348 lines
33 KiB
HTML
348 lines
33 KiB
HTML
<!DOCTYPE html>
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<title>std::set_difference</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_algorithm_set_difference skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>set_difference</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-algorithm.html">algorithm</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-algorithm.html"><algorithm></a></code></div>
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<td></td>
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<td></td>
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<td rowspan="142">(1)</td>
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<td></td>
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<tr class="t-dcl t-until-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> InputIt1, <span class="kw1">class</span> InputIt2, <span class="kw1">class</span> OutputIt <span class="sy1">></span><br /></span>
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<p>OutputIt set_difference<span class="br0">(</span> InputIt1 first1, InputIt1 last1,<br />
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InputIt2 first2, InputIt2 last2,<br /></p>
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OutputIt d_first <span class="br0">)</span><span class="sy4">;</span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> InputIt1, <span class="kw1">class</span> InputIt2, <span class="kw1">class</span> OutputIt <span class="sy1">></span><br /></span>
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<p><span class="kw4">constexpr</span> OutputIt set_difference<span class="br0">(</span> InputIt1 first1, InputIt1 last1,<br />
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InputIt2 first2, InputIt2 last2,<br /></p>
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OutputIt d_first <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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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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</tbody>
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<tbody>
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<tr class="t-dcl t-since-cxx17">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> ExecutionPolicy, <span class="kw1">class</span> ForwardIt1, <span class="kw1">class</span> ForwardIt2,<br /></span>
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<p> <span class="kw1">class</span> ForwardIt3 <span class="sy1">></span><br />
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ForwardIt3 set_difference<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy,<br />
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ForwardIt1 first1, ForwardIt1 last1,<br />
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ForwardIt2 first2, ForwardIt2 last2,<br /></p>
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ForwardIt3 d_first <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tbody>
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<tbody class="t-dcl-rev t-dcl-rev-num">
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<tr class="t-dcl-rev-aux">
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<td rowspan="142">(3)</td>
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<td></td>
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<tr class="t-dcl t-until-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> InputIt1, <span class="kw1">class</span> InputIt2,<br /></span>
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<p> <span class="kw1">class</span> OutputIt, <span class="kw1">class</span> Compare <span class="sy1">></span><br />
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OutputIt set_difference<span class="br0">(</span> InputIt1 first1, InputIt1 last1,<br />
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InputIt2 first2, InputIt2 last2,<br /></p>
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OutputIt d_first, Compare comp <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> InputIt1, <span class="kw1">class</span> InputIt2,<br /></span>
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<p> <span class="kw1">class</span> OutputIt, <span class="kw1">class</span> Compare <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> OutputIt set_difference<span class="br0">(</span> InputIt1 first1, InputIt1 last1,<br />
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InputIt2 first2, InputIt2 last2,<br /></p>
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OutputIt d_first, Compare comp <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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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>
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</tbody>
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<tbody>
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<tr class="t-dcl t-since-cxx17">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> ExecutionPolicy, <span class="kw1">class</span> ForwardIt1, <span class="kw1">class</span> ForwardIt2,<br /></span>
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<p> <span class="kw1">class</span> ForwardIt3, <span class="kw1">class</span> Compare <span class="sy1">></span><br />
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ForwardIt3 set_difference<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy,<br />
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ForwardIt1 first1, ForwardIt1 last1,<br />
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ForwardIt2 first2, ForwardIt2 last2,<br /></p>
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ForwardIt3 d_first, Compare comp <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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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>复制来自已排序范围 <code>[first1, last1)</code> 并且不在已排序范围 <code>[first2, last2)</code> 中找到的元素到始于 <code>d_first</code> 的范围。</p>
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<p>结果范围亦已排序。单独对待等价元素，即若某元素在 <code>[first1, last1)</code> 中找到 <code>n</code> 次而在 <code>[first2, last2)</code> 中找到 <code>m</code> 次，则准确复制它 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-max.html"><span class="kw1639">std::<span class="me2">max</span></span></a><span class="br0">(</span>m<span class="sy2">-</span>n, <span class="nu0">0</span><span class="br0">)</span></span></span> 次到 <code>d_first</code> 。结果范围不能与任一输入范围重叠。</p>
