docs/latex/wx/tmbconv.tex

   1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   2 %% Name:        tmbconv.tex
   3 %% Purpose:     Overview of the wxMBConv classes in wxWidgets
   4 %% Author:      Ove Kaaven
   5 %% Modified by:
   6 %% Created:     25.03.00
   7 %% RCS-ID:      $Id$
   8 %% Copyright:   (c) 2000 Ove Kaaven
   9 %% Licence:     wxWidgets license
  10 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  11
  12 \section{wxMBConv classes overview}\label{mbconvclasses}
  13
  14 Classes: \helpref{wxMBConv}{wxmbconv}, wxMBConvLibc,
  15 \helpref{wxMBConvUTF7}{wxmbconvutf7}, \helpref{wxMBConvUTF8}{wxmbconvutf8},
  16 \helpref{wxCSConv}{wxcsconv},
  17 \helpref{wxMBConvUTF16}{wxmbconvutf16}, \helpref{wxMBConvUTF32}{wxmbconvutf32}
  18
  19 The wxMBConv classes in wxWidgets enables an Unicode-aware application to
  20 easily convert between Unicode and the variety of 8-bit encoding systems still
  21 in use.
  22
  23 \subsection{Background: The need for conversion}
  24
  25 As programs are becoming more and more globalized, and users exchange documents
  26 across country boundaries as never before, applications increasingly need to
  27 take into account all the different character sets in use around the world. It
  28 is no longer enough to just depend on the default byte-sized character set that
  29 computers have traditionally used.
  30
  31 A few years ago, a solution was proposed: the Unicode standard. Able to contain
  32 the complete set of characters in use in one unified global coding system,
  33 it would resolve the character set problems once and for all.
  34
  35 But it hasn't happened yet, and the migration towards Unicode has created new
  36 challenges, resulting in "compatibility encodings" such as UTF-8. A large
  37 number of systems out there still depends on the old 8-bit encodings, hampered
  38 by the huge amounts of legacy code still widely deployed. Even sending
  39 Unicode data from one Unicode-aware system to another may need encoding to an
  40 8-bit multibyte encoding (UTF-7 or UTF-8 is typically used for this purpose), to
  41 pass unhindered through any traditional transport channels.
  42
  43 \subsection{Background: The wxString class}
  44
  45 If you have compiled wxWidgets in Unicode mode, the wxChar type will become
  46 identical to wchar\_t rather than char, and a wxString stores wxChars. Hence,
  47 all wxString manipulation in your application will then operate on Unicode
  48 strings, and almost as easily as working with ordinary char strings (you
  49 just need to remember to use the wxT() macro to encapsulate any string
  50 literals).
  51
  52 But often, your environment doesn't want Unicode strings. You could be sending
  53 data over a network, or processing a text file for some other application. You
  54 need a way to quickly convert your easily-handled Unicode data to and from a
  55 traditional 8-bit-encoding. And this is what the wxMBConv classes do.
  56
  57 \subsection{wxMBConv classes}
  58
  59 The base class for all these conversions is the wxMBConv class (which itself
  60 implements standard libc locale conversion). Derived classes include
  61 wxMBConvLibc, several different wxMBConvUTFxxx classes, and wxCSConv, which
  62 implement different kinds of conversions. You can also derive your own class
  63 for your own custom encoding and use it, should you need it. All you need to do
  64 is override the MB2WC and WC2MB methods.
  65
  66 \subsection{wxMBConv objects}
  67
  68 Several of the wxWidgets-provided wxMBConv classes have predefined instances
  69 (wxConvLibc, wxConvFile, wxConvUTF7, wxConvUTF8, wxConvLocal). You can use
  70 these predefined objects directly, or you can instantiate your own objects.
  71
  72 A variable, wxConvCurrent, points to the conversion object that the user
  73 interface is supposed to use, in the case that the user interface is not
  74 Unicode-based (like with GTK+ 1.2). By default, it points to wxConvLibc or
  75 wxConvLocal, depending on which works best on the current platform.
  76
  77 \subsection{wxCSConv}
  78
  79 The wxCSConv class is special because when it is instantiated, you can tell it
  80 which character set it should use, which makes it meaningful to keep many
  81 instances of them around, each with a different character set (or you can
  82 create a wxCSConv instance on the fly).
