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[wxWidgets.git] / docs / doxygen / overviews / mbconvclasses.h

/////////////////////////////////////////////////////////////////////////////
// Name:        mbconvclasses
// Purpose:     topic overview
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
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/*!

 @page mbconvclasses_overview wxMBConv classes overview

 Classes: #wxMBConv, wxMBConvLibc,
 #wxMBConvUTF7, #wxMBConvUTF8,
 #wxCSConv,
 #wxMBConvUTF16, #wxMBConvUTF32
 The wxMBConv classes in wxWidgets enable an Unicode-aware application to
 easily convert between Unicode and the variety of 8-bit encoding systems still
 in use.
 @ref needforconversion_overview
 @ref conversionandwxstring_overview
 @ref mbconvclasses_overview
 @ref mbconvobjects_overview
 #wxCSConv
 @ref convertingstrings_overview
 @ref convertingbuffers_overview


 @section needforconversion Background: The need for conversion

 As programs are becoming more and more globalized, and users exchange documents
 across country boundaries as never before, applications increasingly need to
 take into account all the different character sets in use around the world. It
 is no longer enough to just depend on the default byte-sized character set that
 computers have traditionally used.
 A few years ago, a solution was proposed: the Unicode standard. Able to contain
 the complete set of characters in use in one unified global coding system,
 it would resolve the character set problems once and for all.
 But it hasn't happened yet, and the migration towards Unicode has created new
 challenges, resulting in "compatibility encodings" such as UTF-8. A large
 number of systems out there still depends on the old 8-bit encodings, hampered
 by the huge amounts of legacy code still widely deployed. Even sending
 Unicode data from one Unicode-aware system to another may need encoding to an
 8-bit multibyte encoding (UTF-7 or UTF-8 is typically used for this purpose), to
 pass unhindered through any traditional transport channels.

 @section conversionandwxstring Background: The wxString class

 If you have compiled wxWidgets in Unicode mode, the wxChar type will become
 identical to wchar_t rather than char, and a wxString stores wxChars. Hence,
 all wxString manipulation in your application will then operate on Unicode
 strings, and almost as easily as working with ordinary char strings (you
 just need to remember to use the wxT() macro to encapsulate any string
 literals).
 But often, your environment doesn't want Unicode strings. You could be sending
 data over a network, or processing a text file for some other application. You
 need a way to quickly convert your easily-handled Unicode data to and from a
 traditional 8-bit encoding. And this is what the wxMBConv classes do.

 @section wxmbconvclasses wxMBConv classes

 The base class for all these conversions is the wxMBConv class (which itself
 implements standard libc locale conversion). Derived classes include
 wxMBConvLibc, several different wxMBConvUTFxxx classes, and wxCSConv, which
 implement different kinds of conversions. You can also derive your own class
 for your own custom encoding and use it, should you need it. All you need to do
 is override the MB2WC and WC2MB methods.

 @section wxmbconvobjects wxMBConv objects

 Several of the wxWidgets-provided wxMBConv classes have predefined instances
 (wxConvLibc, wxConvFileName, wxConvUTF7, wxConvUTF8, wxConvLocal). You can use
 these predefined objects directly, or you can instantiate your own objects.
 A variable, wxConvCurrent, points to the conversion object that the user
 interface is supposed to use, in the case that the user interface is not
 Unicode-based (like with GTK+ 1.2). By default, it points to wxConvLibc or
 wxConvLocal, depending on which works best on the current platform.

 @section wxcsconvclass wxCSConv

 The wxCSConv class is special because when it is instantiated, you can tell it
 which character set it should use, which makes it meaningful to keep many
 instances of them around, each with a different character set (or you can
 create a wxCSConv instance on the fly).
 The predefined wxCSConv instance, wxConvLocal, is preset to use the
 default user character set, but you should rarely need to use it directly,
 it is better to go through wxConvCurrent.

 @section convertingstrings Converting strings

 Once you have chosen which object you want to use to convert your text,
 here is how you would use them with wxString. These examples all assume
 that you are using a Unicode build of wxWidgets, although they will still
 compile in a non-Unicode build (they just won't convert anything).
 Example 1: Constructing a wxString from input in current encoding.

 @code
 wxString str(input_data, *wxConvCurrent);
 @endcode

 Example 2: Input in UTF-8 encoding.

 @code
 wxString str(input_data, wxConvUTF8);
 @endcode

 Example 3: Input in KOI8-R. Construction of wxCSConv instance on the fly.

 @code
 wxString str(input_data, wxCSConv(wxT("koi8-r")));
 @endcode

 Example 4: Printing a wxString to stdout in UTF-8 encoding.

 @code
 puts(str.mb_str(wxConvUTF8));
 @endcode

 Example 5: Printing a wxString to stdout in custom encoding.
 Using preconstructed wxCSConv instance.

 @code
 wxCSConv cust(user_encoding);
 printf("Data: %s\n", (const char*) str.mb_str(cust));
 @endcode

 Note: Since mb_str() returns a temporary wxCharBuffer to hold the result
 of the conversion, you need to explicitly cast it to const char* if you use
 it in a vararg context (like with printf).

 @section convertingbuffers Converting buffers

 If you have specialized needs, or just don't want to use wxString, you
 can also use the conversion methods of the conversion objects directly.
 This can even be useful if you need to do conversion in a non-Unicode
 build of wxWidgets; converting a string from UTF-8 to the current
 encoding should be possible by doing this:

 @code
 wxString str(wxConvUTF8.cMB2WC(input_data), *wxConvCurrent);
 @endcode

 Here, cMB2WC of the UTF8 object returns a wxWCharBuffer containing a Unicode
 string. The wxString constructor then converts it back to an 8-bit character
 set using the passed conversion object, *wxConvCurrent. (In a Unicode build
 of wxWidgets, the constructor ignores the passed conversion object and
 retains the Unicode data.)
 This could also be done by first making a wxString of the original data:

 @code
 wxString input_str(input_data);
 wxString str(input_str.wc_str(wxConvUTF8), *wxConvCurrent);
 @endcode

 To print a wxChar buffer to a non-Unicode stdout:

 @code
 printf("Data: %s\n", (const char*) wxConvCurrent-cWX2MB(unicode_data));
 @endcode

 If you need to do more complex processing on the converted data, you
 may want to store the temporary buffer in a local variable:

 @code
 const wxWX2MBbuf tmp_buf = wxConvCurrent-cWX2MB(unicode_data);
 const char *tmp_str = (const char*) tmp_buf;
 printf("Data: %s\n", tmp_str);
 process_data(tmp_str);
 @endcode

 If a conversion had taken place in cWX2MB (i.e. in a Unicode build),
 the buffer will be deallocated as soon as tmp_buf goes out of scope.
 (The macro wxWX2MBbuf reflects the correct return value of cWX2MB
 (either char* or wxCharBuffer), except for the const.)

 */