360 lines
39 KiB
HTML
360 lines
39 KiB
HTML
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<title>std::ranges::transform, std::ranges::unary_transform_result, std::ranges::binary_transfor_result</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::</span>transform, <span style="font-size:0.7em; line-height:130%">std::ranges::</span>unary_transform_result, <span style="font-size:0.7em; line-height:130%">std::ranges::</span>binary_transfor_result</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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<td></td>
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<td></td>
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<td>
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<div>调用签名</div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">input_iterator</span> I, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I<span class="sy1">></span> S, std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> O,<br /></span>
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<p> std<span class="sy4">::</span><span class="me2">copy_constructible</span> F, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">></span><br />
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requires std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>O,<br />
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std<span class="sy4">::</span><span class="me2">indirect_result_t</span><span class="sy1"><</span>F<span class="sy3">&</span>, std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>I, Proj<span class="sy1">>>></span><br />
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">unary_transform_result</span><span class="sy1"><</span>I, O<span class="sy1">></span><br /></p>
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transform<span class="br0">(</span> I first1, S last1, O result, F op, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> ranges<span class="sy4">::</span><span class="me2">input_range</span> R, std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> O,<br /></span>
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<p> std<span class="sy4">::</span><span class="me2">copy_constructible</span> F, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">></span><br />
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requires std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span><br />
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O,<br />
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std<span class="sy4">::</span><span class="me2">indirect_result_t</span><span class="sy1"><</span>F<span class="sy3">&</span>, std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>, Proj<span class="sy1">>>></span><br />
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">unary_transform_result</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>, O<span class="sy1">></span><br /></p>
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transform<span class="br0">(</span> R<span class="sy3">&&</span> r, O result, F op, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">input_iterator</span> I1, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I1<span class="sy1">></span> S1,<br /></span>
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<p> std<span class="sy4">::</span><span class="me2">input_iterator</span> I2, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I2<span class="sy1">></span> S2,<br />
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std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> O,<br />
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std<span class="sy4">::</span><span class="me2">copy_constructible</span> F,<br />
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<span class="kw1">class</span> Proj1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>, <span class="kw1">class</span> Proj2 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">></span><br />
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requires std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span><br />
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O,<br />
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std<span class="sy4">::</span><span class="me2">indirect_result_t</span><span class="sy1"><</span>F<span class="sy3">&</span>,<br />
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std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>I1, Proj1<span class="sy1">></span>,<br />
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std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>I2, Proj2<span class="sy1">>>></span><br />
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">binary_transform_result</span><span class="sy1"><</span>I1, I2, O<span class="sy1">></span><br />
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transform<span class="br0">(</span> I1 first1, S1 last1, I2 first2, S2 last2, O result,<br /></p>
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F binary_op, Proj1 proj1 <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span>, Proj2 proj2 <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">input_range</span> R1,<br /></span>
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<p> std<span class="sy4">::</span><span class="me2">input_range</span> R2,<br />
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std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> O,<br />
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std<span class="sy4">::</span><span class="me2">copy_constructible</span> F,<br />
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<span class="kw1">class</span> Proj1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>, <span class="kw1">class</span> Proj2 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">></span><br />
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requires std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span><br />
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O,<br />
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std<span class="sy4">::</span><span class="me2">indirect_result_t</span><span class="sy1"><</span><br />
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F<span class="sy3">&</span>,<br />
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std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R1<span class="sy1">></span>, Proj<span class="sy1">></span>,<br />
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std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R2<span class="sy1">></span>, Proj<span class="sy1">>>></span><br />
