651 lines
62 KiB
HTML
651 lines
62 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>用户定义字面量 (C++11 起)</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_language_user_literal 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">用户定义字面量 <span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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-language.html">language</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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<p>通过定义用户定义的后缀，允许整数、浮点数、字符及字符串字面量产生用户定义类型的对象。</p>
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<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
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<p>用户定义字面量是下列形式的表达式之一</p>
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<table class="t-sdsc-begin">
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><span class="t-spar">十进制字面量</span> <span class="t-spar">用户定义后缀</span></td>
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<td>(1)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><span class="t-spar">八进制字面量</span> <span class="t-spar">用户定义后缀</span></td>
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<td>(2)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><span class="t-spar">十六进制字面量</span> <span class="t-spar">用户定义后缀</span></td>
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<td>(3)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><span class="t-spar">二进制字面量</span> <span class="t-spar">用户定义后缀</span></td>
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<td>(4)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><span class="t-spar">分数常量</span> <span class="t-spar">指数部分</span><span class="t-mark">(可选)</span> <span class="t-spar">用户定义后缀</span></td>
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<td>(5)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><span class="t-spar">数字序列</span> <span class="t-spar">指数部分</span> <span class="t-spar">用户定义后缀</span></td>
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<td>(6)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><span class="t-spar">字符字面量</span> <span class="t-spar">用户定义后缀</span></td>
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<td>(7)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><span class="t-spar">字符串字面量</span> <span class="t-spar">用户定义后缀</span></td>
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<td>(8)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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</table>
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<div class="t-li1"><span class="t-li">1-4)</span> 用户定义整数字面量，例如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">12</span>_km</span></span></div>
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<div class="t-li1"><span class="t-li">5-6)</span> 用户定义浮点字面量，例如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu16">0.5</span>_Pa</span></span></div>
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<div class="t-li1"><span class="t-li">7)</span> 用户定义字符字面量，例如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">'c'</span>_X</span></span></div>
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<div class="t-li1"><span class="t-li">8)</span> 用户定义字符串字面量，例如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">"abd"</span>_L</span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">u<span class="st0">"xyz"</span>_M</span></span></div>
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<table class="t-par-begin">
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<tr class="t-par">
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<td><span class="t-spar">十进制字面量</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-integer_literal.html">整数字面量</a>中相同，非零的十进制数位后随零或多个十进制数位</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">八进制字面量</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-integer_literal.html">整数字面量</a>中相同，零后随零或多个八进制数位</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">十六进制字面量</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-integer_literal.html">整数字面量</a>中相同，<code>0x</code> 或 <code>0X</code> 后随一个或多个十六进制数位</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">二进制字面量</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-integer_literal.html">整数字面量</a>中相同，<code>0b</code> 或 <code>0B</code> 后随一或多个二进制数位</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">数字序列</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-floating_literal.html">浮点字面量</a>中相同，一个十进制数字序列</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">分数常量</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-floating_literal.html">浮点字面量</a>中相同，要么是一个后随小数点的 <span class="t-spar">数字序列</span>（<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">123</span>.</span></span>），要么是一个可选的 <span class="t-spar">数字序列</span> 后随小数点和另一个 <span class="t-spar">数字序列</span>（<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu16">1.0</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu18">.12</span></span></span>）</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">指数部分</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-floating_literal.html">浮点字面量</a>中相同，字母 <code>e</code> 或字母 <code>E</code> 后随可选的正负号，后随 <span class="t-spar">数字序列</span></td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">字符字面量</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-character_literal.html">字符字面量</a>中相同</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">字符串字面量</span></td>
