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131 lines
6.3 KiB
131 lines
6.3 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/unicode.doc:36 -->
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>About Unicode</title>
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<style type="text/css"><!--
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fn { margin-left: 1cm; text-indent: -1cm; }
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a:link { color: #004faf; text-decoration: none }
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a:visited { color: #672967; text-decoration: none }
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body { background: #ffffff; color: black; }
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--></style>
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</head>
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<body>
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<table border="0" cellpadding="0" cellspacing="0" width="100%">
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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| <a href="classes.html">
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<font color="#004faf">All Classes</font></a>
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| <a href="mainclasses.html">
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<font color="#004faf">Main Classes</font></a>
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| <a href="annotated.html">
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<font color="#004faf">Annotated</font></a>
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| <a href="groups.html">
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<font color="#004faf">Grouped Classes</font></a>
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| <a href="functions.html">
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<font color="#004faf">Functions</font></a>
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</td>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>About Unicode</h1>
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<p> Unicode is a multi-byte character set, portable across all major
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computing platforms and with decent coverage over most of the world.
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It is also single-locale; it includes no code pages or other
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complexities that make software harder to write and test. There is no
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competing character set that's reasonably multiplatform. For these
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reasons, Trolltech uses Unicode as the native character set for Qt
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(since version 2.0).
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<p> <h2> Information about Unicode on the web.
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</h2>
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<a name="1"></a><p> The <a href="http://www.unicode.org">Unicode Consortium</a>
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has a number of documents available, including
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<p> <ul>
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<p> <li> <a href="http://www.unicode.org/unicode/standard/principles.html">A technical introduction to Unicode</a>
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<li> <a href="http://www.unicode.org/unicode/standard/standard.html">The home page for the standard</a>
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<p> </ul>
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<p> <h2> The Standard
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</h2>
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<a name="2"></a><p> The current version of the standard is 3.2
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<p> <ul>
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<p> <li> <a href="http://www.amazon.com/exec/obidos/ASIN/0201616335/trolltech/t">The Unicode Standard, version 3.2.</a> See also
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<a href="http://www.unicode.org/unicode/standard/versions/">its home page.</a>
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<li> <a href="http://www.amazon.com/exec/obidos/ASIN/0201473459/trolltech/t">The Unicode Standard, version 2.0.</a> See also the
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<a href="http://www.unicode.org/unicode/reports/tr8.html">2.1
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update</a> and
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<a href="http://www.unicode.org/unicode/standard/versions/enumeratedversions.html#Unicode">2.1.9 the 2.1.9 data files</a> at www.unicode.org.
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<p> </ul>
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<p> <h2> Unicode in Qt
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</h2>
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<a name="3"></a><p> In Qt, and in most applications that use Qt, most or all user-visible
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strings are stored using Unicode. Qt provides:
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<p> <ul>
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<p> <li> Translation to/from legacy encodings for file I/O: see <a href="qtextcodec.html">QTextCodec</a> and <a href="qtextstream.html">QTextStream</a>.
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<li> Translation from Input Methods and 8-bit keyboard input.
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<li> Translation to legacy character sets for on-screen display.
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<li> A string class, <a href="qstring.html">QString</a>, that stores Unicode characters, with
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support for migrating from C strings including fast (cached)
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translation to and from US-ASCII, and all the usual string
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operations.
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<li> Unicode-aware widgets where appropriate.
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<li> Unicode support detection on Windows, so that Qt provides Unicode
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even on Windows platforms that do not support it natively.
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<p> </ul>
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<p> To fully benefit from Unicode, we recommend using <a href="qstring.html">QString</a> for storing
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all user-visible strings, and performing all text file I/O using
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<a href="qtextstream.html">QTextStream</a>. Use <a href="qkeyevent.html#text">QKeyEvent::text</a>() for keyboard input in any custom
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widgets you write; it does not make much difference for slow typists
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in Western Europe or North America, but for fast typists or people
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using special input methods using text() is beneficial.
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<p> All the function arguments in Qt that may be user-visible strings, <a href="qlabel.html#setText">QLabel::setText</a>() and a many others, take <tt>const QString &</tt>s.
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<a href="qstring.html">QString</a> provides implicit casting from <tt>const char *</tt>
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so that things like
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<pre>
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myLabel->setText( "Hello, Dolly!" );
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</pre>
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will work. There is also a function, <a href="qobject.html#tr">QObject::tr</a>(), that provides
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translation support, like this:
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<pre>
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myLabel->setText( tr("Hello, Dolly!") );
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</pre>
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<p> tr() (simplifying somewhat) maps from <tt>const char *</tt> to a
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Unicode string, and uses installable <a href="qtranslator.html">QTranslator</a> objects to do the
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mapping.
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<p> Qt provides a number of built-in <a href="qtextcodec.html">QTextCodec</a> classes, that is,
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classes that know how to translate between Unicode and legacy
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encodings to support programs that must talk to other programs or
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read/write files in legacy file formats.
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<p> By default, conversion to/from <tt>const char *</tt> uses a
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locale-dependent codec. However, applications can easily find codecs
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for other locales, and set any open file or network connection to use
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a special codec. It is also possible to install new codecs, for
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encodings that the built-in ones do not support. (At the time of
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writing, Vietnamese/VISCII is one such example.)
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<p> Since US-ASCII and ISO-8859-1 are so common, there are also especially
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fast functions for mapping to and from them. For example, to open an
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application's icon one might do this:
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<pre>
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<a href="qfile.html">QFile</a> f( QString::<a href="qstring.html#fromLatin1">fromLatin1</a>("appicon.png") );
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</pre>
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<p> Regarding output, Qt will do a best-effort conversion from
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Unicode to whatever encoding the system and fonts provide.
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Depending on operating system, locale, font availability and Qt's
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support for the characters used, this conversion may be good or bad.
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We will extend this in upcoming versions, with emphasis on the most
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common locales first.
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<p>
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<!-- eof -->
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<p><address><hr><div align=center>
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|
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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