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Unicode support in wxWidgets

This section briefly describes the state of the Unicode support in wxWidgets. Read it if you want to know more about how to write programs able to work with characters from languages other than English.

What is Unicode?
Unicode and ANSI modes
Unicode support in wxWidgets
Unicode and the outside world
Unicode-related compilation settings


What is Unicode?

Starting with release 2.1 wxWidgets has support for compiling in Unicode mode on the platforms which support it. Unicode is a standard for character encoding which addresses the shortcomings of the previous, 8 bit standards, by using at least 16 (and possibly 32) bits for encoding each character. This allows to have at least 65536 characters (what is called the BMP, or basic multilingual plane) and possible 2^32 of them instead of the usual 256 and is sufficient to encode all of the world languages at once. More details about Unicode may be found at www.unicode.org.

As this solution is obviously preferable to the previous ones (think of incompatible encodings for the same language, locale chaos and so on), many modern operating systems support it. The probably first example is Windows NT which uses only Unicode internally since its very first version.

Writing internationalized programs is much easier with Unicode and, as the support for it improves, it should become more and more so. Moreover, in the Windows NT/2000 case, even the program which uses only standard ASCII can profit from using Unicode because they will work more efficiently - there will be no need for the system to convert all strings the program uses to/from Unicode each time a system call is made.


Unicode and ANSI modes

As not all platforms supported by wxWidgets support Unicode (fully) yet, in many cases it is unwise to write a program which can only work in Unicode environment. A better solution is to write programs in such way that they may be compiled either in ANSI (traditional) mode or in the Unicode one.

This can be achieved quite simply by using the means provided by wxWidgets. Basically, there are only a few things to watch out for:

Let's look at them in order. First of all, each character in an Unicode program takes 2 bytes instead of usual one, so another type should be used to store the characters (char only holds 1 byte usually). This type is called wchar_t which stands for wide-character type.

Also, the string and character constants should be encoded using wide characters (wchar_t type) which typically take 2 or 4 bytes instead of char which only takes one. This is achieved by using the standard C (and C++) way: just put the letter 'L' after any string constant and it becomes a long constant, i.e. a wide character one. To make things a bit more readable, you are also allowed to prefix the constant with 'L' instead of putting it after it.

Of course, the usual standard C functions don't work with wchar_t strings, so another set of functions exists which do the same thing but accept wchar_t * instead of char *. For example, a function to get the length of a wide-character string is called wcslen() (compare with strlen() - you see that the only difference is that the "str" prefix standing for "string" has been replaced with "wcs" standing for "wide-character string").

And finally, the standard preprocessor tokens enumerated above expand to ANSI strings but it is more likely that Unicode strings are wanted in the Unicode build. wxWidgets provides the macros __TFILE__, __TDATE__ and __TTIME__ which behave exactly as the standard ones except that they produce ANSI strings in ANSI build and Unicode ones in the Unicode build.

To summarize, here is a brief example of how a program which can be compiled in both ANSI and Unicode modes could look like:

#ifdef __UNICODE__
    wchar_t wch = L'*';
    const wchar_t *ws = L"Hello, world!";
    int len = wcslen(ws);

    wprintf(L"Compiled at %s\n", __TDATE__);
#else // ANSI
    char ch = '*';
    const char *s = "Hello, world!";
    int len = strlen(s);

    printf("Compiled at %s\n", __DATE__);
#endif // Unicode/ANSI
Of course, it would be nearly impossibly to write such programs if it had to be done this way (try to imagine the number of #ifdef UNICODE an average program would have had!). Luckily, there is another way - see the next section.


Unicode support in wxWidgets

In wxWidgets, the code fragment from above should be written instead:

    wxChar ch = wxT('*');
    wxString s = wxT("Hello, world!");
    int len = s.Len();
What happens here? First of all, you see that there are no more #ifdefs at all. Instead, we define some types and macros which behave differently in the Unicode and ANSI builds and allows us to avoid using conditional compilation in the program itself.

We have a wxChar type which maps either on char or wchar_t depending on the mode in which program is being compiled. There is no need for a separate type for strings though, because the standard wxString supports Unicode, i.e. it stores either ANSI or Unicode strings depending on the compile mode.

Finally, there is a special wxT() macro which should enclose all literal strings in the program. As it is easy to see comparing the last fragment with the one above, this macro expands to nothing in the (usual) ANSI mode and prefixes 'L' to its argument in the Unicode mode.

The important conclusion is that if you use wxChar instead of char, avoid using C style strings and use wxString instead and don't forget to enclose all string literals inside wxT() macro, your program automatically becomes (almost) Unicode compliant!

Just let us state once again the rules:


Unicode and the outside world

We have seen that it was easy to write Unicode programs using wxWidgets types and macros, but it has been also mentioned that it isn't quite enough. Although everything works fine inside the program, things can get nasty when it tries to communicate with the outside world which, sadly, often expects ANSI strings (a notable exception is the entire Win32 API which accepts either Unicode or ANSI strings and which thus makes it unnecessary to ever perform any conversions in the program). GTK 2.0 only accepts UTF-8 strings.

To get a ANSI string from a wxString, you may use the mb_str() function which always returns an ANSI string (independently of the mode - while the usual c_str() returns a pointer to the internal representation which is either ASCII or Unicode). More rarely used, but still useful, is wc_str() function which always returns the Unicode string.


Unicode-related compilation settings

You should define wxUSE_UNICODE to 1 to compile your program in Unicode mode. Note that it currently only works in Win32 and GTK 2.0 and that some parts of wxWidgets are not Unicode-compliant yet (ODBC classes, for example). If you compile your program in ANSI mode you can still define wxUSE_WCHAR_T to get some limited support for wchar_t type.

This will allow your program to perform conversions between Unicode strings and ANSI ones (wxEncodingConverter depends on this partially) and construct wxString objects from Unicode strings (presumably read from some external file or elsewhere).