docs/latex/wx/tunicode.tex

   1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   2 %% Name:        tunicode.tex
   3 %% Purpose:     Overview of the Unicode support in wxWindows
   4 %% Author:      Vadim Zeitlin
   5 %% Modified by:
   6 %% Created:     22.09.99
   7 %% RCS-ID:      $Id$
   8 %% Copyright:   (c) 1999 Vadim Zeitlin <zeitlin@dptmaths.ens-cachan.fr>
   9 %% Licence:     wxWindows license
  10 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  11
  12 \section{Unicode support in wxWindows}\label{unicode}
  13
  14 This section briefly describes the state of the Unicode support in wxWindows.
  15 Read it if you want to know more about how to write programs able to work with
  16 characters from languages other than English.
  17
  18 \subsection{What is Unicode?}
  19
  20 Starting with release 2.1 wxWindows has support for compiling in Unicode mode
  21 on the platforms which support it. Unicode is a standard for character
  22 encoding which addreses the shortcomings of the previous, 8 bit standards, by
  23 using 16 bit for encoding each character. This allows to have 65536 characters
  24 instead of the usual 256 and is sufficient to encode all of the world
  25 languages at once. More details about Unicode may be found at {\tt www.unicode.org}.
  26
  27 % TODO expand on it, say that Unicode extends ASCII, mention ISO8859, ...
  28
  29 As this solution is obviously preferable to the previous ones (think of
  30 incompatible encodings for the same language, locale chaos and so on), many
  31 modern ooperating systems support it. The probably first example is Windows NT
  32 which uses only Unicode internally since its very first version.
  33
  34 Writing internationalized programs is much easier with Unicode and, as the
  35 support for it improves, it should become more and more so. Moreover, in the
  36 Windows NT/2000 case, even the program which uses only standard ASCII can profit
  37 from using Unicode because they will work more efficiently - there will be no
  38 need for the system to convert all strings hte program uses to/from Unicode
  39 each time a system call is made.
  40
  41 \subsection{Unicode and ANSI modes}
  42
  43 As not all platforms supported by wxWindows support Unicode (fully) yet, in
  44 many cases it is unwise to write a program which can only work in Unicode
  45 environment. A better solution is to write programs in such way that they may
  46 be compiled either in ANSI (traditional) mode or in the Unicode one.
  47
  48 This can be achieved quite simply by using the means provided by wxWindows.
  49 Basicly, there are only a few things to watch out for:
  50 \begin{itemize}
  51 \item Character type ({\tt char} or {\tt wchar\_t})
  52 \item Literal strings (i.e. {\tt "Hello, world!"} or {\tt '*'})
  53 \item String functions ({\tt strlen()}, {\tt strcpy()}, ...)
  54 \end{itemize}
  55
  56 Let's look at them in order. First of all, each character in an Unicode
  57 program takes 2 bytes instead of usual one, so another type should be used to
  58 store the characters ({\tt char} only holds 1 byte usually). This type is
  59 called {\tt wchar\_t} which stands for {\it wide-character type}.
  60
  61 Also, the string and character constants should be encoded on 2 bytes instead
  62 of one. This is achieved by using the standard C (and C++) way: just put the
  63 letter {\tt 'L'} after any string constant and it becomes a {\it long}
  64 constant, i.e. a wide character one. To make things a bit more readable, you
  65 are also allowed to prefix the constant with {\tt 'L'} instead of putting it
  66 after it.
  67
  68 Finally, the standard C functions don't work with {\tt wchar\_t} strings, so
  69 another set of functions exists which do the same thing but accept
  70 {\tt wchar\_t *} instead of {\tt char *}. For example, a function to get the
  71 length of a wide-character string is called {\tt wcslen()} (compare with
  72 {\tt strlen()} - you see that the only difference is that the "str" prefix
  73 standing for "string" has been replaced with "wcs" standing for
  74 "wide-character string").
