454 lines
41 KiB
HTML
454 lines
41 KiB
HTML
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<title>std::ranges::views::iota, std::ranges::iota_view</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_iota_view 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::</span><span style="font-size:0.7em; line-height:130%">views::</span>iota, <span style="font-size:0.7em; line-height:130%">std::ranges::</span>iota_view</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-ranges.html">ranges</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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<div>定义于头文件 <code><a href="cpp-header-ranges.html"><ranges></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> W,<br /></span>
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<p> std<span class="sy4">::</span><span class="me2">semiregular</span> Bound <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">unreachable_sentinel_t</span><span class="sy1">></span><br />
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requires __WeaklyEqualityComparableWith<span class="sy1"><</span>W, Bound<span class="sy1">></span> <span class="sy3">&&</span> std<span class="sy4">::</span><span class="me2">copyable</span><span class="sy1"><</span>W<span class="sy1">></span><br /></p>
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<span class="kw1">class</span> iota_view <span class="sy4">:</span> <span class="kw1">public</span> ranges<span class="sy4">::</span><span class="me2">view_interface</span><span class="sy1"><</span>iota_view<span class="sy1"><</span>W, Bound<span class="sy1">>></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="kw1">namespace</span> views <span class="br0">{</span><br /></span>
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<p> <span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="coMULTI">/*unspecified*/</span> iota <span class="sy1">=</span> <span class="coMULTI">/*unspecified*/</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</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-cxx20">(C++20 起)</span></td>
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<div class="t-li1"><span class="t-li">1)</span> 以重复自增初值生成序列的范围工厂。能为有界或无界（无限）。</div>
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<div class="t-li1"><span class="t-li">2)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp">views<span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span>e<span class="br0">)</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">views<span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span>e, f<span class="br0">)</span></span></span> 对于适合的子表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> 分别<i>表达式等价</i>于 <span class="t-c"><span class="mw-geshi cpp source-cpp">iota_view<span class="br0">(</span>e<span class="br0">)</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">iota_view<span class="br0">(</span>e, f<span class="br0">)</span></span></span> 。</div>
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<h3><span class="mw-headline" id=".E8.A1.A8.E8.BE.BE.E5.BC.8F.E7.AD.89.E4.BB.B7">表达式等价</span></h3>
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<p>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> <i>表达式等价</i>于表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> 拥有相同效果，均为<a href="cpp-language-noexcept_spec.html">潜在抛出</a>或均非潜在抛出（即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>e<span class="br0">)</span> <span class="sy1">==</span> <span class="kw1">noexcept</span><span class="br0">(</span>f<span class="br0">)</span></span></span> ），且均为<a href="cpp-language-constant_expression.html">常量子表达式</a>或均非常量子表达式。</p>
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<h3><span class="mw-headline" id=".E5.AE.9A.E5.88.B6.E7.82.B9.E5.AF.B9.E8.B1.A1">定制点对象</span></h3>
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<p>名字 <code>views::iota</code> 代表一个<i>定制点对象</i>，它是<a href="cpp-named_req-LiteralType.html">字面</a> <a href="cpp-concepts-semiregular.html"><code>semiregular</code></a> 类类型的 const <a href="cpp-named_req-FunctionObject.html">函数对象</a>。为说明目的，以 <code><i>__iota_fn</i></code> 表示其类型的 cv 无限定版本。</p>
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<p><code><i>__iota_fn</i></code> 的所有实例均相等。在相同参数上调用类型 <code><i>__iota_fn</i></code> 的不同实例的效果是等价的，无关乎指代该实例的表达式是左值还是右值，以及是否为 const 限定（然而不要求 volatile 限定的实例可调用）。从而能自由地复制 <code>views::iota</code> 并且能彼此替代地使用其副本。</p>
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<p>给定类型集合 <code>Args...</code> ，若 <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>Args<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span>...</span></span> 满足上面对于 <code>views::iota</code> 的参数要求，则 <code><i>__iota_fn</i></code> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span>__iota_fn, Args...<span class="sy1">></span></span></span>、 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span><span class="kw4">const</span> __iota_fn, Args...<span class="sy1">></span></span></span>、 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span>__iota_fn<span class="sy3">&</span>, Args...<span class="sy1">></span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span><span class="kw4">const</span> __iota_fn<span class="sy3">&</span>, Args...<span class="sy1">></span></span></span> 。否则， <code><i>__iota_fn</i></code> 的函数调用运算符不参与重载决议。</p>
