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2025年07月08日 15時33分39秒
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<div class="identifier-type">function template</div><div class="header"><algorithm></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">for_each</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">InputIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Function</span><span class="o">></span>
<span class="w"> </span><span class="n">Function</span><span class="w"> </span><span class="n">for_each</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">Function</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++03</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">InputIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Function</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n">Function</span><span class="w"> </span><span class="n">for_each</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">Function</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++20</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">ForwardIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Function</span><span class="o">></span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">for_each</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">exec</span><span class="p">,</span>
<span class="w"> </span><span class="n">ForwardIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">ForwardIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">Function</span><span class="w"> </span><span class="n">f</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++17</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p><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>の全ての要素に、指定された関数を適用する。</p>
<h2>要件</h2>
<p><code>Function</code> は <code>MoveConstructible</code> の要件を満たす必要があるが、<code>CopyConstructible</code> の要件を満たす必要はない。（C++11のみ）</p>
<h2>効果</h2>
<p><code>[first,last)</code> 内の全てのイテレータ <code>i</code> に <code>f(*i)</code> という操作を行う。<code>first</code> から順番に処理し、<code>last - 1</code> まで行う。</p>
<p>このアルゴリズムはその他のアルゴリズムと違い、関数 <code>f</code> の内部で <code>*i</code> の値を書き換えても構わない（もちろんイテレータの型が <code>mutable iterator</code> の要件を満たしている場合に限る）。</p>
<h2><a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a></h2>
<ul>
<li>C++03 の場合 : <code>f</code></li>
<li>C++11 の場合 : <code>std::move(f)</code></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。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>
<p>正確に <code>f</code> を <code>last - first</code> 回適用する</p>
<h2>備考</h2>
<ul>
<li><code>f</code> に<a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a>がある場合、それは単に無視される</li>
<li>(1)は、<a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a>の型が<code>Function</code>となっている。シングルスレッドでの順次実行では関数オブジェクト<code>f</code>の状態を次々に変更していき、最終的な関数オブジェクトの状態を<a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a>として取得できる</li>
<li>(2)の並列アルゴリズム版は、<a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a>の型が<code>Function</code>ではなく<code>void</code>となっている。並列数だけ関数オブジェクトをコピーするため、関数オブジェクトの状態を順次変更していくような設計は、並列アルゴリズム版ではできないようになっている</li>
</ul>
<h2>例</h2>
<h3>C++03での例</h3>
<p><div class="yata" id="8dbc2a3a330e8e8d229ebc188f0110149887b5ed"><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="../algorithm.html"><algorithm></a></span>
<span class="kt">void</span><span class="w"> </span><span class="nf">disp</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</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="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">mutate</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">n</span><span class="p">;</span>
<span class="w"> </span><span class="n">mutate</span><span class="p">()</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="p">(</span><span class="mi">0</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="kt">void</span><span class="w"> </span><span class="k">operator</span><span class="p">()(</span><span class="kt">int</span><span class="o">&</span><span class="w"> </span><span class="n">v</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">n</span><span class="o">++</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</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="p">;</span>
<span class="w"> </span><span class="n"><a href="../vector/vector/push_back.html">v.push_back</a></span><span class="p">(</span><span class="mi">3</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../vector/vector/push_back.html">v.push_back</a></span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../vector/vector/push_back.html">v.push_back</a></span><span class="p">(</span><span class="mi">4</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// vの全ての要素にdisp()関数を適用する</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::for_each</span></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/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="n">disp</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="s">"----"</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="c1">// 要素の内容を書き換えても構わないし、呼び出し順序に依存した処理を書いても構わない</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::for_each</span></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/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="n">mutate</span><span class="p">());</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::for_each</span></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/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="n">disp</span><span class="p">);</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h4>出力</h4>
<p><pre><code>3
1
4
----
3
2
6
</code></pre></p>
<h2>例</h2>
<h3>C++11での例</h3>
<p><div class="yata" id="3ac6bfd68f3b818a097ffaa967b5dd4430025f11"><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="../algorithm.html"><algorithm></a></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</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="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="p">};</span>
<span class="w"> </span><span class="c1">// vの全ての要素にラムダ式を適用する</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::for_each</span></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/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="p">[](</span><span class="kt">int</span><span class="w"> </span><span class="n">x</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="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="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"----"</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="c1">// 要素の内容を書き換えても構わないし、呼び出し順序に依存した処理を書いても構わない</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::for_each</span></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/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="p">[</span><span class="n">n</span><span class="p">](</span><span class="kt">int</span><span class="o">&</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"> </span><span class="k">mutable</span><span class="w"> </span><span class="p">{</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">n</span><span class="o">++</span><span class="p">;</span><span class="w"> </span><span class="p">});</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::for_each</span></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/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="p">[](</span><span class="kt">int</span><span class="w"> </span><span class="n">x</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="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>
<h4>出力</h4>
<p><pre><code>3
1
4
----
3
2
6
</code></pre></p>
<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#icc">ICC</a>: </li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: 2005 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2008 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2010 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2012 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2013 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2015 <span aria-label="検証済" role="img" title="検証済">✅</span><ul>
<li>C++11への対応（<a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a>のムーブ）は2012から。</li>
</ul>
</li>
</ul>
<h2>実装例</h2>
<p><div class="codehilite"><pre><span></span><code><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">InputIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">Function</span><span class="o">></span>
<span class="n">Function</span><span class="w"> </span><span class="n">for_each</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span><span class="w"> </span><span class="n">Function</span><span class="w"> </span><span class="n">f</span><span class="p">)</span><span class="w"> </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="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="n">f</span><span class="p">(</span><span class="o">*</span><span class="n">first</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">move</span><span class="p">(</span><span class="n">f</span><span class="p">);</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>参照</h2>
<ul>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0202r3.html" target="_blank">P0202R3 Add Constexpr Modifiers to Functions in <code><algorithm></code> and <code><utility></code> Headers</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0467r2.html" target="_blank">P0467R2 Iterator Concerns for Parallel Algorithms</a></li>
</ul></div>
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