  75
  76 To summarize, here is a brief example of how a program which can be compiled
  77 in both ANSI and Unicode modes could look like:
  78
  79 \begin{verbatim}
  80 #ifdef __UNICODE__
  81     wchar_t wch = L'*';
  82     const wchar_t *ws = L"Hello, world!";
  83     int len = wcslen(ws);
  84 #else // ANSI
  85     char ch = '*';
  86     const char *s = "Hello, world!";
  87     int len = strlen(s);
  88 #endif // Unicode/ANSI
  89 \end{verbatim}
  90
  91 Of course, it would be nearly impossibly to write such programs if it had to
  92 be done this way (try to imagine the number of {\tt #ifdef UNICODE} an average
  93 program would have had!). Luckily, there is another way - see the next
  94 section.
  95
  96 \subsection{Unicode support in wxWindows}
  97
  98 In wxWindows, the code fragment froim above should be written instead:
  99
 100 \begin{verbatim}
 101     wxChar ch = T('*');
 102     wxString s = T("Hello, world!");
 103     int len = s.Len();
 104 \end{verbatim}
 105
 106 What happens here? First of all, you see that there are no more {\tt #ifdef}s
 107 at all. Instead, we define some types and macros which behave differently in
 108 the Unicode and ANSI builds and allows us to avoid using conditional
 109 compilation in the program itself.
 110
 111 We have a {\tt wxChar} type which maps either on {\tt char} or {\tt wchar\_t}
 112 depending on the mode in which program is being compiled. There is no need for
 113 a separate type for strings though, because the standard
 114 \helpref{wxString}{wxstring} supports Unicode, i.e. it stores iether ANSI or
 115 Unicode strings depending on the mode.
 116
 117 Finally, there is a special {\tt T()} macro which should enclose all literal
 118 strings in the program. As it's easy to see comparing the last fragment with
 119 the one above, this macro expands to nothing in the (usual) ANSI mode and
 120 prefixes {\tt 'L'} to its argument in the Unicode mode.
 121
 122 The important conclusion is that if you use {\tt wxChar} instead of
 123 {\tt char}, avoid using C style strings and use {\tt wxString} instead and
 124 don't forget to enclose all string literals inside {\tt T()} macro, your
 125 program automatically becomes (almost) Unicode compliant!
 126
 127 Just let us state once again the rules:
 128 \begin{itemize}
 129 \item Always use {\tt wxChar} instead of {\tt char}
 130 \item Always enclose literal string constants in {\tt T()} macro unless
 131 they're already converted to the right representation (another standard
 132 wxWindows macro {\tt \_()} does it, so there is no need for {\tt T()} in this
 133 case) or you intend to pass the constant directly to an external function
 134 which doesn't accept wide-character strings.
 135 \item Use {\tt wxString} instead of C style strings.
 136 \end{itemize}
 137
 138 \subsection{Unicode and the outside world}
 139
 140 We have seen that it was easy to write Unicode programs using wxWindows types
 141 and macros, but it has been also mentioned that it isn't quite enough.
 142 Although everything works fine inside the program, things can get nasty when
 143 it tries to communicate with the outside world which, sadly, often expects
 144 ANSI strings (a notable exception is the entire Win32 API which accepts either
 145 Unicode or ANSI strings and which thus makes it unnecessary to ever perform
 146 any convertions in the program).
 147
 148 To get a ANSI string from a wxString, you may use
 149 \helpref{mb\_str()}{wxstringmbstr} function which always returns an ANSI
 150 string (independently of the mode - while the usual
 151 \helpref{c\_str()}{wxstringcstr} returns a pointer to the internal
 152 representation which is either ASCII or Unicode). More rarely used, but still
 153 useful, is \helpref{wc\_str()}{wxstringwcstr} function which always returns
 154 the Unicode string.
 155
 156 % TODO describe fn_str(), wx_str(), wxCharBuf classes, ...