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">binary_transform_result</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1"><</span>R1<span class="sy1">></span>,<br />
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ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1"><</span>R2<span class="sy1">></span>, O<span class="sy1">></span><br /></p>
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transform<span class="br0">(</span> R1<span class="sy3">&&</span> r1, R2<span class="sy3">&&</span> r2, O result, F binary_op, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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<tr class="t-dcl-h">
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<div>辅助类型</div>
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</td>
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<td></td>
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<td></td>
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</tr>
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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> I, <span class="kw1">class</span> O <span class="sy1">></span><br />
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<span class="kw1">using</span> unary_transform_result <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">in_out_result</span><span class="sy1"><</span>I, O<span class="sy1">></span><span class="sy4">;</span></span></div>
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</td>
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<td>(5)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<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> I1, <span class="kw1">class</span> I2, <span class="kw1">class</span> O <span class="sy1">></span><br />
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<span class="kw1">using</span> binary_transform_result <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">in_in_out_result</span><span class="sy1"><</span>I1, I2, O<span class="sy1">></span><span class="sy4">;</span></span></div>
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</td>
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<td>(6)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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<p><code>ranges::transform</code> 应用给定的函数到范围并存储结果于始于 <code>result</code> 的另一范围。</p>
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<div class="t-li1"><span class="t-li">1)</span> 应用一元运算 <code>op</code> 到 <code>[first1, last1)</code> 所定义的范围（在以投影 <code>proj</code> 投影后）。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，但以 <code>r</code> 为源范围，如同以 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r<span class="br0">)</span></span></span> 为 <code>first</code> 并以 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r<span class="br0">)</span></span></span> 为 <code>last</code> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 应用二元运算 <code>binary_op</code> 到来自二个范围的元素：一个由 <code>[first1, last1)</code> 定义而另一个由 <code>[first2, last2)</code> 定义（在分别以投影 <code>proj1</code> 与 <code>proj2</code> 投影后）。</div>
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<div class="t-li1"><span class="t-li">4)</span> 同 <span class="t-v">(3)</span> ，但以 <code>r1</code> 为第一源范围，如同以 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r1<span class="br0">)</span></span></span> 为 <code>first1</code> 并以 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r1<span class="br0">)</span></span></span> 为 <code>last1</code> ，而对 <code>r2</code> 也类似。</div>
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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>first1, last1</td>
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<td>-</td>
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<td>要变换的元素范围</td>
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</tr>
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<tr class="t-par">
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<td>r, r1</td>
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<td>-</td>
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<td>要变换的元素范围
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<p>{{par | first2, last2 |要变换的第二元素范围}</p>
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</td>
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</tr>
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<tr class="t-par">
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<td>r2</td>
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<td>-</td>
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<td>要变换的第二元素范围</td>
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</tr>
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<tr class="t-par">
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<td>result</td>
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<td>-</td>
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<td>目标范围的起始，可以等于 <code>first1</code> 或 <code>first2</code></td>
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</tr>
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<tr class="t-par">
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<td>op, binary_op</td>
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<td>-</td>
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<td>应用到投影后元素的操作</td>
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</tr>
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<tr class="t-par">
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<td>proj1</td>
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<td>-</td>
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<td>应用到第一范围中的元素的投影</td>
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</tr>
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<tr class="t-par">
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<td>proj2</td>
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<td>-</td>
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<td>应用到第二范围中的元素的投影</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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<div class="t-li1"><span class="t-li">1-2)</span> <code>unary_transform_result</code> ，含有等于 <code>last</code> 的输入迭代器与指向最后变换元素后一元素的输出迭代器。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> <code>binary_transform_result</code> ，含有分别作为 <code>in1</code> 与 <code>in2</code> 的指向来自范围 <code>[first1, last1)</code> 与 <code>[first2, last2)</code> 的最后变换元素的输入迭代器，与作为 <code>out</code> 的指向最后变换元素后一元素的输出迭代器。</div>
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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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<div class="t-li1"><span class="t-li">1-2)</span> 准确应用 <span class="t-c"><span class="mw-geshi cpp source-cpp">last1 <span class="sy2">-</span> first1</span></span> 次 <code>op</code> 与 <code>proj</code> 。</div>
