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<header data-kunai-mdinfo="{&#34;meta&#34;: {&#34;header&#34;: [&#34;span&#34;], &#34;namespace&#34;: [&#34;std&#34;], &#34;class&#34;: [&#34;span&#34;], &#34;id-type&#34;: [&#34;function&#34;], &#34;cpp&#34;: [&#34;cpp20&#34;]}, &#34;sources&#34;: [{&#34;id&#34;: &#34;3e7974f36e36096d6ef9a62836cff436b207522c&#34;, &#34;source&#34;: &#34;#include &lt;cassert&gt;\n#include &lt;span&gt;\n#include &lt;vector&gt;\n#include &lt;array&gt;\n#include &lt;string&gt;\n\nint main()\n{\n  std::vector&lt;int&gt; v = {1, 2, 3, 4, 5};\n\n  // (1) \u30c7\u30d5\u30a9\u30eb\u30c8\u30b3\u30f3\u30b9\u30c8\u30e9\u30af\u30bf\n  {\n    // \u9577\u30550\u306e\u53c2\u7167\u7bc4\u56f2\u3092\u3082\u3064span\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\n    std::span&lt;int, 0&gt; s1;\n    assert(s1.empty());\n\n    // \u52d5\u7684\u306a\u8981\u7d20\u6570\u3092\u3082\u3064span\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\n    std::span&lt;int&gt; s2;\n    assert(s2.empty());\n\n    // \u4ee5\u4e0b\u306f\u30b3\u30f3\u30d1\u30a4\u30eb\u30a8\u30e9\u30fc\u306b\u306a\u308b\u3002\n    // \u9577\u30551\u4ee5\u4e0a\u306espan\u306f\u3001\u53c2\u7167\u7bc4\u56f2\u3092\u8a2d\u5b9a\u3057\u306a\u3051\u308c\u3070\u306a\u3089\u306a\u3044\n    // std::span&lt;int, 1&gt; s3{};\n  }\n\n  // (2) \u30a4\u30c6\u30ec\u30fc\u30bf\u3068\u8981\u7d20\u6570\u306e\u7d44\u3092\u6307\u5b9a\n  {\n    // v\u306e\u5148\u982d3\u8981\u7d20\u3092\u53c2\u7167\u3059\u308b\u3002\n    std::span&lt;int&gt; s{v.begin(), 3};\n    assert(s.size() == 3);\n    assert(s[0] == 1);\n    assert(s[1] == 2);\n    assert(s[2] == 3);\n  }\n\n  // (3) \u7bc4\u56f2\u3092\u6307\u5b9a\n  {\n    std::span&lt;int&gt; s{v.begin(), v.begin() + 3};\n    assert(s.size() == 3);\n    assert(s[0] == 1);\n    assert(s[1] == 2);\n    assert(s[2] == 3);\n  }\n\n  // (4) \u7d44\u307f\u8fbc\u307f\u914d\u5217\u3078\u306e\u53c2\u7167\u3092\u6307\u5b9a\n  {\n    int ar[] = {1, 2, 3, 4, 5};\n    std::span&lt;int&gt; s{ar};\n    assert(s.size() == 5);\n    assert(s.data() == ar); // \u5143\u306e\u914d\u5217\u3092\u30b3\u30d4\u30fc\u305b\u305a\u3001\u53c2\u7167\u3057\u3066\u3044\u308b\n  }\n\n  // (5) std::array\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3078\u306e\u53c2\u7167\u3092\u6307\u5b9a\n  {\n    std::array ar = {1, 2, 3, 4, 5};\n    std::span&lt;int&gt; s{ar};\n    assert(s.size() == ar.size());\n    assert(s.data() == ar.data());\n  }\n\n  // (6) const std::array\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3078\u306e\u53c2\u7167\u3092\u6307\u5b9a\n  {\n    std::array ar = {1, 2, 3, 4, 5};\n    const auto&amp; car = ar;\n    std::span&lt;const int&gt; s{car};\n\n    assert(s.size() == car.size());\n    assert(s.data() == car.data());\n  }\n\n  // (7) \u30e1\u30e2\u30ea\u306e\u9023\u7d9a\u6027\u3092\u3082\u3064\u30a4\u30c6\u30ec\u30fc\u30bf\u3092\u3082\u3064\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u8981\u7d20\u5168\u4f53\u3092\u53c2\u7167\u3055\u305b\u308b\n  {\n    std::span&lt;int&gt; s1{v};\n    assert(s1.size() == v.size());\n    assert(s1.data() == v.data());\n\n    // std::string_view\u306e\u4ee3\u308f\u308a\n    std::string str = \&#34;Hello\&#34;;\n    std::span&lt;char&gt; s2{str};\n    assert(s2.size() == str.size());\n    assert(s2.data() == str.data());\n  }\n\n  // (8) \u30b3\u30d4\u30fc\u30b3\u30f3\u30b9\u30c8\u30e9\u30af\u30bf\n  {\n    std::span&lt;int&gt; s1{v};\n    std::span&lt;int&gt; s2 = s1;\n\n    // \u30b3\u30d4\u30fc\u5143\u3068\u30b3\u30d4\u30fc\u5148\u304c\u540c\u3058\u7bc4\u56f2\u3092\u53c2\u7167\u3059\u308b\n    assert(s1.data() == v.data());\n    assert(s2.data() == v.data());\n  }\n\n  // (9) \u5909\u63db\u30b3\u30f3\u30b9\u30c8\u30e9\u30af\u30bf\n  {\n    int ar[] = {1, 2, 3};\n\n    std::span&lt;int, 3&gt; s1{ar};\n    std::span&lt;int&gt; s2 = s1;\n    std::span&lt;int&gt; s3 = s2.first(2);\n    std::span&lt;const int&gt; s4 = s3;\n\n    assert(s4.size() == 2);\n    assert(s4.data() == ar);\n  }\n}\n&#34;}], &#34;page_id&#34;: [&#34;reference&#34;, &#34;span&#34;, &#34;span&#34;, &#34;op_constructor&#34;]}">