  83
  84 The predefined wxCSConv instance, wxConvLocal, is preset to use the
  85 default user character set, but you should rarely need to use it directly,
  86 it is better to go through wxConvCurrent.
  87
  88 \subsection{Converting strings}
  89
  90 Once you have chosen which object you want to use to convert your text,
  91 here is how you would use them with wxString. These examples all assume
  92 that you are using a Unicode build of wxWidgets, although they will still
  93 compile in a non-Unicode build (they just won't convert anything).
  94
  95 Example 1: Constructing a wxString from input in current encoding.
  96
  97 \begin{verbatim}
  98 wxString str(input_data, *wxConvCurrent);
  99 \end{verbatim}
 100
 101 Example 2: Input in UTF-8 encoding.
 102
 103 \begin{verbatim}
 104 wxString str(input_data, wxConvUTF8);
 105 \end{verbatim}
 106
 107 Example 3: Input in KOI8-R. Construction of wxCSConv instance on the fly.
 108
 109 \begin{verbatim}
 110 wxString str(input_data, wxCSConv(wxT("koi8-r")));
 111 \end{verbatim}
 112
 113 Example 4: Printing a wxString to stdout in UTF-8 encoding.
 114
 115 \begin{verbatim}
 116 puts(str.mb_str(wxConvUTF8));
 117 \end{verbatim}
 118
 119 Example 5: Printing a wxString to stdout in custom encoding.
 120 Using preconstructed wxCSConv instance.
 121
 122 \begin{verbatim}
 123 wxCSConv cust(user_encoding);
 124 printf("Data: %s\n", (const char*) str.mb_str(cust));
 125 \end{verbatim}
 126
 127 Note: Since mb\_str() returns a temporary wxCharBuffer to hold the result
 128 of the conversion, you need to explicitly cast it to const char* if you use
 129 it in a vararg context (like with printf).
 130
 131 \subsection{Converting buffers}
 132
 133 If you have specialized needs, or just don't want to use wxString, you
 134 can also use the conversion methods of the conversion objects directly.
 135 This can even be useful if you need to do conversion in a non-Unicode
 136 build of wxWidgets; converting a string from UTF-8 to the current
 137 encoding should be possible by doing this:
 138
 139 \begin{verbatim}
 140 wxString str(wxConvUTF8.cMB2WC(input_data), *wxConvCurrent);
 141 \end{verbatim}
 142
 143 Here, cMB2WC of the UTF8 object returns a wxWCharBuffer containing a Unicode
 144 string. The wxString constructor then converts it back to an 8-bit character
 145 set using the passed conversion object, *wxConvCurrent. (In a Unicode build
 146 of wxWidgets, the constructor ignores the passed conversion object and
 147 retains the Unicode data.)
 148
 149 This could also be done by first making a wxString of the original data:
 150
 151 \begin{verbatim}
 152 wxString input_str(input_data);
 153 wxString str(input_str.wc_str(wxConvUTF8), *wxConvCurrent);
 154 \end{verbatim}
 155
 156 To print a wxChar buffer to a non-Unicode stdout:
 157
 158 \begin{verbatim}
 159 printf("Data: %s\n", (const char*) wxConvCurrent->cWX2MB(unicode_data));
 160 \end{verbatim}
 161
 162 If you need to do more complex processing on the converted data, you
 163 may want to store the temporary buffer in a local variable:
 164
 165 \begin{verbatim}
 166 const wxWX2MBbuf tmp_buf = wxConvCurrent->cWX2MB(unicode_data);
 167 const char *tmp_str = (const char*) tmp_buf;
 168 printf("Data: %s\n", tmp_str);
 169 process_data(tmp_str);
 170 \end{verbatim}
 171
 172 If a conversion had taken place in cWX2MB (i.e. in a Unicode build),
 173 the buffer will be deallocated as soon as tmp\_buf goes out of scope.
 174 (The macro wxWX2MBbuf reflects the correct return value of cWX2MB
 175 (either char* or wxCharBuffer), except for the const.)
 176