1<?xml version="1.0" encoding="utf-8" ?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4<head> 5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 6<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> 7<title>The MPL Reference Manual: size</title> 8<link rel="stylesheet" href="../style.css" type="text/css" /> 9</head> 10<body class="docframe refmanual"> 11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./sequence-tag.html" class="navigation-link">Prev</a> <a href="./value-type.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./sequence-tag.html" class="navigation-link">Back</a> <a href="./value-type.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./intrinsic-metafunctions.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 12<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./sequences.html" class="navigation-link">Sequences</a> / <a href="./intrinsic-metafunctions.html" class="navigation-link">Intrinsic Metafunctions</a> / <a href="./size.html" class="navigation-link">size</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="size"> 15<h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1446">size</a></h1> 16<div class="section" id="id362"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19template< 20 typename Sequence 21 > 22struct <a href="./size.html" class="identifier">size</a> 23{ 24 typedef <em>unspecified</em> type; 25}; 26</pre> 27</div> 28<div class="section" id="id363"> 29<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 30<p><tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a></span></tt> returns the number of elements in the sequence, that is, the number of elements 31in the range [<tt class="literal"><span class="pre"><a href="./begin.html" class="identifier">begin</a><Sequence>::type</span></tt>, <tt class="literal"><span class="pre"><a href="./end.html" class="identifier">end</a><Sequence>::type</span></tt>).</p> 32</div> 33<div class="section" id="id364"> 34<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 35<pre class="literal-block"> 36#include <<a href="../../../../boost/mpl/size.hpp" class="header">boost/mpl/size.hpp</a>> 37</pre> 38</div> 39<div class="section" id="id365"> 40<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3> 41<p><a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a></p> 42</div> 43<div class="section" id="id366"> 44<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> 45<table border="1" class="docutils table"> 46<colgroup> 47<col width="18%" /> 48<col width="27%" /> 49<col width="55%" /> 50</colgroup> 51<thead valign="bottom"> 52<tr><th class="head">Parameter</th> 53<th class="head">Requirement</th> 54<th class="head">Description</th> 55</tr> 56</thead> 57<tbody valign="top"> 58<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td> 59<td><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a></td> 60<td>A sequence to query.</td> 61</tr> 62</tbody> 63</table> 64</div> 65<div class="section" id="id367"> 66<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 67<p>For any <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt>:</p> 68<pre class="literal-block"> 69typedef <a href="./size.html" class="identifier">size</a><s>::type n; 70</pre> 71<table class="docutils field-list" frame="void" rules="none"> 72<col class="field-name" /> 73<col class="field-body" /> 74<tbody valign="top"> 75<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</p> 76</td> 77</tr> 78<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p> 79<pre class="literal-block"> 80typedef <a href="./distance.html" class="identifier">distance</a>< <a href="./begin.html" class="identifier">begin</a><s>::type,<a href="./end.html" class="identifier">end</a><s>::type >::type n; 81</pre> 82</td> 83</tr> 84<tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><p class="first last"><tt class="literal"><span class="pre">n::value</span> <span class="pre">>=</span> <span class="pre">0</span></tt>.</p> 85</td> 86</tr> 87</tbody> 88</table> 89</div> 90<div class="section" id="id368"> 91<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3> 92<p>The complexity of the <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a></span></tt> metafunction directly depends on the implementation of 93the particular sequence it is applied to. In the worst case, <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a></span></tt> guarantees a 94linear complexity.</p> 95<p>If the <tt class="literal"><span class="pre">s</span></tt> is a <a class="reference internal" href="./random-access-sequence.html">Random Access Sequence</a>, <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a><s>::type</span></tt> is an <em>O(1)</em> operation. 96The opposite is not necessarily true — for example, a sequence class that models 97<a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> might still give us an <em>O(1)</em> <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a></span></tt> implementation.</p> 98</div> 99<div class="section" id="id369"> 100<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 101<pre class="literal-block"> 102typedef list0<> empty_list; 103typedef <a href="./vector-c.html" class="identifier">vector_c</a><int,0,1,2,3,4,5> numbers; 104typedef <a href="./range-c.html" class="identifier">range_c</a><int,0,100> more_numbers; 105 106<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a><<a href="./list.html" class="identifier">list</a>>::value, ==, 0 ); 107<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a><numbers>::value, ==, 5 ); 108<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( <a href="./size.html" class="identifier">size</a><more_numbers>::value, ==, 100 ); 109</pre> 110</div> 111<div class="section" id="id370"> 112<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 113<p><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference internal" href="./random-access-sequence.html">Random Access Sequence</a>, <a class="reference internal" href="./empty.html">empty</a>, <a class="reference internal" href="./begin.html">begin</a>, <a class="reference internal" href="./end.html">end</a>, <a class="reference internal" href="./distance.html">distance</a></p> 114<!-- Sequences/Intrinsic Metafunctions//value_type --> 115</div> 116</div> 117 118<div class="footer-separator"></div> 119<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./sequence-tag.html" class="navigation-link">Prev</a> <a href="./value-type.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./sequence-tag.html" class="navigation-link">Back</a> <a href="./value-type.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./intrinsic-metafunctions.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 120<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 121Distributed under the Boost Software License, Version 1.0. (See accompanying 122file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> 123</html> 124