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60 lines
5.6 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 11. Algorithms</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, library, algorithm" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="std_contents.html" title="Part II. Standard Contents" /><link rel="prev" href="iterators.html" title="Chapter 10. Iterators" /><link rel="next" href="numerics.html" title="Chapter 12. Numerics" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 11.
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Algorithms
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</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="iterators.html">Prev</a> </td><th width="60%" align="center">Part II.
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Standard Contents
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</th><td width="20%" align="right"> <a accesskey="n" href="numerics.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="std.algorithms"></a>Chapter 11.
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Algorithms
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<a id="idm140623070692736" class="indexterm"></a>
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</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><a href="algorithms.html#std.algorithms.mutating">Mutating</a></span></dt><dd><dl><dt><span class="section"><a href="algorithms.html#algorithms.mutating.swap"><code class="function">swap</code></a></span></dt><dd><dl><dt><span class="section"><a href="algorithms.html#algorithms.swap.specializations">Specializations</a></span></dt></dl></dd></dl></dd></dl></div><p>
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The neatest accomplishment of the algorithms section is that all the
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work is done via iterators, not containers directly. This means two
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important things:
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</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
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Anything that behaves like an iterator can be used in one of
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these algorithms. Raw pointers make great candidates, thus
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built-in arrays are fine containers, as well as your own
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iterators.
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</p></li><li class="listitem"><p>
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The algorithms do not (and cannot) affect the container as a
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whole; only the things between the two iterator endpoints. If
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you pass a range of iterators only enclosing the middle third of
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a container, then anything outside that range is inviolate.
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</p></li></ol></div><p>
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Even strings can be fed through the algorithms here, although the
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string class has specialized versions of many of these functions
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(for example, <code class="code">string::find()</code>). Most of the examples
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on this page will use simple arrays of integers as a playground
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for algorithms, just to keep things simple. The use of
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<span class="emphasis"><em>N</em></span> as a size in the examples is to keep things
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easy to read but probably won't be valid code. You can use wrappers
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such as those described in
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the <a class="link" href="containers.html" title="Chapter 9. Containers">containers section</a> to keep
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real code readable.
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</p><p>
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The single thing that trips people up the most is the definition
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of <span class="emphasis"><em>range</em></span> used with iterators; the famous
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"past-the-end" rule that everybody loves to hate. The
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<a class="link" href="iterators.html" title="Chapter 10. Iterators">iterators section</a> of this
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document has a complete explanation of this simple rule that seems
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to cause so much confusion. Once you
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get <span class="emphasis"><em>range</em></span> into your head (it's not that hard,
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honest!), then the algorithms are a cakewalk.
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</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.algorithms.mutating"></a>Mutating</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="algorithms.mutating.swap"></a><code class="function">swap</code></h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="algorithms.swap.specializations"></a>Specializations</h4></div></div></div><p>If you call <code class="code"> std::swap(x,y); </code> where x and y are standard
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containers, then the call will automatically be replaced by a call to
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<code class="code"> x.swap(y); </code> instead.
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</p><p>This allows member functions of each container class to take over, and
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containers' swap functions should have O(1) complexity according to
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the standard. (And while "should" allows implementations to
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behave otherwise and remain compliant, this implementation does in
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fact use constant-time swaps.) This should not be surprising, since
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for two containers of the same type to swap contents, only some
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internal pointers to storage need to be exchanged.
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</p></div></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="iterators.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="std_contents.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="numerics.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 10.
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Iterators
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</td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 12.
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Numerics
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