mirror of git://gcc.gnu.org/git/gcc.git
96 lines
3.5 KiB
XML
96 lines
3.5 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook" version="5.0"
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xml:id="std.algorithms" xreflabel="Algorithms">
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<?dbhtml filename="algorithms.html"?>
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<info><title>
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Algorithms
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<indexterm><primary>Algorithms</primary></indexterm>
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</title>
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<keywordset>
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<keyword>ISO C++</keyword>
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<keyword>library</keyword>
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<keyword>algorithm</keyword>
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</keywordset>
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</info>
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<para>
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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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</para>
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<orderedlist inheritnum="ignore" continuation="restarts">
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<listitem>
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<para>
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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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</para>
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</listitem>
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<listitem>
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<para>
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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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</para>
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</listitem>
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</orderedlist>
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<para>
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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>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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<emphasis>N</emphasis> 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 <link linkend="std.containers">containers section</link> to keep
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real code readable.
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</para>
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<para>
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The single thing that trips people up the most is the definition
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of <emphasis>range</emphasis> used with iterators; the famous
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"past-the-end" rule that everybody loves to hate. The
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<link linkend="std.iterators">iterators section</link> 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 <emphasis>range</emphasis> into your head (it's not that hard,
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honest!), then the algorithms are a cakewalk.
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</para>
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<!-- Sect1 01 : Non Modifying -->
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<!-- Sect1 02 : Mutating -->
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<section xml:id="std.algorithms.mutating" xreflabel="Mutating"><info><title>Mutating</title></info>
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<section xml:id="algorithms.mutating.swap" xreflabel="swap"><info><title><function>swap</function></title></info>
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<section xml:id="algorithms.swap.specializations" xreflabel="Specializations"><info><title>Specializations</title></info>
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<para>If you call <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> x.swap(y); </code> instead.
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</para>
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<para>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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</para>
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</section>
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</section>
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</section>
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<!-- Sect1 03 : Sorting -->
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</chapter>
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