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<td>-</td>
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<td>与<a href="cpp-language-string_literal.html">字符串字面量</a>中相同，包括原始字符串字面量</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">用户定义后缀</span></td>
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<td>-</td>
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<td>标识符，由<i>字面量运算符</i>或<i>字面量运算符模板</i>声明引入（见下文）。所有程序引入的 <span class="t-spar">用户定义后缀</span> 必须以下划线字符 <code><b>_</b></code> 开始。标准库的 <span class="t-spar">用户定义后缀</span> 不以下划线开始。</td>
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</tr>
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</table>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx14">
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<td>
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<p>在整数和浮点数字序列中，允许在任何两个数位间插入可选的分隔符 <code><b>'</b></code>，并忽略它们。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
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</tr>
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</table>
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<p>如果一个记号同时匹配用户定义字面量的语法和常规字面量的语法，则它被假定为常规字面量（即不可能重载 <span class="t-c"><span class="mw-geshi cpp source-cpp">123LL</span></span> 中的 <span class="t-c"><span class="mw-geshi cpp source-cpp">LL</span></span>）</p>
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<p>当编译器遇到一个带有 <span class="t-spar">用户定义后缀</span> <code>X</code> 的用户定义字面量时，它进行<a href="cpp-language-unqualified_lookup.html">无限定名字查找</a>，寻找名为 <code>operator "" X</code> 的函数。-如果该查找找不到任何声明，则程序非良构。否则，</p>
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<div class="t-li1"><span class="t-li">1)</span> 对于用户定义整数字面量</div>
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<div class="t-li2"><span class="t-li">a)</span> 如果重载集包含带有形参类型 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span></span></span> 的字面量运算符，则用户定义字面量表达式被当做函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X<span class="br0">(</span>nULL<span class="br0">)</span></span></span>，其中 <code>n</code> 是无 <span class="t-spar">用户定义后缀</span> 的该字面量</div>
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<div class="t-li2"><span class="t-li">b)</span> 否则，重载集必须包含以下之一，但不是二者：原始字面量运算符或数值字面量运算符模板。如果重载集包含原始字面量运算符，则用户定义字面量表达式被当做函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X<span class="br0">(</span><span class="st0">"n"</span><span class="br0">)</span></span></span></div>
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<div class="t-li2"><span class="t-li">c)</span> 否则，如果重载集包含数值字面量运算符模板，则用户定义字面量表达式被当做函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X<span class="sy1"><</span><span class="st0">'c1'</span>, <span class="st0">'c2'</span>, <span class="st0">'c3'</span>..., <span class="st0">'ck'</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span></span></span>，其中 c1..ck 是 <code>n</code> 中的各个字符且它们都来自<span class="t-rev-inl t-until-cxx23"><span><a href="cpp-language-charset.html#.E5.9F.BA.E7.A1.80.E6.BA.90.E5.AD.97.E7.AC.A6.E9.9B.86">基础源字符集</a></span> <span><span class="t-mark-rev t-until-cxx23">(C++23 前)</span></span></span><span class="t-rev-inl t-since-cxx23"><span><a href="cpp-language-charset.html#.E5.9F.BA.E7.A1.80.E5.AD.97.E7.AC.A6.E9.9B.86">基础字符集</a></span> <span><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></span></span></div>
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<div class="t-li1"><span class="t-li">2)</span> 对于用户定义浮点字面量，</div>
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<div class="t-li2"><span class="t-li">a)</span> 如果重载集包含带有形参类型 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的字面量运算符，则用户定义字面量表达式被当做函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X<span class="br0">(</span>fL<span class="br0">)</span></span></span>，其中 <code>f</code> 是无 <span class="t-spar">用户定义后缀</span> 的该字面量</div>
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<div class="t-li2"><span class="t-li">b)</span> 否则，重载集必须包含下列之一，但不是二者：原始字面量运算符或数值字面量运算符模板。如果重载集包含原始字面量运算符，则用户定义字面量表达式被当做函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X<span class="br0">(</span><span class="st0">"f"</span><span class="br0">)</span></span></span></div>
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<div class="t-li2"><span class="t-li">c)</span> 否则，如果重载集包含数值字面量运算符模板，则用户定义字面量表达式被当做函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X<span class="sy1"><</span><span class="st0">'c1'</span>, <span class="st0">'c2'</span>, <span class="st0">'c3'</span>..., <span class="st0">'ck'</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span></span></span>，其中 c1..ck 是 <code>f</code> 中的各个字符且它们都来自<span class="t-rev-inl t-until-cxx23"><span><a href="cpp-language-charset.html#.E5.9F.BA.E7.A1.80.E6.BA.90.E5.AD.97.E7.AC.A6.E9.9B.86">基础源字符集</a></span> <span><span class="t-mark-rev t-until-cxx23">(C++23 前)</span></span></span><span class="t-rev-inl t-since-cxx23"><span><a href="cpp-language-charset.html#.E5.9F.BA.E7.A1.80.E5.AD.97.E7.AC.A6.E9.9B.86">基础字符集</a></span> <span><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></span></span>。</div>
