added initial version of the Doxygen manual
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Francesco Montorsi
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docs/doxygen/overviews/unicode.h
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docs/doxygen/overviews/unicode.h
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/////////////////////////////////////////////////////////////////////////////
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// Name: unicode
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// Purpose: topic overview
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// Author: wxWidgets team
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// RCS-ID: $Id$
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// Licence: wxWindows license
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/////////////////////////////////////////////////////////////////////////////
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/*!
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@page unicode_overview Unicode support in wxWidgets
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This section briefly describes the state of the Unicode support in wxWidgets.
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Read it if you want to know more about how to write programs able to work with
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characters from languages other than English.
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@ref whatisunicode_overview
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@ref unicodeandansi_overview
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@ref unicodeinsidewxw_overview
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@ref unicodeoutsidewxw_overview
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@ref unicodesettings_overview
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@ref topic8_overview
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@section whatisunicode What is Unicode?
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wxWidgets has support for compiling in Unicode mode
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on the platforms which support it. Unicode is a standard for character
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encoding which addresses the shortcomings of the previous, 8 bit standards, by
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using at least 16 (and possibly 32) bits for encoding each character. This
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allows to have at least 65536 characters (what is called the BMP, or basic
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multilingual plane) and possible 2^32 of them instead of the usual 256 and
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is sufficient to encode all of the world languages at once. More details about
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Unicode may be found at #http://www.unicode.org.
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As this solution is obviously preferable to the previous ones (think of
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incompatible encodings for the same language, locale chaos and so on), many
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modern operating systems support it. The probably first example is Windows NT
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which uses only Unicode internally since its very first version.
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Writing internationalized programs is much easier with Unicode and, as the
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support for it improves, it should become more and more so. Moreover, in the
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Windows NT/2000 case, even the program which uses only standard ASCII can profit
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from using Unicode because they will work more efficiently - there will be no
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need for the system to convert all strings the program uses to/from Unicode
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each time a system call is made.
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@section unicodeandansi Unicode and ANSI modes
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As not all platforms supported by wxWidgets support Unicode (fully) yet, in
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many cases it is unwise to write a program which can only work in Unicode
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environment. A better solution is to write programs in such way that they may
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be compiled either in ANSI (traditional) mode or in the Unicode one.
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This can be achieved quite simply by using the means provided by wxWidgets.
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Basically, there are only a few things to watch out for:
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Character type (@c char or @c wchar_t)
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Literal strings (i.e. @c "Hello, world!" or @c '*')
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String functions (@c strlen(), @c strcpy(), ...)
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Special preprocessor tokens (@c __FILE__, @c __DATE__
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and @c __TIME__)
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Let's look at them in order. First of all, each character in an Unicode
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program takes 2 bytes instead of usual one, so another type should be used to
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store the characters (@c char only holds 1 byte usually). This type is
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called @c wchar_t which stands for @e wide-character type.
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Also, the string and character constants should be encoded using wide
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characters (@c wchar_t type) which typically take 2 or 4 bytes instead
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of @c char which only takes one. This is achieved by using the standard C
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(and C++) way: just put the letter @c 'L' after any string constant and it
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becomes a @e long constant, i.e. a wide character one. To make things a bit
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more readable, you are also allowed to prefix the constant with @c 'L'
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instead of putting it after it.
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Of course, the usual standard C functions don't work with @c wchar_t
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strings, so another set of functions exists which do the same thing but accept
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@c wchar_t * instead of @c char *. For example, a function to get the
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length of a wide-character string is called @c wcslen() (compare with
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@c strlen() - you see that the only difference is that the "str" prefix
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standing for "string" has been replaced with "wcs" standing for "wide-character
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string").
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And finally, the standard preprocessor tokens enumerated above expand to ANSI
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strings but it is more likely that Unicode strings are wanted in the Unicode
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build. wxWidgets provides the macros @c __TFILE__, @c __TDATE__
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and @c __TTIME__ which behave exactly as the standard ones except that
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they produce ANSI strings in ANSI build and Unicode ones in the Unicode build.
