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 license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_mbconv wxMBConv Overview
  12
  13 Classes: wxMBConv, wxMBConvLibc, wxMBConvUTF7, wxMBConvUTF8, wxCSConv,
  14          wxMBConvUTF16, wxMBConvUTF32
  15
  16 The wxMBConv classes in wxWidgets enable an Unicode-aware application to easily
  17 convert between Unicode and the variety of 8-bit encoding systems still in use.
  18
  19 @li @ref overview_mbconv_need
  20 @li @ref overview_mbconv_string
  21 @li @ref overview_mbconv_classes
  22 @li @ref overview_mbconv_objects
  23 @li @ref overview_mbconv_csconv
  24 @li @ref overview_mbconv_converting
  25 @li @ref overview_mbconv_buffers
  26
  27
  28 <hr>
  29
  30
  31 @section overview_mbconv_need Background: The Need for Conversion
  32
  33 As programs are becoming more and more globalized, and users exchange documents
  34 across country boundaries as never before, applications increasingly need to
  35 take into account all the different character sets in use around the world. It
  36 is no longer enough to just depend on the default byte-sized character set that
  37 computers have traditionally used.
  38
  39 A few years ago, a solution was proposed: the Unicode standard. Able to contain
  40 the complete set of characters in use in one unified global coding system, it
  41 would resolve the character set problems once and for all.
  42
  43 But it hasn't happened yet, and the migration towards Unicode has created new
  44 challenges, resulting in "compatibility encodings" such as UTF-8. A large
  45 number of systems out there still depends on the old 8-bit encodings, hampered
  46 by the huge amounts of legacy code still widely deployed. Even sending Unicode
  47 data from one Unicode-aware system to another may need encoding to an 8-bit
  48 multibyte encoding (UTF-7 or UTF-8 is typically used for this purpose), to pass
  49 unhindered through any traditional transport channels.
  50
  51
  52 @section overview_mbconv_string Background: The wxString Class
  53
  54 If you have compiled wxWidgets in Unicode mode, the wxChar type will become
  55 identical to wchar_t rather than char, and a wxString stores wxChars. Hence,
  56 all wxString manipulation in your application will then operate on Unicode
  57 strings, and almost as easily as working with ordinary char strings (you just
  58 need to remember to use the wxT() macro to encapsulate any string literals).
  59
  60 But often, your environment doesn't want Unicode strings. You could be sending
  61 data over a network, or processing a text file for some other application. You
  62 need a way to quickly convert your easily-handled Unicode data to and from a
  63 traditional 8-bit encoding. And this is what the wxMBConv classes do.
  64
  65
  66 @section overview_mbconv_classes wxMBConv Classes
  67
  68 The base class for all these conversions is the wxMBConv class (which itself
  69 implements standard libc locale conversion). Derived classes include
  70 wxMBConvLibc, several different wxMBConvUTFxxx classes, and wxCSConv, which
  71 implement different kinds of conversions. You can also derive your own class
  72 for your own custom encoding and use it, should you need it. All you need to do
  73 is override the MB2WC and WC2MB methods.
  74
  75
  76 @section overview_mbconv_objects wxMBConv Objects
  77
  78 Several of the wxWidgets-provided wxMBConv classes have predefined instances
  79 (wxConvLibc, wxConvFileName, wxConvUTF7, wxConvUTF8, wxConvLocal). You can use
  80 these predefined objects directly, or you can instantiate your own objects.
  81
  82 A variable, wxConvCurrent, points to the conversion object that the user
  83 interface is supposed to use, in the case that the user interface is not
  84 Unicode-based (like with GTK+ 1.2). By default, it points to wxConvLibc or
  85 wxConvLocal, depending on which works best on the current platform.
  86
  87
  88 @section overview_mbconv_csconv wxCSConv
  89
  90 The wxCSConv class is special because when it is instantiated, you can tell it
  91 which character set it should use, which makes it meaningful to keep many
  92 instances of them around, each with a different character set (or you can
  93 create a wxCSConv instance on the fly).
