docs/doxygen/overviews/unicode.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        unicode
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /*!
  10
  11  @page unicode_overview Unicode support in wxWidgets
  12
  13  This section briefly describes the state of the Unicode support in wxWidgets.
  14  Read it if you want to know more about how to write programs able to work with
  15  characters from languages other than English.
  16  @ref whatisunicode_overview
  17  @ref unicodeandansi_overview
  18  @ref unicodeinsidewxw_overview
  19  @ref unicodeoutsidewxw_overview
  20  @ref unicodesettings_overview
  21  @ref topic8_overview
  22
  23
  24  @section whatisunicode What is Unicode?
  25
  26  wxWidgets has support for compiling in Unicode mode
  27  on the platforms which support it. Unicode is a standard for character
  28  encoding which addresses the shortcomings of the previous, 8 bit standards, by
  29  using at least 16 (and possibly 32) bits for encoding each character. This
  30  allows to have at least 65536 characters (what is called the BMP, or basic
  31  multilingual plane) and possible 2^32 of them instead of the usual 256 and
  32  is sufficient to encode all of the world languages at once. More details about
  33  Unicode may be found at #http://www.unicode.org.
  34  As this solution is obviously preferable to the previous ones (think of
  35  incompatible encodings for the same language, locale chaos and so on), many
  36  modern operating systems support it. The probably first example is Windows NT
  37  which uses only Unicode internally since its very first version.
  38  Writing internationalized programs is much easier with Unicode and, as the
  39  support for it improves, it should become more and more so. Moreover, in the
  40  Windows NT/2000 case, even the program which uses only standard ASCII can profit
  41  from using Unicode because they will work more efficiently - there will be no
  42  need for the system to convert all strings the program uses to/from Unicode
  43  each time a system call is made.
  44
  45  @section unicodeandansi Unicode and ANSI modes
  46
  47  As not all platforms supported by wxWidgets support Unicode (fully) yet, in
  48  many cases it is unwise to write a program which can only work in Unicode
  49  environment. A better solution is to write programs in such way that they may
  50  be compiled either in ANSI (traditional) mode or in the Unicode one.
  51  This can be achieved quite simply by using the means provided by wxWidgets.
  52  Basically, there are only a few things to watch out for:
  53
  54
  55   Character type (@c char or @c wchar_t)
  56   Literal strings (i.e. @c "Hello, world!" or @c '*')
  57   String functions (@c strlen(), @c strcpy(), ...)
  58   Special preprocessor tokens (@c __FILE__, @c __DATE__
  59  and @c __TIME__)
  60
  61
  62  Let's look at them in order. First of all, each character in an Unicode
  63  program takes 2 bytes instead of usual one, so another type should be used to
  64  store the characters (@c char only holds 1 byte usually). This type is
  65  called @c wchar_t which stands for @e wide-character type.
  66  Also, the string and character constants should be encoded using wide
  67  characters (@c wchar_t type) which typically take 2 or 4 bytes instead
  68  of @c char which only takes one. This is achieved by using the standard C
  69  (and C++) way: just put the letter @c 'L' after any string constant and it
  70  becomes a @e 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 @c 'L'
  72  instead of putting it after it.
  73  Of course, the usual standard C functions don't work with @c wchar_t
  74  strings, so another set of functions exists which do the same thing but accept
  75  @c wchar_t * instead of @c char *. For example, a function to get the
  76  length of a wide-character string is called @c wcslen() (compare with
  77  @c strlen() - you see that the only difference is that the "str" prefix
  78  standing for "string" has been replaced with "wcs" standing for "wide-character
  79  string").
  80  And finally, the standard preprocessor tokens enumerated above expand to ANSI
  81  strings but it is more likely that Unicode strings are wanted in the Unicode
  82  build. wxWidgets provides the macros @c __TFILE__, @c __TDATE__
  83  and @c __TTIME__ which behave exactly as the standard ones except that
  84  they produce ANSI strings in ANSI build and Unicode ones in the Unicode build.
  85  To summarize, here is a brief example of how a program which can be compiled
  86  in both ANSI and Unicode modes could look like:
  87
  88  @code
  89  #ifdef __UNICODE__
  90      wchar_t wch = L'*';
  91      const wchar_t *ws = L"Hello, world!";
  92      int len = wcslen(ws);
  93
  94      wprintf(L"Compiled at %s\n", __TDATE__);
  95  #else // ANSI
  96      char ch = '*';
  97      const char *s = "Hello, world!";
  98      int len = strlen(s);
  99
 100      printf("Compiled at %s\n", __DATE__);
 101  #endif // Unicode/ANSI
 102  @endcode
 103
 104  Of course, it would be nearly impossibly to write such programs if it had to
 105  be done this way (try to imagine the number of @c #ifdef UNICODE an average
 106  program would have had!). Luckily, there is another way - see the next
 107  section.
