ch15_02.htm

编程珍珠,里面很多好用的代码,大家可以参考学习呵呵,

work right.  This restriction will be lifted in the future.)  See
<a href="ch05_01.htm">Chapter 5, "Pattern Matching"</a>, for details of matching
on Unicode properties.
<a name="INDEX-2845"></a>
</p>
</li>
<li>
<p>
<a name="INDEX-2846"></a><a name="INDEX-2847"></a>
The special pattern <tt class="literal">\X</tt> matches any extended Unicode
sequence (a "combining character sequence" in Standardese), where the
first character is a base character and subsequent characters are mark
characters that apply to the base character.  It is equivalent to
<tt class="literal">(?:\PM\pM*)</tt>:
<blockquote>
<pre class="programlisting">"o\N{COMBINING TILDE BELOW}" =~ /\X/</pre>
</blockquote>

You may not use <tt class="literal">\X</tt> in square brackets, because it
might match multiple characters and it doesn't match any
particular character or set of characters.</p>
</li>
<li>
<p>
<a name="INDEX-2848"></a>
The <tt class="literal">tr///</tt> operator transliterates characters
instead of bytes.  To turn all characters outside the Latin-1 range
into a question mark, you could say:
<blockquote>
<pre class="programlisting">tr/\0-\x{10ffff}/\0-\xff?/;       # utf8 to latin1 char</pre>
</blockquote>
</p>
</li>
<li>
<p>
<a name="INDEX-2849"></a><a name="INDEX-2850"></a><a name="INDEX-2851"></a><a name="INDEX-2852"></a><a name="INDEX-2853"></a>
Case translation operators use the Unicode case translation tables
when provided character input.  Note that <tt class="literal">uc</tt>
translates to uppercase, while <tt class="literal">ucfirst</tt> translates
to titlecase (for languages that make the distinction).  Naturally the
corresponding backslash sequences have the same semantics:
<blockquote>
<pre class="programlisting">$x = "\u$word";       # titlecase first letter of $word
$x = "\U$word";       # uppercase $word
$x = "\l$word";       # lowercase first letter of $word
$x = "\L$word";       # lowercase $word</pre>
</blockquote>
Be careful, because the Unicode case translation tables don't attempt
to provide round-trip mappings in every instance, particularly for
languages that use different numbers of characters for titlecase or
uppercase than they do for the equivalent lowercase letter.  As they
say in the standard, while the case properties themselves are
normative, the case mappings are only informational.
<a name="INDEX-2854"></a>
</p>
</li>
<li>
<p>
<a name="INDEX-2855"></a><a name="INDEX-2856"></a>
Most operators that deal with positions or lengths in the string will
automatically switch to using character positions, including
<tt class="literal">chop</tt>, <tt class="literal">substr</tt>,
<tt class="literal">pos</tt>, <tt class="literal">index</tt>,
<tt class="literal">rindex</tt>, <tt class="literal">sprintf</tt>,
<tt class="literal">write</tt>, and <tt class="literal">length</tt>.  Operators
that deliberately don't switch include <tt class="literal">vec</tt>,
<tt class="literal">pack</tt>, and <tt class="literal">unpack</tt>.  Operators
that really don't care include <tt class="literal">chomp</tt>, as well as
any other operator that treats a string as a bucket of bits, such as
the default <tt class="literal">sort</tt> and the operators dealing with
filenames.
</p>

<blockquote>
<pre class="programlisting">use bytes;
$bytelen = length("I do <img src="figs/he2.gif">&nbsp;<img src="figs/qi4.gif">&nbsp; <img src="figs/dao4.gif"> &nbsp;.");   # 15 bytes
no bytes;
$charlen = length("I do <img src="figs/he2.gif">&nbsp;<img src="figs/qi4.gif">&nbsp;<img src="figs/dao4.gif">&nbsp;.");   # but 9 characters</pre>
</blockquote>
</li>
<li>
<p>
<a name="INDEX-2857"></a><a name="INDEX-2858"></a><a name="INDEX-2859"></a><a name="INDEX-2860"></a>
The <tt class="literal">pack</tt>/<tt class="literal">unpack</tt> letters
"<tt class="literal">c</tt>" and "<tt class="literal">C</tt>" do
<em class="emphasis">not</em> change, since they're often used for
byte-oriented formats.  (Again, think "<tt class="literal">char</tt>" in the
C language.)  However, there is a new "<tt class="literal">U</tt>" specifier
that will convert between UTF-8 characters and integers:
<blockquote>
<pre class="programlisting">pack("U*", 1, 20, 300, 4000) eq v1.20.300.4000</pre>
</blockquote>
</p>
</li>
<li>
<p>
<a name="INDEX-2861"></a><a name="INDEX-2862"></a>
The <tt class="literal">chr</tt> and <tt class="literal">ord</tt> functions work
on characters:
<blockquote>
<pre class="programlisting">chr(1).chr(20).chr(300).chr(4000) eq v1.20.300.4000</pre>
</blockquote>