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  <div class="identifier-type">function</div><div class="header">&lt;span&gt;</div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="class" title="class span">span::</span><span class="token">コンストラクタ</span><span class="cpp cpp20" title="C++20で追加">(C++20)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">constexpr</span><span class="w"> </span><span class="n">span</span><span class="p">()</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w">                                     </span><span class="c1">// (1) C++20</span>
<span class="k">template</span><span class="w"> </span><span class="o">&lt;</span><span class="k">class</span><span class="w"> </span><span class="nc">It</span><span class="o">&gt;</span>
<span class="k">constexpr</span><span class="w"> </span><span class="k">explicit</span><span class="p">(</span><span class="n">extent</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n"><a href="../dynamic_extent.html">dynamic_extent</a></span><span class="p">)</span>
<span class="w">  </span><span class="n">span</span><span class="p">(</span><span class="n">It</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">size_type</span><span class="w"> </span><span class="n">count</span><span class="p">);</span><span class="w">                             </span><span class="c1">// (2) C++20</span>
<span class="k">template</span><span class="w"> </span><span class="o">&lt;</span><span class="k">class</span><span class="w"> </span><span class="nc">It</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">End</span><span class="o">&gt;</span>
<span class="k">constexpr</span><span class="w"> </span><span class="k">explicit</span><span class="p">(</span><span class="n">extent</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n"><a href="../dynamic_extent.html">dynamic_extent</a></span><span class="p">)</span>
<span class="w">  </span><span class="n">span</span><span class="p">(</span><span class="n">It</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">last</span><span class="p">);</span><span class="w">                                    </span><span class="c1">// (3) C++20</span>
<span class="k">template</span><span class="w"> </span><span class="o">&lt;</span><span class="n"><a href="../../cstddef/size_t.html">size_t</a></span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span>
<span class="k">constexpr</span><span class="w"> </span><span class="n">span</span><span class="p">(</span>
<span class="w">  </span><span class="n"><a href="../../type_traits/type_identity.html">type_identity_t</a></span><span class="o">&lt;</span><span class="n">element_type</span><span class="o">&gt;</span><span class="w"> </span><span class="p">(</span><span class="o">&amp;</span><span class="n">arr</span><span class="p">)[</span><span class="n">N</span><span class="p">])</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w">           </span><span class="c1">// (4) C++20</span>
<span class="k">template</span><span class="w"> </span><span class="o">&lt;</span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../cstddef/size_t.html">size_t</a></span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span>
<span class="k">constexpr</span><span class="w"> </span><span class="n">span</span><span class="p">(</span><span class="n"><a href="../../array/array.html">array</a></span><span class="o">&lt;</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;&amp;</span><span class="w"> </span><span class="n">arr</span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w">                     </span><span class="c1">// (5) C++20</span>
