 60.000 codepoints which is enough to cover the whole basic multilingual plane in a single codepage.
A WCHAR is always 16 bit. A TCHAR can be 8bit or 16bit, depending on whether you compile your program as an unicode program or not.
The difference between long-pointers and short-pointers is mostly historical and of not much concern on modern platforms (when you really want to know, check this question). The Windows API has a really long legacy dating back to the first Windows versions, so you find a lot of obsolete cruft in there. The length of a pointer depends on the kind of program. A 32bit program has 32bit long pointers and a 64bit program has 64bit long pointers. When you compile your program for 64bit, a LPWSTR will be a 64bit pointer (to a null-terminated array of 16-bit characters).
The first code will only work when TCHAR is 16bit, because in that case WCHAR and TCHAR are the same thing. When TCHAR is 8 bit, that code won't compile because the find-method requires the same type the string is made from.
When you write a 16bit string to a file, it gets written to the file as a 16bit string. When you then open it with a text editor and only see garbage, that's likely because your text editor interprets it with 8bit character encoding. Switch the encoding of the text editor to the encoding with which you wrote the file (UTF-16 might work). Or convert the wstring to a string before your write it, as described, in this question. But keep in mind that this can not work well when there are characters in your strings which can not be expressed with 8bit.
This question already has answers here:
How well is Unicode supported in C++11?
(5 answers)
Closed 9 years ago.
There are some posts on this matter but I wanted to double check.
In Joel Spoolsky's article (link) one reads:
In C++ code we just declare strings as wchar_t ("wide char") instead
of char and use the wcs functions instead of the str functions (for
example wcscat and wcslen instead of strcat and strlen). To create a
literal UCS-2 string in C code you just put an L before it as so:
L"Hello".
My question is: Is what is written above, not enough to support Unicodes in a C++ app?
My confusions started when I couldn't output simple text like (in Russian):
wcout<<L"логин";
in console.
Also, recently I saw some code written for an embedded device where one person handles I think Unicode related strings using wchar_t.
Any help greatly appreciated.
This works in C++11 on a linux, utf8 machine:
#include <iostream>
int main(int, char**) {
std::cout << u8"Humberto Massa Guimarães\nлогин\n";
}
First, you can not print non-english characters in command-line
Second, briefly; UNICODE uses two bytes for every character and char uses single byte. For example string "ABC" will be stored in char as ABC\0 (3 bytes + end_of_string_character)
but in UNICODE will be stored as A\0B\0C\0\0\0 (6 + end_of_string_character which is two bytes like other characters)
For view some text, I suggest you to MessageBoxW:
First include windows header file: #include <windows.h>
Second use MessageBoxW API function:
MessageBoxW(0, L"UNICODE text body", L"title", MB_ICONINFORMATION);
I've been using StackOverflow since the beginning, and have on occasion been tempted to post questions, but I've always either figured them out myself or found answers posted eventually... until now. This feels like it should be fairly simple, but I've been wandering around the internet for hours with no success, so I turn here:
I have a pretty standard utf-16 text file, with a mixture of English and Chinese characters. I would like those characters to end up in a string (technically, a wstring). I've seen a lot of related questions answered (here and elsewhere), but they're either looking to solve the much harder problem of reading arbitrary files without knowing the encoding, or converting between encodings, or are just generally confused about "Unicode" being a range of encodings. I know the source of the text file I'm trying to read, it will always be UTF16, it has a BOM and everything, and it can stay that way.
I had been using the solution described here, which worked for text files that were all English, but after encountering certain characters, it stopped reading the file. The only other suggestion I found was to use ICU, which would probably work, but I'd really rather not include a whole large library in an application for distribution, just to read one text file in one place. I don't care about system independence, though - I only need it to compile and work in Windows. A solution that didn't rely on that fact would prettier, of course, but I would be just as happy for a solution that used the stl while relying on assumptions about Windows architecture, or even solutions that involved win32 functions, or ATL; I just don't want to have to include another large 3rd-party library like ICU. Am I still totally out of luck unless I want to reimplement it all myself?
edit: I'm stuck using VS2008 for this particular project, so C++11 code sadly won't help.
edit 2: I realized that the code I had been borrowing before didn't fail on non-English characters like I thought it was doing. Rather, it fails on specific characters in my test document, among them '：' (FULLWIDTH COLON, U+FF1A) and '）' (FULLWIDTH RIGHT PARENTHESIS, U+FF09). bames53's posted solution also mostly works, but is stumped by those same characters?
edit 3 (and the answer!): the original code I had been using -did- mostly work - as bames53 helped me discover, the ifstream just needed to be opened in binary mode for it to work.
