195 lines
12 KiB
HTML
195 lines
12 KiB
HTML
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::ranges::fill_n</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_ranges_fill_n skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::</span>fill_n</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-algorithm.html">algorithm</a>‎ | <a href="cpp-algorithm-ranges.html">ranges</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-algorithm.html"><algorithm></a></code></div>
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<div>调用签名</div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T, std<span class="sy4">::</span><span class="me2">output_iterator</span><span class="sy1"><</span><span class="kw4">const</span> T<span class="sy3">&</span><span class="sy1">></span> O <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> O fill_n<span class="br0">(</span> O first, std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>O<span class="sy1">></span> n, <span class="kw4">const</span> T<span class="sy3">&</span> value <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>赋值给定的 <code>value</code> 给范围 <code>[first, first + n)</code> 中的所有元素。</p>
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<p>此页面上描述的仿函数实体是 <i>niebloid</i> ,即:</p>
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<ul>
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<li>调用它们中的任何一者时不可指定显式模板实参。</li>
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<li>它们无一对<a href="cpp-language-adl.html">实参依赖查找</a>可见。</li>
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<li>在<a href="cpp-language-unqualified_lookup.html">通常无限定查找</a>寻找函数调用运算符左侧的名称找到它们之一时,它禁止<a href="cpp-language-adl.html">实参依赖查找</a>。</li>
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</ul>
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<p>实际上,它们能以函数对象,或以某些特殊编译器扩展实现。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>first</td>
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<td>-</td>
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<td>要修改的元素范围的起始</td>
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</tr>
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<tr class="t-par">
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<td>n</td>
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<td>-</td>
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<td>要修改的元素数</td>
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<td>value</td>
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<td>-</td>
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<td>要赋的值</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>比较等于 <code>first + n</code> 的迭代器。</p>
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<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
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<p>准确赋值 <code>n</code> 次。</p>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<table class="eq-fun-cpp-table">
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="kw1">struct</span> fill_n_fn <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, std<span class="sy4">::</span><span class="me2">output_iterator</span><span class="sy1"><</span><span class="kw4">const</span> T<span class="sy3">&</span><span class="sy1">></span> O<span class="sy1">></span>
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<span class="kw4">constexpr</span> O operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>O first, std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>O<span class="sy1">></span> n, <span class="kw4">const</span> T<span class="sy3">&</span> value<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span>std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>O<span class="sy1">></span> i<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span> i <span class="sy3">!</span><span class="sy1">=</span> n<span class="sy4">;</span> <span class="sy2">*</span>first <span class="sy1">=</span> value, <span class="sy2">++</span>first, <span class="sy2">++</span>i<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> first<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">inline</span> <span class="kw4">constexpr</span> fill_n_fn fill_n<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span></pre></div>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <algorithm></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <vector></span>
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<span class="kw4">auto</span> print<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> v<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> elem <span class="sy4">:</span> v<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> elem <span class="sy1"><<</span> <span class="st0">" "</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">constexpr</span> <span class="kw4">auto</span> n<span class="br0">{</span><span class="nu0">8</span><span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span> v<span class="br0">(</span>n, <span class="st0">"░░"</span><span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span>v<span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">fill_n</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, n, <span class="st0">"▓▓"</span><span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span>v<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出:</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">░░ ░░ ░░ ░░ ░░ ░░ ░░ ░░
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▓▓ ▓▓ ▓▓ ▓▓ ▓▓ ▓▓ ▓▓ ▓▓</pre></div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-ranges-fill.html"><span class="t-lines"><span>ranges::fill</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>将一个给定值复制赋值给一个范围内的每个元素<br />
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<span class="t-mark">(niebloid)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-ranges-copy_n.html"><span class="t-lines"><span>ranges::copy_n</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>将一定数目的元素复制到一个新的位置<br />
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<span class="t-mark">(niebloid)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-ranges-generate.html"><span class="t-lines"><span>ranges::generate</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>保存函数结果到一个范围中<br />
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<span class="t-mark">(niebloid)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-ranges-transform.html"><span class="t-lines"><span>ranges::transform</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>将一个函数应用于某一范围的各个元素<br />
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<span class="t-mark">(niebloid)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-fill_n.html"><span class="t-lines"><span>fill_n</span></span></a></div>
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</div>
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</td>
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<td>将一个给定值复制赋值给一个范围内的 N 个元素<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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