880efa2a13
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52448 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
208 lines
8.8 KiB
C
208 lines
8.8 KiB
C
/////////////////////////////////////////////////////////////////////////////
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// Name: unicode.h
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// Purpose: topic overview
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// Author: wxWidgets team
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// RCS-ID: $Id$
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// Licence: wxWindows license
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/////////////////////////////////////////////////////////////////////////////
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/**
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@page overview_unicode Unicode Support in wxWidgets
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This section briefly describes the state of the Unicode support in wxWidgets.
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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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@li @ref overview_unicode_what
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@li @ref overview_unicode_ansi
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@li @ref overview_unicode_supportin
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@li @ref overview_unicode_supportout
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@li @ref overview_unicode_settings
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@li @ref overview_unicode_traps
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<hr>
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@section overview_unicode_what What is Unicode?
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wxWidgets has support for compiling in Unicode mode on the platforms which
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support it. Unicode is a standard for character encoding which addresses the
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shortcomings of the previous, 8 bit standards, by using at least 16 (and
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possibly 32) bits for encoding each character. This allows to have at least
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65536 characters (what is called the BMP, or basic multilingual plane) and
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possible 2^32 of them instead of the usual 256 and is sufficient to encode all
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of the world languages at once. More details about Unicode may be found at
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<http://www.unicode.org/>.
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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 operating 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
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profit from using Unicode because they will work more efficiently - there will
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be no need for the system to convert all strings the program uses to/from
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Unicode each time a system call is made.
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@section overview_unicode_ansi Unicode and ANSI Modes
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As not all platforms supported by wxWidgets 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 wxWidgets.
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Basically, there are only a few things to watch out for:
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- Character type (@c char or @c wchar_t)
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- Literal strings (i.e. @c "Hello, world!" or @c '*')
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- String functions (@c strlen(), @c strcpy(), ...)
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- Special preprocessor tokens (@c __FILE__, @c __DATE__ and @c __TIME__)
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Let's look at them in order. First of all, each character in an Unicode program
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takes 2 bytes instead of usual one, so another type should be used to store the
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characters (@c char only holds 1 byte usually). This type is called @c wchar_t
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which stands for @e wide-character type.
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Also, the string and character constants should be encoded using wide
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characters (@c wchar_t type) which typically take 2 or 4 bytes instead of
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@c char which only takes one. This is achieved by using the standard C (and
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C++) way: just put the letter @c 'L' after any string constant and it becomes a
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@e long constant, i.e. a wide character one. To make things a bit more
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readable, you are also allowed to prefix the constant with @c 'L' instead of
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putting it after it.
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Of course, the usual standard C functions don't work with @c wchar_t strings,
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so another set of functions exists which do the same thing but accept
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@c wchar_t* instead of @c char*. For example, a function to get the length of a
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wide-character string is called @c wcslen() (compare with @c strlen() - you see
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that the only difference is that the "str" prefix standing for "string" has
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been replaced with "wcs" standing for "wide-character string").
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And finally, the standard preprocessor tokens enumerated above expand to ANSI
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strings but it is more likely that Unicode strings are wanted in the Unicode
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build. wxWidgets provides the macros @c __TFILE__, @c __TDATE__ and
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@c __TTIME__ which behave exactly as the standard ones except that they produce
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ANSI strings in ANSI build and Unicode ones in the Unicode build.
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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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@code
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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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wprintf(L"Compiled at %s\n", __TDATE__);
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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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printf("Compiled at %s\n", __DATE__);
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#endif // Unicode/ANSI
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@endcode
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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 UNICODE checkes an average
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program would have had!). Luckily, there is another way - see the next section.
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@section overview_unicode_supportin Unicode Support in wxWidgets
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In wxWidgets, the code fragment from above should be written instead:
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@code
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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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@endcode
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What happens here? First of all, you see that there are no more UNICODE checks
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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 allow us to avoid using conditional compilation
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in the program itself.
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We have a @c wxChar type which maps either on @c char or @c wchar_t depending
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on the mode in which program is being compiled. There is no need for a separate
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type for strings though, because the standard wxString supports Unicode, i.e.
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it stores either ANSI or Unicode strings depending on the compile mode.
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Finally, there is a special wxT() macro which should enclose all literal
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strings in the program. As it is 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 @c 'L' to its argument in the Unicode mode.
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The important conclusion is that if you use @c wxChar instead of @c char, avoid
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using C style strings and use @c wxString instead and don't forget to enclose
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all string literals inside wxT() macro, your program automatically becomes
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(almost) Unicode compliant!
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Just let us state once again the rules:
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@li Always use wxChar instead of @c char
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@li Always enclose literal string constants in wxT() macro unless they're
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already converted to the right representation (another standard wxWidgets
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macro _() does it, for example, so there is no need for wxT() in this case)
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or you intend to pass the constant directly to an external function which
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doesn't accept wide-character strings.
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@li Use wxString instead of C style strings.
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@section overview_unicode_supportout Unicode and the Outside World
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We have seen that it was easy to write Unicode programs using wxWidgets types
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and macros, but it has been also mentioned that it isn't quite enough. Although
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everything works fine inside the program, things can get nasty when it tries to
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communicate with the outside world which, sadly, often expects ANSI strings (a
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notable exception is the entire Win32 API which accepts either Unicode or ANSI
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strings and which thus makes it unnecessary to ever perform any conversions in
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the program). GTK 2.0 only accepts UTF-8 strings.
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To get an ANSI string from a wxString, you may use the mb_str() function which
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always returns an ANSI string (independently of the mode - while the usual
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c_str() returns a pointer to the internal representation which is either ASCII
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or Unicode). More rarely used, but still useful, is wc_str() function which
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always returns the Unicode string.
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Sometimes it is also necessary to go from ANSI strings to wxStrings. In this
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case, you can use the converter-constructor, as follows:
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@code
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const char* ascii_str = "Some text";
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wxString str(ascii_str, wxConvUTF8);
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@endcode
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This code also compiles fine under a non-Unicode build of wxWidgets, but in
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that case the converter is ignored.
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For more information about converters and Unicode see the @ref overview_mbconv.
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@section overview_unicode_settings Unicode Related Compilation Settings
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You should define @c wxUSE_UNICODE to 1 to compile your program in Unicode
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mode. This currently works for wxMSW, wxGTK, wxMac and wxX11. If you compile
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your program in ANSI mode you can still define @c wxUSE_WCHAR_T to get some
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limited support for @c wchar_t type.
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This will allow your program to perform conversions between Unicode strings and
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ANSI ones (using @ref overview_mbconv "wxMBConv") and construct wxString
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objects from Unicode strings (presumably read from some external file or
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elsewhere).
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@section overview_unicode_traps Traps for the Unwary
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@li Casting c_str() to void* is now char*, not wxChar*
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@li Passing c_str(), mb_str() or wc_str() to variadic functions doesn't work.
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*/
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