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7 <title>The MPL Reference Manual: size
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14 <div class=
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"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">
22 struct
<a href=
"./size.html" class=
"identifier">size
</a>
24 typedef
<em>unspecified
</em> type;
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
31 in 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>
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>>
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>
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">
51 <thead valign=
"bottom">
52 <tr><th class=
"head">Parameter
</th>
53 <th class=
"head">Requirement
</th>
54 <th class=
"head">Description
</th>
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>
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">
69 typedef
<a href=
"./size.html" class=
"identifier">size
</a><s
>::type n;
71 <table class=
"docutils field-list" frame=
"void" rules=
"none">
72 <col class=
"field-name" />
73 <col class=
"field-body" />
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>
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">
80 typedef
<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;
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>
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
93 the 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
94 linear 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.
96 The 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>
99 <div class=
"section" id=
"id369">
100 <h3><a class=
"subsection-title" href=
"#example" name=
"example">Example
</a></h3>
101 <pre class=
"literal-block">
102 typedef list0
<> empty_list;
103 typedef
<a href=
"./vector-c.html" class=
"identifier">vector_c
</a><int,
0,
1,
2,
3,
4,
5> numbers;
104 typedef
<a href=
"./range-c.html" class=
"identifier">range_c
</a><int,
0,
100> more_numbers;
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 );
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 -->
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120 <td><div class=
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"copyright">Copyright ©
2001-
2009 Aleksey Gurtovoy and David Abrahams
</div>
121 Distributed under the Boost Software License, Version
1.0. (See accompanying
122 file LICENSE_1_0.txt or copy at
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