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 at least 16 (and possibly 32) bits for encoding each character. This
  24 allows to have at least 65536 characters (what is called the BMP, or basic
  25 multilingual plane) and possible $2^{32}$ of them instead of the usual 256 and
  26 is sufficient to encode all of the world languages at once. More details about
  27 Unicode may be found at {\tt www.unicode.org}.
  28
  29 % TODO expand on it, say that Unicode extends ASCII, mention ISO8859, ...
  30
  31 As this solution is obviously preferable to the previous ones (think of
  32 incompatible encodings for the same language, locale chaos and so on), many
  33 modern operating systems support it. The probably first example is Windows NT
  34 which uses only Unicode internally since its very first version.
  35
  36 Writing internationalized programs is much easier with Unicode and, as the
  37 support for it improves, it should become more and more so. Moreover, in the
  38 Windows NT/2000 case, even the program which uses only standard ASCII can profit
  39 from using Unicode because they will work more efficiently - there will be no
  40 need for the system to convert all strings the program uses to/from Unicode
  41 each time a system call is made.
  42
  43 \subsection{Unicode and ANSI modes}
  44
  45 As not all platforms supported by wxWindows support Unicode (fully) yet, in
  46 many cases it is unwise to write a program which can only work in Unicode
  47 environment. A better solution is to write programs in such way that they may
  48 be compiled either in ANSI (traditional) mode or in the Unicode one.
  49
  50 This can be achieved quite simply by using the means provided by wxWindows.
  51 Basically, there are only a few things to watch out for:
  52
  53 \begin{itemize}
  54 \item Character type ({\tt char} or {\tt wchar\_t})
  55 \item Literal strings (i.e. {\tt "Hello, world!"} or {\tt '*'})
  56 \item String functions ({\tt strlen()}, {\tt strcpy()}, ...)
  57 \item Special preprocessor tokens ({\tt \_\_FILE\_\_}, {\tt \_\_DATE\_\_}
  58 and {\tt \_\_TIME\_\_})
  59 \end{itemize}
  60
  61 Let's look at them in order. First of all, each character in an Unicode
  62 program takes 2 bytes instead of usual one, so another type should be used to
  63 store the characters ({\tt char} only holds 1 byte usually). This type is
  64 called {\tt wchar\_t} which stands for {\it wide-character type}.
  65
  66 Also, the string and character constants should be encoded using wide
  67 characters ({\tt wchar\_t} type) which typically take $2$ or $4$ bytes instead
  68 of {\tt char} which only takes one. This is achieved by using the standard C
  69 (and C++) way: just put the letter {\tt 'L'} after any string constant and it
  70 becomes a {\it long} constant, i.e. a wide character one. To make things a bit
  71 more readable, you are also allowed to prefix the constant with {\tt 'L'}
  72 instead of putting it after it.
  73
  74 Of course, the usual standard C functions don't work with {\tt wchar\_t}
  75 strings, so another set of functions exists which do the same thing but accept
  76 {\tt wchar\_t *} instead of {\tt char *}. For example, a function to get the
  77 length of a wide-character string is called {\tt wcslen()} (compare with
  78 {\tt strlen()} - you see that the only difference is that the "str" prefix
  79 standing for "string" has been replaced with "wcs" standing for "wide-character
  80 string").
  81
  82 And finally, the standard preprocessor tokens enumerated above expand to ANSI
  83 strings but it is more likely that Unicode strings are wanted in the Unicode
  84 build. wxWindows provides the macros {\tt \_\_TFILE\_\_}, {\tt \_\_TDATE\_\_}
  85 and {\tt \_\_TTIME\_\_} which behave exactly as the standard ones except that
  86 they produce ANSI strings in ANSI build and Unicode ones in the Unicode build.
  87
  88 To summarize, here is a brief example of how a program which can be compiled
  89 in both ANSI and Unicode modes could look like:
  90
  91 \begin{verbatim}
  92 #ifdef __UNICODE__
  93     wchar_t wch = L'*';
  94     const wchar_t *ws = L"Hello, world!";
  95     int len = wcslen(ws);
  96
  97     wprintf(L"Compiled at %s\n", __TDATE__);
  98 #else // ANSI
  99     char ch = '*';
 100     const char *s = "Hello, world!";
 101     int len = strlen(s);
 102
 103     printf("Compiled at %s\n", __DATE__);
 104 #endif // Unicode/ANSI
 105 \end{verbatim}
 106
 107 Of course, it would be nearly impossibly to write such programs if it had to
 108 be done this way (try to imagine the number of {\tt \#ifdef UNICODE} an average
 109 program would have had!). Luckily, there is another way - see the next
 110 section.
