152 lines
12 KiB
HTML
152 lines
12 KiB
HTML
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<title>std::experimental::ranges::distance</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_experimental_ranges_iterator_distance 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::experimental::ranges::</span>distance</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-experimental.html">experimental</a>‎ | <a href="cpp-experimental-ranges.html">ranges</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-experimental-ranges-iterator.html"><experimental/ranges/iterator></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">namespace</span> <span class="br0">{</span><br /></span>
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<p> <span class="kw4">constexpr</span> <span class="coMULTI">/* unspecified */</span> distance <span class="sy1">=</span> <span class="coMULTI">/* unspecified */</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</span></div>
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<td><span class="t-mark-rev t-since-ranges-ts t-mark-ts">(范围 TS)</span><br />
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<span class="t-mark">(定制点对象)</span></td>
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<div>调用签名</div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> Iterator I, Sentinel<span class="sy1"><</span>I<span class="sy1">></span> S <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">difference_type_t</span><span class="sy1"><</span>I<span class="sy1">></span> distance<span class="br0">(</span>I first, S last<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"><span class="kw1">template</span><span class="sy1"><</span> Range R <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">difference_type_t</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> distance<span class="br0">(</span>R<span class="sy3">&&</span> r<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> SizedRange R <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">difference_type_t</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> distance<span class="br0">(</span>R<span class="sy3">&&</span> r<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<p>返回 <code>first</code> 与 <code>last</code> 间的距离，或范围 <code>r</code> 的首尾间的距离。</p>
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<div class="t-li1"><span class="t-li">1)</span> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">SizedSentinel<span class="sy1"><</span>S, I<span class="sy1">></span></span></span> 得到满足，则等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> last <span class="sy2">-</span> first<span class="sy4">;</span></span></span> 。否则，返回从 <code>first</code> 得到 <code>last</code> 所需的自增次数。若 <code>[first, last)</code> 不代表范围，则 <code>I</code> 与 <code>S</code> 必须为同一类型且必须实现 <a href="cpp-experimental-ranges-iterator-SizedSentinel.html"><code>SizedSentinel</code></a> ，而 <code>[last, first)</code> 必须指代一个范围。否则，行为未定义。</div>
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<div class="t-li1"><span class="t-li">2)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> ranges<span class="sy4">::</span><span class="me2">distance</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><span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> ranges<span class="sy4">::</span><span class="me2">size</span><span class="br0">(</span>r<span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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<p>若在实例化点前未包含头文件 <a href="cpp-header-experimental-ranges-range.html"><tt><experimental/ranges/range></tt></a> ，则实例化重载 <span class="t-v">(2-3)</span> 可能为病式。</p>
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<h3><span class="mw-headline" id=".E5.AE.9A.E5.88.B6.E7.82.B9.E5.AF.B9.E8.B1.A1">定制点对象</span></h3>
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<p>名称 <code>ranges::distance</code> 代表一个<i>定制点对象</i>，它是<a href="cpp-named_req-LiteralType.html">字面</a> <a href="cpp-experimental-ranges-concepts-Semiregular.html"><code>Semiregular</code></a> 类类型的<a href="cpp-named_req-FunctionObject.html">函数对象</a>（为说明目的以 <code>DistanceT</code> 表示）。<code>DistanceT</code> 的所有实例均相等。从而能自由地复制 <code>ranges::distance</code> ，且能交替使用其副本。</p>
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<p>给定类型集合 <code>Args...</code> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-declval.html"><span class="kw1120">std::<span class="me2">declval</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span>...</span></span> 满足上面给 <code>ranges::distance</code> 的参数要求，则 <code>DistanceT</code> 将满足 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-experimental-ranges-concepts-Invocable.html"><span class="kw2556">ranges::<span class="me2">Invocable</span></span></a><span class="sy1"><</span><span class="kw4">const</span> DistanceT, Args...<span class="sy1">></span></span></span> 。否则，没有 <code>DistanceT</code> 的函数调用运算符参与重载决议。</p>
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<p>在每个定义 <code>ranges::distance</code> 的翻译单元中，它都指代定制点对象的同一实例。（这表示能自由地在类似 inline 函数和函数模板的东西中使用它，而不违反<a href="cpp-language-definition.html#.E5.8D.95.E4.B8.80.E5.AE.9A.E4.B9.89.E8.A7.84.E5.88.99.EF.BC.88ODR.EF.BC.89">单一定义规则</a>。）</p>
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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><code>first</code> 与 <code>last</code> 间的距离，或范围 <code>r</code> 的首尾间的距离。</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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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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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-iterator-distance.html"><span class="t-lines"><span>distance</span></span></a></div>
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<td>返回两个迭代器间的距离<br />
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<span class="t-mark">(函数模板)</span></td>
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<div><a href="cpp-experimental-ranges-iterator-advance.html"><span class="t-lines"><span>advance</span></span></a></div>
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<td>令迭代器前进给定的距离<br />
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<span class="t-mark">(函数模板)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-experimental-ranges-iterator-next.html"><span class="t-lines"><span>next</span></span></a></div>
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</div>
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</td>
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<td>自增迭代器<br />
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<span class="t-mark">(函数模板)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-experimental-ranges-iterator-prev.html"><span class="t-lines"><span>prev</span></span></a></div>
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</div>
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<td>自减迭代器<br />
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<span class="t-mark">(函数模板)</span></td>
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<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/ranges/range/size&action=edit&redlink=1" class="new" title="cpp/experimental/ranges/range/size（页面不存在）"><span class="t-lines"><span>size</span></span></a></div>
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</div>
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</td>
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<td>获得能在常数时间计算大小的范围的大小<br />
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<span class="t-mark">(定制点对象)</span></td>
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</div>
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<div class="visualClear"></div>
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