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10<title>The MPL Reference Manual: at_c</title>
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13<body class="docframe refmanual">
14<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./at.html" class="navigation-link">Prev</a>&nbsp;<a href="./back.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./at.html" class="navigation-link">Back</a>&nbsp;<a href="./back.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./intrinsic-metafunctions.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
15<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="./at-c.html" class="navigation-link">at_c</a></td>
16</tr></table><div class="header-separator"></div>
17<div class="section" id="at-c">
18<h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id354" name="at-c">at_c</a></h1>
19<div class="section" id="intrinsic-at-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22template&lt;
23      typename Sequence
24    , long n
25    &gt;
26struct <a href="./at-c.html" class="identifier">at_c</a>
27{
28    typedef <em>unspecified</em> type;
29};
30</pre>
31</div>
32<div class="section" id="intrinsic-at-description">
33<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
34<p>Returns a type identical to the <tt class="literal"><span class="pre">n</span></tt>th element from the beginning of
35the sequence. <tt class="literal"><span class="pre"><a href="./at-c.html" class="identifier">at_c</a>&lt;Sequence,n&gt;::type</span></tt> is a shorcut notation for
36<tt class="literal"><span class="pre"><a href="./at.html" class="identifier">at</a>&lt;</span> <span class="pre">Sequence,</span> <span class="pre"><a href="./long.html" class="identifier">long_</a>&lt;n&gt;</span> <span class="pre">&gt;::type</span></tt>.</p>
37</div>
38<div class="section" id="intrinsic-at-header">
39<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
40<pre class="literal-block">
41#include &lt;<a href="../../../../boost/mpl/at.hpp" class="header">boost/mpl/at.hpp</a>&gt;
42</pre>
43</div>
44<div class="section" id="intrinsic-at-parameters">
45<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
46<table border="1" class="table">
47<colgroup>
48<col width="15%" />
49<col width="36%" />
50<col width="48%" />
51</colgroup>
52<thead valign="bottom">
53<tr><th>Parameter</th>
54<th>Requirement</th>
55<th>Description</th>
56</tr>
57</thead>
58<tbody valign="top">
59<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
60<td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
61<td>A sequence to be examined.</td>
62</tr>
63<tr><td><tt class="literal"><span class="pre">n</span></tt></td>
64<td>A compile-time integral constant</td>
65<td>An offset from the beginning of the sequence
66specifying the element to be retrieved.</td>
67</tr>
68</tbody>
69</table>
70</div>
71<div class="section" id="intrinsic-at-expression-semantics">
72<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
73<pre class="literal-block">
74typedef <a href="./at-c.html" class="identifier">at_c</a>&lt;Sequence,n&gt;::type t;
75</pre>
76<table class="field-list" frame="void" rules="none">
77<col class="field-name" />
78<col class="field-body" />
79<tbody valign="top">
80<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type</td>
81</tr>
82<tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">0</span> <span class="pre">&lt;=</span> <span class="pre">n</span> <span class="pre">&lt;</span> <span class="pre"><a href="./size.html" class="identifier">size</a>&lt;Sequence&gt;::value</span></tt></td>
83</tr>
84<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
85<pre class="last literal-block">
86typedef <a href="./at.html" class="identifier">at</a>&lt; Sequence, <a href="./long.html" class="identifier">long_</a>&lt;n&gt; &gt;::type t;
87</pre>
88</td>
89</tr>
90</tbody>
91</table>
92</div>
93<div class="section" id="at-complexity">
94<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
95<table border="1" class="table">
96<colgroup>
97<col width="47%" />
98<col width="53%" />
99</colgroup>
100<thead valign="bottom">
101<tr><th>Sequence archetype</th>
102<th>Complexity</th>
103</tr>
104</thead>
105<tbody valign="top">
106<tr><td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
107<td>Linear.</td>
108</tr>
109<tr><td><a class="reference" href="./random-access-sequence.html">Random Access Sequence</a></td>
110<td>Amortized constant time.</td>
111</tr>
112</tbody>
113</table>
114</div>
115<div class="section" id="intrinsic-at-example">
116<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
117<pre class="literal-block">
118typedef <a href="./range-c.html" class="identifier">range_c</a>&lt;long,10,50&gt; range;
119<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( (<a href="./at-c.html" class="identifier">at_c</a>&lt; range,0 &gt;::value), ==, 10 );
120<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( (<a href="./at-c.html" class="identifier">at_c</a>&lt; range,10 &gt;::value), ==, 20 );
121<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( (<a href="./at-c.html" class="identifier">at_c</a>&lt; range,40 &gt;::value), ==, 50 );
122</pre>
123</div>
124<div class="section" id="intrinsic-at-see-also">
125<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
126<p><a class="reference" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference" href="./random-access-sequence.html">Random Access Sequence</a>, <a class="refentry reference" href="./at.html"><tt class="refentry literal"><span class="pre">at</span></tt></a>, <a class="refentry reference" href="./front.html"><tt class="refentry literal"><span class="pre">front</span></tt></a>, <a class="refentry reference" href="./back.html"><tt class="refentry literal"><span class="pre">back</span></tt></a></p>
127<!-- modtime: November 13, 2004 01:23:57 +0000 -->
128<!-- Sequences/Intrinsic Metafunctions//back -->
129</div>
130</div>
131
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