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<h3><span class="mw-headline" id=".E6.95.B0.E6.8D.AE.E6.88.90.E5.91.98">数据成员</span></h3>
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<p><code>iota_view</code> 的典型实现保有二个非静态数据成员：类型为 <code>W</code> 的起始值 <code>value_</code> 及类型为 <code>Bound</code> 的哨位值 <code>bound_</code> 。此处显示的名字仅用于阐释。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><span class="t-lines"><span>(构造函数)</span></span></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>创建 <code>iota_view</code><br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><span class="t-lines"><span>begin</span></span></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>获得 <code>iota_view</code> 的起始迭代器<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><span class="t-lines"><span>end</span></span></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>获得指代 <code>iota_view</code> 末尾的哨位<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><span class="t-lines"><span>size</span></span></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>若 <code>iota_view</code> 具有大小则获得其大小<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E7.BB.A7.E6.89.BF.E8.87.AA_std::ranges::view_interface">继承自 <span class="t-lc">std::ranges::view_interface</span></span></h5>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-empty.html"><span class="t-lines"><span>empty</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>返回视图是否为空。若视图满足 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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<div><a href="cpp-ranges-view_interface-operator_bool.html"><span class="t-lines"><span>operator bool</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>返回派生视图是否为非空。若 <span class="t-lc">ranges::empty</span> 可应用于它则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-front.html"><span class="t-lines"><span>front</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>返回派生视图中的首元素。若视图满足 <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-view_interface-back.html"><span class="t-lines"><span>back</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>返回派生视图中的末元素。若视图满足 <a href="cpp-ranges-bidirectional_range.html"><code>bidirectional_range</code></a> 与 <a href="cpp-ranges-common_range.html"><code>common_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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<div><a href="cpp-ranges-view_interface-operator_at.html"><span class="t-lines"><span>operator[]</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>返回派生视图中的第 n 个元素。若视图满足 <a href="cpp-ranges-random_access_range.html"><code>random_access_range</code></a> 则提供。<br />
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<span class="t-mark">(<code>std::ranges::view_interface<D></code> 的公开成员函数)</span></td>
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</tr>
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</table>
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<div class="t-member">
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<h2><span class="mw-headline" id="std::ranges::iota_view::iota_view"><span style="font-size:0.7em; line-height:130%">std::ranges::iota_view::</span>iota_view</span></h2>
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<div><span class="mw-geshi cpp source-cpp">iota_view<span class="br0">(</span><span class="br0">)</span> requires std<span class="sy4">::</span><span class="me2">default_initializable</span><span class="sy1"><</span>W<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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</tr>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw1">explicit</span> iota_view<span class="br0">(</span> W value <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> iota_view<span class="br0">(</span> std<span class="sy4">::</span><span class="me2">type_identity_t</span><span class="sy1"><</span>W<span class="sy1">></span> value,<br />
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std<span class="sy4">::</span><span class="me2">type_identity_t</span><span class="sy1"><</span>Bound<span class="sy1">></span> bound <span class="br0">)</span><span class="sy4">;</span></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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</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="kw4">constexpr</span> iota_view<span class="br0">(</span> <span class="coMULTI">/*iterator*/</span> first, <span class="coMULTI">/*see below*/</span> last <span class="br0">)</span><span class="sy4">;</span></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-cxx20">(C++20 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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<div class="t-li1"><span class="t-li">1)</span> 由其默认成员初始化器（ <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">=</span> W<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> Bound<span class="br0">(</span><span class="br0">)</span></span></span> ）值初始化 <code>value_</code> 与 <code>bound_</code> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 以 <span class="t-c"><span class="mw-geshi cpp source-cpp">value</span></span> 初始化 <code>value_</code> 。此构造函数用于创建无界 <code>iota_view</code> ，例如 <span class="t-c"><span class="mw-geshi cpp source-cpp">iota<span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span></span></span> 产生数 0、 1、 2 ……无穷大。</div>
