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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