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<div class="identifier-type">function template</div><div class="header"><mdspan></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">copy</span><span class="cpp cpp29" title="C++29で追加">(C++29)</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">Src</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Dst</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">copy</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">Src</span><span class="o">&</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Dst</span><span class="o">&</span><span class="w"> </span><span class="n">dst</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++29</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"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Src</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Dst</span><span class="o">></span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">copy</span><span class="p">(</span><span class="n"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="o">&&</span><span class="w"> </span><span class="n">policy</span><span class="p">,</span>
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Src</span><span class="o">&</span><span class="w"> </span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Dst</span><span class="o">&</span><span class="w"> </span><span class="n">dst</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++29</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>多次元配列ビュー<code><a href="mdspan.html">std::mdspan</a></code>の全要素を、対応する要素どうしで別の<code>mdspan</code>へコピーする。</p>
<ul>
<li>(1) : 各要素を順次コピーする</li>
<li>(2) : 指定した実行ポリシーによって並列にコピーする</li>
</ul>
<p>コピー元とコピー先は、要素型やレイアウト・アクセサが異なっていてもよい。</p>
<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>
<ul>
<li><code>Src</code>および<code>Dst</code>が<code>mdspan</code>の特殊化であること</li>
<li><code><a href="../type_traits/is_assignable.html">is_assignable_v</a><typename Dst::reference, typename Src::reference></code>が<code>true</code>であること</li>
<li><code><a href="../type_traits/is_constructible.html">is_constructible_v</a><typename Src::extents_type, typename Dst::extents_type></code>が<code>true</code>であること<ul>
<li>この制約は実質的に、両者の次元数（ランク）が等しく、対応する各次元が「同じ値の静的サイズ」または<code><a href="../span/dynamic_extent.html">dynamic_extent</a></code>であることを検証する</li>
</ul>
</li>
</ul>
<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。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。満たさなければ未定義の動作。契約属性の`[[expects]]`に相当">事前条件</a></h2>
<ul>
<li><code>dst.<a href="LayoutMapping.html">is_unique()</a></code>が<code>true</code>であること（レイアウトマッピングが各要素へ一意に対応すること）</li>
<li><code>src.<a href="mdspan/extents.html">extents()</a></code>内の各多次元インデックス<code>i</code>について、<code>src[i]</code>と<code>dst[j]</code>が同じ要素を参照するような<code>dst.extents()</code>内の多次元インデックス<code>j</code>が存在しないこと（コピー元とコピー先の要素が重ならないこと）</li>
</ul>
<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>
<ul>
<li><code>src.<a href="mdspan/extents.html">extents()</a></code>が<code>dst.extents()</code>と等値であること</li>
</ul>
<h2>効果</h2>
<p><code>src</code>の各要素を、<code>dst</code>の対応する要素へ代入する。</p>
<h2>備考</h2>
<ul>
<li>対象の範囲が<code><a href="mdspan.html">std::mdspan</a></code>の次元情報として閉じているため、<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>のアルゴリズムと違い、終端を越えた書き込みを実装が検査できる（サイズの不一致は<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>の違反となる）</li>
<li>サイズの異なる<code>mdspan</code>どうしの部分的なコピーはサポートされない。コピーしたい領域を<code><a href="submdspan.html">std::submdspan()</a></code>で部分ビューとして明示的に取り出してからコピーすること</li>
<li>両者が同じ連続レイアウトかつデフォルトアクセサである場合など、レイアウト情報を利用した効率的な実装（<code>memcpy</code>相当への最適化など）が期待できる</li>
</ul>
<h2>例</h2>
<p><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../mdspan.html"><mdspan></a></span>
<span class="cp">#include <a href="../iostream.html"><iostream></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="kt">double</span><span class="w"> </span><span class="n">a</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="mi">6</span><span class="p">};</span>
<span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">b</span><span class="p">[</span><span class="mi">6</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{};</span>
<span class="w"> </span><span class="c1">// 行優先のビューから列優先のビューへ、対応する要素どうしでコピーする</span>
<span class="w"> </span><span class="n"><a href="mdspan.html">std::mdspan</a></span><span class="o"><</span><span class="kt">double</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="extents.html">std::extents</a></span><span class="o"><</span><span class="n"><a href="../cstddef/size_t.html">std::size_t</a></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="o">>></span><span class="w"> </span><span class="n">src</span><span class="p">{</span><span class="n">a</span><span class="p">};</span>
<span class="w"> </span><span class="n"><a href="mdspan.html">std::mdspan</a></span><span class="o"><</span><span class="kt">double</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="extents.html">std::extents</a></span><span class="o"><</span><span class="n"><a href="../cstddef/size_t.html">std::size_t</a></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="o">></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="layout_left.html">std::layout_left</a></span><span class="o">></span><span class="w"> </span><span class="n">dst</span><span class="p">{</span><span class="n">b</span><span class="p">};</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::copy</span></span><span class="p">(</span><span class="n">src</span><span class="p">,</span><span class="w"> </span><span class="n">dst</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// メモリ上は列優先の並びになる</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">double</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="p">)</span><span class="w"> </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">x</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="sc">' '</span><span class="p">;</span>
<span class="w"> </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"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h3>出力</h3>
<p><pre><code>1 4 2 5 3 6
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++29</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: ??</li>
<li><a href="../../implementation.html#gcc">GCC</a>: ??</li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: ??</li>
</ul>
<h2>関連項目</h2>
<ul>
<li><code><a href="fill.html">fill</a></code></li>
<li><code><a href="mdspan.html">std::mdspan</a></code></li>
<li><code><a href="submdspan.html">std::submdspan()</a></code></li>
<li><code><a href="../algorithm/copy.html">std::copy()</a></code> (<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>に対するコピー)</li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2026/p3242r4.html" target="_blank">P3242R4 Copy and fill for <code>mdspan</code></a></li>
</ul></div>
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