The C++11 solution (supported, on your platform, by Visual Studio since 2010, as far as I know), would be:
#include <fstream>
#include <iostream>
#include <locale>
#include <codecvt>
int main()
{
// open as a byte stream
std::wifstream fin("text.txt", std::ios::binary);
// apply BOM-sensitive UTF-16 facet
fin.imbue(std::locale(fin.getloc(),
new std::codecvt_utf16<wchar_t, 0x10ffff, std::consume_header>));
// read
for(wchar_t c; fin.get(c); )
std::cout << std::showbase << std::hex << c << '\n';
}
When you open a file for UTF-16, you must open it in binary mode. This is because in text mode, certain characters are interpreted specially - specifically, 0x0d is filtered out completely and 0x1a marks the end of the file. There are some UTF-16 characters that will have one of those bytes as half of the character code and will mess up the reading of the file. This is not a bug, it is intentional behavior and is the sole reason for having separate text and binary modes.
For the reason why 0x1a is considered the end of a file, see this blog post from Raymond Chen tracing the history of Ctrl-Z. It's basically backwards compatibility run amok.
Edit:
So it appears that the issue was that the Windows treats certain magic byte sequences as the end of the file in text mode. This is solved by using binary mode to read the file, std::ifstream fin("filename", std::ios::binary);, and then copying the data into a wstring as you already do.
The simplest, non-portable solution would be to just copy the file data into a wchar_t array. This relies on the fact that wchar_t on Windows is 2 bytes and uses UTF-16 as its encoding.
You'll have a bit of difficulty converting UTF-16 to the locale specific wchar_t encoding in a completely portable fashion.
Here's the unicode conversion functionality available in the standard C++ library (though VS 10 and 11 implement only items 3, 4, and 5)
codecvt<char32_t,char,mbstate_t>
codecvt<char16_t,char,mbstate_t>
codecvt_utf8
codecvt_utf16
codecvt_utf8_utf16
c32rtomb/mbrtoc32
c16rtomb/mbrtoc16
And what each one does
A codecvt facet that always converts between UTF-8 and UTF-32
converts between UTF-8 and UTF-16
converts between UTF-8 and UCS-2 or UCS-4 depending on the size of target element (characters outside BMP are probably truncated)
converts between a sequence of chars using a UTF-16 encoding scheme and UCS-2 or UCS-4
converts between UTF-8 and UTF-16
If the macro __STDC_UTF_32__ is defined these functions convert between the current locale's char encoding and UTF-32
If the macro __STDC_UTF_16__ is defined these functions convert between the current locale's char encoding and UTF-16
If __STDC_ISO_10646__ is defined then converting directly using codecvt_utf16<wchar_t> should be fine since that macro indicates that wchar_t values in all locales correspond to the short names of Unicode charters (and so implies that wchar_t is large enough to hold any such value).
Unfortunately there's nothing defined that goes directly from UTF-16 to wchar_t. It's possible to go UTF-16 -> UCS-4 -> mb (if __STDC_UTF_32__) -> wc, but you'll loose anything that's not representable in the locale's multi-byte encoding. And of course no matter what, converting from UTF-16 to wchar_t will lose anything not representable in the locale's wchar_t encoding.
So it's probably not worth being portable, and instead you can just read the data into a wchar_t array, or use some other Windows specific facility, such as the _O_U16TEXT mode on files.
This should build and run anywhere, but makes a bunch of assumptions to actually work:
#include <fstream>
#include <sstream>
#include <iostream>
int main ()
{
std::stringstream ss;
std::ifstream fin("filename");
ss << fin.rdbuf(); // dump file contents into a stringstream
std::string const &s = ss.str();
if (s.size()%sizeof(wchar_t) != 0)
{
std::cerr << "file not the right size\n"; // must be even, two bytes per code unit
return 1;
}
std::wstring ws;
ws.resize(s.size()/sizeof(wchar_t));
std::memcpy(&ws[0],s.c_str(),s.size()); // copy data into wstring
}
You should probably at least add code to handle endianess and the 'BOM'. Also Windows newlines don't get converted automatically so you need to do that manually.
