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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::ranges">std::ranges::</span><span class="token">generate</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">namespace</span><span class="w"> </span><span class="nn">std</span><span class="o">::</span><span class="nn">ranges</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="n"><a href="../iterator/input_or_output_iterator.html">input_or_output_iterator</a></span><span class="w"> </span><span class="n">O</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="../iterator/sentinel_for.html">sentinel_for</a></span><span class="o"><</span><span class="n">O</span><span class="o">></span><span class="w"> </span><span class="n">S</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="../concepts/copy_constructible.html">copy_constructible</a></span><span class="w"> </span><span class="n">F</span><span class="o">></span>
<span class="w"> </span><span class="k">requires</span><span class="w"> </span><span class="n"><a href="../concepts/invocable.html">invocable</a></span><span class="o"><</span><span class="n">F</span><span class="o">&></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n"><a href="../iterator/indirectly_writable.html">indirectly_writable</a></span><span class="o"><</span><span class="n">O</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../type_traits/invoke_result.html">invoke_result_t</a></span><span class="o"><</span><span class="n">F</span><span class="o">&>></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n">O</span>
<span class="w"> </span><span class="n">generate</span><span class="p">(</span><span class="n">O</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">gen</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">R</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="../concepts/copy_constructible.html">copy_constructible</a></span><span class="w"> </span><span class="n">F</span><span class="o">></span>
<span class="w"> </span><span class="k">requires</span><span class="w"> </span><span class="n"><a href="../concepts/invocable.html">invocable</a></span><span class="o"><</span><span class="n">F</span><span class="o">&></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n"><a href="../ranges/output_range.html">output_range</a></span><span class="o"><</span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../type_traits/invoke_result.html">invoke_result_t</a></span><span class="o"><</span><span class="n">F</span><span class="o">&>></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n"><a href="../ranges/borrowed_iterator_t.html">borrowed_iterator_t</a></span><span class="o"><</span><span class="n">R</span><span class="o">></span>
<span class="w"> </span><span class="n">generate</span><span class="p">(</span><span class="n">R</span><span class="o">&&</span><span class="w"> </span><span class="n">r</span><span class="p">,</span>
<span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">gen</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++20</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>出力の範囲へ関数の結果を書き込む。</p>
<ul>
<li>(1): <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>を指定する</li>
<li>(2): Rangeを直接指定する</li>
</ul>
<h2>効果</h2>
<p><code>[first,last)</code> のそれぞれのイテレータについて関数オブジェクト <code>gen</code> を呼び出し、その<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>を代入する。</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>
<p><code>last</code></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。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>last - first</code> 回の <code>gen</code> の呼び出しと代入が行われる。</p>
<h2>例</h2>
<h3>基本的な使い方</h3>
<p><div class="yata" id="4642e11e87002d1ec506125e233b32949c5ad04e"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../algorithm.html"><algorithm></a></span>
<span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../vector.html"><vector></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="p">(</span><span class="mi">10</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// 2 の累乗の値を生成する</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">1</span><span class="p">;</span>
<span class="w"> </span><span class="n"><span style="color:#ff0000">std::ranges::generate</span></span><span class="p">(</span><span class="n">v</span><span class="p">,</span><span class="w"> </span><span class="p">[</span><span class="o">&</span><span class="n">n</span><span class="p">]()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">n</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="mi">2</span><span class="p">;</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">t</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="kt">int</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">v</span><span class="w"> </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="s">","</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>1,2,4,8,16,32,64,128,256,512,
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++20</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>: 10.1.0 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#icc">ICC</a>: ??</li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: 2019 Update 10 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://timsong-cpp.github.io/cppwp/n4861/algorithms" target="_blank">N4861 25 Algorithms library</a></li>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3179r9.html" target="_blank">P3179R9 C++ parallel range algorithms</a><ul>
<li>C++26で<code>ranges::generate</code>の並列アルゴリズム版が追加された</li>
</ul>
</li>
<li><a href="https://cplusplus.github.io/LWG/issue4492" target="_blank">LWG Issue 4492. <code>std::generate</code> and <code>std::ranges::generate</code> wording is unclear for parallel algorithms</a><ul>
<li>並列実行時の「successive（連続した）」評価という意味付けが不明確であるため、P3179R9で追加された<code>ranges::generate</code>の並列アルゴリズム版はC++26で削除された（C++29での再検討が予定されている）</li>
</ul>
</li>
</ul></div>
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