74 lines
7.8 KiB
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74 lines
7.8 KiB
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<title>std::deque 的推导指引</title>
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<h1 id="firstHeading" class="firstHeading"><code>std::deque</code> 的推导指引</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-container.html">container</a>‎ | <a href="cpp-container-deque.html">deque</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-deque.html"><deque></a></code></div>
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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> InputIt,<br /></span>
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<p> <span class="kw1">class</span> Alloc <span class="sy1">=</span> <a href="cpp-memory-allocator.html"><span class="kw700">std::<span class="me2">allocator</span></span></a><span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>InputIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span><span class="sy1">>></span><br />
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deque<span class="br0">(</span>InputIt, InputIt, Alloc <span class="sy1">=</span> Alloc<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><br /></p>
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<span class="sy2">-</span><span class="sy1">></span> deque<span class="sy1"><</span><span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>InputIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span>, Alloc<span class="sy1">></span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>为 deque 提供此<a href="cpp-language-class_template_argument_deduction.html">推导指引</a>，以允许从迭代器范围推导。此重载仅若<code>InputIt</code> 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> 且 <code>Alloc</code> 满足<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> 才参与重载决议</p>
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<p>注意：库确定类型是否满足<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> 的程度是未指定的，除了最低要求是整数类型不具备输入迭代器的条件。类似地，确定类型是否满足<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> 是未指定的，除了最低要求是成员类型 <code>Alloc::value_type</code> 必须存在，且表达式 <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>Alloc<span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">allocate</span><span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span></span></span> 在作为不求值操作数时必须为良构。</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <deque></span>
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<span class="co2">#include <vector></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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<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> v <span class="sy1">=</span> <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="br0">}</span><span class="sy4">;</span>
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<span class="co1">// 使用显式推导指引推导 std::deque<int></span>
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<a href="cpp-container-deque.html"><span class="kw1271">std::<span class="me2">deque</span></span></a> x<span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 推导 std::deque<std::vector<int>::iterator></span>
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<span class="co1">// 列表初始化的重载决议第一阶段选择从 initializer_list 构造函数合成的候选</span>
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<span class="co1">// 不进行第二阶段且推导指引无效果</span>
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<a href="cpp-container-deque.html"><span class="kw1271">std::<span class="me2">deque</span></span></a> y<span class="br0">{</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</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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