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<title>Unicode Regular Expression Algorithms</title>
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<div class="titlepage"><div><div><h5 class="title">
<a name="boost_regex.ref.non_std_strings.icu.unicode_algo"></a><a class="link" href="unicode_algo.html" title="Unicode Regular Expression Algorithms">Unicode
Regular Expression Algorithms</a>
</h5></div></div></div>
<p>
The regular expression algorithms <a class="link" href="../../regex_match.html" title="regex_match"><code class="computeroutput"><span class="identifier">regex_match</span></code></a>, <a class="link" href="../../regex_search.html" title="regex_search"><code class="computeroutput"><span class="identifier">regex_search</span></code></a> and <a class="link" href="../../regex_replace.html" title="regex_replace"><code class="computeroutput"><span class="identifier">regex_replace</span></code></a> all expect that
the character sequence upon which they operate, is encoded in the same
character encoding as the regular expression object with which they are
used. For Unicode regular expressions that behavior is undesirable: while
we may want to process the data in UTF-32 "chunks", the actual
data is much more likely to encoded as either UTF-8 or UTF-16. Therefore
the header <boost/regex/icu.hpp> provides a series of thin wrappers
around these algorithms, called <code class="computeroutput"><span class="identifier">u32regex_match</span></code>,
<code class="computeroutput"><span class="identifier">u32regex_search</span></code>, and
<code class="computeroutput"><span class="identifier">u32regex_replace</span></code>. These
wrappers use iterator-adapters internally to make external UTF-8 or UTF-16
data look as though it's really a UTF-32 sequence, that can then be passed
on to the "real" algorithm.
</p>
<h5>
<a name="boost_regex.ref.non_std_strings.icu.unicode_algo.h0"></a>
<span class="phrase"><a name="boost_regex.ref.non_std_strings.icu.unicode_algo.u32regex_match"></a></span><a class="link" href="unicode_algo.html#boost_regex.ref.non_std_strings.icu.unicode_algo.u32regex_match">u32regex_match</a>
</h5>
<p>
For each <a class="link" href="../../regex_match.html" title="regex_match"><code class="computeroutput"><span class="identifier">regex_match</span></code></a>
algorithm defined by <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">regex</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>,
then <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">regex</span><span class="special">/</span><span class="identifier">icu</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> defines an overloaded algorithm that
takes the same arguments, but which is called <code class="computeroutput"><span class="identifier">u32regex_match</span></code>,
and which will accept UTF-8, UTF-16 or UTF-32 encoded data, as well as
an ICU UnicodeString as input.
</p>
<p>
Example: match a password, encoded in a UTF-16 UnicodeString:
</p>
<pre class="programlisting"><span class="comment">//</span>
<span class="comment">// Find out if *password* meets our password requirements,</span>
<span class="comment">// as defined by the regular expression *requirements*.</span>
<span class="comment">//</span>
<span class="keyword">bool</span> <span class="identifier">is_valid_password</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">UnicodeString</span><span class="special">&</span> <span class="identifier">password</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">UnicodeString</span><span class="special">&</span> <span class="identifier">requirements</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">u32regex_match</span><span class="special">(</span><span class="identifier">password</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_u32regex</span><span class="special">(</span><span class="identifier">requirements</span><span class="special">));</span>
<span class="special">}</span>
</pre>
<p>
Example: match a UTF-8 encoded filename:
</p>
<pre class="programlisting"><span class="comment">//</span>
<span class="comment">// Extract filename part of a path from a UTF-8 encoded std::string and return the result</span>
<span class="comment">// as another std::string:</span>
<span class="comment">//</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">get_filename</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">path</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">u32regex</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_u32regex</span><span class="special">(</span><span class="string">"(?:\\A|.*\\\\)([^\\\\]+)"</span><span class="special">);</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">smatch</span> <span class="identifier">what</span><span class="special">;</span>
<span class="keyword">if</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">u32regex_match</span><span class="special">(</span><span class="identifier">path</span><span class="special">,</span> <span class="identifier">what</span><span class="special">,</span> <span class="identifier">r</span><span class="special">))</span>
<span class="special">{</span>
<span class="comment">// extract $1 as a std::string:</span>
<span class="keyword">return</span> <span class="identifier">what</span><span class="special">.</span><span class="identifier">str</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
<span class="special">}</span>
<span class="keyword">else</span>
<span class="special">{</span>
<span class="keyword">throw</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span><span class="special">(</span><span class="string">"Invalid pathname"</span><span class="special">);</span>
<span class="special">}</span>
<span class="special">}</span>
</pre>
<h5>
<a name="boost_regex.ref.non_std_strings.icu.unicode_algo.h1"></a>
<span class="phrase"><a name="boost_regex.ref.non_std_strings.icu.unicode_algo.u32regex_search"></a></span><a class="link" href="unicode_algo.html#boost_regex.ref.non_std_strings.icu.unicode_algo.u32regex_search">u32regex_search</a>
</h5>
<p>
For each <a class="link" href="../../regex_search.html" title="regex_search"><code class="computeroutput"><span class="identifier">regex_search</span></code></a>
algorithm defined by <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">regex</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>,
then <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">regex</span><span class="special">/</span><span class="identifier">icu</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> defines an overloaded algorithm that
takes the same arguments, but which is called <code class="computeroutput"><span class="identifier">u32regex_search</span></code>,
and which will accept UTF-8, UTF-16 or UTF-32 encoded data, as well as
an ICU UnicodeString as input.