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<div class="t-li1"><span class="t-li">1)</span> 用 <code>operator<</code> 比较元素，而范围必须对于相同者排序。</div>
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<div class="t-li1"><span class="t-li">3)</span> 用给定的二元比较函数 <code>comp</code> 比较元素，而范围必须对于相同者排序。</div>
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<div class="t-li1"><span class="t-li">2,4)</span> 同 <span class="t-v">(1,3)</span> ，但按照 <code>policy</code> 执行。这些重载仅若 <span class="t-rev-inl t-until-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-is_execution_policy.html"><span class="kw1564">std::<span class="me2">is_execution_policy_v</span></span></a><span class="sy1"><</span><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>ExecutionPolicy<span class="sy1">>></span></span></span></span> <span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span></span><span class="t-rev-inl t-since-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-is_execution_policy.html"><span class="kw1564">std::<span class="me2">is_execution_policy_v</span></span></a><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span>ExecutionPolicy<span class="sy1">>></span></span></span></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span> 为 true 才参与重载决议。</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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<table class="t-par-begin">
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<tr class="t-par">
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<td>first1, last1</td>
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<td>-</td>
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<td>要检验的元素范围</td>
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</tr>
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<tr class="t-par">
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<td>first2, last2</td>
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<td>-</td>
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<td>要搜索的元素范围</td>
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</tr>
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<tr class="t-par">
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<td>d_first</td>
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<td>-</td>
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<td>目标范围的起始</td>
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</tr>
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<tr class="t-par">
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<td>policy</td>
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<td>-</td>
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<td>所用的执行策略。细节见<a href="cpp-algorithm-execution_policy_tag_t.html">执行策略</a>。</td>
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</tr>
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<tr class="t-par">
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<td>comp</td>
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<td>-</td>
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<td>比较函数对象（即满足<a href="cpp-named_req-Compare.html"><span style="font-style:italic">比较</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Compare)</span></a> 概念的对象），若第一参数<i>小于</i>（即<i>先</i>序于）第二参数则返回 ​<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。<br />
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<p>比较函数的签名应等价于如下：</p>
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<p><span class="t-cc"><span class="mw-geshi cpp source-cpp"> <span class="kw4">bool</span> cmp<span class="br0">(</span><span class="kw4">const</span> Type1 <span class="sy3">&</span>a, <span class="kw4">const</span> Type2 <span class="sy3">&</span>b<span class="br0">)</span><span class="sy4">;</span></span></span></p>
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<p>虽然签名不必有 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="sy3">&</span></span></span> ，函数也不能修改传递给它的对象，而且必须接受（可为 const 的）类型 <code>Type1</code> 与 <code>Type2</code> 的值，无关乎<a href="cpp-language-value_category.html">值类别</a>（从而不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1 <span class="sy3">&</span></span></span> <span class="t-rev-inl t-since-cxx11"><span>，亦不允许 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1</span></span> ，除非 <code>Type1</code> 的移动等价于复制</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>）。<br />
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类型 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type2</span></span> 必须使得 <span class="t-c"><span class="mw-geshi cpp source-cpp">InputIt1</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">InputIt2</span></span> 类型的对象在解引用后能隐式转换到 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type1</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type2</span></span> 两者。 ​</p>
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</td>
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</tr>
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<tr class="t-par-hitem">
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<td colspan="3">类型要求</td>
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</tr>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>InputIt1, InputIt2</code> 必须满足<a href="cpp-named_req-InputIterator.html"><span style="font-style:italic">老式输入迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyInputIterator)</span></a> 的要求。</td>
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</tr>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>OutputIt</code> 必须满足<a href="cpp-named_req-OutputIterator.html"><span style="font-style:italic">老式输出迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyOutputIterator)</span></a> 的要求。</td>
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</tr>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>ForwardIt1, ForwardIt2, ForwardIt3</code> 必须满足<a href="cpp-named_req-ForwardIterator.html"><span style="font-style:italic">老式向前迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyForwardIterator)</span></a> 的要求。</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>构造的范围的尾后迭代器。</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>至多比较 <span class="mjax" style="display:none">\(\scriptsize 2\cdot(N_1+N_2)-1\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">2·(N<span class="t-su t-su-b"><br />
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1</span>+N<span class="t-su t-su-b"><br />