I am not able to understand the differences between std::string and std::wstring. I know wstring supports wide characters such as Unicode characters. I have got the following questions:
When should I use std::wstring over std::string?
Can std::string hold the entire ASCII character set, including the special characters?
Is std::wstring supported by all popular C++ compilers?
What is exactly a "wide character"?
string? wstring?
std::string is a basic_string templated on a char, and std::wstring on a wchar_t.
char vs. wchar_t
char is supposed to hold a character, usually an 8-bit character.
wchar_t is supposed to hold a wide character, and then, things get tricky:
On Linux, a wchar_t is 4 bytes, while on Windows, it's 2 bytes.
What about Unicode, then?
The problem is that neither char nor wchar_t is directly tied to unicode.
On Linux?
Let's take a Linux OS: My Ubuntu system is already unicode aware. When I work with a char string, it is natively encoded in UTF-8 (i.e. Unicode string of chars). The following code:
#include <cstring>
#include <iostream>
int main()
{
const char text[] = "olé";
std::cout << "sizeof(char) : " << sizeof(char) << "\n";
std::cout << "text : " << text << "\n";
std::cout << "sizeof(text) : " << sizeof(text) << "\n";
std::cout << "strlen(text) : " << strlen(text) << "\n";
std::cout << "text(ordinals) :";
for(size_t i = 0, iMax = strlen(text); i < iMax; ++i)
{
unsigned char c = static_cast<unsigned_char>(text[i]);
std::cout << " " << static_cast<unsigned int>(c);
}
std::cout << "\n\n";
// - - -
const wchar_t wtext[] = L"olé" ;
std::cout << "sizeof(wchar_t) : " << sizeof(wchar_t) << "\n";
//std::cout << "wtext : " << wtext << "\n"; <- error
std::cout << "wtext : UNABLE TO CONVERT NATIVELY." << "\n";
std::wcout << L"wtext : " << wtext << "\n";
std::cout << "sizeof(wtext) : " << sizeof(wtext) << "\n";
std::cout << "wcslen(wtext) : " << wcslen(wtext) << "\n";
std::cout << "wtext(ordinals) :";
for(size_t i = 0, iMax = wcslen(wtext); i < iMax; ++i)
{
unsigned short wc = static_cast<unsigned short>(wtext[i]);
std::cout << " " << static_cast<unsigned int>(wc);
}
std::cout << "\n\n";
}
outputs the following text:
sizeof(char) : 1
text : olé
sizeof(text) : 5
strlen(text) : 4
text(ordinals) : 111 108 195 169
sizeof(wchar_t) : 4
wtext : UNABLE TO CONVERT NATIVELY.
wtext : ol�
sizeof(wtext) : 16
wcslen(wtext) : 3
wtext(ordinals) : 111 108 233
You'll see the "olé" text in char is really constructed by four chars: 110, 108, 195 and 169 (not counting the trailing zero). (I'll let you study the wchar_t code as an exercise)
So, when working with a char on Linux, you should usually end up using Unicode without even knowing it. And as std::string works with char, so std::string is already unicode-ready.
Note that std::string, like the C string API, will consider the "olé" string to have 4 characters, not three. So you should be cautious when truncating/playing with unicode chars because some combination of chars is forbidden in UTF-8.
On Windows?
On Windows, this is a bit different. Win32 had to support a lot of application working with char and on different charsets/codepages produced in all the world, before the advent of Unicode.
So their solution was an interesting one: If an application works with char, then the char strings are encoded/printed/shown on GUI labels using the local charset/codepage on the machine, which could not be UTF-8 for a long time. For example, "olé" would be "olé" in a French-localized Windows, but would be something different on an cyrillic-localized Windows ("olй" if you use Windows-1251). Thus, "historical apps" will usually still work the same old way.
For Unicode based applications, Windows uses wchar_t, which is 2-bytes wide, and is encoded in UTF-16, which is Unicode encoded on 2-bytes characters (or at the very least, UCS-2, which just lacks surrogate-pairs and thus characters outside the BMP (>= 64K)).
Applications using char are said "multibyte" (because each glyph is composed of one or more chars), while applications using wchar_t are said "widechar" (because each glyph is composed of one or two wchar_t. See MultiByteToWideChar and WideCharToMultiByte Win32 conversion API for more info.
