148 lines
19 KiB
HTML
148 lines
19 KiB
HTML
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<title>std::ranges::subrange<I,S,K>::subrange</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::subrange<I,S,K>::</span>subrange</h1>
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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-subrange.html">subrange</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">subrange<span class="br0">(</span><span class="br0">)</span> requires std<span class="sy4">::</span><span class="me2">default_initializable</span><span class="sy1"><</span>I<span class="sy1">></span> <span class="sy1">=</span> <span class="kw1">default</span><span class="sy4">;</span></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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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> subrange<span class="br0">(</span> <span class="coMULTI">/*convertible-to-non-slicing*/</span><span class="sy1"><</span>I<span class="sy1">></span> <span class="kw4">auto</span> i, S s <span class="br0">)</span><br />
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requires <span class="br0">(</span><span class="sy3">!</span><span class="coMULTI">/*store-size*/</span><span class="br0">)</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-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> subrange<span class="br0">(</span> <span class="coMULTI">/*convertible-to-non-slicing*/</span><span class="sy1"><</span>I<span class="sy1">></span> <span class="kw4">auto</span> i, S s,<br /></span>
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<p> <span class="coMULTI">/*make-unsigned-like-t*/</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">>></span> n <span class="br0">)</span><br /></p>
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requires <span class="br0">(</span>K <span class="sy1">==</span> ranges<span class="sy4">::</span><span class="me2">subrange_kind</span><span class="sy4">::</span><span class="me2">sized</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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="coMULTI">/*different-from*/</span><span class="sy1"><</span>subrange<span class="sy1">></span> R <span class="sy1">></span><br /></span>
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<p> requires ranges<span class="sy4">::</span><span class="me2">borrowed_range</span><span class="sy1"><</span>R<span class="sy1">></span> <span class="sy3">&&</span><br />
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<span class="coMULTI">/*convertible-to-non-slicing*/</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>, I<span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">sentinel_t</span><span class="sy1"><</span>R<span class="sy1">></span>, S<span class="sy1">></span><br /></p>
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<span class="kw4">constexpr</span> subrange<span class="br0">(</span> R<span class="sy3">&&</span> r <span class="br0">)</span> requires <span class="br0">(</span><span class="sy3">!</span><span class="coMULTI">/*store-size*/</span> <span class="sy3">||</span> ranges<span class="sy4">::</span><span class="me2">sized_range</span><span class="sy1"><</span>R<span class="sy1">></span><span class="br0">)</span><span class="sy4">;</span></div>
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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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<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">borrowed_range</span> R<span class="sy1">></span><br /></span>
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<p> requires <span class="coMULTI">/*convertible-to-non-slicing*/</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>, I<span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">sentinel_t</span><span class="sy1"><</span>R<span class="sy1">></span>, S<span class="sy1">></span><br />
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<span class="kw4">constexpr</span> subrange<span class="br0">(</span> R<span class="sy3">&&</span> r, <span class="coMULTI">/*make-unsigned-like-t*/</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">>></span> n <span class="br0">)</span><br />
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requires <span class="br0">(</span>K <span class="sy1">==</span> ranges<span class="sy4">::</span><span class="me2">subrange_kind</span><span class="sy4">::</span><span class="me2">sized</span><span class="br0">)</span><br />
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<span class="sy4">:</span> subrange<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>, n<span class="br0">}</span><br /></p>
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<span class="br0">{</span><span class="br0">}</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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<td></td>
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<td></td>
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<td></td>
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<p>构造 <code>subrange</code> 。</p>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">K <span class="sy1">==</span> ranges<span class="sy4">::</span><span class="me2">subrange_kind</span><span class="sy4">::</span><span class="me2">sized</span> <span class="sy3">&&</span> <span class="sy3">!</span>std<span class="sy4">::</span><span class="me2">sized_sentinel_for</span><span class="sy1"><</span>S, I<span class="sy1">></span></span></span> ，则存储范围大小到 <code>subrange</code> 中，如同用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*make-unsigned-like-t*/</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">>></span></span></span> 类型的成员子对象存储，其中 <code><i>make-unsigned-like-t</i></code> 是仅用于阐释的别名模板，将每个<a href="cpp-iterator-weakly_incrementable.html#.E6.95.B4.E6.95.B0.E5.BC.8F.E7.B1.BB.E5.9E.8B">整数式类型</a>映射到其对应的无符号版本。否则不存储大小。若存储大小则常量 <code><i>store-size</i></code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<div class="t-li1"><span class="t-li">1)</span> 默认构造函数。值初始化存储的迭代器与哨位，如同分别用默认成员初始化器 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">=</span> I<span class="br0">(</span><span class="br0">)</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">=</span> S<span class="br0">(</span><span class="br0">)</span></span></span> 。若存储大小，则将它初始化为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ，如同通过默认成员初始化器 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">=</span> <span class="nu0">0</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 从迭代器-哨位对构造 <code>subrange</code> 。分别以 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>i<span class="br0">)</span></span></span> 与 <code>s</code> 初始化存储的迭代器与哨位。若 <code>[i, s)</code> 不是合法范围则行为未定义。</div>