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<div class="t-li1"><span class="t-li">3-4)</span> 准确应用 <span class="t-c"><span class="mw-geshi cpp source-cpp">min<span class="br0">(</span>last1 <span class="sy2">-</span> first1, last2 <span class="sy2">-</span> first2<span class="br0">)</span></span></span> 次 <code>binary_op</code> 与投影。</div>
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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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<tr>
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<td>
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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> transform_fn <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">input_iterator</span> I, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I<span class="sy1">></span> S, std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> O,
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std<span class="sy4">::</span><span class="me2">copy_constructible</span> F, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">></span>
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requires std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>O, std<span class="sy4">::</span><span class="me2">indirect_result_t</span><span class="sy1"><</span>F<span class="sy3">&</span>, std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>I, Proj<span class="sy1">>>></span>
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">unary_transform_result</span><span class="sy1"><</span>I, O<span class="sy1">></span>
|
|
operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> I first1, S last1, O result, F op, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span> <span class="kw4">const</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> first1 <span class="sy3">!</span><span class="sy1">=</span> last1<span class="sy4">;</span> <span class="sy2">++</span>first1, <span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span><span class="sy2">++</span>result<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="sy2">*</span>result <span class="sy1">=</span> <a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>op, <a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>proj, <span class="sy2">*</span>first1<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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|
<span class="br0">}</span>
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|
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|
<span class="kw1">return</span> <span class="br0">{</span>first1, result<span class="br0">}</span><span class="sy4">;</span>
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|
<span class="br0">}</span>
|
|
|
|
<span class="kw1">template</span><span class="sy1"><</span> ranges<span class="sy4">::</span><span class="me2">input_range</span> R, std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> O,
|
|
std<span class="sy4">::</span><span class="me2">copy_constructible</span> F, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">></span>
|
|
requires std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>
|
|
O,
|
|
std<span class="sy4">::</span><span class="me2">indirect_result_t</span><span class="sy1"><</span>F<span class="sy3">&</span>, std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>, Proj<span class="sy1">>>></span>
|
|
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">unary_transform_result</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>, O<span class="sy1">></span>
|
|
operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> R<span class="sy3">&&</span> r, O result, F op, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span> <span class="kw4">const</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">return</span> <span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r<span class="br0">)</span>, ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r<span class="br0">)</span>, result, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>proj<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">input_iterator</span> I1, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I1<span class="sy1">></span> S1,
|
|
std<span class="sy4">::</span><span class="me2">input_iterator</span> I2, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1"><</span>I2<span class="sy1">></span> S2,
|
|
std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> O,
|
|
std<span class="sy4">::</span><span class="me2">copy_constructible</span> F,
|
|
<span class="kw1">class</span> Proj1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>, <span class="kw1">class</span> Proj2 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">></span>
|
|
requires std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>
|
|
O,
|
|
std<span class="sy4">::</span><span class="me2">indirect_result_t</span><span class="sy1"><</span>F<span class="sy3">&</span>,
|
|
std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>I1, Proj1<span class="sy1">></span>,
|
|
std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>I2, Proj2<span class="sy1">>>></span>
|
|
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">binary_transform_result</span><span class="sy1"><</span>I1, I2, O<span class="sy1">></span>
|
|
operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> I1 first1, S1 last1, I2 first2, S2 last2, O result,
|
|
F binary_op, Proj1 proj1 <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span>, Proj2 proj2 <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span> <span class="kw4">const</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> first1 <span class="sy3">!</span><span class="sy1">=</span> last1 <span class="sy3">&&</span> first2 <span class="sy3">!</span><span class="sy1">=</span> last2<span class="sy4">;</span> <span class="sy2">++</span>first1, <span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span><span class="sy2">++</span>first2, <span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span><span class="sy2">++</span>result<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="sy2">*</span>result <span class="sy1">=</span> <a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>binary_op,
|
|
<a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>proj1, <span class="sy2">*</span>first1<span class="br0">)</span>,
|
|