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<div class="t-li1"><span class="t-li">3)</span> 对于用户定义字符串字面量，令 <code>str</code> 为无 <span class="t-spar">用户定义后缀</span> 的字面量：</div>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx20">
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<td>
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<div class="t-li2"><span class="t-li">a)</span> 如果重载集包含带非类型模板形参的字符串字面量运算符模板，且 <code>str</code> 对它是良构的模板实参，则用户定义字面量表达式被当作函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X<span class="sy1"><</span>str<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span></span></span>，</div>
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</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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</table>
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<div class="t-li2"><span class="t-li">b)</span> 否则，用户定义字面量表达式被当做函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X <span class="br0">(</span>str, len<span class="br0">)</span></span></span>，其中 <code>len</code> 是字符串字面量的长度，不包含终止空字符</div>
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<div class="t-li1"><span class="t-li">4)</span> 对于用户定义字符字面量，用户定义字面量表达式被当做函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span> X <span class="br0">(</span>ch<span class="br0">)</span></span></span>，其中 <code>ch</code> 是无 <span class="t-spar">用户定义后缀</span> 的该字面量。</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="kw4">long</span> <span class="kw4">double</span> operator <span class="st0">""</span> _w<span class="br0">(</span><span class="kw4">long</span> <span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> operator <span class="st0">""</span> _w<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char16_t</span><span class="sy2">*</span>, size_t<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">unsigned</span> operator <span class="st0">""</span> _w<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span><span class="br0">)</span><span class="sy4">;</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="nu16">1.2</span>_w<span class="sy4">;</span> <span class="co1">// 调用运算符 "" _w(1.2L)</span>
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u<span class="st0">"one"</span>_w<span class="sy4">;</span> <span class="co1">// 调用运算符 "" _w(u"one", 3)</span>
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<span class="nu0">12</span>_w<span class="sy4">;</span> <span class="co1">// 调用运算符 "" _w("12")</span>
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<span class="st0">"two"</span>_w<span class="sy4">;</span> <span class="co1">// 错误：无适用的字面量运算符</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>当在<a href="cpp-language-translation_phases.html#.E9.98.B6.E6.AE.B5_6">翻译阶段 6</a> 中发生字符串字面量的拼接时，用户定义字符串字面量也被拼接，且其 <span class="t-spar">用户定义后缀</span> 在拼接时被忽略，但所有被拼接的字面量中只可以出现一个后缀：</p>
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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="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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L<span class="st0">"A"</span> <span class="st0">"B"</span> <span class="st0">"C"</span>_x<span class="sy4">;</span> <span class="co1">// OK：同 L"ABC"_x</span>
|
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<span class="st0">"P"</span>_x <span class="st0">"Q"</span> <span class="st0">"R"</span>_y<span class="sy4">;</span><span class="co1">// 错误：两个不同的用户定义后缀（_x 与 _y）</span>
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<span class="br0">}</span></pre></div>
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</div>
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<h3><span class="mw-headline" id=".E5.AD.97.E9.9D.A2.E9.87.8F.E8.BF.90.E7.AE.97.E7.AC.A6">字面量运算符</span></h3>
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<p>用户定义字面量所调用的函数被称为<i>字面量运算符</i>（如果它是模板，则被称为<i>字面量运算符模板</i>）。它的声明恰如任何其他命名空间作用域的<a href="cpp-language-function.html">函数</a>或<a href="cpp-language-function_template.html">函数模板</a>一样（它可以是友元函数、函数模板的显式实例化或特化，或通过 using 声明引入），但有下列限制：</p>
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<p>此函数的名称可拥有两种形式之一：</p>
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<table class="t-sdsc-begin">
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td class="t-sdsc-nopad"><code><b>operator</b></code> <code><b>""</b></code> <span class="t-spar">标识符</span></td>
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<td class="t-sdsc-nopad"></td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td class="t-sdsc-nopad"><code><b>operator</b></code> <span class="t-spar">用户定义字符串字面量</span></td>
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<td class="t-sdsc-nopad"></td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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</table>