 111
 112 \subsection{Unicode support in wxWindows}
 113
 114 In wxWindows, the code fragment from above should be written instead:
 115
 116 \begin{verbatim}
 117     wxChar ch = wxT('*');
 118     wxString s = wxT("Hello, world!");
 119     int len = s.Len();
 120 \end{verbatim}
 121
 122 What happens here? First of all, you see that there are no more {\tt \#ifdef}s
 123 at all. Instead, we define some types and macros which behave differently in
 124 the Unicode and ANSI builds and allows us to avoid using conditional
 125 compilation in the program itself.
 126
 127 We have a {\tt wxChar} type which maps either on {\tt char} or {\tt wchar\_t}
 128 depending on the mode in which program is being compiled. There is no need for
 129 a separate type for strings though, because the standard
 130 \helpref{wxString}{wxstring} supports Unicode, i.e. it stores either ANSI or
 131 Unicode strings depending on the compile mode.
 132
 133 Finally, there is a special {\tt wxT()} macro which should enclose all literal
 134 strings in the program. As it is easy to see comparing the last fragment with
 135 the one above, this macro expands to nothing in the (usual) ANSI mode and
 136 prefixes {\tt 'L'} to its argument in the Unicode mode.
 137
 138 The important conclusion is that if you use {\tt wxChar} instead of
 139 {\tt char}, avoid using C style strings and use {\tt wxString} instead and
 140 don't forget to enclose all string literals inside {\tt wxT()} macro, your
 141 program automatically becomes (almost) Unicode compliant!
 142
 143 Just let us state once again the rules:
 144
 145 \begin{itemize}
 146 \item Always use {\tt wxChar} instead of {\tt char}
 147 \item Always enclose literal string constants in {\tt wxT()} macro unless
 148 they're already converted to the right representation (another standard
 149 wxWindows macro {\tt \_()} does it, so there is no need for {\tt wxT()} in this
 150 case) or you intend to pass the constant directly to an external function
 151 which doesn't accept wide-character strings.
 152 \item Use {\tt wxString} instead of C style strings.
 153 \end{itemize}
 154
 155 \subsection{Unicode and the outside world}
 156
 157 We have seen that it was easy to write Unicode programs using wxWindows types
 158 and macros, but it has been also mentioned that it isn't quite enough.
 159 Although everything works fine inside the program, things can get nasty when
 160 it tries to communicate with the outside world which, sadly, often expects
 161 ANSI strings (a notable exception is the entire Win32 API which accepts either
 162 Unicode or ANSI strings and which thus makes it unnecessary to ever perform
 163 any conversions in the program).
 164
 165 To get a ANSI string from a wxString, you may use the
 166 mb\_str() function which always returns an ANSI
 167 string (independently of the mode - while the usual
 168 \helpref{c\_str()}{wxstringcstr} returns a pointer to the internal
 169 representation which is either ASCII or Unicode). More rarely used, but still
 170 useful, is wc\_str() function which always returns
 171 the Unicode string.
 172
 173 % TODO describe fn_str(), wx_str(), wxCharBuf classes, ...
 174
 175 \subsection{Unicode-related compilation settings}
 176
 177 You should define {\tt wxUSE\_UNICODE} to $1$ to compile your program in
 178 Unicode mode. Note that it currently only works in Win32 and that some parts of
 179 wxWindows are not Unicode-compliant yet (ODBC classes, for example). If you
 180 compile your program in ANSI mode you can still define {\tt wxUSE\_WCHAR\_T}
 181 to get some limited support for {\tt wchar\_t} type.
 182
 183 This will allow your program to perform conversions between Unicode strings and
 184 ANSI ones (\helpref{wxEncodingConverter}{wxencodingconverter} depends on this
 185 partially) and construct wxString objects from Unicode strings (presumably read
 186 from some external file or elsewhere).
 187