docs/doxygen/overviews/mbconvclasses.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        mbconvclasses.h
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows licence
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_mbconv wxMBConv Overview
  12
  13 @tableofcontents
  14
  15 The wxMBConv classes in wxWidgets enable an Unicode-aware application to easily
  16 convert between Unicode and the variety of 8-bit encoding systems still in use.
  17
  18 @see @ref group_class_conv
  19
  20
  21
  22 @section overview_mbconv_need Background: The Need for Conversion
  23
  24 As programs are becoming more and more globalized, and users exchange documents
  25 across country boundaries as never before, applications increasingly need to
  26 take into account all the different character sets in use around the world. It
  27 is no longer enough to just depend on the default byte-sized character set that
  28 computers have traditionally used.
  29
  30 A few years ago, a solution was proposed: the Unicode standard. Able to contain
  31 the complete set of characters in use in one unified global coding system, it
  32 would resolve the character set problems once and for all.
  33
  34 But it hasn't happened yet, and the migration towards Unicode has created new
  35 challenges, resulting in "compatibility encodings" such as UTF-8. A large
  36 number of systems out there still depends on the old 8-bit encodings, hampered
  37 by the huge amounts of legacy code still widely deployed. Even sending Unicode
  38 data from one Unicode-aware system to another may need encoding to an 8-bit
  39 multibyte encoding (UTF-7 or UTF-8 is typically used for this purpose), to pass
  40 unhindered through any traditional transport channels.
  41
  42
  43 @section overview_mbconv_string Background: The wxString Class
  44
  45 @todo rewrite this overview; it's not up2date with wxString changes
  46
  47 If you have compiled wxWidgets in Unicode mode, the wxChar type will become
  48 identical to wchar_t rather than char, and a wxString stores wxChars. Hence,
  49 all wxString manipulation in your application will then operate on Unicode
  50 strings, and almost as easily as working with ordinary char strings (you just
  51 need to remember to use the wxT() macro to encapsulate any string literals).
  52
  53 But often, your environment doesn't want Unicode strings. You could be sending
  54 data over a network, or processing a text file for some other application. You
  55 need a way to quickly convert your easily-handled Unicode data to and from a
  56 traditional 8-bit encoding. And this is what the wxMBConv classes do.
  57
  58
  59 @section overview_mbconv_classes wxMBConv Classes
  60
  61 The base class for all these conversions is the wxMBConv class (which itself
  62 implements standard libc locale conversion). Derived classes include
  63 wxMBConvLibc, several different wxMBConvUTFxxx classes, and wxCSConv, which
  64 implement different kinds of conversions. You can also derive your own class
  65 for your own custom encoding and use it, should you need it. All you need to do
  66 is override the MB2WC and WC2MB methods.
  67
  68
  69 @section overview_mbconv_objects wxMBConv Objects
  70
  71 Several of the wxWidgets-provided wxMBConv classes have predefined instances
  72 (wxConvLibc, wxConvFileName, wxConvUTF7, wxConvUTF8, wxConvLocal). You can use
  73 these predefined objects directly, or you can instantiate your own objects.
  74
  75 A variable, wxConvCurrent, points to the conversion object that the user
  76 interface is supposed to use, in the case that the user interface is not
  77 Unicode-based (like with GTK+ 1.2). By default, it points to wxConvLibc or
  78 wxConvLocal, depending on which works best on the current platform.
  79
  80
  81 @section overview_mbconv_csconv wxCSConv
  82
  83 The wxCSConv class is special because when it is instantiated, you can tell it
  84 which character set it should use, which makes it meaningful to keep many
  85 instances of them around, each with a different character set (or you can
  86 create a wxCSConv instance on the fly).
  87
  88 The predefined wxCSConv instance, wxConvLocal, is preset to use the default
  89 user character set, but you should rarely need to use it directly, it is better
  90 to go through wxConvCurrent.
  91
  92
  93 @section overview_mbconv_converting Converting Strings
  94
  95 Once you have chosen which object you want to use to convert your text, here is
  96 how you would use them with wxString. These examples all assume that you are
  97 using a Unicode build of wxWidgets, although they will still compile in a
  98 non-Unicode build (they just won't convert anything).
  99
 100 Example 1: Constructing a wxString from input in current encoding.
 101
 102 @code
 103 wxString str(input_data, *wxConvCurrent);
 104 @endcode
 105
 106 Example 2: Input in UTF-8 encoding.
 107
 108 @code
 109 wxString str(input_data, wxConvUTF8);
 110 @endcode
 111
 112 Example 3: Input in KOI8-R. Construction of wxCSConv instance on the fly.
 113
 114 @code
 115 wxString str(input_data, wxCSConv(wxT("koi8-r")));
 116 @endcode
 117
 118 Example 4: Printing a wxString to stdout in UTF-8 encoding.
 119
 120 @code
 121 puts(str.mb_str(wxConvUTF8));
 122 @endcode
 123
 124 Example 5: Printing a wxString to stdout in custom encoding. Using
 125 preconstructed wxCSConv instance.
 126
 127 @code
 128 wxCSConv cust(user_encoding);
 129 printf("Data: %s\n", (const char*) str.mb_str(cust));
 130 @endcode
 131
 132 @note Since mb_str() returns a temporary wxCharBuffer to hold the result of the
 133 conversion, you need to explicitly cast it to const char* if you use it in a
 134 vararg context (like with printf).
 135
 136
 137 @section overview_mbconv_buffers Converting Buffers
 138
 139 If you have specialized needs, or just don't want to use wxString, you can also
 140 use the conversion methods of the conversion objects directly. This can even be
 141 useful if you need to do conversion in a non-Unicode build of wxWidgets;
 142 converting a string from UTF-8 to the current encoding should be possible by
 143 doing this:
 144
 145 @code
 146 wxString str(wxConvUTF8.cMB2WC(input_data), *wxConvCurrent);
 147 @endcode
 148
 149 Here, cMB2WC of the UTF8 object returns a wxWCharBuffer containing a Unicode
 150 string. The wxString constructor then converts it back to an 8-bit character
 151 set using the passed conversion object, *wxConvCurrent. (In a Unicode build of
 152 wxWidgets, the constructor ignores the passed conversion object and retains the
 153 Unicode data.)
 154
 155 This could also be done by first making a wxString of the original data:
 156
 157 @code
 158 wxString input_str(input_data);
 159 wxString str(input_str.wc_str(wxConvUTF8), *wxConvCurrent);
 160 @endcode
 161
 162 To print a wxChar buffer to a non-Unicode stdout:
 163
 164 @code
 165 printf("Data: %s\n", (const char*) wxConvCurrent->cWX2MB(unicode_data));
 166 @endcode
 167
 168 If you need to do more complex processing on the converted data, you may want
 169 to store the temporary buffer in a local variable:
 170
 171 @code
 172 const wxWX2MBbuf tmp_buf = wxConvCurrent->cWX2MB(unicode_data);
 173 const char *tmp_str = (const char*) tmp_buf;
 174 printf("Data: %s\n", tmp_str);
 175 process_data(tmp_str);
 176 @endcode
 177
 178 If a conversion had taken place in cWX2MB (i.e. in a Unicode build), the buffer
 179 will be deallocated as soon as tmp_buf goes out of scope. The macro wxWX2MBbuf
 180 reflects the correct return value of cWX2MB (either char* or wxCharBuffer),
 181 except for the const.
 182
 183 */