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<div class="t-li1"><span class="t-li">3)</span> 以 <span class="t-c"><span class="mw-geshi cpp source-cpp">value</span></span> 初始化 <code>value_</code> 并以 <code>bound</code> 初始化 <code>bound_</code> 。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">totally_ordered_with</span><span class="sy1"><</span>W, Bound<span class="sy1">></span></span></span> 得到实现且 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span><span class="br0">(</span>value <span class="sy1"><=</span> bound<span class="br0">)</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 则行为未定义。此构造函数用于创建有界 <code>iota_view</code> ，例如 <span class="t-c"><span class="mw-geshi cpp source-cpp">iota<span class="br0">(</span><span class="nu0">10</span>, <span class="nu0">20</span><span class="br0">)</span></span></span> 产生从 10 到 19 的数。</div>
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<div class="t-li1"><span class="t-li">4)</span> 同 <span class="t-v">(3)</span> ，除了以存储于 <code>first</code> 的 <code>W</code> 值初始化 <code>value_</code> ，以及
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<ul>
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<li>若 <code>W</code> 与 <code>Bound</code> 为同一类型，则 <code>last</code> 的类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*iterator*/</span></span></span> 并且以存储于 <code>last</code> 的 <code>W</code> 值初始化 <code>bound_</code> ，</li>
|
|
<li>否则，若 <code>iota_view</code> 无界（即 <code>Bound</code> 为 <span class="t-lc">std::unreachable_sentinel_t</span> ），则 <code>last</code> 的类型为 <span class="t-lc">std::unreachable_sentinel_t</span> 并且以 <span class="t-lc">std::unreachable_sentinel</span> 初始化 <code>bound_</code> 。</li>
|
|
<li>否则 <code>last</code> 的类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*sentinel*/</span></span></span> 并且以存储于 <code>last</code> 的 <code>Bound</code> 值初始化 <code>bound_</code> 。</li>
|
|
</ul>
|
|
任何情况下， <code>last</code> 的类型均与 <span class="t-c"><span class="mw-geshi cpp source-cpp">decltype<span class="br0">(</span>end<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 相同。</div>
|
|
<p>对于 <span class="t-v">(2)</span>、 <span class="t-v">(3)</span> 与 <span class="t-v">(4)</span> ，若 <code>iota_view</code> 有界（即 <code>Bound</code> 不是 <span class="t-lc">std::unreachable_sentinel_t</span> ）且初始化 <code>bound_</code> 为不可从 <code>value_</code> 抵达的值，则行为未定义。</p>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>value</td>
|
|
<td>-</td>
|
|
<td>起始值</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>bound</td>
|
|
<td>-</td>
|
|
<td>边界</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>first</td>
|
|
<td>-</td>
|
|
<td>指代起始值的迭代器</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>last</td>
|
|
<td>-</td>
|
|
<td>指代边界的哨位</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="t-member">
|
|
<h2><span class="mw-headline" id="std::ranges::iota_view::begin"><span style="font-size:0.7em; line-height:130%">std::ranges::iota_view::</span>begin</span></h2>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="coMULTI">/*iterator*/</span> begin<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>返回以 <span class="t-c"><span class="mw-geshi cpp source-cpp">value_</span></span> 初始化的<a href="cpp-ranges-iota_view-iterator.html">迭代器</a>。</p>
|
|
</div>
|
|
<div class="t-member">
|
|
<h2><span class="mw-headline" id="std::ranges::iota_view::end"><span style="font-size:0.7em; line-height:130%">std::ranges::iota_view::</span>end</span></h2>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">auto</span> end<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(1)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="coMULTI">/*iterator*/</span> end<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> requires std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1"><</span>W, Bound<span class="sy1">></span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<div class="t-li1"><span class="t-li">1)</span> 若视图有界则返回以 <span class="t-c"><span class="mw-geshi cpp source-cpp">bound_</span></span> 初始化的特定类型的<a href="cpp-ranges-iota_view-sentinel.html">哨位</a>（此处显示为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*sentinel*/</span></span></span> ），或若视图无界则返回 <span class="t-lc">std::unreachable_sentinel</span> 。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 返回以 <span class="t-c"><span class="mw-geshi cpp source-cpp">bound_</span></span> 初始化的<a href="cpp-ranges-iota_view-iterator.html">迭代器</a>。</div>
|
|
</div>
|
|
<div class="t-member">
|
|
