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<header data-kunai-mdinfo="{"meta": {"header": ["iterator"], "namespace": ["std"], "id-type": ["class template"]}, "sources": [{"id": "e5b8999d705b9ee9155459fd71c137b83b4c6702", "source": "#include <iostream>\n#include <vector>\n#include <iterator>\n\n// \u7bc4\u56f2\u306e\u5408\u8a08\u5024\u3092\u8a08\u7b97\u3059\u308b\ntemplate <class Iterator>\ntypename std::iterator_traits<Iterator>::value_type\n sum(Iterator first, Iterator last)\n{\n // \u30a4\u30c6\u30ec\u30fc\u30bf\u306e\u578b\u304b\u3089\u5024\u578b\u3092\u53d6\u5f97\u3059\u308b\n using value_type = typename std::iterator_traits<Iterator>::value_type;\n\n // \u53d6\u5f97\u3057\u305f\u5024\u578b\u306e\u5909\u6570\u3092\u5b9a\u7fa9\u3057\u3001\u5408\u8a08\u5024\u3092\u8a08\u7b97\u3059\u308b\n value_type result = value_type();\n for (; first != last; ++first) {\n result += *first;\n }\n return result;\n}\n\nint main()\n{\n // std::vector\n {\n std::vector<int> v = {1, 2, 3, 4, 5};\n\n int result = sum(std::begin(v), std::end(v));\n std::cout << result << std::endl;\n }\n // \u30dd\u30a4\u30f3\u30bf\n {\n int ar[] = {1, 2, 3, 4, 5};\n\n int result = sum(std::begin(ar), std::end(ar));\n std::cout << result << std::endl;\n }\n}\n"}], "page_id": ["reference", "iterator", "iterator_traits"]}">
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最終更新日時(UTC):
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2025年07月14日 14時12分05秒
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<div class="identifier-type">class template</div><div class="header"><iterator></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">iterator_traits</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">Iterator</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc"><a href="">iterator_traits</a></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">difference_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">Iterator</span><span class="o">::</span><span class="n">difference_type</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">Iterator</span><span class="o">::</span><span class="n">value_type</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">Iterator</span><span class="o">::</span><span class="n">pointer</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">Iterator</span><span class="o">::</span><span class="n">reference</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">iterator_category</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">Iterator</span><span class="o">::</span><span class="n">iterator_category</span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="w"> </span><span class="c1">// ポインタに対する特殊化、C++20から</span>
<span class="w"> </span><span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="w"> </span><span class="k">requires</span><span class="w"> </span><span class="n"><a href="../type_traits/is_object.html">is_object_v</a></span><span class="o"><</span><span class="n">T</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc"><a href="">iterator_traits</a></span><span class="o"><</span><span class="n">T</span><span class="o">*></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">iterator_concept</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="iterator_tag.html">contiguous_iterator_tag</a></span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">iterator_category</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="iterator_tag.html">random_access_iterator_tag</a></span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../type_traits/remove_cv.html">remove_cv_t</a></span><span class="o"><</span><span class="n">T</span><span class="o">></span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">difference_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../cstddef/ptrdiff_t.html">ptrdiff_t</a></span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="o">*</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="o">&</span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="w"> </span><span class="c1">// ポインタに対する特殊化、C++17まで</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc"><a href="">iterator_traits</a></span><span class="o"><</span><span class="n">T</span><span class="o">*></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">difference_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../cstddef/ptrdiff_t.html">ptrdiff_t</a></span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="p">;</span><span class="w"> </span><span class="c1">// C++03</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../type_traits/remove_cv.html">remove_cv_t</a></span><span class="o"><</span><span class="n">T</span><span class="o">></span><span class="p">;</span><span class="w"> </span><span class="c1">// C++17</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="o">*</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="o">&</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">iterator_category</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="iterator_tag.html">random_access_iterator_tag</a></span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc"><a href="">iterator_traits</a></span><span class="o"><</span><span class="k">const</span><span class="w"> </span><span class="n">T</span><span class="o">*></span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="c1">// C++14まで</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">difference_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../cstddef/ptrdiff_t.html">ptrdiff_t</a></span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">T</span><span class="o">*</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">T</span><span class="o">&</span><span class="p">;</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">iterator_category</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="iterator_tag.html">random_access_iterator_tag</a></span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p><code>iterator_traits</code>は、イテレータに関する型情報を取得するためのクラスである。</p>
