291 lines
15 KiB
HTML
291 lines
15 KiB
HTML
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<title>std::basic_format_parse_context</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_format_basic_format_parse_context 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::</span>basic_format_parse_context</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-format.html">format</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-format.html"><format></a></code></div>
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<td></td>
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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> CharT<span class="sy1">></span><br />
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<span class="kw1">class</span> basic_format_parse_context<span class="sy4">;</span></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">using</span> format_parse_context <span class="sy1">=</span> basic_format_parse_context<span class="sy1"><</span><span class="kw4">char</span><span class="sy1">></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="kw1">using</span> wformat_parse_context <span class="sy1">=</span> basic_format_parse_context<span class="sy1"><</span><span class="kw4">wchar_t</span><span class="sy1">></span><span class="sy4">;</span></span></div>
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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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<p>提供到分析由正在分析的格式字符串范围，和自动下标参数计数组成的格式字符串分析状态的访问。</p>
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<p>分析格式说明时，传递 <code>basic_format_parse_context</code> 实例给<a href="cpp-named_req-Formatter.html"><span style="font-style:italic">格式化器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Formatter)</span></a> 。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>类型</td>
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<td>定义</td>
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<td><code>char_type</code></td>
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<td><code>CharT</code></td>
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<td><code>iterator</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1"><</span>CharT<span class="sy1">></span><span class="sy4">::</span><span class="me2">const_iterator</span></span></span></td>
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<td><code>const_iterator</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1"><</span>CharT<span class="sy1">></span><span class="sy4">::</span><span class="me2">const_iterator</span></span></span></td>
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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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<div><span class="t-lines"><span>(构造函数)</span></span></div>
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</td>
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<td>从格式字符串和参数计数构造 <code>std::basic_format_parse_context</code><br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>operator=</span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[被删除]</span></span></span></div>
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<td><code>std::basic_format_parse_context</code> 不可复制<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>begin</span></span></div>
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</td>
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<td>返回指向格式字符串范围起始的迭代器<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>end</span></span></div>
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</td>
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<td>返回指向格式字符串范围末尾的迭代器<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>advance_to</span></span></div>
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<td>使起始迭代器前进到给定位置<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>next_arg_id</span></span></div>
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<td>进入自动索引模式，并返回下一个参数下标<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>check_arg_id</span></span></div>
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<td>进入手动索引模式，检查给定参数下标是否在范围中<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h2><span class="mw-headline" id="std::basic_format_parse_context::basic_format_parse_context"><span style="font-size:0.7em; line-height:130%">std::basic_format_parse_context::</span>basic_format_parse_context</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw1">explicit</span> basic_format_parse_context<span class="br0">(</span><a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1"><</span>CharT<span class="sy1">></span> fmt,<br />
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<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> num_args <span class="sy1">=</span> <span class="nu0">0</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">basic_format_parse_context<span class="br0">(</span><span class="kw4">const</span> basic_format_parse_context<span class="sy3">&</span><span class="br0">)</span> <span class="sy1">=</span> delete<span class="sy4">;</span></span></div>
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<div class="t-li1"><span class="t-li">1)</span> 构造 <code>std::basic_format_parse_context</code> 实例。初始化格式字符串范围为 <code>[fmt.begin(), fmt.end())</code> ，并初始化参数计数为 <code>num_args</code> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 复制构造函数被删除。 <code>std::basic_format_parse_context</code> 不可复制。</div>
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<h2><span class="mw-headline" id="std::basic_format_parse_context::begin"><span style="font-size:0.7em; line-height:130%">std::basic_format_parse_context::</span>begin</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> const_iterator begin<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<p>返回指向格式字符串范围起始的迭代器。</p>
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<h2><span class="mw-headline" id="std::basic_format_parse_context::end"><span style="font-size:0.7em; line-height:130%">std::basic_format_parse_context::</span>end</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> const_iterator end<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<p>返回指向格式字符串范围末尾的迭代器。</p>
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<h2><span class="mw-headline" id="std::basic_format_parse_context::advance_to"><span style="font-size:0.7em; line-height:130%">std::basic_format_parse_context::</span>advance_to</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">void</span> advance_to<span class="br0">(</span>const_iterator it<span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>设置格式字符串范围的起始为 <code>it</code> 。调用 <code>advance_to</code> 后，对 <code>begin()</code> 的后继调用将返回 <code>it</code> 的副本。</p>
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<p>若 <code>end()</code> 从 <code>it</code> 不可达则行为未定义。</p>
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<h2><span class="mw-headline" id="std::basic_format_parse_context::next_arg_id"><span style="font-size:0.7em; line-height:130%">std::basic_format_parse_context::</span>next_arg_id</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> next_arg_id<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>进入自动参数索引模式，并返回从 0 开始的下个参数下标。</p>
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<p>若 <code>*this</code> 已进入手动参数索引模式，则抛出 <span class="t-lc">std::format_error</span> 。</p>
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<h2><span class="mw-headline" id="std::basic_format_parse_context::check_arg_id"><span style="font-size:0.7em; line-height:130%">std::basic_format_parse_context::</span>check_arg_id</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">void</span> check_arg_id<span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> id<span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>进入手动参数索引模式。</p>
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<p>若 <code>*this</code> 以进入自动参数索引模式，则抛出 <span class="t-lc">std::format_error</span> 。</p>
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<p>若 <code>id</code> 大于或等于构造函数中提供的参数数量，则该调用不是常量表达式。</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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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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