91 lines
6.9 KiB
HTML
91 lines
6.9 KiB
HTML
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<title>std::span<T,Extent>::subspan</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::span<T,Extent>::</span>subspan</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-container.html">container</a>‎ | <a href="cpp-container-span.html">span</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Offset,<br /></span>
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<p> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Count <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">dynamic_extent</span> <span class="sy1">></span><br /></p>
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<span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>element_type, E <span class="coMULTI">/* see below */</span><span class="sy1">></span> subspan<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span>element_type, std<span class="sy4">::</span><span class="me2">dynamic_extent</span><span class="sy1">></span><br /></span>
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<p> subspan<span class="br0">(</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Offset,<br /></p>
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<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Count <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">dynamic_extent</span> <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></div>
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<td>(2)</td>
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<p>获得 span ，它是此 span 的始于偏移 <code>Offset</code> 的 <code>Count</code> 个元素上的视图。若 <code>Count</code> 为 <code>std::dynamic_extent</code> ，则子段中的元素数为 <code>size() - offset</code> （即它结束于 <code>*this</code> 的结尾）。</p>
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<p>若</p>
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<ul>
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<li><code>Offset</code> 大于 <code>Extent</code> ，或</li>
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<li><code>Count</code> 不是 <code>std::dynamic_extent</code> 且 <code>Count</code> 大于 <code>Extent - Offset</code></li>
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</ul>
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<p>则 <span class="t-v">(1)</span> 为谬构。</p>
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<p>若 <code>Offset</code> 或 <code>Count</code> 在范围外则行为未定义。若出现以下条件则这会发生：</p>
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<ul>
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<li><code>Offset</code> 大于 <code>size()</code> ；</li>
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<li><code>Count</code> 非 <code>std::dynamic_extent</code> 且 <code>Count</code> 大于 <code>size() - Offset</code> 。</li>
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</ul>
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<p>按下列方式确定 <span class="t-v">(1)</span> 所返回的 span 的长度模板实参 <code>E</code> ：</p>
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<li>若 <code>Count</code> 不是 <code>std::dynamic_extent</code> 则为 <code>Count</code> ；</li>
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<li>否则，若 <code>Extent</code> 不是 <code>std::dynamic_extent</code> ，则为 <code>Extent - Offset</code> ；</li>
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<li>否则为 <code>std::dynamic_extent</code> 。</li>
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</ul>
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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>请求的子段 <code>r</code> ，满足 <span class="t-c"><span class="mw-geshi cpp source-cpp">r.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> this<span class="sy2">-</span><span class="sy1">></span>data<span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> Offset</span></span> 。若 <code>Count</code> 为 <code>std::dynamic_extent</code> ，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">r.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> this<span class="sy2">-</span><span class="sy1">></span>size<span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> Offset</span></span> ；否则 <span class="t-c"><span class="mw-geshi cpp source-cpp">r.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> Count</span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-span-first.html"><span class="t-lines"><span>first</span></span></a></div>
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</div>
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</td>
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<td>获得由序列首 N 个元素组成的子段<br />
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<span class="t-mark">(公开成员函数)</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-container-span-last.html"><span class="t-lines"><span>last</span></span></a></div>
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</div>
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</td>
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<td>获得由序列末 N 个元素组成的子段<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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</table>
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</div>
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