<p>イテレータが指す値型、分類を取得でき、ポインタに対しても一様に適用できる。</p>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>型</th>
<th>説明</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>difference_type</code></td>
<td>イテレータの差を表す符号付き整数型</td>
</tr>
<tr>
<td><code>value_type</code></td>
<td>イテレータが指している値型</td>
</tr>
<tr>
<td><code>pointer</code></td>
<td>ポインタ型</td>
</tr>
<tr>
<td><code>reference</code></td>
<td>イテレータが指している参照型</td>
</tr>
<tr>
<td><code>iterator_category</code></td>
<td>イテレータの分類を表す型(参照： <a href="iterator_tag.html">iterator tag</a>)</td>
</tr>
</tbody>
</table>
<h2>定義</h2>
<p>任意のイテレータ型を<code>I</code>とする。</p>
<h3>C++17</h3>
<ul>
<li><code>iterator_traits<I></code>の特殊化がある場合、それが使用される。</li>
<li>特殊化されておらず、<code>I</code>が5つのメンバ型（<code>difference_type, value_type, pointer, reference, iterator_category</code>）を定義している場合、それを用いて上記にあるように定義される。</li>
<li>それ以外の場合、<code>iterator_traits<I></code>は5つのメンバ型のいずれも定義しない。</li>
</ul>
<h3>C++20</h3>
<ul>
<li>
<p><code>iterator_traits<I></code>の特殊化がある場合、それが使用される。</p>
</li>
<li>
<p>特殊化されておらず、<code>I</code>が4つのメンバ型（<code>difference_type, value_type, reference, iterator_category</code>）を定義している場合、それぞれのメンバ型は次のように定義される
<br />
<div class="codehilite"><pre><span></span><code><span class="k">using</span><span class="w"> </span><span class="n">difference_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">I</span><span class="o">::</span><span class="n">difference_type</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">I</span><span class="o">::</span><span class="n">value_type</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kt">void</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">I</span><span class="o">::</span><span class="n">reference</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">iterator_category</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">I</span><span class="o">::</span><span class="n">iterator_category</span><span class="p">;</span>
</code></pre></div>
</p>
<ul>
<li>この時、<code>I::pointer</code>も定義されているならば、<code>pointer</code>はそれを用いて定義される。</li>
</ul>
</li>
<li>
<p>いずれかのメンバ型が定義されておらず、<code>I</code>が<code>cpp17-input-iterator</code>コンセプトを満たす場合、それぞれのメンバ型は次のように定義される
<br />
<div class="codehilite"><pre><span></span><code><span class="k">using</span><span class="w"> </span><span class="n">difference_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="incrementable_traits.html">incrementable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">difference_type</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="indirectly_readable_traits.html">indirectly_readable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">value_type</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><i>see below</i></span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><i>see below</i></span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">iterator_category</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><i>see below</i></span><span class="p">;</span>
</code></pre></div>
</p>
<ul>
<li><code>pointer</code>は、上から順に次のいずれか</li>
</ul>
<p><div class="codehilite"><pre><span></span><code><span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="o">::</span><span class="n">pointer</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">decltype</span><span class="p">(</span><span class="n"><a href="../utility/declval.html">declval</a></span><span class="o"><</span><span class="n">I</span><span class="o">&></span><span class="p">().</span><span class="k">operator</span><span class="o">-></span><span class="p">());</span>
<span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kt">void</span><span class="p">;</span>
</code></pre></div>
</p>
<ul>
<li><code>reference</code>は、上から順に次のいずれか</li>
</ul>
<p><div class="codehilite"><pre><span></span><code><span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">I</span><span class="o">::</span><span class="n">reference</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="p">;</span>
</code></pre></div>
</p>
<ul>
<li><code>iterator_category</code>は、上から順に次のいずれか<ul>
<li><code>I</code>が<code>cpp17-random-access-iterator</code>コンセプトを満たす場合、<code>random_access_iterator_tag</code></li>
<li><code>I</code>が<code>cpp17-bidirectional-iterator</code>コンセプトを満たす場合、<code>bidirectional_iterator_tag</code></li>
<li><code>I</code>が<code>cpp17-forward-iterator</code>コンセプトを満たす場合、<code>forward_iterator_tag</code></li>
<li>それ以外の場合、<code>input_iterator_tag</code></li>
</ul>
</li>
</ul>
</li>
<li>
<p>そうではなく、<code>I</code>が<code>cpp17-iterator</code>コンセプトを満たす場合、それぞれのメンバ型は次のように定義される
<br />
<div class="codehilite"><pre><span></span><code><span class="k">using</span><span class="w"> </span><span class="n">difference_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="incrementable_traits.html">incrementable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">difference_type</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kt">void</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">pointer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kt">void</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">reference</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kt">void</span><span class="p">;</span>
<span class="k">using</span><span class="w"> </span><span class="n">iterator_category</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">output_iterator_tag</span><span class="p">;</span>
</code></pre></div>
</p>
<ul>
<li>この時、<code>incrementable_traits<I>::difference_type</code>が定義されない場合、<code>difference_type = void</code></li>
</ul>
</li>
<li>
<p>それ以外の場合、<code>iterator_traits<I></code>は5つのメンバ型のいずれも定義しない。</p>
</li>
</ul>
<p>登場した<code>cpp17-input-iterator</code>等のコンセプトは全て次のように定義される説明専用のものである。</p>
<p><div class="codehilite"><pre><span></span><code><span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">I</span><span class="o">></span>
<span class="k">concept</span><span class="w"> </span><span class="nc">cpp17</span><span class="o">-</span><span class="n">iterator</span><span class="w"> </span><span class="o">=</span>