<h2><span class="mw-headline" id="std::ranges::iota_view::size"><span style="font-size:0.7em; line-height:130%">std::ranges::iota_view::</span>size</span></h2>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<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><br /></span>
|
|
<p> requires <span class="br0">(</span>std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1"><</span>W, Bound<span class="sy1">></span> <span class="sy3">&&</span> <span class="coMULTI">/*advanceable*/</span><span class="sy1"><</span>W<span class="sy1">></span><span class="br0">)</span> <span class="sy3">||</span><br />
|
|
<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">integral</span><span class="sy1"><</span>W<span class="sy1">></span> <span class="sy3">&&</span> std<span class="sy4">::</span><span class="me2">integral</span><span class="sy1"><</span>Bound<span class="sy1">></span><span class="br0">)</span> <span class="sy3">||</span><br />
|
|
std<span class="sy4">::</span><span class="me2">sized_sentinel_for</span><span class="sy1"><</span>Bound, W<span class="sy1">></span><br />
|
|
<span class="br0">{</span><br />
|
|
<span class="kw1">if</span> <span class="kw4">constexpr</span> <span class="br0">(</span><span class="coMULTI">/*is-integer-like*/</span><span class="sy1"><</span>W<span class="sy1">></span> <span class="sy3">&&</span> <span class="coMULTI">/*is-integer-like*/</span><span class="sy1"><</span>Bound<span class="sy1">></span><span class="br0">)</span><br />
|
|
<span class="kw1">return</span> <span class="br0">(</span>value_ <span class="sy1"><</span> <span class="nu0">0</span><span class="br0">)</span><br />
|
|
<span class="sy4">?</span> <span class="br0">(</span><span class="br0">(</span>bound_ <span class="sy1"><</span> <span class="nu0">0</span><span class="br0">)</span><br />
|
|
<span class="sy4">?</span> <span class="coMULTI">/*to-unsigned-like*/</span><span class="br0">(</span><span class="sy2">-</span>value_<span class="br0">)</span> <span class="sy2">-</span> <span class="coMULTI">/*to-unsigned-like*/</span><span class="br0">(</span><span class="sy2">-</span>bound_<span class="br0">)</span><br />
|
|
<span class="sy4">:</span> <span class="coMULTI">/*to-unsigned-like*/</span><span class="br0">(</span>bound_<span class="br0">)</span> <span class="sy2">+</span> <span class="coMULTI">/*to-unsigned-like*/</span><span class="br0">(</span><span class="sy2">-</span>value_<span class="br0">)</span><span class="br0">)</span><br />
|
|
<span class="sy4">:</span> <span class="coMULTI">/*to-unsigned-like*/</span><span class="br0">(</span>bound_<span class="br0">)</span> <span class="sy2">-</span> <span class="coMULTI">/*to-unsigned-like*/</span><span class="br0">(</span>value_<span class="br0">)</span><span class="sy4">;</span><br />
|
|
<span class="kw1">else</span><br />
|
|
<span class="kw1">return</span> <span class="coMULTI">/*to-unsigned-like*/</span><span class="br0">(</span>bound_ <span class="sy2">-</span> value_<span class="br0">)</span><span class="sy4">;</span><br /></p>
|
|
<span class="br0">}</span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>若视图有界则返回视图的大小。</p>
|
|
<p>仅用于阐释的概念 <code><i>advanceable</i></code> 描述于<a href="cpp-ranges-iota_view-iterator.html">此页面</a>。</p>
|
|
<p>仅用于阐释的函数模板 <code><i>to-unsigned-like</i></code> 将其参数（必须为<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</a>）转换为参数类型的对应无符号版本。</p>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E6.8E.A8.E5.AF.BC.E6.8C.87.E5.BC.95">推导指引</span></h3>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> W, <span class="kw1">class</span> Bound<span class="sy1">></span><br /></span>
|
|
<p> requires <span class="br0">(</span><span class="sy3">!</span><span class="coMULTI">/*is-integer-like*/</span><span class="sy1"><</span>W<span class="sy1">></span> <span class="sy3">||</span> <span class="sy3">!</span><span class="coMULTI">/*is-integer-like*/</span><span class="sy1"><</span>Bound<span class="sy1">></span> <span class="sy3">||</span><br />
|
|
<span class="coMULTI">/*is-signed-integer-like*/</span><span class="sy1"><</span>W<span class="sy1">></span> <span class="sy1">==</span> <span class="coMULTI">/*is-signed-integer-like*/</span><span class="sy1"><</span>Bound<span class="sy1">></span><span class="br0">)</span><br /></p>
|
|
iota_view<span class="br0">(</span>W, Bound<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">></span> iota_view<span class="sy1"><</span>W, Bound<span class="sy1">></span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>对于任何类型 <code>T</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*is-integer-like*/</span><span class="sy1"><</span>T<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 当且仅当 <code>T</code> 为<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</a>，而 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*is-integer-signed-like*/</span><span class="sy1"><</span>T<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 当且仅当它为整数式且能够表示负值。</p>
|
|
