101 lines
7.8 KiB
HTML
101 lines
7.8 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::in_range</title>
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_in_range skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>in_range</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-utility.html">utility</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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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-utility.html"><utility></a></code></div>
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<td></td>
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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> R, <span class="kw1">class</span> T <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> in_range<span class="br0">(</span> T t <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>若 <code>t</code> 的值在能以 <code>R</code> 表示的值的范围内，即 <code>t</code> 能转换到 <code>R</code> 而无数据损失则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</p>
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<p>若 <code>T</code> 或 <code>R</code> 不是有符号或无符号整数类型（包括标准整数类型与扩展整数类型），则为编译时错误。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>t</td>
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<td>-</td>
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<td>要测试的值</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>若 <code>t</code> 的值可以 <code>R</code> 表示则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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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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<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> R, <span class="kw1">class</span> T <span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="kw4">bool</span> in_range<span class="br0">(</span> T t <span class="br0">)</span> <span class="kw1">noexcept</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> std<span class="sy4">::</span><span class="me2">cmp_greater_equal</span><span class="br0">(</span>t, <a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1"><</span>R<span class="sy1">></span><span class="sy4">::</span><span class="me2">min</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy3">&&</span>
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std<span class="sy4">::</span><span class="me2">cmp_less_equal</span><span class="br0">(</span>t, <a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1"><</span>R<span class="sy1">></span><span class="sy4">::</span><span class="me2">max</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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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>此函数不能用于<a href="cpp-language-enum.html">枚举</a>（包括 <a href="cpp-types-byte.html"><tt>std::byte</tt></a> ）、 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp">char8_t</span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char16_t</span></span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char32_t</span></span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">wchar_t</span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <utility></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <iomanip></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">in_range</span><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">in_range</span><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="nu0">42</span><span class="br0">)</span> <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">false
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true</pre></div>
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</html>
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