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<table class="t-par-begin">
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<tr class="t-par">
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<td><span class="t-spar">标识符</span></td>
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<td>-</td>
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<td>作为用户定义字面量所用的 <span class="t-spar">用户定义后缀</span> 的标识符，其将调用此函数。必须以下划线 <code><b>_</b></code> 开始：不以下划线开始的后缀为标准库提供的字面量运算符所保留。</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">用户定义字符串字面量</span></td>
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<td>-</td>
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<td>字符序列 <code><b>""</b></code> 后不带空格，后随将作为 <span class="t-spar">用户定义后缀</span> 的字符序列。这种特殊语法使得将语言关键词和<a href="cpp-keywords.html" class="mw-redirect">保留标识符</a>用作 <span class="t-spar">用户定义后缀</span> 成为可能，并由来自头文件 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1"><</span>complex<span class="sy1">></span></span></span> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span><span class="kw1">if</span></span></span> 的声明所用。注意，使用此形式不改变用户定义字面量必须以下划线开始的规则：类似 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="st0">""</span><span class="kw1">if</span></span></span> 的声明只可出现作标准库头文件的一部分。然而，它允许下划线后随大写字母的用法（其他情况下这是<a href="cpp-language-identifiers.html">保留标识符</a>）。</td>
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</tr>
|
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</table>
|
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<p>如果字面量运算符是模板，则它必须有空形参列表，而且只能有一个模板形参，模板形参必须是元素类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span> 的非类型模板形参包（此时称之为<i>数值字面量运算符模板</i>）</p>
|
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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="kw4">char</span>...<span class="sy1">></span> <span class="kw4">double</span> operator <span class="st0">""</span> _x<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></pre></div>
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</div>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx20">
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<td>
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<p>或类类型的非类型模板形参（此时称之为<i>字符串字面量运算符模板</i>）</p>
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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">struct</span> A <span class="br0">{</span> <span class="kw4">constexpr</span> A<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span>A a<span class="sy1">></span> A operator <span class="st0">""</span>_a<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></pre></div>
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</div>
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</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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</table>
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<p>字面量运算符仅允许下列形参列表：</p>
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<table class="t-sdsc-begin">
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span></span></span> <code><b>)</b></code></td>
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<td>(1)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span> <code><b>)</b></code></td>
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<td>(2)</td>
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<td class="t-sdsc-nopad"></td>
|
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> <code><b>)</b></code></td>
|
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<td>(3)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span> <code><b>)</b></code></td>
|
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<td>(4)</td>
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<td class="t-sdsc-nopad"></td>
|
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</tr>
|
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">wchar_t</span></span></span> <code><b>)</b></code></td>
|
|
<td>(5)</td>
|
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<td class="t-sdsc-nopad"></td>
|
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</tr>
|
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
|
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</tr>
|
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp">char8_t</span></span> <code><b>)</b></code></td>
|
|
<td>(6)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="10" class="t-sdsc-sep"></td>
|
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</tr>
|
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char16_t</span></span></span> <code><b>)</b></code></td>
|
|
<td>(7)</td>
|
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<td class="t-sdsc-nopad"></td>
|
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
|
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char32_t</span></span></span> <code><b>)</b></code></td>
|
|
<td>(8)</td>
|
|
<td class="t-sdsc-nopad"></td>
|
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</tr>
|