Thus, if you work on Windows, you badly want to use wchar_t (unless you use a framework hiding that, like GTK or QT...). The fact is that behind the scenes, Windows works with wchar_t strings, so even historical applications will have their char strings converted in wchar_t when using API like SetWindowText() (low level API function to set the label on a Win32 GUI).
Memory issues?
UTF-32 is 4 bytes per characters, so there is no much to add, if only that a UTF-8 text and UTF-16 text will always use less or the same amount of memory than an UTF-32 text (and usually less).
If there is a memory issue, then you should know than for most western languages, UTF-8 text will use less memory than the same UTF-16 one.
Still, for other languages (chinese, japanese, etc.), the memory used will be either the same, or slightly larger for UTF-8 than for UTF-16.
All in all, UTF-16 will mostly use 2 and occassionally 4 bytes per characters (unless you're dealing with some kind of esoteric language glyphs (Klingon? Elvish?), while UTF-8 will spend from 1 to 4 bytes.
See https://en.wikipedia.org/wiki/UTF-8#Compared_to_UTF-16 for more info.
Conclusion
When I should use std::wstring over std::string?
On Linux? Almost never (§).
On Windows? Almost always (§).
On cross-platform code? Depends on your toolkit...
(§) : unless you use a toolkit/framework saying otherwise
Can std::string hold all the ASCII character set including special characters?
Notice: A std::string is suitable for holding a 'binary' buffer, where a std::wstring is not!
On Linux? Yes.
On Windows? Only special characters available for the current locale of the Windows user.
Edit (After a comment from Johann Gerell):
a std::string will be enough to handle all char-based strings (each char being a number from 0 to 255). But:
ASCII is supposed to go from 0 to 127. Higher chars are NOT ASCII.
a char from 0 to 127 will be held correctly
a char from 128 to 255 will have a signification depending on your encoding (unicode, non-unicode, etc.), but it will be able to hold all Unicode glyphs as long as they are encoded in UTF-8.
Is std::wstring supported by almost all popular C++ compilers?
Mostly, with the exception of GCC based compilers that are ported to Windows.
It works on my g++ 4.3.2 (under Linux), and I used Unicode API on Win32 since Visual C++ 6.
What is exactly a wide character?
On C/C++, it's a character type written wchar_t which is larger than the simple char character type. It is supposed to be used to put inside characters whose indices (like Unicode glyphs) are larger than 255 (or 127, depending...).
I recommend avoiding std::wstring on Windows or elsewhere, except when required by the interface, or anywhere near Windows API calls and respective encoding conversions as a syntactic sugar.
My view is summarized in http://utf8everywhere.org of which I am a co-author.
Unless your application is API-call-centric, e.g. mainly UI application, the suggestion is to store Unicode strings in std::string and encoded in UTF-8, performing conversion near API calls. The benefits outlined in the article outweigh the apparent annoyance of conversion, especially in complex applications. This is doubly so for multi-platform and library development.
And now, answering your questions:
A few weak reasons. It exists for historical reasons, where widechars were believed to be the proper way of supporting Unicode. It is now used to interface APIs that prefer UTF-16 strings. I use them only in the direct vicinity of such API calls.
This has nothing to do with std::string. It can hold whatever encoding you put in it. The only question is how You treat its content. My recommendation is UTF-8, so it will be able to hold all Unicode characters correctly. It's a common practice on Linux, but I think Windows programs should do it also.
No.
Wide character is a confusing name. In the early days of Unicode, there was a belief that a character can be encoded in two bytes, hence the name. Today, it stands for "any part of the character that is two bytes long". UTF-16 is seen as a sequence of such byte pairs (aka Wide characters). A character in UTF-16 takes either one or two pairs.
So, every reader here now should have a clear understanding about the facts, the situation. If not, then you must read paercebal's outstandingly comprehensive answer [btw: thanks!].
My pragmatical conclusion is shockingly simple: all that C++ (and STL) "character encoding" stuff is substantially broken and useless. Blame it on Microsoft or not, that will not help anyway.