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<div class="t-li1"><span class="t-li">3)</span> 从迭代器-哨位对与大小提示构造 <code>subrange</code> 。分别以 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>i<span class="br0">)</span></span></span> 与 <code>s</code> 初始化存储的迭代器与哨位。若存储大小，则以 <code>n</code> 初始化它。若 <code>[i, s)</code> 不是合法范围，或 <code>n</code> 不等于显式转换到其类型的 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">distance</span><span class="br0">(</span>i, s<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">4)</span> 从范围构造 <code>subrange</code> 。若存储大小则等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">subrange<span class="br0">(</span>r, <span class="kw1">static_cast</span><span class="sy1"><</span><span class="coMULTI">/*make-unsigned-like-t*/</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">>>></span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">size</span><span class="br0">(</span>r<span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span> 。否则等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">subrange<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></span> 。</div>
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<div class="t-li1"><span class="t-li">5)</span> 从范围与大小提示构造 <code>subrange</code> 。若 <code>n</code> 不等于显式转换到其类型的 <span class="t-c"><span class="mw-geshi cpp source-cpp">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></span> 则行为未定义。</div>
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<p>仅用于阐释的概念 <code><i>different-from</i></code> 为类型 <code>T</code> 与 <code>U</code> 实现，当且仅当 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>T<span class="sy1">></span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>U<span class="sy1">></span></span></span> 是不同的类型。</p>
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<p>仅用于阐释的概念 <code><i>convertible-to-non-slicing</i></code> 为 <code>From</code> 与 <code>To</code> 满足或实现，当且仅当 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">convertible_to</span><span class="sy1"><</span>From, To<span class="sy1">></span></span></span> 得到满足或实现，且任一下列条件得到满足：</p>
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>From<span class="sy1">></span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>To<span class="sy1">></span></span></span> 不是指针类型、</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-remove_pointer.html"><span class="kw613">std::<span class="me2">remove_pointer_t</span></span></a><span class="sy1"><</span>From<span class="sy1">></span><span class="br0">(</span><span class="sy2">*</span><span class="br0">)</span><span class="br0">[</span><span class="br0">]</span></span></span> 可隐式转换为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-remove_pointer.html"><span class="kw613">std::<span class="me2">remove_pointer_t</span></span></a><span class="sy1"><</span>To<span class="sy1">></span><span class="br0">(</span><span class="sy2">*</span><span class="br0">)</span><span class="br0">[</span><span class="br0">]</span></span></span> ，即从 <code>From</code> 到 <code>To</code> 的转换至多为限定转换。</li>
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</ul>
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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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<td>i</td>
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<td>-</td>
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<td>代表范围起始的迭代器</td>
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</tr>
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<tr class="t-par">
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<td>s</td>
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<td>-</td>
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<td>代表范围末尾的哨位</td>
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<tr class="t-par">
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<td>r</td>
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<td>-</td>
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<td>范围</td>
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<tr class="t-par">
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<td>n</td>
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<td>-</td>
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<td>大小提示，必须等于范围大小</td>
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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>仅用于阐释的概念 <code><i>convertible-to-non-slicing</i></code> 禁止从指向派生类的指针到指向基类的指针的转换。</p>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3470">LWG 3470</a></td>
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<td>C++20</td>
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<td><code><i>convertible-to-non-slicing</i></code> 曾拒绝一些合法的限定转换</td>
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<td>使之接受</td>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P2393R1">P2393R1</a></td>
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<td>C++20</td>
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<td>到整数类类型的隐式转换可能非法</td>
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<td>使之为显式</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<td class="mbox-empty-cell"></td>
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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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</table>
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</div>
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<div class="visualClear"></div>
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</body>
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