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
|
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</tr>
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span></span></span> <code><b>,</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a></span></span> <code><b>)</b></code></td>
|
|
<td>(9)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
|
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<tr>
|
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
|
|
<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">wchar_t</span> <span class="sy2">*</span></span></span> <code><b>,</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a></span></span> <code><b>)</b></code></td>
|
|
<td>(10)</td>
|
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<td class="t-sdsc-nopad"></td>
|
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</tr>
|
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<tr>
|
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<td colspan="10" class="t-sdsc-sep"></td>
|
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</tr>
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> char8_t <span class="sy2">*</span></span></span> <code><b>,</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a></span></span> <code><b>)</b></code></td>
|
|
<td>(11)</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
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</tr>
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<tr>
|
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<td colspan="10" class="t-sdsc-sep"></td>
|
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</tr>
|
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">char16_t</span> <span class="sy2">*</span></span></span> <code><b>,</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a></span></span> <code><b>)</b></code></td>
|
|
<td>(12)</td>
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<td class="t-sdsc-nopad"></td>
|
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><code><b>(</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">char32_t</span> <span class="sy2">*</span></span></span> <code><b>,</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a></span></span> <code><b>)</b></code></td>
|
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<td>(13)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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</table>
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<div class="t-li1"><span class="t-li">1)</span> 拥有此形参列表的字面量运算符是<i>原始字面量运算符</i>，用于整数和浮点用户定义字面量的后备方式（见上文）</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 拥有这些形参列表的字面量运算符是用户定义整数字面量的首选字面量运算符</div>
|
|
<div class="t-li1"><span class="t-li">3)</span> 拥有这些形参列表的字面量运算符是用于定义浮点字面量的首选字面量运算符</div>
|
|
<div class="t-li1"><span class="t-li">4-8)</span> 拥有这些形参列表的字面量运算符由用户定义的字符字面量所调用</div>
|
|
<div class="t-li1"><span class="t-li">9-13)</span> 拥有这些形参列表的字面量运算符由用户定义的字符串字面量所调用</div>
|
|
<p>不允许<a href="cpp-language-default_arguments.html">默认实参</a>。</p>
|
|
<p>不允许 C <a href="cpp-language-language_linkage.html">语言连接</a>。</p>
|
|
<p>除了上述限制外，字面量运算符和字面量运算符模板都是普通的函数（和函数模板），它们可声明为 inline 或 constexpr，它们可拥有内部或外部连接，它们可显式调用，可被取地址，等等。</p>
|
|
<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 <string></span>
|
|
<span class="kw4">void</span> operator <span class="st0">""</span> _km<span class="br0">(</span><span class="kw4">long</span> <span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK ，将为 1.0_km 所调用</span>
|
|
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> operator <span class="st0">""</span> _i18n<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</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="sy4">;</span> <span class="co1">// OK</span>
|
|
<span class="kw1">template</span> <span class="sy1"><</span><span class="kw4">char</span>...<span class="sy1">></span> <span class="kw4">double</span> operator <span class="st0">""</span> _π<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
<span class="kw4">float</span> operator <span class="st0">""</span>_e<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
|
|
<span class="kw4">float</span> operator <span class="st0">""</span>Z<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 错误：后缀必须以下划线开始</span>
|
|
<span class="kw4">double</span> operator<span class="st0">""</span> _Z<span class="br0">(</span><span class="kw4">long</span> <span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 错误：所有以下划线后随大写字母开始的名称受到保留</span>
|
|
<span class="kw4">double</span> operator<span class="st0">""</span>_Z<span class="br0">(</span><span class="kw4">long</span> <span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK：虽然 _Z 被保留，但允许 ""_Z</span>
|
|
<span class="kw4">double</span> operator <span class="st0">""</span>_Z<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> args<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK：能重载字面量运算符</span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></pre></div>
|
|
</div>
|
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</div>
|