My solution, after in-depth investigation, much frustration and the consequential experiences is the following:
accept, that you have to be responsible on your own for the encoding and conversion stuff (and you will see that much of it is rather trivial)
use std::string for any UTF-8 encoded strings (just a typedef std::string UTF8String)
accept that such an UTF8String object is just a dumb, but cheap container. Do never ever access and/or manipulate characters in it directly (no search, replace, and so on). You could, but you really just really, really do not want to waste your time writing text manipulation algorithms for multi-byte strings! Even if other people already did such stupid things, don't do that! Let it be! (Well, there are scenarios where it makes sense... just use the ICU library for those).
use std::wstring for UCS-2 encoded strings (typedef std::wstring UCS2String) - this is a compromise, and a concession to the mess that the WIN32 API introduced). UCS-2 is sufficient for most of us (more on that later...).
use UCS2String instances whenever a character-by-character access is required (read, manipulate, and so on). Any character-based processing should be done in a NON-multibyte-representation. It is simple, fast, easy.
add two utility functions to convert back & forth between UTF-8 and UCS-2:
UCS2String ConvertToUCS2( const UTF8String &str );
UTF8String ConvertToUTF8( const UCS2String &str );
The conversions are straightforward, google should help here ...
That's it. Use UTF8String wherever memory is precious and for all UTF-8 I/O. Use UCS2String wherever the string must be parsed and/or manipulated. You can convert between those two representations any time.
Alternatives & Improvements
conversions from & to single-byte character encodings (e.g. ISO-8859-1) can be realized with help of plain translation tables, e.g. const wchar_t tt_iso88951[256] = {0,1,2,...}; and appropriate code for conversion to & from UCS2.
if UCS-2 is not sufficient, than switch to UCS-4 (typedef std::basic_string<uint32_t> UCS2String)
ICU or other unicode libraries?
For advanced stuff.
When you want to have wide characters stored in your string. wide depends on the implementation. Visual C++ defaults to 16 bit if i remember correctly, while GCC defaults depending on the target. It's 32 bits long here. Please note wchar_t (wide character type) has nothing to do with unicode. It's merely guaranteed that it can store all the members of the largest character set that the implementation supports by its locales, and at least as long as char. You can store unicode strings fine into std::string using the utf-8 encoding too. But it won't understand the meaning of unicode code points. So str.size() won't give you the amount of logical characters in your string, but merely the amount of char or wchar_t elements stored in that string/wstring. For that reason, the gtk/glib C++ wrapper folks have developed a Glib::ustring class that can handle utf-8.
If your wchar_t is 32 bits long, then you can use utf-32 as an unicode encoding, and you can store and handle unicode strings using a fixed (utf-32 is fixed length) encoding. This means your wstring's s.size() function will then return the right amount of wchar_t elements and logical characters.
Yes, char is always at least 8 bit long, which means it can store all ASCII values.
Yes, all major compilers support it.
I frequently use std::string to hold utf-8 characters without any problems at all. I heartily recommend doing this when interfacing with API's which use utf-8 as the native string type as well.
For example, I use utf-8 when interfacing my code with the Tcl interpreter.
The major caveat is the length of the std::string, is no longer the number of characters in the string.
A good question!
I think DATA ENCODING (sometimes a CHARSET also involved) is a MEMORY EXPRESSION MECHANISM in order to save data to a file or transfer data via a network, so I answer this question as:
1. When should I use std::wstring over std::string?
If the programming platform or API function is a single-byte one, and we want to process or parse some Unicode data, e.g read from Windows'.REG file or network 2-byte stream, we should declare std::wstring variable to easily process them. e.g.: wstring ws=L"中国a"(6 octets memory: 0x4E2D 0x56FD 0x0061), we can use ws[0] to get character '中' and ws[1] to get character '国' and ws[2] to get character 'a', etc.
2. Can std::string hold the entire ASCII character set, including the special characters?
Yes. But notice: American ASCII, means each 0x00~0xFF octet stands for one character, including printable text such as "123abc&*_&" and you said special one, mostly print it as a '.' avoid confusing editors or terminals. And some other countries extend their own "ASCII" charset, e.g. Chinese, use 2 octets to stand for one character.
3.Is std::wstring supported by all popular C++ compilers?
Maybe, or mostly. I have used: VC++6 and GCC 3.3, YES
4. What is exactly a "wide character"?
a wide character mostly indicates using 2 octets or 4 octets to hold all countries' characters. 2 octet UCS2 is a representative sample, and further e.g. English 'a', its memory is 2 octet of 0x0061(vs in ASCII 'a's memory is 1 octet 0x61)
When you want to store 'wide' (Unicode) characters.
