168 lines
13 KiB
HTML
168 lines
13 KiB
HTML
<!DOCTYPE html>
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<title>std::iota</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_iota skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>iota</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-algorithm.html">algorithm</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-numeric.html"><numeric></a></code></div>
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<td></td>
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<td></td>
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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> ForwardIt, <span class="kw1">class</span> T <span class="sy1">></span><br />
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<span class="kw4">void</span> iota<span class="br0">(</span> ForwardIt first, ForwardIt last, T 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-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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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> ForwardIt, <span class="kw1">class</span> T <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> <span class="kw4">void</span> iota<span class="br0">(</span> ForwardIt first, ForwardIt last, T 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>以始于 <code>value</code> 并重复地求值 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>value</span></span> 的顺序递增值填充范围 <code>[first, last)</code> 。</p>
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<p>等价操作：</p>
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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="sy2">*</span><span class="br0">(</span>d_first<span class="br0">)</span> <span class="sy1">=</span> value<span class="sy4">;</span>
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<span class="sy2">*</span><span class="br0">(</span>d_first<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span> <span class="sy1">=</span> <span class="sy2">++</span>value<span class="sy4">;</span>
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<span class="sy2">*</span><span class="br0">(</span>d_first<span class="sy2">+</span><span class="nu0">2</span><span class="br0">)</span> <span class="sy1">=</span> <span class="sy2">++</span>value<span class="sy4">;</span>
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<span class="sy2">*</span><span class="br0">(</span>d_first<span class="sy2">+</span><span class="nu0">3</span><span class="br0">)</span> <span class="sy1">=</span> <span class="sy2">++</span>value<span class="sy4">;</span>
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...</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<td>first, last</td>
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<td>-</td>
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<td>以 value 开始，按顺序递增填充的值的范围</td>
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</tr>
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<tr class="t-par">
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<td>value</td>
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<td>-</td>
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<td>要存储的初始值，表达式 ++value 必须为良式</td>
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</tr>
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</table>
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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>（无）</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>正好 <code>last - first</code> 次自增与赋值。</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">template</span><span class="sy1"><</span><span class="kw1">class</span> ForwardIterator, <span class="kw1">class</span> T<span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="co1">// C++20 起</span>
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<span class="kw4">void</span> iota<span class="br0">(</span>ForwardIterator first, ForwardIterator last, T value<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">while</span><span class="br0">(</span>first <span class="sy3">!</span><span class="sy1">=</span> last<span class="br0">)</span> <span class="br0">{</span>
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<span class="sy2">*</span>first<span class="sy2">++</span> <span class="sy1">=</span> value<span class="sy4">;</span>
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<span class="sy2">++</span>value<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>此函数命名来源于编程语言 APL 中的整数函数 ⍳ 。它是 C++98 所不曾包含的 <a rel="nofollow" class="external text" href="http://www.sgi.com/tech/stl/iota.html">STL 组件</a>之一，但最终于 C++11 进入了标准库。</p>
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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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<p>下列代码应用 <span class="t-lc"><a href="cpp-algorithm-random_shuffle.html">std::shuffle</a></span> 到 <span class="t-lc"><a href="cpp-container-list.html">std::list</a></span> 迭代器的 vector ，因为不能直接应用 <span class="t-lc"><a href="cpp-algorithm-random_shuffle.html">std::shuffle</a></span> 到 <span class="t-lc"><a href="cpp-container-list.html">std::list</a></span> 。用 <code>std::iota</code> 填充二个容器。</p>
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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 <list></span>
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<span class="co2">#include <numeric></span>
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<span class="co2">#include <random></span>
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<span class="co2">#include <vector></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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<a href="cpp-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> l<span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span>l.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, l.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <span class="sy2">-</span><span class="nu0">4</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-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">iterator</span><span class="sy1">></span> v<span class="br0">(</span>l.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, l.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-algorithm-random_shuffle.html"><span class="kw1607">std::<span class="me2">shuffle</span></span></a><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <a href="cpp-numeric-random-mersenne_twister_engine.html"><span class="kw1489">std::<span class="me2">mt19937</span></span></a><span class="br0">{</span><a href="cpp-numeric-random-random_device.html"><span class="kw1486">std::<span class="me2">random_device</span></span></a><span class="br0">{</span><span class="br0">}</span><span class="br0">(</span><span class="br0">)</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Contents of the list: "</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> n<span class="sy4">:</span> l<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> n <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">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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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Contents of the list, shuffled: "</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> i<span class="sy4">:</span> v<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="sy2">*</span>i <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">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></pre></div>
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</div>
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<p>可能的输出：</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">Contents of the list: -4 -3 -2 -1 0 1 2 3 4 5
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Contents of the list, shuffled: 0 -1 3 4 -4 1 -2 -3 2 5</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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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-fill.html"><span class="t-lines"><span>fill</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每个元素<br />
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<span class="t-mark">(函数模板)</span></td>
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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-generate.html"><span class="t-lines"><span>generate</span></span></a></div>
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</div>
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</td>
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<td>将相继的函数调用结果赋值给一个范围中的每个元素<br />
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<span class="t-mark">(函数模板)</span></td>
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</table>
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</div>
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<div class="visualClear"></div>
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