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p>自从引入用户定义字面量之后，使用<a href="cpp-types-integer.html">定宽整数类型格式化宏常量</a>且未在前导字符串字面量后加空格的情况变为非法：<span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c-fprintf.html"><span class="kw1845">std::<span class="me2">printf</span></span></a><span class="br0">(</span><span class="st0">"%"</span><a href="cpp-types-integer.html"><span class="kw179">PRId64</span></a><span class="st0">"<span class="es1">\n</span>"</span>,<a href="cpp-types-integer.html"><span class="kw137">INT64_MIN</span></a><span class="br0">)</span><span class="sy4">;</span></span></span> 必须替换成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c-fprintf.html"><span class="kw1845">std::<span class="me2">printf</span></span></a><span class="br0">(</span><span class="st0">"%"</span> <a href="cpp-types-integer.html"><span class="kw179">PRId64</span></a><span class="st0">"<span class="es1">\n</span>"</span>,<a href="cpp-types-integer.html"><span class="kw137">INT64_MIN</span></a><span class="br0">)</span><span class="sy4">;</span></span></span></p>
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|
<p>由于<a href="cpp-language-translation_phases.html#.E6.9C.80.E5.A4.A7.E5.90.9E.E5.99.AC">最大吞噬规则</a>，以 <span class="t-rev-inl t-since-cxx17"><span><code>p</code>、<code>P</code>、</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span><code>e</code> 和 <code>E</code> 结束的用户定义整数和浮点字面量，在后随运算符 <code>+</code> 或 <code>-</code> 时，必须在源码中以空白符或括号与运算符分隔：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="kw4">long</span> <span class="kw4">double</span> operator<span class="st0">""</span>_E<span class="br0">(</span><span class="kw4">long</span> <span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">long</span> <span class="kw4">double</span> operator<span class="st0">""</span>_a<span class="br0">(</span><span class="kw4">long</span> <span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">int</span> operator<span class="st0">""</span>_p<span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">auto</span> x <span class="sy1">=</span> <span class="nu16">1.0</span>_E<span class="sy2">+</span><span class="nu16">2.0</span><span class="sy4">;</span> <span class="co1">// 错误</span>
|
|
<span class="kw4">auto</span> y <span class="sy1">=</span> <span class="nu16">1.0</span>_a<span class="sy2">+</span><span class="nu16">2.0</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
<span class="kw4">auto</span> z <span class="sy1">=</span> <span class="nu16">1.0</span>_E <span class="sy2">+</span><span class="nu16">2.0</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
<span class="kw4">auto</span> q <span class="sy1">=</span> <span class="br0">(</span><span class="nu16">1.0</span>_E<span class="br0">)</span><span class="sy2">+</span><span class="nu16">2.0</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
<span class="kw4">auto</span> w <span class="sy1">=</span> <span class="nu0">1</span>_p<span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span> <span class="co1">// 错误</span>
|
|
<span class="kw4">auto</span> u <span class="sy1">=</span> <span class="nu0">1</span>_p <span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span> <span class="co1">// OK</span></pre></div>
|
|
</div>
|
|
<p>同样的规则适用于后随整数或浮点用户定义字面量的点运算符：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <chrono></span>
|
|
<span class="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">literals</span><span class="sy4">;</span>
|
|
<span class="kw4">auto</span> a <span class="sy1">=</span> 4s.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 错误</span>
|
|
<span class="kw4">auto</span> b <span class="sy1">=</span> 4s .<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
<span class="kw4">auto</span> c <span class="sy1">=</span> <span class="br0">(</span>4s<span class="br0">)</span>.<span class="me1">count</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span></pre></div>
|
|
</div>
|
|
<p>否则会组成单个非法预处理数字记号（例如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu16">1.0</span>_E<span class="sy2">+</span><span class="nu16">2.0</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">4s.<span class="me1">count</span></span></span>），这导致编译失败。</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 <cstddef></span>
|
|
<span class="co2">#include <algorithm></span>
|
|
<span class="co2">#include <iostream></span>
|
|
<span class="co2">#include <numbers></span>
|
|
<span class="co2">#include <string></span>
|
|
|
|
<span class="co1">// 用作从度（输入参数）转换为弧度（返回输出）</span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">long</span> <span class="kw4">double</span> operator<span class="st0">""</span> _deg_to_rad <span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">double</span> deg <span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw4">long</span> <span class="kw4">double</span> radians <span class="sy1">=</span> deg <span class="sy2">*</span> std<span class="sy4">::</span><span class="me2">numbers</span><span class="sy4">::</span><span class="me2">pi_v</span><span class="sy1"><</span><span class="kw4">long</span> <span class="kw4">double</span><span class="sy1">></span> <span class="sy2">/</span> <span class="nu0">180</span><span class="sy4">;</span>