<span class="w"> </span><span class="n"><a href="../concepts/copyable.html">copyable</a></span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="k">requires</span><span class="p">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="o">*</span><span class="n">i</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="dereferenceable.html">can-reference</a></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n">I</span><span class="o">&></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="o">*</span><span class="n">i</span><span class="o">++</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="dereferenceable.html">can-reference</a></span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">I</span><span class="o">></span>
<span class="k">concept</span><span class="w"> </span><span class="nc">cpp17</span><span class="o">-</span><span class="n">input</span><span class="o">-</span><span class="n">iterator</span><span class="w"> </span><span class="o">=</span>
<span class="w"> </span><span class="n">cpp17</span><span class="o">-</span><span class="n">iterator</span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n"><a href="../concepts/equality_comparable.html">equality_comparable</a></span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="k">requires</span><span class="p">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="incrementable_traits.html">incrementable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">difference_type</span><span class="p">;</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="indirectly_readable_traits.html">indirectly_readable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">value_type</span><span class="p">;</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="../type_traits/common_reference.html">common_reference_t</a></span><span class="o"><</span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">I</span><span class="o">>&&</span><span class="p">,</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="indirectly_readable_traits.html">indirectly_readable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">value_type</span><span class="o">&></span><span class="p">;</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="../type_traits/common_reference.html">common_reference_t</a></span><span class="o"><</span><span class="k">decltype</span><span class="p">(</span><span class="o">*</span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="o">&&</span><span class="p">,</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="indirectly_readable_traits.html">indirectly_readable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">value_type</span><span class="o">&></span><span class="p">;</span>
<span class="w"> </span><span class="k">requires</span><span class="w"> </span><span class="n"><a href="../concepts/signed_integral.html">signed_integral</a></span><span class="o"><</span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="incrementable_traits.html">incrementable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">difference_type</span><span class="o">></span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">I</span><span class="o">></span>
<span class="k">concept</span><span class="w"> </span><span class="nc">cpp17</span><span class="o">-</span><span class="n">forward</span><span class="o">-</span><span class="n">iterator</span><span class="w"> </span><span class="o">=</span>
<span class="w"> </span><span class="n">cpp17</span><span class="o">-</span><span class="n">input</span><span class="o">-</span><span class="n">iterator</span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n"><a href="../concepts/constructible_from.html">constructible_from</a></span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="w"> </span><span class="o">&&</span>
<span class="w"> </span><span class="n"><a href="../type_traits/is_lvalue_reference.html">is_lvalue_reference_v</a></span><span class="o"><</span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">I</span><span class="o">>></span><span class="w"> </span><span class="o">&&</span>
<span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n"><a href="../type_traits/remove_cvref.html">remove_cvref_t</a></span><span class="o"><</span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">I</span><span class="o">>></span><span class="p">,</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="indirectly_readable_traits.html">indirectly_readable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">value_type</span><span class="o">></span><span class="w"> </span><span class="o">&&</span>
<span class="w"> </span><span class="k">requires</span><span class="p">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/convertible_to.html">convertible_to</a></span><span class="o"><</span><span class="k">const</span><span class="w"> </span><span class="n">I</span><span class="o">&></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="o">*</span><span class="n">i</span><span class="o">++</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">I</span><span class="o">>></span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">I</span><span class="o">></span>
<span class="k">concept</span><span class="w"> </span><span class="nc">cpp17</span><span class="o">-</span><span class="n">bidirectional</span><span class="o">-</span><span class="n">iterator</span><span class="w"> </span><span class="o">=</span>
<span class="w"> </span><span class="n">cpp17</span><span class="o">-</span><span class="n">forward</span><span class="o">-</span><span class="n">iterator</span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="k">requires</span><span class="p">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="o">--</span><span class="n">i</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n">I</span><span class="o">&></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">i</span><span class="o">--</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/convertible_to.html">convertible_to</a></span><span class="o"><</span><span class="k">const</span><span class="w"> </span><span class="n">I</span><span class="o">&></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="o">*</span><span class="n">i</span><span class="o">--</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">I</span><span class="o">>></span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