 108
 109  @section unicodeinsidewxw Unicode support in wxWidgets
 110
 111  In wxWidgets, the code fragment from above should be written instead:
 112
 113  @code
 114  wxChar ch = wxT('*');
 115      wxString s = wxT("Hello, world!");
 116      int len = s.Len();
 117  @endcode
 118
 119  What happens here? First of all, you see that there are no more @c #ifdefs
 120  at all. Instead, we define some types and macros which behave differently in
 121  the Unicode and ANSI builds and allow us to avoid using conditional
 122  compilation in the program itself.
 123  We have a @c wxChar type which maps either on @c char or @c wchar_t
 124  depending on the mode in which program is being compiled. There is no need for
 125  a separate type for strings though, because the standard
 126  #wxString supports Unicode, i.e. it stores either ANSI or
 127  Unicode strings depending on the compile mode.
 128  Finally, there is a special #wxT() macro which should enclose all
 129  literal strings in the program. As it is easy to see comparing the last
 130  fragment with the one above, this macro expands to nothing in the (usual) ANSI
 131  mode and prefixes @c 'L' to its argument in the Unicode mode.
 132  The important conclusion is that if you use @c wxChar instead of
 133  @c char, avoid using C style strings and use @c wxString instead and
 134  don't forget to enclose all string literals inside #wxT() macro, your
 135  program automatically becomes (almost) Unicode compliant!
 136  Just let us state once again the rules:
 137
 138
 139   Always use @c wxChar instead of @c char
 140   Always enclose literal string constants in #wxT() macro
 141  unless they're already converted to the right representation (another standard
 142  wxWidgets macro #_() does it, for example, so there is no
 143  need for @c wxT() in this case) or you intend to pass the constant directly
 144  to an external function which doesn't accept wide-character strings.
 145   Use @c wxString instead of C style strings.
 146
 147
 148
 149  @section unicodeoutsidewxw Unicode and the outside world
 150
 151  We have seen that it was easy to write Unicode programs using wxWidgets types
 152  and macros, but it has been also mentioned that it isn't quite enough.
 153  Although everything works fine inside the program, things can get nasty when
 154  it tries to communicate with the outside world which, sadly, often expects
 155  ANSI strings (a notable exception is the entire Win32 API which accepts either
 156  Unicode or ANSI strings and which thus makes it unnecessary to ever perform
 157  any conversions in the program). GTK 2.0 only accepts UTF-8 strings.
 158  To get an ANSI string from a wxString, you may use the
 159  mb_str() function which always returns an ANSI
 160  string (independently of the mode - while the usual
 161  #c_str() returns a pointer to the internal
 162  representation which is either ASCII or Unicode). More rarely used, but still
 163  useful, is wc_str() function which always returns
 164  the Unicode string.
 165  Sometimes it is also necessary to go from ANSI strings to wxStrings.
 166  In this case, you can use the converter-constructor, as follows:
 167
 168
 169  @code
 170  const char* ascii_str = "Some text";
 171     wxString str(ascii_str, wxConvUTF8);
 172  @endcode
 173
 174  This code also compiles fine under a non-Unicode build of wxWidgets,
 175  but in that case the converter is ignored.
 176  For more information about converters and Unicode see
 177  the @ref mbconvclasses_overview.
 178
 179  @section unicodesettings Unicode-related compilation settings
 180
 181  You should define @c wxUSE_UNICODE to 1 to compile your program in
 182  Unicode mode. This currently works for wxMSW, wxGTK, wxMac and wxX11. If you
 183  compile your program in ANSI mode you can still define @c wxUSE_WCHAR_T
 184  to get some limited support for @c wchar_t type.
 185  This will allow your program to perform conversions between Unicode strings and
 186  ANSI ones (using @ref mbconvclasses_overview)
 187  and construct wxString objects from Unicode strings (presumably read
 188  from some external file or elsewhere).
 189
 190  @section topic8 Traps for the unwary
 191
 192
 193
 194       Casting c_str() to void* is now char*, not wxChar*
 195       Passing c_str(), mb_str() or wc_str() to variadic functions
 196  doesn't work
 197
 198  */
 199
 200