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2</span>)-1</span> 次，其中 <span class="mjax" style="display:none">\(\scriptsize N_1\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">N<span class="t-su t-su-b"><br />
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1</span></span> 与 <span class="mjax" style="display:none">\(\scriptsize N_2\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">N<span class="t-su t-su-b"><br />
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2</span></span> 分别为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-distance.html"><span class="kw673">std::<span class="me2">distance</span></span></a><span class="br0">(</span>first1, last1<span class="br0">)</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-distance.html"><span class="kw673">std::<span class="me2">distance</span></span></a><span class="br0">(</span>first2, last2<span class="br0">)</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>拥有名为 <code>ExecutionPolicy</code> 的模板形参的重载按下列方式报告错误：</p>
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<ul>
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<li>若作为算法一部分调用的函数的执行抛出异常，且 <code>ExecutionPolicy</code> 为<a href="cpp-algorithm-execution_policy_tag_t.html">标准策略</a>之一，则调用 <span class="t-lc"><a href="cpp-error-terminate.html">std::terminate</a></span> 。对于任何其他 <code>ExecutionPolicy</code> ，行为是实现定义的。</li>
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<li>若算法无法分配内存，则抛出 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 。</li>
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</ul>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<table class="eq-fun-cpp-table">
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<tr>
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<th>版本一</th>
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</tr>
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<tr>
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<td>
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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="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> InputIt1, <span class="kw1">class</span> InputIt2, <span class="kw1">class</span> OutputIt<span class="sy1">></span>
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OutputIt set_difference<span class="br0">(</span>InputIt1 first1, InputIt1 last1,
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InputIt2 first2, InputIt2 last2,
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OutputIt d_first<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">while</span> <span class="br0">(</span>first1 <span class="sy3">!</span><span class="sy1">=</span> last1<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>first2 <span class="sy1">==</span> last2<span class="br0">)</span> <span class="kw1">return</span> <a href="cpp-algorithm-copy.html"><span class="kw1582">std::<span class="me2">copy</span></span></a><span class="br0">(</span>first1, last1, d_first<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span><span class="sy2">*</span>first1 <span class="sy1"><</span> <span class="sy2">*</span>first2<span class="br0">)</span> <span class="br0">{</span>
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<span class="sy2">*</span>d_first<span class="sy2">++</span> <span class="sy1">=</span> <span class="sy2">*</span>first1<span class="sy2">++</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span><span class="sy3">!</span> <span class="br0">(</span><span class="sy2">*</span>first2 <span class="sy1"><</span> <span class="sy2">*</span>first1<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="sy2">++</span>first1<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="sy2">++</span>first2<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="kw1">return</span> d_first<span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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</tr>
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<tr>
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<th>版本二</th>
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</tr>
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<tr>
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<td>
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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="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> InputIt1, <span class="kw1">class</span> InputIt2,
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<span class="kw1">class</span> OutputIt, <span class="kw1">class</span> Compare<span class="sy1">></span>
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OutputIt set_difference<span class="br0">(</span> InputIt1 first1, InputIt1 last1,
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InputIt2 first2, InputIt2 last2,
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OutputIt d_first, Compare comp<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">while</span> <span class="br0">(</span>first1 <span class="sy3">!</span><span class="sy1">=</span> last1<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>first2 <span class="sy1">==</span> last2<span class="br0">)</span> <span class="kw1">return</span> <a href="cpp-algorithm-copy.html"><span class="kw1582">std::<span class="me2">copy</span></span></a><span class="br0">(</span>first1, last1, d_first<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>comp<span class="br0">(</span><span class="sy2">*</span>first1, <span class="sy2">*</span>first2<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="sy2">*</span>d_first<span class="sy2">++</span> <span class="sy1">=</span> <span class="sy2">*</span>first1<span class="sy2">++</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span><span class="sy3">!</span>comp<span class="br0">(</span><span class="sy2">*</span>first2, <span class="sy2">*</span>first1<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="sy2">++</span>first1<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="sy2">++</span>first2<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="kw1">return</span> d_first<span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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</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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<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 <iostream></span>
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<span class="co2">#include <iterator></span>
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<span class="co2">#include <vector></span>