<span class="k">template</span><span class="w"> </span><span class="o">&lt;</span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../cstddef/size_t.html">size_t</a></span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span>
<span class="k">constexpr</span><span class="w"> </span><span class="n">span</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../../array/array.html">array</a></span><span class="o">&lt;</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;&amp;</span><span class="w"> </span><span class="n">arr</span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w">               </span><span class="c1">// (6) C++20</span>
<span class="k">template</span><span class="w"> </span><span class="o">&lt;</span><span class="k">class</span><span class="w"> </span><span class="nc">R</span><span class="o">&gt;</span>
<span class="k">constexpr</span><span class="w"> </span><span class="k">explicit</span><span class="p">(</span><span class="n">extent</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n"><a href="../dynamic_extent.html">dynamic_extent</a></span><span class="p">)</span>
<span class="w">  </span><span class="n">span</span><span class="p">(</span><span class="n">R</span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="n">r</span><span class="p">);</span><span class="w">                                                 </span><span class="c1">// (7) C++20</span>
<span class="k">constexpr</span><span class="w"> </span><span class="n">span</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">span</span><span class="o">&amp;</span><span class="w"> </span><span class="n">other</span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">default</span><span class="p">;</span><span class="w">          </span><span class="c1">// (8) C++20</span>
<span class="k">template</span><span class="w"> </span><span class="o">&lt;</span><span class="k">class</span><span class="w"> </span><span class="nc">OtherElementType</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../cstddef/size_t.html">size_t</a></span><span class="w"> </span><span class="n">OtherExtent</span><span class="o">&gt;</span>
<span class="k">constexpr</span><span class="w"> </span><span class="k">explicit</span><span class="p">(</span><span class="n">extent</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n"><a href="../dynamic_extent.html">dynamic_extent</a></span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="n">OtherExtent</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../dynamic_extent.html">dynamic_extent</a></span><span class="p">)</span>
<span class="w">  </span><span class="n">span</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">span</span><span class="o">&lt;</span><span class="n">OtherElementType</span><span class="p">,</span><span class="w"> </span><span class="n">OtherExtent</span><span class="o">&gt;&amp;</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w"> </span><span class="c1">// (9) C++20</span>
</code></pre></div>
<h2>概要</h2>
<p><code>span</code>オブジェクトを構築する。</p>
<li>(1) : デフォルトコンストラクタ。空の<code>span</code>オブジェクトを構築する</li>
<li>(2) : 参照範囲として先頭要素を指すイテレータと、そこからの要素数を指定して、それらの要素を参照する<code>span</code>オブジェクトを構築する</li>
<li>(3) : 参照範囲として先頭要素を指すイテレータと、末尾要素の次を指すイテレータを指定して、それらの要素を参照する<code>span</code>オブジェクトを構築する</li>
<li>(4) : 指定された組み込み配列の全体を参照する<code>span</code>オブジェクトを構築する</li>
<li>(5) : 指定された非<code>const</code>左辺値参照の<code><a href="../../array/array.html">std::array</a></code>の全体を参照する<code>span</code>オブジェクトを構築する</li>
<li>(6) : 指定された<code>const</code>左辺値参照の<code><a href="../../array/array.html">std::array</a></code>の全体を参照する<code>span</code>オブジェクトを構築する</li>
<li>(7) : 指定された、メモリ連続性をもつイテレータを持つオブジェクトの要素全体を参照する<code>span</code>オブジェクトを構築する</li>
<li>(8) : コピーコンストラクタ。<code>other</code>と同じ範囲を参照する<code>span</code>オブジェクトを構築する</li>
<li>(9) : テンプレートパラメータの異なる<code>span</code>オブジェクトを変換する。以下のような変換ができる：<ul>
<li>静的な要素数をもつ<code>span</code>から動的な要素数をもつ<code>span</code>への変換。</li>
