110 lines
9.1 KiB
HTML
110 lines
9.1 KiB
HTML
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<title>std::valarray<T>::apply</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_valarray_apply 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::valarray<T>::</span>apply</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-numeric.html">numeric</a>‎ | <a href="cpp-numeric-valarray.html">valarray</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span> apply<span class="br0">(</span> T func<span class="br0">(</span>T<span class="br0">)</span> <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span> apply<span class="br0">(</span> T func<span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&</span><span class="br0">)</span> <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<p>返回同大小的新 valarray ，拥有通过应用 <code>func</code> 函数到元素先前值取得的值。</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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<td>func</td>
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<td>-</td>
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<td>应用到值的函数</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>作为结果的 valarray ，拥有通过应用 <code>func</code> 取得的值</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>函数能实现为拥有不同于 <span class="t-lc"><a href="cpp-numeric-valarray.html">std::valarray</a></span> 的返回类型。此情况下，替换类型拥有下列属性：</p>
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<dd>
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<ul>
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<li>提供 <span class="t-lc"><a href="cpp-numeric-valarray.html">std::valarray</a></span> 的所有 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span></span></span> 成员函数。</li>
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<li>能从替换类型构造 <span class="t-lc"><a href="cpp-numeric-valarray.html">std::valarray</a></span> 、 <span class="t-lc"><a href="cpp-numeric-valarray-slice_array.html">std::slice_array</a></span> 、 <span class="t-lc"><a href="cpp-numeric-valarray-gslice_array.html">std::gslice_array</a></span> 、 <span class="t-lc"><a href="cpp-numeric-valarray-mask_array.html">std::mask_array</a></span> 和 <span class="t-lc"><a href="cpp-numeric-valarray-indirect_array.html">std::indirect_array</a></span> 。</li>
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<li>所有接受一个 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <a href="cpp-numeric-valarray.html"><span class="kw1473">std::<span class="me2">valarray</span></span></a><span class="sy3">&</span></span></span> 类型参数的函数<span class="t-rev-inl t-since-cxx11"><span>，除了 <a href="cpp-numeric-valarray-begin2.html"><tt>begin()</tt></a> 和 <a href="cpp-numeric-valarray-end2.html"><tt>end()</tt></a></span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>也应该接受替换类型。</li>
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<li>所有接受二个 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <a href="cpp-numeric-valarray.html"><span class="kw1473">std::<span class="me2">valarray</span></span></a><span class="sy3">&</span></span></span> 类型参数的函数都应该接受 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <a href="cpp-numeric-valarray.html"><span class="kw1473">std::<span class="me2">valarray</span></span></a><span class="sy3">&</span></span></span> 和替换类型的每种组合。</li>
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<li>返回类型添加不多于二层嵌套在最深层嵌套的参数类型上的模板。</li>
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</ul>
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</dd>
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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>计算并打印前 10 个正整数的阶乘</p>
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<div class="t-example-live-link"></div>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <valarray></span>
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<span class="co2">#include <cmath></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-numeric-valarray.html"><span class="kw1473">std::<span class="me2">valarray</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> v <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span>,<span class="nu0">6</span>,<span class="nu0">7</span>,<span class="nu0">8</span>,<span class="nu0">9</span>,<span class="nu0">10</span><span class="br0">}</span><span class="sy4">;</span>
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v <span class="sy1">=</span> v.<span class="me1">apply</span><span class="br0">(</span><span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> n<span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span><span class="kw4">int</span> <span class="br0">{</span>
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<span class="kw1">return</span> <a href="cpp-numeric-math-round.html"><span class="kw1353">std::<span class="me2">round</span></span></a><span class="br0">(</span><a href="cpp-numeric-math-tgamma.html"><span class="kw1349">std::<span class="me2">tgamma</span></span></a><span class="br0">(</span>n<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="br0">)</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> 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> n <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></pre></div>
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</div>
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<p>输出：</p>
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<div class="text source-text">
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<pre class="de1">1 2 6 24 120 720 5040 40320 362880 3628800</pre></div>
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<h3><span class="mw-headline" id="See_also">See also</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-for_each.html"><span class="t-lines"><span>for_each</span></span></a></div>
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</div>
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</td>
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<td>应用函数到范围中的元素<br />
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<span class="t-mark">(函数模板)</span></td>
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<div class="visualClear"></div>
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