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/****************************************************************************
**
** Documentation of Unicode support in Qt.
**
** Copyright (C) 1992-2008 Trolltech ASA. All rights reserved.
**
** This file is part of the Qt GUI Toolkit.
**
** This file may be used under the terms of the GNU General
** Public License versions 2.0 or 3.0 as published by the Free
** Software Foundation and appearing in the files LICENSE.GPL2
** and LICENSE.GPL3 included in the packaging of this file.
** Alternatively you may (at your option) use any later version
** of the GNU General Public License if such license has been
** publicly approved by Trolltech ASA (or its successors, if any)
** and the KDE Free Qt Foundation.
**
** Please review the following information to ensure GNU General
** Public Licensing requirements will be met:
** http://trolltech.com/products/qt/licenses/licensing/opensource/.
** If you are unsure which license is appropriate for your use, please
** review the following information:
** http://trolltech.com/products/qt/licenses/licensing/licensingoverview
** or contact the sales department at [email protected].
**
** This file may be used under the terms of the Q Public License as
** defined by Trolltech ASA and appearing in the file LICENSE.QPL
** included in the packaging of this file. Licensees holding valid Qt
** Commercial licenses may use this file in accordance with the Qt
** Commercial License Agreement provided with the Software.
**
** This file is provided "AS IS" with NO WARRANTY OF ANY KIND,
** INCLUDING THE WARRANTIES OF DESIGN, MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted
** herein.
**
**********************************************************************/
/*! \page unicode.html
\title About Unicode
Unicode is a multi-byte character set, portable across all major
computing platforms and with decent coverage over most of the world.
It is also single-locale; it includes no code pages or other
complexities that make software harder to write and test. There is no
competing character set that's reasonably multiplatform. For these
reasons, Trolltech uses Unicode as the native character set for Qt
(since version 2.0).
\section1 Information about Unicode on the web.
The \link http://www.unicode.org Unicode Consortium\endlink
has a number of documents available, including
\list
\i \link http://www.unicode.org/unicode/standard/principles.html
A technical introduction to Unicode\endlink
\i \link http://www.unicode.org/unicode/standard/standard.html
The home page for the standard\endlink
\endlist
\section1 The Standard
The current version of the standard is 3.2
\list
\i \link http://www.amazon.com/exec/obidos/ASIN/0201616335/trolltech/t
The Unicode Standard, version 3.2.\endlink See also
\link http://www.unicode.org/unicode/standard/versions/
its home page.\endlink
\i \link http://www.amazon.com/exec/obidos/ASIN/0201473459/trolltech/t
The Unicode Standard, version 2.0.\endlink See also the
\link http://www.unicode.org/unicode/reports/tr8.html 2.1
update\endlink and
\link http://www.unicode.org/unicode/standard/versions/enumeratedversions.html#Unicode 2.1.9 the 2.1.9 data files\endlink at www.unicode.org.
\endlist
\section1 Unicode in Qt
In Qt, and in most applications that use Qt, most or all user-visible
strings are stored using Unicode. Qt provides:
\list
\i Translation to/from legacy encodings for file I/O: see \l
QTextCodec and \l QTextStream.
\i Translation from Input Methods and 8-bit keyboard input.
\i Translation to legacy character sets for on-screen display.
\i A string class, \l QString, that stores Unicode characters, with
support for migrating from C strings including fast (cached)
translation to and from US-ASCII, and all the usual string
operations.
\i Unicode-aware widgets where appropriate.
\i Unicode support detection on Windows, so that Qt provides Unicode
even on Windows platforms that do not support it natively.
\endlist
To fully benefit from Unicode, we recommend using QString for storing
all user-visible strings, and performing all text file I/O using
QTextStream. Use \l QKeyEvent::text() for keyboard input in any custom
widgets you write; it does not make much difference for slow typists
in Western Europe or North America, but for fast typists or people
using special input methods using text() is beneficial.
All the function arguments in Qt that may be user-visible strings, \l
QLabel::setText() and a many others, take \c{const QString &}s.
\l QString provides implicit casting from \c{const char *}
so that things like
\code
myLabel->setText( "Hello, Dolly!" );
\endcode
will work. There is also a function, \l QObject::tr(), that provides
translation support, like this:
\code
myLabel->setText( tr("Hello, Dolly!") );
\endcode
tr() (simplifying somewhat) maps from \c{const char *} to a
Unicode string, and uses installable \l QTranslator objects to do the
mapping.
Qt provides a number of built-in \l QTextCodec classes, that is,
classes that know how to translate between Unicode and legacy
encodings to support programs that must talk to other programs or
read/write files in legacy file formats.
By default, conversion to/from \c{const char *} uses a
locale-dependent codec. However, applications can easily find codecs
for other locales, and set any open file or network connection to use
a special codec. It is also possible to install new codecs, for
encodings that the built-in ones do not support. (At the time of
writing, Vietnamese/VISCII is one such example.)
Since US-ASCII and ISO-8859-1 are so common, there are also especially
fast functions for mapping to and from them. For example, to open an
application's icon one might do this:
\code
QFile f( QString::fromLatin1("appicon.png") );
\endcode
Regarding output, Qt will do a best-effort conversion from
Unicode to whatever encoding the system and fonts provide.
Depending on operating system, locale, font availability and Qt's
support for the characters used, this conversion may be good or bad.
We will extend this in upcoming versions, with emphasis on the most
common locales first.
*/
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