<li>動的な要素数をもつ<code>span</code>同士の変換</li>
<li><code>span&lt;T&gt;</code>から<code>span&lt;const T&gt;</code>への変換</li>
<li>バイト数が同じ暗黙の型変換が可能な要素型をもつ<code>span</code>同士の変換</li>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Constraints。関数であればオーバーロード解決に参加するための条件、それ以外であれば受け付ける型の条件">テンプレートパラメータ制約</a></h2>
<li>(1) :<ul>
<li><code>Extent == <a href="../dynamic_extent.html">dynamic_extent</a> || Extent == 0</code>が<code>true</code>であること<ul>
<li>値<code>-1</code>はオーバーフローによって正の最大値になるので<code>false</code></li>
<li>(2) :<ul>
<li>型 <code>U</code> を <code><a href="../../type_traits/remove_reference.html">std::remove_reference_t</a>&lt;<a href="../../iterator/iter_reference_t.html">std::iter_reference_t</a>&lt;It&gt;&gt;</code>とするとき<ul>
<li>型 <code>It</code> はコンセプト <code><a href="../../iterator/contiguous_iterator.html">std::contiguous_iterator</a></code> を満たしていること</li>
<li><code><a href="../../type_traits/is_convertible.html">std::is_convertible_v</a>&lt;U(*)[], element_type(*)[]&gt;</code> が <code>true</code> であること。(この制約の意図は、イテレータ参照型から <code>element_type</code> への修飾の変換のみを許可すること)</li>
<li>(3) :<ul>
<li>型 <code>U</code> を <code><a href="../../type_traits/remove_reference.html">std::remove_reference_t</a>&lt;<a href="../../iterator/iter_reference_t.html">std::iter_reference_t</a>&lt;It&gt;&gt;</code>とするとき<ul>
<li>型 <code>It</code> はコンセプト <code><a href="../../iterator/contiguous_iterator.html">std::contiguous_iterator</a></code> を満たしていること</li>
<li><code><a href="../../type_traits/is_convertible.html">std::is_convertible_v</a>&lt;U(*)[], element_type(*)[]&gt;</code> が <code>true</code> であること。(この制約の意図は、イテレータ参照型から <code>element_type</code> への修飾の変換のみを許可すること)</li>
<li>型 <code>End</code> はコンセプト <code><a href="../../iterator/sized_sentinel_for.html">std::sized_sentinel_for&lt;It&gt;</a></code> を満たしていること</li>
<li><code><a href="../../type_traits/is_convertible.html">std::is_convertible_v</a>&lt;End, size_t&gt;</code> が <code>false</code>であること</li>
<li>(4), (5), (6) :<ul>
<li><code>extent == <a href="../dynamic_extent.html">dynamic_extent</a> || N == extent</code>が<code>true</code>であること</li>
<li><code><a href="../../type_traits/remove_pointer.html">remove_pointer_t</a>&lt;decltype(<a href="../../iterator/data.html">data</a>(arr))&gt;</code>を型<code>U</code>であるとして、<ul>
<li><code><a href="../../type_traits/is_convertible.html">is_convertible_v</a>&lt;U(*)[], element_type(*)[]&gt;</code>が<code>true</code>であること (この制約の意図は、配列の要素型から<code>element_type</code>へ、修飾の変換のみを許可すること)</li>
<li>(7) :<ul>
<li>型 <code>U</code> を <code><a href="../../type_traits/remove_reference.html">std::remove_reference_t</a>&lt;<a href="../../iterator/iter_reference_t.html">std::iter_reference_t</a>&lt;R&gt;&gt;</code>とするとき<ul>
<li>型 <code>R</code> はコンセプト <code>std::ranges::contiguous_range</code> 及び <code>std::ranges::sized_range</code> を満たしていること</li>
<li>型 <code>R</code> がコンセプト <code><a href="../../ranges/borrowed_range.html">std::ranges::borrowed_range</a></code> を満たすか、<code>std::is_const_v&lt;element_type&gt;</code> が<code>true</code>であること</li>
<li><code>std::remove_cvref_t&lt;R&gt;</code>が<code>std::span</code>の特殊化ではないこと</li>
<li><code>std::remove_cvref_t&lt;R&gt;</code>が<code>std::array</code>の特殊化ではないこと</li>
<li><code>std::is_array_v&lt;std::remove_cvref_t&lt;R&gt;&gt;</code> が <code>false</code> であること</li>
<li><code>std::is_convertible_v&lt;U(*)[], element_type(*)[]&gt;</code> が <code>true</code> であること。(この制約の意図は、イテレータ参照型から <code>element_type</code> への修飾変換のみを許可すること)</li>
<li>(9) :<ul>
<li><code>extent == <a href="../dynamic_extent.html">dynamic_extent</a> || OtherExtent == <a href="../dynamic_extent.html">dynamic_extent</a> || extent == OtherExtent</code>が<code>true</code>であること (受け取り側が<code><a href="../dynamic_extent.html">dynamic_extent</a></code>を持っていれば任意の<code>Extent</code>から変換できる)</li>