  94
  95 The predefined wxCSConv instance, wxConvLocal, is preset to use the default
  96 user character set, but you should rarely need to use it directly, it is better
  97 to go through wxConvCurrent.
  98
  99
 100 @section overview_mbconv_converting Converting Strings
 101
 102 Once you have chosen which object you want to use to convert your text, here is
 103 how you would use them with wxString. These examples all assume that you are
 104 using a Unicode build of wxWidgets, although they will still compile in a
 105 non-Unicode build (they just won't convert anything).
 106
 107 Example 1: Constructing a wxString from input in current encoding.
 108
 109 @code
 110 wxString str(input_data, *wxConvCurrent);
 111 @endcode
 112
 113 Example 2: Input in UTF-8 encoding.
 114
 115 @code
 116 wxString str(input_data, wxConvUTF8);
 117 @endcode
 118
 119 Example 3: Input in KOI8-R. Construction of wxCSConv instance on the fly.
 120
 121 @code
 122 wxString str(input_data, wxCSConv(wxT("koi8-r")));
 123 @endcode
 124
 125 Example 4: Printing a wxString to stdout in UTF-8 encoding.
 126
 127 @code
 128 puts(str.mb_str(wxConvUTF8));
 129 @endcode
 130
 131 Example 5: Printing a wxString to stdout in custom encoding. Using
 132 preconstructed wxCSConv instance.
 133
 134 @code
 135 wxCSConv cust(user_encoding);
 136 printf("Data: %s\n", (const char*) str.mb_str(cust));
 137 @endcode
 138
 139 @note Since mb_str() returns a temporary wxCharBuffer to hold the result of the
 140 conversion, you need to explicitly cast it to const char* if you use it in a
 141 vararg context (like with printf).
 142
 143
 144 @section overview_mbconv_buffers Converting Buffers
 145
 146 If you have specialized needs, or just don't want to use wxString, you can also
 147 use the conversion methods of the conversion objects directly. This can even be
 148 useful if you need to do conversion in a non-Unicode build of wxWidgets;
 149 converting a string from UTF-8 to the current encoding should be possible by
 150 doing this:
 151
 152 @code
 153 wxString str(wxConvUTF8.cMB2WC(input_data), *wxConvCurrent);
 154 @endcode
 155
 156 Here, cMB2WC of the UTF8 object returns a wxWCharBuffer containing a Unicode
 157 string. The wxString constructor then converts it back to an 8-bit character
 158 set using the passed conversion object, *wxConvCurrent. (In a Unicode build of
 159 wxWidgets, the constructor ignores the passed conversion object and retains the
 160 Unicode data.)
 161
 162 This could also be done by first making a wxString of the original data:
 163
 164 @code
 165 wxString input_str(input_data);
 166 wxString str(input_str.wc_str(wxConvUTF8), *wxConvCurrent);
 167 @endcode
 168
 169 To print a wxChar buffer to a non-Unicode stdout:
 170
 171 @code
 172 printf("Data: %s\n", (const char*) wxConvCurrent->cWX2MB(unicode_data));
 173 @endcode
 174
 175 If you need to do more complex processing on the converted data, you may want
 176 to store the temporary buffer in a local variable:
 177
 178 @code
 179 const wxWX2MBbuf tmp_buf = wxConvCurrent->cWX2MB(unicode_data);
 180 const char *tmp_str = (const char*) tmp_buf;
 181 printf("Data: %s\n", tmp_str);
 182 process_data(tmp_str);
 183 @endcode
 184
 185 If a conversion had taken place in cWX2MB (i.e. in a Unicode build), the buffer
 186 will be deallocated as soon as tmp_buf goes out of scope. The macro wxWX2MBbuf
 187 reflects the correct return value of cWX2MB (either char* or wxCharBuffer),
 188 except for the const.
 189
 190 */
 191