<span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">I</span><span class="o">></span>
<span class="k">concept</span><span class="w"> </span><span class="nc">cpp17</span><span class="o">-</span><span class="n">random</span><span class="o">-</span><span class="n">access</span><span class="o">-</span><span class="n">iterator</span><span class="w"> </span><span class="o">=</span>
<span class="w"> </span><span class="n">cpp17</span><span class="o">-</span><span class="n">bidirectional</span><span class="o">-</span><span class="n">iterator</span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n"><a href="../concepts/totally_ordered.html">totally_ordered</a></span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="w"> </span><span class="o">&&</span>
<span class="w"> </span><span class="k">requires</span><span class="p">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="incrementable_traits.html">incrementable_traits</a></span><span class="o"><</span><span class="n">I</span><span class="o">>::</span><span class="n">difference_type</span><span class="w"> </span><span class="n">n</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n">I</span><span class="o">&></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">-=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n">I</span><span class="o">&></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n">I</span><span class="o">></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="k">decltype</span><span class="p">(</span><span class="n">n</span><span class="p">)</span><span class="o">></span><span class="p">;</span>
<span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">i</span><span class="p">[</span><span class="n">n</span><span class="p">]</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">-></span><span class="w"> </span><span class="n"><a href="../concepts/convertible_to.html">convertible_to</a></span><span class="o"><</span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">I</span><span class="o">>></span><span class="p">;</span>
<span class="w"> </span><span class="p">};</span>
</code></pre></div>
</p>
<h2>例</h2>
<p><div class="yata" id="e5b8999d705b9ee9155459fd71c137b83b4c6702"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../vector.html"><vector></a></span>
<span class="cp">#include <a href="../iterator.html"><iterator></a></span>
<span class="c1">// 範囲の合計値を計算する</span>
<span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">Iterator</span><span class="o">></span>
<span class="k">typename</span><span class="w"> </span><span class="nc"><span style="color:#ff0000">std::iterator_traits<Iterator>::value_type</span></span>
<span class="w"> </span><span class="n">sum</span><span class="p">(</span><span class="n">Iterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">Iterator</span><span class="w"> </span><span class="n">last</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="c1">// イテレータの型から値型を取得する</span>
<span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><span style="color:#ff0000">std::iterator_traits<Iterator>::value_type</span></span><span class="p">;</span>
<span class="w"> </span><span class="c1">// 取得した値型の変数を定義し、合計値を計算する</span>
<span class="w"> </span><span class="n">value_type</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">value_type</span><span class="p">();</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(;</span><span class="w"> </span><span class="n">first</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">last</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">first</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="o">*</span><span class="n">first</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">result</span><span class="p">;</span>
<span class="p">}</span>
<span class="kt">int</span><span class="w"> </span><span class="n">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="c1">// <a href="../vector/vector.html">std::vector</a></span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../vector/vector.html">std::vector</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">};</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">sum</span><span class="p">(</span><span class="n"><a href="begin.html">std::begin</a></span><span class="p">(</span><span class="n">v</span><span class="p">),</span><span class="w"> </span><span class="n"><a href="end.html">std::end</a></span><span class="p">(</span><span class="n">v</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">// ポインタ</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">ar</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">};</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">sum</span><span class="p">(</span><span class="n"><a href="begin.html">std::begin</a></span><span class="p">(</span><span class="n">ar</span><span class="p">),</span><span class="w"> </span><span class="n"><a href="end.html">std::end</a></span><span class="p">(</span><span class="n">ar</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><pre><code>15
15
</code></pre></p>
<h2>参照</h2>
<ul>
<li><a href="https://wg21.cmeerw.net/lwg/issue2952" target="_blank">LWG 2952. <code>iterator_traits</code> should work for pointers to cv <code>T</code></a><ul>
<li>C++17から、<code>const T*</code>の部分特殊化が、<code>T*</code>の部分特殊化に統合され、<code>volatile</code>付きのポインタもこのクラスで扱えるようになった</li>
</ul>
</li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0896r4.pdf" target="_blank">P0896R4 The One Ranges Proposal (was Merging the Ranges TS)</a></li>
</ul></div>
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