<a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>proj2, <span class="sy2">*</span>first2<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw1">return</span> <span class="br0">{</span>first1, first2, result<span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw1">template</span><span class="sy1"><</span> ranges<span class="sy4">::</span><span class="me2">input_range</span> R1, ranges<span class="sy4">::</span><span class="me2">input_range</span> R2,
|
|
std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> O, std<span class="sy4">::</span><span class="me2">copy_constructible</span> F,
|
|
<span class="kw1">class</span> Proj1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>, <span class="kw1">class</span> Proj2 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">></span>
|
|
requires std<span class="sy4">::</span><span class="me2">indirectly_writable</span><span class="sy1"><</span>
|
|
O,
|
|
std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R1<span class="sy1">></span>, Proj1<span class="sy1">></span>,
|
|
std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R2<span class="sy1">></span>, Proj2<span class="sy1">>>></span>
|
|
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">binary_transform_result</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1"><</span>R1<span class="sy1">></span>,
|
|
ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1"><</span>R2<span class="sy1">></span>, O<span class="sy1">></span>
|
|
operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> R1<span class="sy3">&&</span> r1, R2<span class="sy3">&&</span> r2, O result,
|
|
F binary_op, Proj1 proj1 <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span>, Proj2 proj2 <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span> <span class="kw4">const</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">return</span> <span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r1<span class="br0">)</span>, ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r1<span class="br0">)</span>,
|
|
ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r2<span class="br0">)</span>, ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r2<span class="br0">)</span>,
|
|
result, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>binary_op<span class="br0">)</span>,
|
|
<a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>proj1<span class="br0">)</span>, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>proj2<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">inline</span> <span class="kw4">constexpr</span> transform_fn transform<span class="sy4">;</span></pre></div>
|
|
</div>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p><code>std::ranges::transform</code> 不保证按顺序应用 <code>op</code> 或 <code>binary_op</code> 。为按顺序应用函数导序列或应用修改元素的函数到序列，请用 <span class="t-lc">std::ranges::for_each</span> 。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<p>下列代码用 <code>transform</code> 以 <code>toupper</code> 函数原地转换为大写然后变换每个 <code>char</code> 为其序数值：</p>
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <algorithm></span>
|
|
<span class="co2">#include <cctype></span>
|
|
<span class="co2">#include <functional></span>
|
|
<span class="co2">#include <iostream></span>
|
|
<span class="co2">#include <string></span>
|
|
<span class="co2">#include <vector></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> s<span class="br0">(</span><span class="st0">"hello"</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">namespace</span> ranges <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">;</span>
|
|
|
|
ranges<span class="sy4">::</span><span class="me2">transform</span><span class="br0">(</span>s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>,
|
|
<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span> c<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span> <span class="kw4">unsigned</span> <span class="kw4">char</span> <span class="br0">{</span> <span class="kw1">return</span> std<span class="sy4">::</span><span class="me2">toupper</span><span class="br0">(</span>c<span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</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> ordinals<span class="sy4">;</span>
|
|
ranges<span class="sy4">::</span><span class="me2">transform</span><span class="br0">(</span>s, <a href="cpp-iterator-back_inserter.html"><span class="kw665">std::<span class="me2">back_inserter</span></span></a><span class="br0">(</span>ordinals<span class="br0">)</span>,
|
|
<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span> c<span class="br0">)</span> <span class="sy2">-</span><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="br0">{</span> <span class="kw1">return</span> c<span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> s <span class="sy1"><<</span> <span class="st0">':'</span><span class="sy4">;</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> ord <span class="sy4">:</span> ordinals<span class="br0">)</span> <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> <span class="st0">' '</span> <span class="sy1"><<</span> ord<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
ranges<span class="sy4">::</span><span class="me2">transform</span><span class="br0">(</span>ordinals, ordinals, ordinals.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, <a href="cpp-utility-functional-plus.html"><span class="kw1029">std::<span class="me2">plus</span></span></a><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<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>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> ord <span class="sy4">:</span> ordinals<span class="br0">)</span> <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> ord <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
|
|
<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> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">HELLO: 72 69 76 76 79
|
|
144 138 152 152 158</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-ranges-for_each.html"><span class="t-lines"><span>ranges::for_each</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>应用函数到范围中的元素<br />
|
|
<span class="t-mark">(niebloid)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-ranges-transform_view.html"><span class="t-lines"><span>ranges::transform_view</span><span>views::transform</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>对序列的每个元素应用某个变换函数的 <a href="cpp-ranges-view.html"><code>view</code></a><br />
|
|
<span class="t-mark">(类模板)</span> <span class="t-mark">(范围适配器对象)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-transform.html"><span class="t-lines"><span>transform</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>将一个函数应用于某一范围的各个元素，并在目标范围存储结果<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|