<li><code>OtherElementType(*)[]</code>型が<code>ElementType(*)[]</code>型に変換可能であること</li>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Hardened preconditions。関数呼び出し時に満たされていると関数が想定する条件。満たさない場合は契約違反となる動作。セキュリティ上の脆弱性につながる操作に対して設定される事前条件">堅牢化された事前条件</a></h2>
<li>(2) :<ul>
<li><code>[first, first + count)</code>が妥当な<a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a>であること</li>
<li>型 <code>It</code> はコンセプト <code><a href="../../iterator/contiguous_iterator.html">std::contiguous_iterator</a></code> のモデルであること</li>
<li>メンバ定数<code>extent</code>が<code><a href="../dynamic_extent.html">dynamic_extent</a></code>と等値ではない場合、<code>count</code>と<code>extent</code>が等値であること</li>
<li>(3) :<ul>
<li><code>[first, last)</code>が妥当な<a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a>であること</li>
<li>メンバ定数<code>extent</code>が<code><a href="../dynamic_extent.html">dynamic_extent</a></code>と等値ではない場合、<code>last - first</code>と<code>extent</code>が等値であること</li>
<li>型 <code>It</code> はコンセプト <code><a href="../../iterator/contiguous_iterator.html">std::contiguous_iterator</a></code> のモデルであること</li>
<li>型 <code>End</code> はコンセプト <code><a href="../../iterator/sized_sentinel_for.html">std::sized_sentinel_for</a>&lt;It&gt;</code> のモデルであること</li>
<li>(7) :<ul>
<li><code>extent</code>が<code><a href="../dynamic_extent.html">dynamic_extent</a></code>と等値でない場合、<code>extent</code>は<code><a href="../../ranges/size.html">ranges::size</a>(r)</code>と等値になる</li>
<li>型 <code>R</code> はコンセプト <code>std::ranges::contiguous_range</code> 及び <code>std::ranges::sized_range</code> のモデルであること</li>
<li><code><a href="../../type_traits/is_const.html">std::is_const_v</a>&lt;element_type&gt;</code> が <code>false</code>であるとき、型 <code>R</code> はコンセプト <code><a href="../../ranges/borrowed_range.html">std::ranges::borrowed_range</a></code> のモデルであること</li>
<li>(9) :<ul>
<li><code>extent</code>が<code><a href="../dynamic_extent.html">dynamic_extent</a></code>と等値でない場合、<code>extent</code>は<code><a href="size.html">s.size()</a></code>と等値になる</li>
<h2>効果</h2>
<li>(2) : <a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[first, first + count)</code>を参照する<code>span</code>オブジェクトを構築する</li>
<li>(3) : <a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[first, last)</code>を参照する<code>span</code>オブジェクトを構築する</li>
<li>(4), (5), (6) : 範囲<code>[<a href="../../iterator/data.html">data</a>(arr), <a href="../../iterator/data.html">data</a>(arr) + N)</code>を参照する<code>span</code>オブジェクトを構築する</li>
<li>(7) : 範囲<code>[std::ranges::data(r), std::ranges::data(r) + std::ranges::size(r))</code>を参照する<code>span</code>オブジェクトを構築する</li>
<li>(9) : 範囲<code>[s.<a href="data.html">data()</a>, s.<a href="data.html">data()</a> + s.<a href="size.html">size()</a>)</code>を参照する<code>span</code>オブジェクトを構築する</li>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Postconditions。関数を実行後に満たされている条件。契約属性の`[[ensures]]`に相当">事後条件</a></h2>
<li>(1) : <code><a href="size.html">size()</a> == 0 &amp;&amp; <a href="data.html">data()</a> == nullptr</code>が<code>true</code>であること</li>
<li>(4), (5), (6) : <code><a href="size.html">size()</a> == N &amp;&amp; <a href="data.html">data()</a> == <a href="../../iterator/data.html">data</a>(arr)</code>が<code>true</code>であること</li>
<li>(8) : <code><a href="size.html">size()</a> == <a href="../../iterator/size.html">size</a>(cont) &amp;&amp; <a href="data.html">data()</a> == <a href="../../iterator/data.html">data</a>(cont)</code>が<code>true</code>であること</li>
<li>(9) : <code><a href="size.html">size()</a> == s.<a href="size.html">size()</a> &amp;&amp; <a href="data.html">data()</a> == s.<a href="data.html">data()</a></code>が<code>true</code>であること</li>
<h2><a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a></h2>
<li>(1), (2), (4), (5), (6) : 投げない</li>
<li>(3) : <code>last - first</code>がなんらかの<a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a>を送出する可能性がある</li>
<li>(7) : コンテナ型によっては、<code>std::ranges::data(r)</code>と<code>std::ranges::size(r)</code>の呼び出しがなんらかの<a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a>を送出する可能性がある</li>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Complexity。関数が使うアルゴリズムの空間計算量・時間計算量">計算量</a></h2>