<p>注意推导指引自身抵御有符号/无符号不匹配漏洞，如 <span class="t-c"><span class="mw-geshi cpp source-cpp">views<span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span><span class="nu0">0</span>, v.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> ，其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 为（有符号） <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> 而 <span class="t-c"><span class="mw-geshi cpp source-cpp">v.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span></span></span> 为（无符号） <span class="t-lc"><a href="cpp-types-size_t.html">std::size_t</a></span> 。</p>
|
|
<h3><span class="mw-headline" id=".E5.B5.8C.E5.A5.97.E7.B1.BB">嵌套类</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-ranges-iota_view-iterator.html"><i><span class="t-lines"><span>iterator</span></span></i></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>迭代器类型<br />
|
|
<span class="t-mark">(仅用于阐释的成员类)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-ranges-iota_view-sentinel.html"><i><span class="t-lines"><span>sentinel</span></span></i></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>当 <code>iota_view</code> 有界且 <code>Bound</code> 与 <code>W</code> 不是同一类型时使用的哨位类型<br />
|
|
<span class="t-mark">(仅用于阐释的成员类)</span></td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BE.85.E5.8A.A9.E6.A8.A1.E6.9D.BF">辅助模板</span></h3>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">weakly_incrementable</span> W, std<span class="sy4">::</span><span class="me2">semiregular</span> Bound<span class="sy1">></span><br />
|
|
<span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> enable_borrowed_range<span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iota_view</span><span class="sy1"><</span>W, Bound<span class="sy1">>></span> <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p><a href="cpp-ranges-borrowed_range.html"><tt>std::ranges::enable_borrowed_range</tt></a> 的此特化使得 <code>iota_view</code> 满足 <a href="cpp-ranges-borrowed_range.html"><code>borrowed_range</code></a> 。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <ranges></span>
|
|
<span class="co2">#include <iostream></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> i <span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">iota_view</span><span class="br0">{</span><span class="nu0">1</span>, <span class="nu0">10</span><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> i <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
|
|
<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>
|
|
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> i <span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span><span class="nu0">1</span>, <span class="nu0">10</span><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> i <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
|
|
<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>
|
|
|
|
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> i <span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span> <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">take</span><span class="br0">(</span><span class="nu0">9</span><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> i <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
|
|
<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></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 2 3 4 5 6 7 8 9
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1 2 3 4 5 6 7 8 9
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1 2 3 4 5 6 7 8 9</pre></div>
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</div>
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</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">
|
|
<tr>
|
|
<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/issue3523">LWG 3523</a></td>
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<td>C++20</td>
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|
<td>迭代器-哨位对构造函数可能使用错误的哨位类型</td>
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|
<td>已更正</td>
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</tr>
|
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<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://wg21.link/P2325R3">P2325R3</a></td>
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|
<td>C++20</td>
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|
<td><code>iota_view</code> 要求 <code>W</code> 为 <a href="cpp-concepts-semiregular.html"><code>semiregular</code></a> 因为 <a href="cpp-ranges-view.html"><code>view</code></a> 要求 <a href="cpp-concepts-default_initializable.html"><code>default_initializable</code></a></td>
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<td>仅要求 <code>W</code> 为 <a href="cpp-concepts-copyable.html"><code>copyable</code></a></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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<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-algorithm-iota.html"><span class="t-lines"><span>iota</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>用从起始值开始连续递增的值填充一个范围<br />
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<span class="t-mark">(函数模板)</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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