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 addresses 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 operating 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 the 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 Basically, there are only a few things to watch out for:
  50
  51 \begin{itemize}
  52 \item Character type ({\tt char} or {\tt wchar\_t})
  53 \item Literal strings (i.e. {\tt "Hello, world!"} or {\tt '*'})
  54 \item String functions ({\tt strlen()}, {\tt strcpy()}, ...)
  55 \end{itemize}
  56
  57 Let's look at them in order. First of all, each character in an Unicode
  58 program takes 2 bytes instead of usual one, so another type should be used to
  59 store the characters ({\tt char} only holds 1 byte usually). This type is
  60 called {\tt wchar\_t} which stands for {\it wide-character type}.
  61
  62 Also, the string and character constants should be encoded on 2 bytes instead
  63 of one. This is achieved by using the standard C (and C++) way: just put the
  64 letter {\tt 'L'} after any string constant and it becomes a {\it long}
  65 constant, i.e. a wide character one. To make things a bit more readable, you
  66 are also allowed to prefix the constant with {\tt 'L'} instead of putting it
  67 after it.
  68
  69 Finally, the standard C functions don't work with {\tt wchar\_t} strings, so
  70 another set of functions exists which do the same thing but accept
  71 {\tt wchar\_t *} instead of {\tt char *}. For example, a function to get the
  72 length of a wide-character string is called {\tt wcslen()} (compare with
  73 {\tt strlen()} - you see that the only difference is that the "str" prefix
  74 standing for "string" has been replaced with "wcs" standing for
  75 "wide-character string").
  76
  77 To summarize, here is a brief example of how a program which can be compiled
  78 in both ANSI and Unicode modes could look like:
  79
  80 \begin{verbatim}
  81 #ifdef __UNICODE__
  82     wchar_t wch = L'*';
  83     const wchar_t *ws = L"Hello, world!";
  84     int len = wcslen(ws);
  85 #else // ANSI
  86     char ch = '*';
  87     const char *s = "Hello, world!";
  88     int len = strlen(s);
  89 #endif // Unicode/ANSI
  90 \end{verbatim}
  91
  92 Of course, it would be nearly impossibly to write such programs if it had to
  93 be done this way (try to imagine the number of {\tt \#ifdef UNICODE} an average
  94 program would have had!). Luckily, there is another way - see the next
  95 section.
  96
  97 \subsection{Unicode support in wxWindows}
  98
  99 In wxWindows, the code fragment from above should be written instead:
 100
 101 \begin{verbatim}
 102     wxChar ch = wxT('*');
 103     wxString s = wxT("Hello, world!");
 104     int len = s.Len();
 105 \end{verbatim}
 106
 107 What happens here? First of all, you see that there are no more {\tt \#ifdef}s
 108 at all. Instead, we define some types and macros which behave differently in
 109 the Unicode and ANSI builds and allows us to avoid using conditional
 110 compilation in the program itself.
 111
 112 We have a {\tt wxChar} type which maps either on {\tt char} or {\tt wchar\_t}
 113 depending on the mode in which program is being compiled. There is no need for
 114 a separate type for strings though, because the standard
 115 \helpref{wxString}{wxstring} supports Unicode, i.e. it stores either ANSI or
 116 Unicode strings depending on the compile mode.
 117
 118 Finally, there is a special {\tt wxT()} macro which should enclose all literal
 119 strings in the program. As it is easy to see comparing the last fragment with
 120 the one above, this macro expands to nothing in the (usual) ANSI mode and
 121 prefixes {\tt 'L'} to its argument in the Unicode mode.
 122
 123 The important conclusion is that if you use {\tt wxChar} instead of
 124 {\tt char}, avoid using C style strings and use {\tt wxString} instead and
 125 don't forget to enclose all string literals inside {\tt wxT()} macro, your
 126 program automatically becomes (almost) Unicode compliant!
 127
 128 Just let us state once again the rules:
 129
 130 \begin{itemize}
 131 \item Always use {\tt wxChar} instead of {\tt char}
 132 \item Always enclose literal string constants in {\tt wxT()} macro unless
 133 they're already converted to the right representation (another standard
 134 wxWindows macro {\tt \_()} does it, so there is no need for {\tt wxT()} in this
 135 case) or you intend to pass the constant directly to an external function
 136 which doesn't accept wide-character strings.
 137 \item Use {\tt wxString} instead of C style strings.
 138 \end{itemize}
 139
 140 \subsection{Unicode and the outside world}
 141
 142 We have seen that it was easy to write Unicode programs using wxWindows types
 143 and macros, but it has been also mentioned that it isn't quite enough.
 144 Although everything works fine inside the program, things can get nasty when
 145 it tries to communicate with the outside world which, sadly, often expects
 146 ANSI strings (a notable exception is the entire Win32 API which accepts either
 147 Unicode or ANSI strings and which thus makes it unnecessary to ever perform
 148 any conversions in the program).
 149
 150 To get a ANSI string from a wxString, you may use the
 151 mb\_str() function which always returns an ANSI
 152 string (independently of the mode - while the usual
 153 \helpref{c\_str()}{wxstringcstr} returns a pointer to the internal
 154 representation which is either ASCII or Unicode). More rarely used, but still
 155 useful, is wc\_str() function which always returns
 156 the Unicode string.
 157
 158 % TODO describe fn_str(), wx_str(), wxCharBuf classes, ...
 159
 160 \subsection{Unicode-related compilation settings}
 161
 162 You should define {\tt wxUSE\_UNICODE} to $1$ to compile your program in
 163 Unicode mode. Note that it currently only works in Win32 and that some parts of
 164 wxWindows are not Unicode-compliant yet (ODBC classes, for example). If you
 165 compile your program in ANSI mode you can still define {\tt wxUSE\_WCHAR\_T}
 166 to get some limited support for {\tt wchar\_t} type.
 167
 168 This will allow your program to perform conversions between Unicode strings and
 169 ANSI ones (\helpref{wxEncodingConverter}{wxencodingconverter} depends on this
 170 partially) and construct wxString objects from Unicode strings (presumably read
 171 from some external file or elsewhere).
 172