<li>(1)-(9) : 定数時間</li>
<h3>基本的な使い方 (C++20)</h3>
<p><div class="yata" id="3e7974f36e36096d6ef9a62836cff436b207522c"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../../cassert.html">&lt;cassert&gt;</a></span>
<span class="cp">#include <a href="../../span.html">&lt;span&gt;</a></span>
<span class="cp">#include <a href="../../vector.html">&lt;vector&gt;</a></span>
<span class="cp">#include <a href="../../array.html">&lt;array&gt;</a></span>
<span class="cp">#include <a href="../../string.html">&lt;string&gt;</a></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w">  </span><span class="n"><a href="../../vector/vector.html">std::vector</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</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="c1">// (1) デフォルトコンストラクタ</span>
<span class="w">  </span><span class="p">{</span>
<span class="w">    </span><span class="c1">// 長さ0の参照範囲をもつspanオブジェクト</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s1</span><span class="p">;</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="empty.html">s1.empty()</a></span><span class="p">);</span>
<span class="w">    </span><span class="c1">// 動的な要素数をもつspanオブジェクト</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s2</span><span class="p">;</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="empty.html">s2.empty()</a></span><span class="p">);</span>
<span class="w">    </span><span class="c1">// 以下はコンパイルエラーになる。</span>
<span class="w">    </span><span class="c1">// 長さ1以上のspanは、参照範囲を設定しなければならない</span>
<span class="w">    </span><span class="c1">// <a href="../span.html">std::span</a>&lt;int, 1&gt; s3{};</span>
<span class="w">  </span><span class="p">}</span>
<span class="w">  </span><span class="c1">// (2) イテレータと要素数の組を指定</span>
<span class="w">  </span><span class="p">{</span>
<span class="w">    </span><span class="c1">// vの先頭3要素を参照する。</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s</span><span class="p">{</span><span class="n"><a href="../../vector/vector/begin.html">v.begin()</a></span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="size.html">s.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n">s</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n">s</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n">s</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="p">);</span>
<span class="w">  </span><span class="p">}</span>
<span class="w">  </span><span class="c1">// (3) 範囲を指定</span>
<span class="w">  </span><span class="p">{</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s</span><span class="p">{</span><span class="n"><a href="../../vector/vector/begin.html">v.begin()</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../vector/vector/begin.html">v.begin()</a></span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="size.html">s.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n">s</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n">s</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n">s</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="p">);</span>
<span class="w">  </span><span class="p">}</span>
<span class="w">  </span><span class="c1">// (4) 組み込み配列への参照を指定</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="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s</span><span class="p">{</span><span class="n">ar</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="size.html">s.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="data.html">s.data()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">ar</span><span class="p">);</span><span class="w"> </span><span class="c1">// 元の配列をコピーせず、参照している</span>
<span class="w">  </span><span class="p">}</span>
<span class="w">  </span><span class="c1">// (5) <a href="../../array/array.html">std::array</a>オブジェクトへの参照を指定</span>