Yes: 255 of them (excluding 0).
Yes.
Here's an introductory article: http://www.joelonsoftware.com/articles/Unicode.html
There are some very good answers here, but I think there are a couple of things I can add regarding Windows/Visual Studio. Tis is based on my experience with VS2015. On Linux, basically the answer is to use UTF-8 encoded std::string everywhere. On Windows/VS it gets more complex. Here is why. Windows expects strings stored using chars to be encoded using the locale codepage. This is almost always the ASCII character set followed by 128 other special characters depending on your location. Let me just state that this in not just when using the Windows API, there are three other major places where these strings interact with standard C++. These are string literals, output to std::cout using << and passing a filename to std::fstream.
I will be up front here that I am a programmer, not a language specialist. I appreciate that USC2 and UTF-16 are not the same, but for my purposes they are close enough to be interchangeable and I use them as such here. I'm not actually sure which Windows uses, but I generally don't need to know either. I've stated UCS2 in this answer, so sorry in advance if I upset anyone with my ignorance of this matter and I'm happy to change it if I have things wrong.
String literals
If you enter string literals that contain only characters that can be represented by your codepage then VS stores them in your file with 1 byte per character encoding based on your codepage. Note that if you change your codepage or give your source to another developer using a different code page then I think (but haven't tested) that the character will end up different. If you run your code on a computer using a different code page then I'm not sure if the character will change too.
If you enter any string literals that cannot be represented by your codepage then VS will ask you to save the file as Unicode. The file will then be encoded as UTF-8. This means that all Non ASCII characters (including those which are on your codepage) will be represented by 2 or more bytes. This means if you give your source to someone else the source will look the same. However, before passing the source to the compiler, VS converts the UTF-8 encoded text to code page encoded text and any characters missing from the code page are replaced with ?.
The only way to guarantee correctly representing a Unicode string literal in VS is to precede the string literal with an L making it a wide string literal. In this case VS will convert the UTF-8 encoded text from the file into UCS2. You then need to pass this string literal into a std::wstring constructor or you need to convert it to utf-8 and put it in a std::string. Or if you want you can use the Windows API functions to encode it using your code page to put it in a std::string, but then you may as well have not used a wide string literal.
std::cout
When outputting to the console using << you can only use std::string, not std::wstring and the text must be encoded using your locale codepage. If you have a std::wstring then you must convert it using one of the Windows API functions and any characters not on your codepage get replaced by ? (maybe you can change the character, I can't remember).
std::fstream filenames
Windows OS uses UCS2/UTF-16 for its filenames so whatever your codepage, you can have files with any Unicode character. But this means that to access or create files with characters not on your codepage you must use std::wstring. There is no other way. This is a Microsoft specific extension to std::fstream so probably won't compile on other systems. If you use std::string then you can only utilise filenames that only include characters on your codepage.
Your options
If you are just working on Linux then you probably didn't get this far. Just use UTF-8 std::string everywhere.
If you are just working on Windows just use UCS2 std::wstring everywhere. Some purists may say use UTF8 then convert when needed, but why bother with the hassle.
If you are cross platform then it's a mess to be frank. If you try to use UTF-8 everywhere on Windows then you need to be really careful with your string literals and output to the console. You can easily corrupt your strings there. If you use std::wstring everywhere on Linux then you may not have access to the wide version of std::fstream, so you have to do the conversion, but there is no risk of corruption. So personally I think this is a better option. Many would disagree, but I'm not alone - it's the path taken by wxWidgets for example.
Another option could be to typedef unicodestring as std::string on Linux and std::wstring on Windows, and have a macro called UNI() which prefixes L on Windows and nothing on Linux, then the code
#include <fstream>
#include <string>
#include <iostream>
#include <Windows.h>
#ifdef _WIN32
typedef std::wstring unicodestring;
#define UNI(text) L ## text
std::string formatForConsole(const unicodestring &str)
{
std::string result;
//Call WideCharToMultiByte to do the conversion
return result;
}
#else
typedef std::string unicodestring;
#define UNI(text) text
std::string formatForConsole(const unicodestring &str)
{
return str;
}
#endif
int main()
{
unicodestring fileName(UNI("fileName"));
std::ofstream fout;
fout.open(fileName);
std::cout << formatForConsole(fileName) << std::endl;
return 0;
}
would be fine on either platform I think.
