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| 6 | <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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| 7 | <head>
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| 8 | <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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| 9 | <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" />
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| 10 | <meta name="KEYWORDS" content="HOWTO, libstdc++, GCC, g++, libg++, STL" />
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| 11 | <meta name="DESCRIPTION" content="HOWTO for the libstdc++ chapter 25." />
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| 12 | <meta name="GENERATOR" content="vi and eight fingers" />
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| 13 | <title>libstdc++-v3 HOWTO: Chapter 25</title>
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| 14 | <link rel="StyleSheet" href="../lib3styles.css" />
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| 15 | </head>
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| 16 | <body>
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| 17 |
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| 18 | <h1 class="centered"><a name="top">Chapter 25: Algorithms</a></h1>
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| 19 |
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| 20 | <p>Chapter 25 deals with the generalized subroutines for automatically
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| 21 | transforming lemmings into gold.
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| 22 | </p>
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| 23 |
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| 24 |
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| 25 | <!-- ####################################################### -->
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| 26 | <hr />
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| 27 | <h1>Contents</h1>
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| 28 | <ul>
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| 29 | <li><a href="#1">Prerequisites</a></li>
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| 30 | <li><a href="#2">Special <code>swap</code>s</a></li>
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| 31 | </ul>
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| 32 |
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| 33 | <hr />
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| 34 |
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| 35 | <!-- ####################################################### -->
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| 36 |
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| 37 | <h2><a name="1">Prerequisites</a></h2>
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| 38 | <p>The neatest accomplishment of the algorithms chapter is that all the
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| 39 | work is done via iterators, not containers directly. This means two
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| 40 | important things:
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| 41 | </p>
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| 42 | <ol>
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| 43 | <li>Anything that behaves like an iterator can be used in one of
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| 44 | these algorithms. Raw pointers make great candidates, thus
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| 45 | built-in arrays are fine containers, as well as your own iterators.
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| 46 | </li>
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| 47 | <li>The algorithms do not (and cannot) affect the container as a
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| 48 | whole; only the things between the two iterator endpoints. If
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| 49 | you pass a range of iterators only enclosing the middle third of
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| 50 | a container, then anything outside that range is inviolate.
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| 51 | </li>
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| 52 | </ol>
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| 53 | <p>Even strings can be fed through the algorithms here, although the
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| 54 | string class has specialized versions of many of these functions (for
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| 55 | example, <code>string::find()</code>). Most of the examples on this
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| 56 | page will use simple arrays of integers as a playground for
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| 57 | algorithms, just to keep things simple.
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| 58 | <a name="Nsize">The use of <strong>N</strong></a> as a size in the
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| 59 | examples is to keep things easy to read but probably won't be valid
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| 60 | code. You can use wrappers such as those described in the
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| 61 | <a href="../23_containers/howto.html">containers chapter</a> to keep
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| 62 | real code readable.
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| 63 | </p>
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| 64 | <p>The single thing that trips people up the most is the definition of
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| 65 | <em>range</em> used with iterators; the famous
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| 66 | "past-the-end" rule that everybody loves to hate. The
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| 67 | <a href="../24_iterators/howto.html#2">iterators chapter</a> of this
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| 68 | document has a complete explanation of this simple rule that seems to
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| 69 | cause so much confusion. Once you get <em>range</em> into your head
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| 70 | (it's not that hard, honest!), then the algorithms are a cakewalk.
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| 71 | </p>
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| 72 | <p>Return <a href="#top">to top of page</a> or
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| 73 | <a href="../faq/index.html">to the FAQ</a>.
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| 74 | </p>
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| 75 |
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| 76 | <hr />
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| 77 | <h2><a name="2">Special <code>swap</code>s</a></h2>
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| 78 | <p>If you call <code> std::swap(x,y); </code> where x and y are standard
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| 79 | containers, then the call will automatically be replaced by a call to
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| 80 | <code> x.swap(y); </code> instead.
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| 81 | </p>
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| 82 | <p>This allows member functions of each container class to take over, and
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| 83 | containers' swap functions should have O(1) complexity according to
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| 84 | the standard. (And while "should" allows implementations to
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| 85 | behave otherwise and remain compliant, this implementation does in
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| 86 | fact use constant-time swaps.) This should not be surprising, since
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| 87 | for two containers of the same type to swap contents, only some
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| 88 | internal pointers to storage need to be exchanged.
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| 89 | </p>
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| 90 | <p>Return <a href="#top">to top of page</a> or
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| 91 | <a href="../faq/index.html">to the FAQ</a>.
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| 92 | </p>
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| 93 |
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| 94 |
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| 95 |
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| 96 |
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| 97 | <!-- ####################################################### -->
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| 98 |
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| 99 | <hr />
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| 100 | <p class="fineprint"><em>
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| 101 | See <a href="../17_intro/license.html">license.html</a> for copying conditions.
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| 102 | Comments and suggestions are welcome, and may be sent to
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| 103 | <a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
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| 104 | </em></p>
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| 105 |
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| 106 |
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| 107 | </body>
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| 108 | </html>
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