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To summarize, here is a brief example of how a program which can be compiled
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in both ANSI and Unicode modes could look like:
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@code
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#ifdef __UNICODE__
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wchar_t wch = L'*';
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const wchar_t *ws = L"Hello, world!";
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int len = wcslen(ws);
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wprintf(L"Compiled at %s\n", __TDATE__);
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#else // ANSI
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char ch = '*';
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const char *s = "Hello, world!";
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int len = strlen(s);
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printf("Compiled at %s\n", __DATE__);
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#endif // Unicode/ANSI
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@endcode
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Of course, it would be nearly impossibly to write such programs if it had to
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be done this way (try to imagine the number of @c #ifdef UNICODE an average
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program would have had!). Luckily, there is another way - see the next
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section.
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@section unicodeinsidewxw Unicode support in wxWidgets
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In wxWidgets, the code fragment from above should be written instead:
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@code
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wxChar ch = wxT('*');
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wxString s = wxT("Hello, world!");
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int len = s.Len();
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@endcode
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What happens here? First of all, you see that there are no more @c #ifdefs
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at all. Instead, we define some types and macros which behave differently in
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the Unicode and ANSI builds and allow us to avoid using conditional
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compilation in the program itself.
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We have a @c wxChar type which maps either on @c char or @c wchar_t
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depending on the mode in which program is being compiled. There is no need for
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a separate type for strings though, because the standard
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#wxString supports Unicode, i.e. it stores either ANSI or
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Unicode strings depending on the compile mode.
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Finally, there is a special #wxT() macro which should enclose all
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literal strings in the program. As it is easy to see comparing the last
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fragment with the one above, this macro expands to nothing in the (usual) ANSI
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mode and prefixes @c 'L' to its argument in the Unicode mode.
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The important conclusion is that if you use @c wxChar instead of
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@c char, avoid using C style strings and use @c wxString instead and
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don't forget to enclose all string literals inside #wxT() macro, your
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program automatically becomes (almost) Unicode compliant!
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Just let us state once again the rules:
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Always use @c wxChar instead of @c char
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Always enclose literal string constants in #wxT() macro
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unless they're already converted to the right representation (another standard
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wxWidgets macro #_() does it, for example, so there is no
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need for @c wxT() in this case) or you intend to pass the constant directly
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to an external function which doesn't accept wide-character strings.
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Use @c wxString instead of C style strings.
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@section unicodeoutsidewxw Unicode and the outside world
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We have seen that it was easy to write Unicode programs using wxWidgets types
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and macros, but it has been also mentioned that it isn't quite enough.
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Although everything works fine inside the program, things can get nasty when
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it tries to communicate with the outside world which, sadly, often expects
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ANSI strings (a notable exception is the entire Win32 API which accepts either
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Unicode or ANSI strings and which thus makes it unnecessary to ever perform
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any conversions in the program). GTK 2.0 only accepts UTF-8 strings.
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To get an ANSI string from a wxString, you may use the
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mb_str() function which always returns an ANSI
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string (independently of the mode - while the usual
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#c_str() returns a pointer to the internal
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representation which is either ASCII or Unicode). More rarely used, but still
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useful, is wc_str() function which always returns
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the Unicode string.
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Sometimes it is also necessary to go from ANSI strings to wxStrings.
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In this case, you can use the converter-constructor, as follows:
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@code
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const char* ascii_str = "Some text";
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wxString str(ascii_str, wxConvUTF8);
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@endcode
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This code also compiles fine under a non-Unicode build of wxWidgets,
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but in that case the converter is ignored.
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For more information about converters and Unicode see
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the @ref mbconvclasses_overview.
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@section unicodesettings Unicode-related compilation settings
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You should define @c wxUSE_UNICODE to 1 to compile your program in
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Unicode mode. This currently works for wxMSW, wxGTK, wxMac and wxX11. If you
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compile your program in ANSI mode you can still define @c wxUSE_WCHAR_T
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to get some limited support for @c wchar_t type.
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This will allow your program to perform conversions between Unicode strings and
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ANSI ones (using @ref mbconvclasses_overview)
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and construct wxString objects from Unicode strings (presumably read
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from some external file or elsewhere).
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@section topic8 Traps for the unwary
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Casting c_str() to void* is now char*, not wxChar*
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Passing c_str(), mb_str() or wc_str() to variadic functions
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doesn't work
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*/
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