</p>
<p>
Example: search for a character sequence in a specific language block:
</p>
<pre class="programlisting"><span class="identifier">UnicodeString</span> <span class="identifier">extract_greek</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">UnicodeString</span><span class="special">&</span> <span class="identifier">text</span><span class="special">)</span>
<span class="special">{</span>
<span class="comment">// searches through some UTF-16 encoded text for a block encoded in Greek,</span>
<span class="comment">// this expression is imperfect, but the best we can do for now - searching</span>
<span class="comment">// for specific scripts is actually pretty hard to do right.</span>
<span class="comment">//</span>
<span class="comment">// Here we search for a character sequence that begins with a Greek letter,</span>
<span class="comment">// and continues with characters that are either not-letters ( [^[:L*:]] )</span>
<span class="comment">// or are characters in the Greek character block ( [\\x{370}-\\x{3FF}] ).</span>
<span class="comment">//</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">u32regex</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_u32regex</span><span class="special">(</span>
<span class="identifier">L</span><span class="string">"[\\x{370}-\\x{3FF}](?:[^[:L*:]]|[\\x{370}-\\x{3FF}])*"</span><span class="special">);</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">u16match</span> <span class="identifier">what</span><span class="special">;</span>
<span class="keyword">if</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">u32regex_search</span><span class="special">(</span><span class="identifier">text</span><span class="special">,</span> <span class="identifier">what</span><span class="special">,</span> <span class="identifier">r</span><span class="special">))</span>
<span class="special">{</span>
<span class="comment">// extract $0 as a UnicodeString:</span>
<span class="keyword">return</span> <span class="identifier">UnicodeString</span><span class="special">(</span><span class="identifier">what</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">what</span><span class="special">.</span><span class="identifier">length</span><span class="special">(</span><span class="number">0</span><span class="special">));</span>
<span class="special">}</span>
<span class="keyword">else</span>
<span class="special">{</span>
<span class="keyword">throw</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span><span class="special">(</span><span class="string">"No Greek found!"</span><span class="special">);</span>
<span class="special">}</span>
<span class="special">}</span>
</pre>
<h5>
<a name="boost_regex.ref.non_std_strings.icu.unicode_algo.h2"></a>
<span class="phrase"><a name="boost_regex.ref.non_std_strings.icu.unicode_algo.u32regex_replace"></a></span><a class="link" href="unicode_algo.html#boost_regex.ref.non_std_strings.icu.unicode_algo.u32regex_replace">u32regex_replace</a>
</h5>
<p>
For each <a class="link" href="../../regex_replace.html" title="regex_replace"><code class="computeroutput"><span class="identifier">regex_replace</span></code></a> algorithm defined
by <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">regex</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>, then <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">regex</span><span class="special">/</span><span class="identifier">icu</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
defines an overloaded algorithm that takes the same arguments, but which
is called <code class="computeroutput"><span class="identifier">u32regex_replace</span></code>,
and which will accept UTF-8, UTF-16 or UTF-32 encoded data, as well as
an ICU UnicodeString as input. The input sequence and the format string
specifier passed to the algorithm, can be encoded independently (for
example one can be UTF-8, the other in UTF-16), but the result string
/ output iterator argument must use the same character encoding as the
text being searched.
</p>
<p>
Example: Credit card number reformatting:
</p>
<pre class="programlisting"><span class="comment">//</span>
<span class="comment">// Take a credit card number as a string of digits, </span>
<span class="comment">// and reformat it as a human readable string with "-"</span>
<span class="comment">// separating each group of four digit;, </span>
<span class="comment">// note that we're mixing a UTF-32 regex, with a UTF-16</span>
<span class="comment">// string and a UTF-8 format specifier, and it still all </span>
<span class="comment">// just works:</span>
<span class="comment">//</span>
<span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">u32regex</span> <span class="identifier">e</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_u32regex</span><span class="special">(</span>
<span class="string">"\\A(\\d{3,4})[- ]?(\\d{4})[- ]?(\\d{4})[- ]?(\\d{4})\\z"</span><span class="special">);</span>
<span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">human_format</span> <span class="special">=</span> <span class="string">"$1-$2-$3-$4"</span><span class="special">;</span>
<span class="identifier">UnicodeString</span> <span class="identifier">human_readable_card_number</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">UnicodeString</span><span class="special">&</span> <span class="identifier">s</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">u32regex_replace</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">human_format</span><span class="special">);</span>
<span class="special">}</span>
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 1998-2013 John Maddock<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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