<span class="w">  </span><span class="p">{</span>
<span class="w">    </span><span class="n"><a href="../../array/array.html">std::array</a></span><span class="w"> </span><span class="n">ar</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="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s</span><span class="p">{</span><span class="n">ar</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="size.html">s.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../array/array/size.html">ar.size()</a></span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="data.html">s.data()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../array/array/data.html">ar.data()</a></span><span class="p">);</span>
<span class="w">  </span><span class="p">}</span>
<span class="w">  </span><span class="c1">// (6) const <a href="../../array/array.html">std::array</a>オブジェクトへの参照を指定</span>
<span class="w">  </span><span class="p">{</span>
<span class="w">    </span><span class="n"><a href="../../array/array.html">std::array</a></span><span class="w"> </span><span class="n">ar</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="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&amp;</span><span class="w"> </span><span class="n">car</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ar</span><span class="p">;</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="k">const</span><span class="w"> </span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s</span><span class="p">{</span><span class="n">car</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="size.html">s.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../array/array/size.html">car.size()</a></span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="data.html">s.data()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../array/array/data.html">car.data()</a></span><span class="p">);</span>
<span class="w">  </span><span class="p">}</span>
<span class="w">  </span><span class="c1">// (7) メモリの連続性をもつイテレータをもつオブジェクトの要素全体を参照させる</span>
<span class="w">  </span><span class="p">{</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s1</span><span class="p">{</span><span class="n">v</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="size.html">s1.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../vector/vector/size.html">v.size()</a></span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="data.html">s1.data()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../vector/vector/data.html">v.data()</a></span><span class="p">);</span>
<span class="w">    </span><span class="c1">// <a href="../../string_view/basic_string_view.html">std::string_view</a>の代わり</span>
<span class="w">    </span><span class="n"><a href="../../string/basic_string.html">std::string</a></span><span class="w"> </span><span class="n">str</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Hello"</span><span class="p">;</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">char</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s2</span><span class="p">{</span><span class="n">str</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="size.html">s2.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../string/basic_string/size.html">str.size()</a></span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="data.html">s2.data()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../string/basic_string/data.html">str.data()</a></span><span class="p">);</span>
<span class="w">  </span><span class="p">}</span>
<span class="w">  </span><span class="c1">// (8) コピーコンストラクタ</span>
<span class="w">  </span><span class="p">{</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s1</span><span class="p">{</span><span class="n">v</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s1</span><span class="p">;</span>
