605d715ddd
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@5109 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
161 lines
7.2 KiB
TeX
161 lines
7.2 KiB
TeX
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%% Name: tunicode.tex
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%% Purpose: Overview of the Unicode support in wxWindows
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%% Author: Vadim Zeitlin
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%% Modified by:
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%% Created: 22.09.99
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%% RCS-ID: $Id$
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%% Copyright: (c) 1999 Vadim Zeitlin <zeitlin@dptmaths.ens-cachan.fr>
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%% Licence: wxWindows license
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{Unicode support in wxWindows}\label{unicode}
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This section briefly describes the state of the Unicode support in wxWindows.
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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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\subsection{What is Unicode?}
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Starting with release 2.1 wxWindows 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 addreses the shortcomings of the previous, 8 bit standards, by
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using 16 bit for encoding each character. This allows to have 65536 characters
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instead of the usual 256 and is sufficient to encode all of the world
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languages at once. More details about Unicode may be found at {\tt www.unicode.org}.
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% TODO expand on it, say that Unicode extends ASCII, mention ISO8859, ...
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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 ooperating 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 hte program uses to/from Unicode
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each time a system call is made.
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\subsection{Unicode and ANSI modes}
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As not all platforms supported by wxWindows 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 wxWindows.
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Basicly, there are only a few things to watch out for:
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\begin{itemize}
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\item Character type ({\tt char} or {\tt wchar\_t})
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\item Literal strings (i.e. {\tt "Hello, world!"} or {\tt '*'})
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\item String functions ({\tt strlen()}, {\tt strcpy()}, ...)
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\end{itemize}
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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 ({\tt char} only holds 1 byte usually). This type is
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called {\tt wchar\_t} which stands for {\it wide-character type}.
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Also, the string and character constants should be encoded on 2 bytes instead
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of one. This is achieved by using the standard C (and C++) way: just put the
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letter {\tt 'L'} after any string constant and it becomes a {\it long}
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constant, i.e. a wide character one. To make things a bit more readable, you
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are also allowed to prefix the constant with {\tt 'L'} instead of putting it
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after it.
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Finally, the standard C functions don't work with {\tt wchar\_t} strings, so
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another set of functions exists which do the same thing but accept
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{\tt wchar\_t *} instead of {\tt char *}. For example, a function to get the
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length of a wide-character string is called {\tt wcslen()} (compare with
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{\tt 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
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"wide-character string").
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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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\begin{verbatim}
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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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#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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#endif // Unicode/ANSI
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\end{verbatim}
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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 {\tt \#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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\subsection{Unicode support in wxWindows}
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In wxWindows, the code fragment froim above should be written instead:
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\begin{verbatim}
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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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\end{verbatim}
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What happens here? First of all, you see that there are no more {\tt \#ifdef}s
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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 allows us to avoid using conditional
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compilation in the program itself.
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We have a {\tt wxChar} type which maps either on {\tt char} or {\tt 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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\helpref{wxString}{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 {\tt wxT()} macro which should enclose all literal
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strings in the program. As it's easy to see comparing the last fragment with
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the one above, this macro expands to nothing in the (usual) ANSI mode and
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prefixes {\tt 'L'} to its argument in the Unicode mode.
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The important conclusion is that if you use {\tt wxChar} instead of
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{\tt char}, avoid using C style strings and use {\tt wxString} instead and
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don't forget to enclose all string literals inside {\tt 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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\begin{itemize}
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\item Always use {\tt wxChar} instead of {\tt char}
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\item Always enclose literal string constants in {\tt wxT()} macro unless
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they're already converted to the right representation (another standard
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wxWindows macro {\tt \_()} does it, so there is no need for {\tt wxT()} in this
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case) or you intend to pass the constant directly to an external function
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which doesn't accept wide-character strings.
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\item Use {\tt wxString} instead of C style strings.
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\end{itemize}
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\subsection{Unicode and the outside world}
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We have seen that it was easy to write Unicode programs using wxWindows 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 convertions in the program).
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To get a 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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\helpref{c\_str()}{wxstringcstr} 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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% TODO describe fn_str(), wx_str(), wxCharBuf classes, ...
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% Please remember to put a blank line at the end of each file! (Tex2RTF 'issue')
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