164 lines
16 KiB
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164 lines
16 KiB
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<title>std::valarray<T>::operator=</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::valarray<T>::</span>operator=</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><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&&</span> other <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> T<span class="sy3">&</span> val <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-numeric-valarray-slice_array.html"><span class="kw1476">std::<span class="me2">slice_array</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> other<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-numeric-valarray-gslice_array.html"><span class="kw1477">std::<span class="me2">gslice_array</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> other<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(5)</td>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-numeric-valarray-mask_array.html"><span class="kw1478">std::<span class="me2">mask_array</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(6)</td>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-numeric-valarray-indirect_array.html"><span class="kw1479">std::<span class="me2">indirect_array</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(7)</td>
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<div><span class="mw-geshi cpp source-cpp">valarray<span class="sy1"><</span>T<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <a href="cpp-utility-initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1"><</span>T<span class="sy1">></span> il <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(8)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<td></td>
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<td></td>
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<p>替换数值数组的内容。</p>
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<div class="t-li1"><span class="t-li">1)</span> 复制赋值运算符。 <code>*this</code> 的每个元素被赋 <code>other</code> 的值。若 <code>other</code> 的长度不等于 <code>*this</code> 的长度，则<span class="t-rev-inl t-until-cxx11"><span>行为未定义</span> <span><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></span></span><span class="t-rev-inl t-since-cxx11"><span>首先如通过 <span class="t-c"><span class="mw-geshi cpp source-cpp">resize<span class="br0">(</span>other.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 重置大小</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>。</div>
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<div class="t-li1"><span class="t-li">2)</span> 移动赋值运算符。以 <code>other</code> 的内容替换 <code>*this</code> 的内容。此操作后 <code>other</code> 的内容未指定。若 T 拥有非平凡构造函数则此操作的复杂度可能为线性，但否则通常为常数。</div>
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<div class="t-li1"><span class="t-li">3)</span> 以f <code>val</code> 的副本替换 <code>*this</code> 中的每个值。</div>
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<div class="t-li1"><span class="t-li">4-7)</span> 以泛型化下标运算的结果替换 <code>*this</code> 的内容。若参数的长度不等于 <code>*this</code> 的长度，或若任何左侧的值依赖右侧的值（例如 <span class="t-c"><span class="mw-geshi cpp source-cpp">v<span class="sy1">=</span>v<span class="br0">[</span>v<span class="sy1">></span><span class="nu0">2</span><span class="br0">]</span></span></span> ），则行为未定义。</div>
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<div class="t-li1"><span class="t-li">8)</span> 赋值 <code>il</code> 的内容。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this <span class="sy1">=</span> valarray<span class="br0">(</span>il<span class="br0">)</span></span></span> 。</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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<table class="t-par-begin">
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<tr class="t-par">
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<td>other</td>
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<td>-</td>
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<td>要赋值的另一数值数组（或掩码）</td>
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<td>val</td>
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<td>-</td>
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<td>用以初始化每个元素的值</td>
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<td>il</td>
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<td>-</td>
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<td>要赋值的 initializer_list</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><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span></p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-li1"><span class="t-li">1, 3-8)</span> 可能抛出实现定义的异常。</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iomanip></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <valarray></span>
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<span class="kw4">void</span> print<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> rem, <span class="kw4">const</span> <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><span class="sy3">&</span> v<span class="br0">)</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> <a href="cpp-io-manip-left.html"><span class="kw1779">std::<span class="me2">left</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">36</span><span class="br0">)</span> <span class="sy1"><<</span> rem <span class="sy1"><<</span> <a href="cpp-io-manip-left.html"><span class="kw1780">std::<span class="me2">right</span></span></a><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> n<span class="sy4">:</span> v<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">3</span><span class="br0">)</span> <span class="sy1"><<</span> n<span class="sy4">;</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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<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> v1<span class="br0">(</span><span class="nu0">3</span><span class="br0">)</span><span class="sy4">;</span>
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v1 <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// (3) 从标量</span>
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print<span class="br0">(</span><span class="st0">"assigned from scalar: "</span>, v1<span class="br0">)</span><span class="sy4">;</span>
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v1 <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="br0">}</span><span class="sy4">;</span> <span class="co1">// (8) ：从不同大小的初始化器列表</span>
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print<span class="br0">(</span><span class="st0">"assigned from initializer_list:"</span>, v1<span class="br0">)</span><span class="sy4">;</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> v2<span class="br0">(</span><span class="nu0">3</span><span class="br0">)</span><span class="sy4">;</span>
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v2 <span class="sy1">=</span> v1<span class="br0">[</span><a href="cpp-numeric-valarray-slice.html"><span class="kw1474">std::<span class="me2">slice</span></span></a><span class="br0">(</span><span class="nu0">0</span>,<span class="nu0">3</span>,<span class="nu0">2</span><span class="br0">)</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// (4) ：从切片数组</span>
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print<span class="br0">(</span><span class="st0">"every 2nd element starting at pos 0:"</span>, v2<span class="br0">)</span><span class="sy4">;</span>
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v2 <span class="sy1">=</span> v1<span class="br0">[</span>v1 <span class="sy2">%</span> <span class="nu0">2</span> <span class="sy1">==</span> <span class="nu0">0</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// (6) ：从掩码数组</span>
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print<span class="br0">(</span><span class="st0">"values that are even:"</span>, v2<span class="br0">)</span><span class="sy4">;</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><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="sy1">></span> idx <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">0</span>,<span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">4</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 下标数组</span>
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v2.<span class="me1">resize</span><span class="br0">(</span><span class="nu0">4</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 从生成下标赋值时大小必须匹配</span>
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v2 <span class="sy1">=</span> v1<span class="br0">[</span>idx<span class="br0">]</span><span class="sy4">;</span> <span class="co1">// (7) ：从间接数组</span>
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print<span class="br0">(</span><span class="st0">"values at positions 0, 1, 2, 4:"</span>, v2<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">assigned from scalar: -1 -1 -1
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assigned from initializer_list: 1 2 3 4 5 6
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every 2nd element starting at pos 0: 1 3 5
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values that are even: 2 4 6
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values at positions 0, 1, 2, 4: 1 2 3 5</pre></div>
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