<span class="w">    </span><span class="c1">// コピー元とコピー先が同じ範囲を参照する</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="data.html">s1.data()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../vector/vector/data.html">v.data()</a></span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="data.html">s2.data()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n"><a href="../../vector/vector/data.html">v.data()</a></span><span class="p">);</span>
<span class="w">  </span><span class="p">}</span>
<span class="w">  </span><span class="c1">// (9) 変換コンストラクタ</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="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s1</span><span class="p">{</span><span class="n">ar</span><span class="p">};</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s1</span><span class="p">;</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="first.html">s2.first</a></span><span class="p">(</span><span class="mi">2</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../span.html">std::span</a></span><span class="o">&lt;</span><span class="k">const</span><span class="w"> </span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">s4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">s3</span><span class="p">;</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="size.html">s4.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">);</span>
<span class="w">    </span><span class="n"><a href="../../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="data.html">s4.data()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">ar</span><span class="p">);</span>
<span class="w">  </span><span class="p">}</span>
<span class="p">}</span>
</code></pre></div>
<h4>出力</h4>
<p><pre><code></code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<li>C++20</li>
<h3>処理系</h3>
<li><a href="../../../implementation.html#clang">Clang</a>: (10.0.0 現在、実装は P1394R4 以前の不完全なものである) <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../../implementation.html#gcc">GCC</a>: 10.0.1 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../../implementation.html#visual_cpp">Visual C++</a>: ??</li>
<h2>参照</h2>
<li><a href="https://wg21.cmeerw.net/lwg/issue3100" target="_blank">LWG Issue 3100. Unnecessary and confusing "empty span" wording</a></li>
<li><a href="https://wg21.cmeerw.net/lwg/issue3101" target="_blank">LWG Issue 3101. <code>span</code>'s Container constructors need another constraint</a></li>
<li><a href="https://cplusplus.github.io/LWG/issue3198" target="_blank">LWG Issue 3198. Bad constraint on <code>std::span::span()</code></a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1872r0.pdf" target="_blank">P1872R0 <code>span</code> should have <code>size_type</code>, not <code>index_type</code></a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1394r4.pdf" target="_blank">P1394R4 Range constructor for <code>std::span</code></a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1976r2.html" target="_blank">P1976R2 Fixed-size <code>span</code> construction from dynamic range</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p2117r0.html" target="_blank">P2117R0 C++ Standard Library Issues Resolved Directly In Prague</a></li>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2447r6.html" target="_blank">P2447R6 <code>std::span</code> over an initializer list</a><ul>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2026/p4144r1.html" target="_blank">P4144R1 Remove <code>span</code>’s <code>initializer_list</code> constructor for C++26</a></li>
<li>C++26の策定中に一時期、初期化子リストをとるコンストラクタが追加されたが、その後削除された</li>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3471r4.html" target="_blank">P3471R4 Standard library hardening</a></li>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3878r1.html" target="_blank">P3878R1 Standard library hardening should not use the 'observe' semantic</a></li>
</ul></div>
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