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| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="the_boost_algorithm_library.Misc.gather"></a><a class="link" href="gather.html" title="gather">gather</a> |
| </h3></div></div></div> |
| <p> |
| The header file 'boost/algorithm/gather.hpp' contains two variants of a single |
| algorithm, <code class="computeroutput"><span class="identifier">gather</span></code>. |
| </p> |
| <p> |
| <code class="computeroutput"><span class="identifier">gather</span><span class="special">()</span></code> |
| takes a collection of elements defined by a pair of iterators and moves the |
| ones satisfying a predicate to them to a position (called the pivot) within |
| the sequence. The algorithm is stable. The result is a pair of iterators |
| that contains the items that satisfy the predicate. |
| </p> |
| <h5> |
| <a name="the_boost_algorithm_library.Misc.gather.h0"></a> |
| <span class="phrase"><a name="the_boost_algorithm_library.Misc.gather.interface"></a></span><a class="link" href="gather.html#the_boost_algorithm_library.Misc.gather.interface">Interface</a> |
| </h5> |
| <p> |
| The function <code class="computeroutput"><span class="identifier">gather</span></code> returns |
| a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></code> of iterators that denote the elements |
| that satisfy the predicate. |
| </p> |
| <p> |
| There are two versions; one takes two iterators, and the other takes a range. |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">algorithm</span> <span class="special">{</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">BidirectionalIterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span><span class="special">></span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">BidirectionalIterator</span><span class="special">,</span><span class="identifier">BidirectionalIterator</span><span class="special">></span> |
| <span class="identifier">gather</span> <span class="special">(</span> <span class="identifier">BidirectionalIterator</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">BidirectionalIterator</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">BidirectionalIterator</span> <span class="identifier">pivot</span><span class="special">,</span> <span class="identifier">Pred</span> <span class="identifier">pred</span> <span class="special">);</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">BidirectionalRange</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Pred</span><span class="special">></span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">BidirectionalRange</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">BidirectionalRange</span><span class="special">>::</span><span class="identifier">type</span><span class="special">></span> |
| <span class="identifier">gather</span> <span class="special">(</span> <span class="keyword">const</span> <span class="identifier">BidirectionalRange</span> <span class="special">&</span><span class="identifier">range</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">BidirectionalRange</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">pivot</span><span class="special">,</span> <span class="identifier">Pred</span> <span class="identifier">pred</span> <span class="special">);</span> |
| |
| <span class="special">}}</span> |
| </pre> |
| <p> |
| </p> |
| <h5> |
| <a name="the_boost_algorithm_library.Misc.gather.h1"></a> |
| <span class="phrase"><a name="the_boost_algorithm_library.Misc.gather.examples"></a></span><a class="link" href="gather.html#the_boost_algorithm_library.Misc.gather.examples">Examples</a> |
| </h5> |
| <p> |
| Given an sequence containing: |
| </p> |
| <pre class="programlisting"><span class="number">0</span> <span class="number">1</span> <span class="number">2</span> <span class="number">3</span> <span class="number">4</span> <span class="number">5</span> <span class="number">6</span> <span class="number">7</span> <span class="number">8</span> <span class="number">9</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| a call to gather ( arr, arr + 10, arr + 4, IsEven ) will result in: |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="number">1</span> <span class="number">3</span> <span class="number">0</span> <span class="number">2</span> <span class="number">4</span> <span class="number">6</span> <span class="number">8</span> <span class="number">5</span> <span class="number">7</span> <span class="number">9</span> |
| <span class="special">|---|-----|</span> |
| <span class="identifier">first</span> <span class="special">|</span> <span class="identifier">second</span> |
| <span class="identifier">pivot</span> |
| </pre> |
| <p> |
| where <code class="computeroutput"><span class="identifier">first</span></code> and <code class="computeroutput"><span class="identifier">second</span></code> are the fields of the pair that |
| is returned by the call. |
| </p> |
| <h5> |
| <a name="the_boost_algorithm_library.Misc.gather.h2"></a> |
| <span class="phrase"><a name="the_boost_algorithm_library.Misc.gather.iterator_requirements"></a></span><a class="link" href="gather.html#the_boost_algorithm_library.Misc.gather.iterator_requirements">Iterator |
| Requirements</a> |
| </h5> |
| <p> |
| <code class="computeroutput"><span class="identifier">gather</span></code> work on bidirectional |
| iterators or better. This requirement comes from the usage of <code class="computeroutput"><span class="identifier">stable_partition</span></code>, which requires bidirectional |
| iterators. Some standard libraries (libstdc++ and libc++, for example) have |
| implementations of <code class="computeroutput"><span class="identifier">stable_partition</span></code> |
| that work with forward iterators. If that is the case, then <code class="computeroutput"><span class="identifier">gather</span></code> will work with forward iterators |
| as well. |
| </p> |
| <h5> |
| <a name="the_boost_algorithm_library.Misc.gather.h3"></a> |
| <span class="phrase"><a name="the_boost_algorithm_library.Misc.gather.storage_requirements"></a></span><a class="link" href="gather.html#the_boost_algorithm_library.Misc.gather.storage_requirements">Storage |
| Requirements</a> |
| </h5> |
| <p> |
| <code class="computeroutput"><span class="identifier">gather</span></code> uses <code class="computeroutput"><span class="identifier">stable_partition</span></code>, which will attempt to |
| allocate temporary memory, but will work in-situ if there is none available. |
| </p> |
| <h5> |
| <a name="the_boost_algorithm_library.Misc.gather.h4"></a> |
| <span class="phrase"><a name="the_boost_algorithm_library.Misc.gather.complexity"></a></span><a class="link" href="gather.html#the_boost_algorithm_library.Misc.gather.complexity">Complexity</a> |
| </h5> |
| <p> |
| If there is sufficient memory available, the run time is linear: <code class="computeroutput"><span class="identifier">O</span><span class="special">(</span><span class="identifier">N</span><span class="special">)</span></code> |
| </p> |
| <p> |
| If there is not any memory available, then the run time is <code class="computeroutput"><span class="identifier">O</span><span class="special">(</span><span class="identifier">N</span> |
| <span class="identifier">log</span> <span class="identifier">N</span><span class="special">)</span></code>. |
| </p> |
| <h5> |
| <a name="the_boost_algorithm_library.Misc.gather.h5"></a> |
| <span class="phrase"><a name="the_boost_algorithm_library.Misc.gather.exception_safety"></a></span><a class="link" href="gather.html#the_boost_algorithm_library.Misc.gather.exception_safety">Exception |
| Safety</a> |
| </h5> |
| <h5> |
| <a name="the_boost_algorithm_library.Misc.gather.h6"></a> |
| <span class="phrase"><a name="the_boost_algorithm_library.Misc.gather.notes"></a></span><a class="link" href="gather.html#the_boost_algorithm_library.Misc.gather.notes">Notes</a> |
| </h5> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2010-2012 Marshall Clow<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> |
| </div></td> |
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