104 lines
8.0 KiB
HTML
104 lines
8.0 KiB
HTML
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<title>std::ranges::view_interface<D>::size</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_view_interface_size 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::ranges::view_interface<D>::</span>size</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-ranges.html">ranges</a>‎ | <a href="cpp-ranges-view_interface.html">view interface</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">auto</span> size<span class="br0">(</span><span class="br0">)</span> requires ranges<span class="sy4">::</span><span class="me2">forward_range</span><span class="sy1"><</span>D<span class="sy1">></span> <span class="sy3">&&</span><br /></span>
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<p> std<span class="sy4">::</span><span class="me2">sized_sentinel_for</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">sentinel_t</span><span class="sy1"><</span>D<span class="sy1">></span>,<br /></p>
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ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>D<span class="sy1">>></span><span class="sy4">;</span></div>
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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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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">auto</span> size<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> requires ranges<span class="sy4">::</span><span class="me2">forward_range</span><span class="sy1"><</span><span class="kw4">const</span> D<span class="sy1">></span> <span class="sy3">&&</span><br /></span>
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<p> std<span class="sy4">::</span><span class="me2">sized_sentinel_for</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span><span class="kw4">const</span> D<span class="sy1">></span>,<br /></p>
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ranges<span class="sy4">::</span><span class="me2">sentinel_t</span><span class="sy1"><</span><span class="kw4">const</span> D<span class="sy1">>></span><span class="sy4">;</span></div>
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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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<p><code>size()</code> 成员函数的默认实现通过计算哨位与起始迭代器间的差获得范围的大小。</p>
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<div class="t-li1"><span class="t-li">1)</span> 令 <code>derived</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span>D<span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span></span></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">end</span><span class="br0">(</span>derived<span class="br0">)</span> <span class="sy2">-</span> ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>derived<span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，除了 <code>derived</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">const</span> D<span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span><span class="sy2">*</span>this<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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<p>（无）</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>派生类类型值的哨位与起始迭代器间的差。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>下列派生类型能使用 <code>size()</code> 的默认实现：</p>
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<ul>
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<li><span class="t-lc">std::ranges::drop_while_view</span></li>
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</ul>
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<p>下列类型派生自 <span class="t-lc">std::ranges::view_interface</span> 并且不声明其自身的 <code>size()</code> 成员函数，但它们无法使用默认实现，因为其迭代器与哨位类型决不满足 <a href="cpp-iterator-sized_sentinel_for.html"><code>sized_sentinel_for</code></a> ：</p>
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<ul>
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<li><span class="t-lc">std::ranges::basic_istream_view</span></li>
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<li><span class="t-lc">std::ranges::filter_view</span></li>
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<li><span class="t-lc">std::ranges::join_view</span></li>
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<li><span class="t-lc">std::ranges::split_view</span></li>
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<li><span class="t-lc">std::ranges::lazy_split_view</span></li>
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<li><span class="t-lc">std::ranges::take_while_view</span></li>
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</ul>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-iterator-size.html"><span class="t-lines"><span>size</span><span>ssize</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>返回容器或数组的大小<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-ranges-size.html"><span class="t-lines"><span>ranges::size</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>返回等于范围大小的整数<br />
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<span class="t-mark">(定制点对象)</span></td>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-ssize.html"><span class="t-lines"><span>ranges::ssize</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>返回等于范围大小的有符号整数<br />
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<span class="t-mark">(定制点对象)</span></td>
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</tr>
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</div>
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