source: trunk/doc/src/unicode.qdoc@ 477

Last change on this file since 477 was 2, checked in by Dmitry A. Kuminov, 16 years ago

Initially imported qt-all-opensource-src-4.5.1 from Trolltech.
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3** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
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41
42/*!
43 \page unicode.html
44 \title Unicode
45 \ingroup architecture
46 \ingroup text-processing
47 \brief Information about support for Unicode in Qt.
48
49 Unicode is a multi-byte character set, portable across all major
50 computing platforms and with decent coverage over most of the world.
51 It is also single-locale; it includes no code pages or other
52 complexities that make software harder to write and test. There is no
53 competing character set that's reasonably cross-platform. For these
54 reasons, Unicode 4.0 is used as the native character set for Qt.
55
56
57 \section1 Information about Unicode on the Web
58
59 The \l{http://www.unicode.org/}{Unicode Consortium} has a number
60 of documents available, including
61
62 \list
63
64 \i \l{http://www.unicode.org/unicode/standard/principles.html}{A
65 technical introduction to Unicode}
66 \i \l{http://www.unicode.org/unicode/standard/standard.html}{The
67 home page for the standard}
68
69 \endlist
70
71
72 \section1 The Standard
73
74 The current version of the standard is 4.0.0.
75
76 \list
77
78 \i \link http://www.amazon.com/exec/obidos/ASIN/0321185781/trolltech/t
79 The Unicode Standard, version 4.0.\endlink See also
80 \link http://www.unicode.org/unicode/standard/versions/
81 its home page.\endlink
82 \i \link http://www.amazon.com/exec/obidos/ASIN/0201616335/trolltech/t
83 The Unicode Standard, version 3.2.\endlink
84 \i \link http://www.amazon.com/exec/obidos/ASIN/0201473459/trolltech/t
85 The Unicode Standard, version 2.0.\endlink See also the
86 \link http://www.unicode.org/unicode/reports/tr8.html 2.1
87 update\endlink and
88 \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.
89
90 \endlist
91
92 \section1 Unicode in Qt
93
94 In Qt, and in most applications that use Qt, most or all user-visible
95 strings are stored using Unicode. Qt provides:
96
97 \list
98
99 \i Translation to/from legacy encodings for file I/O: see
100 QTextCodec and QTextStream.
101 \i Translation from Input Methods and 8-bit keyboard input.
102 \i Translation to legacy character sets for on-screen display.
103 \i A string class, QString, that stores Unicode characters, with
104 support for migrating from C strings including fast (cached)
105 translation to and from US-ASCII, and all the usual string
106 operations.
107 \i Unicode-aware widgets where appropriate.
108 \i Unicode support detection on Windows, so that Qt provides Unicode
109 even on Windows platforms that do not support it natively.
110
111 \endlist
112
113 To fully benefit from Unicode, we recommend using QString for storing
114 all user-visible strings, and performing all text file I/O using
115 QTextStream. Use QKeyEvent::text() for keyboard input in any custom
116 widgets you write; it does not make much difference for slow typists
117 in Western Europe or North America, but for fast typists or people
118 using special input methods using text() is beneficial.
119
120 All the function arguments in Qt that may be user-visible strings,
121 QLabel::setText() and a many others, take \c{const QString &}s.
122 QString provides implicit casting from \c{const char *}
123 so that things like
124
125 \snippet doc/src/snippets/code/doc_src_unicode.qdoc 0
126
127 will work. There is also a function, QObject::tr(), that provides
128 translation support, like this:
129
130 \snippet doc/src/snippets/code/doc_src_unicode.qdoc 1
131
132 QObject::tr() maps from \c{const char *} to a Unicode string, and
133 uses installable QTranslator objects to do the mapping.
134
135 Qt provides a number of built-in QTextCodec classes, that is,
136 classes that know how to translate between Unicode and legacy
137 encodings to support programs that must talk to other programs or
138 read/write files in legacy file formats.
139
140 By default, conversion to/from \c{const char *} uses a
141 locale-dependent codec. However, applications can easily find codecs
142 for other locales, and set any open file or network connection to use
143 a special codec. It is also possible to install new codecs, for
144 encodings that the built-in ones do not support. (At the time of
145 writing, Vietnamese/VISCII is one such example.)
146
147 Since US-ASCII and ISO-8859-1 are so common, there are also especially
148 fast functions for mapping to and from them. For example, to open an
149 application's icon one might do this:
150
151 \snippet doc/src/snippets/code/doc_src_unicode.qdoc 2
152
153 or
154
155 \snippet doc/src/snippets/code/doc_src_unicode.qdoc 3
156
157 Regarding output, Qt will do a best-effort conversion from
158 Unicode to whatever encoding the system and fonts provide.
159 Depending on operating system, locale, font availability, and Qt's
160 support for the characters used, this conversion may be good or bad.
161 We will extend this in upcoming versions, with emphasis on the most
162 common locales first.
163
164 \sa {Internationalization with Qt}
165*/
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