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<span class="kw4">auto</span> print <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> v, <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> end <span class="sy1">=</span> <span class="st0">""</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"{ "</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> i <span class="sy4">:</span> v<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> i <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"} "</span> <span class="sy1"><<</span> end<span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">struct</span> Order <span class="co1">// 拥有某些有趣数据的类</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> order_id<span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-io-basic_ostream.html"><span class="kw1728">std::<span class="me2">ostream</span></span></a><span class="sy3">&</span> operator<span class="sy1"><<</span><span class="br0">(</span><a href="cpp-io-basic_ostream.html"><span class="kw1728">std::<span class="me2">ostream</span></span></a><span class="sy3">&</span> os, <span class="kw4">const</span> Order<span class="sy3">&</span> ord<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> os <span class="sy1"><<</span> <span class="st0">"order="</span> <span class="sy1"><<</span> ord.<span class="me1">order_id</span> <span class="sy1"><<</span> <span class="st0">','</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">const</span> <a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> v1 <span class="br0">{</span><span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">5</span>, <span class="nu0">5</span>, <span class="nu0">5</span>, <span class="nu0">9</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">const</span> <a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> v2 <span class="br0">{</span><span class="nu0">2</span>, <span class="nu0">5</span>, <span class="nu0">7</span><span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> diff<span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">set_difference</span><span class="br0">(</span>v1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v1.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, v2.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v2.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>,
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<a href="cpp-iterator-inserter.html"><span class="kw667">std::<span class="me2">inserter</span></span></a><span class="br0">(</span>diff, diff.<span class="me1">begin</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>v1, <span class="st0">"∖ "</span><span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span>v2, <span class="st0">"= "</span><span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span>diff, <span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 我们想知道哪些顺序在旧和新状态之间“改变了”：</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span>Order<span class="sy1">></span> old_orders <span class="br0">{</span> <span class="br0">{</span><span class="nu0">1</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">2</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">5</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">9</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span>Order<span class="sy1">></span> new_orders <span class="br0">{</span> <span class="br0">{</span><span class="nu0">2</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">5</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">7</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span>Order<span class="sy1">></span> changed_orders<span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">set_difference</span><span class="br0">(</span>old_orders.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, old_orders.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>,
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new_orders.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, new_orders.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>,
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<a href="cpp-iterator-back_inserter.html"><span class="kw665">std::<span class="me2">back_inserter</span></span></a><span class="br0">(</span>changed_orders<span class="br0">)</span>,
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<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">auto</span><span class="sy3">&</span> a, <span class="kw4">auto</span><span class="sy3">&</span> b<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> a.<span class="me1">order_id</span> <span class="sy1"><</span> b.<span class="me1">order_id</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="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"old orders = "</span><span class="sy4">;</span> print<span class="br0">(</span>old_orders, <span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"new orders = "</span><span class="sy4">;</span> print<span class="br0">(</span>new_orders, <span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"changed = "</span><span class="sy4">;</span> print<span class="br0">(</span>changed_orders, <span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">{ 1 2 5 5 5 9 } ∖ { 2 5 7 } = { 1 5 5 9 }
|
|
old orders = { order=1, order=2, order=5, order=9, }
|
|
new orders = { order=2, order=5, order=7, }
|
|
changed = { order=1, order=9, }</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-includes.html"><span class="t-lines"><span>includes</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>若一个序列是另一个的子列则返回 true<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-set_symmetric_difference.html"><span class="t-lines"><span>set_symmetric_difference</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>计算两个集合的对称差<br />
|
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<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-algorithm-ranges-set_difference.html"><span class="t-lines"><span>ranges::set_difference</span></span></a></div>
|
|
<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>计算两个集合的差集<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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</div>
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</div>
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</div>
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</body>
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</html>
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