In other words, <tt class="literal">chr</tt> and <tt class="literal">ord</tt> are
like <tt class="literal">pack("U")</tt> and
<tt class="literal">unpack("U")</tt>, not like
<tt class="literal">pack("C")</tt> and
<tt class="literal">unpack("C")</tt>.  In fact, the latter two are how
you now emulate byte-oriented <tt class="literal">chr</tt> and
<tt class="literal">ord</tt> if you're too lazy to <tt class="literal">use
bytes</tt>.</p>
</li>
<li>
<p>
<a name="INDEX-2863"></a>
And finally, <tt class="literal">scalar reverse</tt> reverses by character
rather than by byte:</p>


<p>
<blockquote>
<pre class="programlisting">"<img src="figs/righthand.gif">&nbsp;<img src="figs/lefthand.gif">" eq reverse "<img src="figs/lefthand.gif">&nbsp;<img src="figs/righthand.gif">"</pre>
</blockquote>
</p>
</li>
</ul>
<p>
<a name="INDEX-2864"></a><a name="INDEX-2865"></a>
If you look in directory
<em class="replaceable">PATH_TO_PERLLIB/unicode</em>, you'll find a
number of files that have to do with defining the semantics above.
The Unicode properties database from the Unicode Consortium is in a
file called <em class="emphasis">Unicode.300</em> (for Unicode 3.0).  This
file has already been processed by <em class="emphasis">mktables.PL</em>
into lots of little <em class="emphasis">.pl</em> files in the same
directory (and in subdirectories <em class="emphasis">Is/</em>,
<em class="emphasis">In/</em>, and <em class="emphasis">To/</em>), some
of which are automatically slurped in by Perl to implement things like
<tt class="literal">\p</tt> (see the <em class="emphasis">Is/</em> and
<em class="emphasis">In/</em> directories) and <tt class="literal">uc</tt> (see
the <em class="emphasis">To/</em> directory).  Other files are slurped
in by modules like the <tt class="literal">use charnames</tt> pragma (see
<em class="emphasis">Name.pl</em>).  But as of this writing, there
are still a number of files that are just sitting there waiting for
you to write an access module for them:
<blockquote>
<pre class="programlisting">
<em class="emphasis">ArabLink.pl</em>
<em class="emphasis">ArabLnkGrp.pl</em>
<em class="emphasis">Bidirectional.pl</em>
<em class="emphasis">Block.pl</em>
<em class="emphasis">Category.pl</em>
<em class="emphasis">CombiningClass.pl</em>
<em class="emphasis">Decomposition.pl</em>
<em class="emphasis">JamoShort.pl</em>
<em class="emphasis">Number.pl</em>
<em class="emphasis">To/Digit.pl</em>
</pre>
</blockquote>
A much more readable summary of Unicode, with many hyperlinks, is in <em class="replaceable">PATH_TO_PERLLIB</em><em class="emphasis">/unicode/Unicode3.html</em>.
<a name="INDEX-2866"></a>
</p>

<p>Note that when the Unicode consortium comes out with a new version,
some of these filenames are likely to change, so you'll have to poke
around.  You can find <em class="replaceable">PATH_TO_PERLLIB</em> with
the following incantation:
<blockquote>
<pre class="programlisting">% <tt class="userinput"><b>perl -MConfig -le 'print $Config{privlib}'</b></tt>
</pre>
</blockquote>

To find out just about everything there is to find out about Unicode, you 
should check out <em class="emphasis">The Unicode Standard, Version 3.0</em>
(ISBN 0-201-61633-5). 
<a name="INDEX-2867"></a>
</p>




<!-- BOTTOM NAV BAR -->

<hr width="515" align="left">
<div class="navbar">
<table width="515" border="0">
<tr>
<td align="left" valign="top" width="172"><a href="ch15_01.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="index.htm"><img src="../gifs/txthome.gif" alt="Home" border="0"></a></td><td align="right" valign="top" width="172"><a href="ch15_03.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td>
</tr>
<tr>
<td align="left" valign="top" width="172">15.1. Building Character</td><td align="center" valign="top" width="171"><a href="index/index.htm"><img src="../gifs/index.gif" alt="Book Index" border="0"></a></td><td align="right" valign="top" width="172">15.3. Caution, <img src="figs/ren2_bold.gif"> Working</td>
</tr>
</table>
</div>
<hr width="515" align="left">

<!-- LIBRARY NAV BAR -->

<img src="../gifs/smnavbar.gif" usemap="#library-map" border="0" alt="Library Navigation Links"><p>
<font size="-1"><a href="copyrght.htm">Copyright &copy; 2001</a> O'Reilly &amp; Associates. All rights reserved.</font>
</p>
<map name="library-map"> <area shape="rect" coords="2,-1,79,99" href="../index.htm"><area shape="rect" coords="84,1,157,108" href="../perlnut/index.htm"><area shape="rect" coords="162,2,248,125" href="../prog/index.htm"><area shape="rect" coords="253,2,326,130" href="../advprog/index.htm"><area shape="rect" coords="332,1,407,112" href="../cookbook/index.htm"><area shape="rect" coords="414,2,523,103" href="../sysadmin/index.htm">
</map>

<!-- END OF BODY -->

</body>
</html>