Answers
So To answer your questions
1) If you are programming for Windows, then all the time, if cross platform then maybe all the time, unless you want to deal with possible corruption issues on Windows or write some code with platform specific #ifdefs to work around the differences, if just using Linux then never.
2)Yes. In addition on Linux you can use it for all Unicode too. On Windows you can only use it for all unicode if you choose to manually encode using UTF-8. But the Windows API and standard C++ classes will expect the std::string to be encoded using the locale codepage. This includes all ASCII plus another 128 characters which change depending on the codepage your computer is setup to use.
3)I believe so, but if not then it is just a simple typedef of a 'std::basic_string' using wchar_t instead of char
4)A wide character is a character type which is bigger than the 1 byte standard char type. On Windows it is 2 bytes, on Linux it is 4 bytes.
Applications that are not satisfied with only 256 different characters have the options of either using wide characters (more than 8 bits) or a variable-length encoding (a multibyte encoding in C++ terminology) such as UTF-8. Wide characters generally require more space than a variable-length encoding, but are faster to process. Multi-language applications that process large amounts of text usually use wide characters when processing the text, but convert it to UTF-8 when storing it to disk.
The only difference between a string and a wstring is the data type of the characters they store. A string stores chars whose size is guaranteed to be at least 8 bits, so you can use strings for processing e.g. ASCII, ISO-8859-15, or UTF-8 text. The standard says nothing about the character set or encoding.
Practically every compiler uses a character set whose first 128 characters correspond with ASCII. This is also the case with compilers that use UTF-8 encoding. The important thing to be aware of when using strings in UTF-8 or some other variable-length encoding, is that the indices and lengths are measured in bytes, not characters.
The data type of a wstring is wchar_t, whose size is not defined in the standard, except that it has to be at least as large as a char, usually 16 bits or 32 bits. wstring can be used for processing text in the implementation defined wide-character encoding. Because the encoding is not defined in the standard, it is not straightforward to convert between strings and wstrings. One cannot assume wstrings to have a fixed-length encoding either.
If you don't need multi-language support, you might be fine with using only regular strings. On the other hand, if you're writing a graphical application, it is often the case that the API supports only wide characters. Then you probably want to use the same wide characters when processing the text. Keep in mind that UTF-16 is a variable-length encoding, meaning that you cannot assume length() to return the number of characters. If the API uses a fixed-length encoding, such as UCS-2, processing becomes easy. Converting between wide characters and UTF-8 is difficult to do in a portable way, but then again, your user interface API probably supports the conversion.
when you want to use Unicode strings and not just ascii, helpful for internationalisation
yes, but it doesn't play well with 0
not aware of any that don't
wide character is the compiler specific way of handling the fixed length representation of a unicode character, for MSVC it is a 2 byte character, for gcc I understand it is 4 bytes. and a +1 for http://www.joelonsoftware.com/articles/Unicode.html
If you keep portability for string, you can use tstring, tchar. It is widely used technique from long ago. In this sample, I use self-defined TCHAR, but you can find out tchar.h implementation for linux on internet.
This idea means that wstring/wchar_t/UTF-16 is used on windows and string/char/utf-8(or ASCII..) is used on Linux.
In the sample below, the searching of english/japanese multibyte mixed string works well on both windows/linux platforms.
#include <locale.h>
#include <stdio.h>
#include <algorithm>
#include <string>
using namespace std;
#ifdef _WIN32
#include <tchar.h>
#else
#define _TCHAR char
#define _T
#define _tprintf printf
#endif
#define tstring basic_string<_TCHAR>
int main() {
setlocale(LC_ALL, "");
tstring s = _T("abcあいうえおxyz");
auto pos = s.find(_T("え"));
auto r = s.substr(pos);
_tprintf(_T("r=%s\n"), r.c_str());
}
1) As mentioned by Greg, wstring is helpful for internationalization, that's when you will be releasing your product in languages other than english
4) Check this out for wide character
http://en.wikipedia.org/wiki/Wide_character
When should you NOT use wide-characters?
When you're writing code before the year 1990.
Obviously, I'm being flip, but really, it's the 21st century now. 127 characters have long since ceased to be sufficient. Yes, you can use UTF8, but why bother with the headaches?