154 lines
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154 lines
12 KiB
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<title>std::ranges::subrange<I,S,K>::advance</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>advance</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"><span class="kw4">constexpr</span> subrange<span class="sy3">&</span> advance<span class="br0">(</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><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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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>若 <code>n >= 0</code> ，则自增 <code>n</code> 次存储的迭代器，或直至它等于存储的哨位，二者之一先到来为止。否则，自减存储的迭代器 <code>-n</code> 次。</p>
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<p>存储的大小若存在，则相应地得到调整（若 <code>n < 0</code> 则增加 <code>-n</code> ，否则减少 <code><i>m</i></code> ，其中 <code><i>m</i></code> 是实际应用到迭代器的自增次数）。</p>
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<p>若</p>
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<ul>
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<li><code>I</code> 不实现 <a href="cpp-iterator-bidirectional_iterator.html"><code>bidirectional_iterator</code></a> 且 <code>n < 0</code> ，或</li>
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<li>存储的迭代器在变为不可自减值后被自减，</li>
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</ul>
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<p>则行为未定义。</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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<td>n</td>
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<td>-</td>
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<td>迭代器上的最大自增次数</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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<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span></p>
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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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<p>通常为在 <code>n >= 0</code> 或 <code>n < 0</code> 时分别为迭代器上的 <code>min(n, <a href="cpp-ranges-subrange-size.html">size()</a>)</code> 次自增或 <code>-n</code> 次自减。</p>
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<p>若 <code>I</code> 实现 <a href="cpp-iterator-random_access_iterator.html"><code>random_access_iterator</code></a> ，且 <code>n < 0</code> 或者 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">sized_sentinel_for</span><span class="sy1"><</span>S, I<span class="sy1">></span></span></span> 得到实现则为常数。</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>存储的大小当且仅当 <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></span> 但 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">sized_sentinel_for</span><span class="sy1"><</span>S, I<span class="sy1">></span></span></span> 不被满足才存在。</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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<div class="t-example">
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<div class="t-example-live-link"></div>
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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="co2">#include <algorithm></span>
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<span class="co2">#include <array></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <iterator></span>
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<span class="co2">#include <ranges></span>
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<span class="kw4">void</span> print<span class="br0">(</span><span class="kw4">auto</span> name, <span class="kw4">auto</span> <span class="kw4">const</span> sub<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> name <span class="sy1"><<</span> <span class="st0">".size() == "</span> <span class="sy1"><<</span> sub.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"; { "</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">for_each</span><span class="br0">(</span>sub, <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> x<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> x <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<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>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a> arr<span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span>,<span class="nu0">6</span>,<span class="nu0">7</span><span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">subrange</span> sub<span class="br0">{</span> <a href="cpp-iterator-next.html"><span class="kw674">std::<span class="me2">next</span></span></a><span class="br0">(</span>arr.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>, <a href="cpp-iterator-prev.html"><span class="kw675">std::<span class="me2">prev</span></span></a><span class="br0">(</span>arr.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">}</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"1) sub"</span>, sub<span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"2) sub"</span>, sub.<span class="me1">advance</span><span class="br0">(</span><span class="nu0">3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"3) sub"</span>, sub.<span class="me1">advance</span><span class="br0">(</span><span class="sy2">-</span><span class="nu0">2</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">1) sub.size() == 5; { 2 3 4 5 6 }
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2) sub.size() == 2; { 5 6 }
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3) sub.size() == 4; { 3 4 5 6 }</pre></div>
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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/issue3433">LWG 3433</a></td>
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<td>C++20</td>
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<td>规范错误处理了 <code>n < 0</code> 的情况</td>
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<td>已更正</td>
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</tr>
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</table>
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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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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-subrange-next.html"><span class="t-lines"><span>next</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>以给定距离前进迭代器并返回原 <code>subrange</code><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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-subrange-prev.html"><span class="t-lines"><span>prev</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>以给定距离减少迭代器并返回原 <code>subrange</code><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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-iterator-advance.html"><span class="t-lines"><span>advance</span></span></a></div>
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</div>
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</td>
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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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</tr>
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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-iterator-ranges-advance.html"><span class="t-lines"><span>ranges::advance</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>令迭代器前进给定的距离或到给定的边界<br />
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<span class="t-mark">(niebloid)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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