|
|
<span class="kw1">return</span> radians<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="co1">// 用作自定义类型</span>
|
|
<span class="kw1">struct</span> mytype
|
|
<span class="br0">{</span>
|
|
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> m<span class="sy4">;</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="kw4">constexpr</span> mytype operator<span class="st0">""</span> _mytype <span class="br0">(</span> <span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> n <span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">return</span> mytype<span class="br0">{</span>n<span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="co1">// 用作副作用</span>
|
|
<span class="kw4">void</span> operator<span class="st0">""</span> _print <span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> str <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> str <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="co2">#if __cpp_nontype_template_args < 201911</span>
|
|
|
|
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> operator<span class="st0">""</span> _x2 <span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> str, <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="kw1">return</span> <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="br0">{</span>str<span class="br0">}</span> <span class="sy2">+</span> str<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="co2">#else // C++20 字符串字面量运算符模板</span>
|
|
|
|
<span class="kw1">template</span><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">></span>
|
|
<span class="kw1">struct</span> DoubleString
|
|
<span class="br0">{</span>
|
|
<span class="kw4">char</span> p<span class="br0">[</span>N<span class="sy2">*</span><span class="nu0">2</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">]</span><span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">constexpr</span> DoubleString <span class="br0">(</span> <span class="kw4">char</span> <span class="kw4">const</span><span class="br0">(</span><span class="sy3">&</span>pp<span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span> <span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">copy</span><span class="br0">(</span>pp, p<span class="br0">)</span><span class="sy4">;</span>
|
|
std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">copy</span><span class="br0">(</span>pp, p <span class="sy2">+</span> N <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">template</span><span class="sy1"><</span>DoubleString A<span class="sy1">></span>
|
|
<span class="kw4">constexpr</span> <span class="kw4">auto</span> operator<span class="st0">""</span> _x2<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">return</span> A.<span class="me1">p</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="co2">#endif // C++20</span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw4">double</span> x_rad <span class="sy1">=</span> <span class="nu16">90.0</span>_deg_to_rad<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> <a href="cpp-io-manip-fixed.html"><span class="kw1784">std::<span class="me2">fixed</span></span></a> <span class="sy1"><<</span> x_rad <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
|
|
mytype y <span class="sy1">=</span> <span class="nu0">123</span>_mytype<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> y.<span class="me1">m</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
|
|
<span class="nu12">0x123ABC</span>_print<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">"abc"</span>_x2 <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</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">1.570796
|
|
123
|
|
0x123ABC
|
|
abcabc</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E6.A0.87.E5.87.86.E5.BA.93">标准库</span></h3>
|
|
<p>标准库中定义了下列字面量运算符</p>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc-header">
|
|
<td colspan="2">
|
|
<div>定义于内联命名空间 <code>std::literals::complex_literals</code></div>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-numeric-complex-operator_22_22i.html"><span class="t-lines"><span>operator""if</span><span>operator""i</span><span>operator""il</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>表示纯虚数的 <span class="t-lc"><a href="cpp-numeric-complex.html">std::complex</a></span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc-header">
|
|
<td colspan="2">
|
|
<div>定义于内联命名空间 <code>std::literals::chrono_literals</code></div>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-chrono-operator_22_22h.html"><span class="t-lines"><span>operator""h</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>表示小时的 <span class="t-lc"><a href="cpp-chrono-duration.html">std::chrono::duration</a></span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-chrono-operator_22_22min.html"><span class="t-lines"><span>operator""min</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>表示分钟的 <span class="t-lc"><a href="cpp-chrono-duration.html">std::chrono::duration</a></span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-chrono-operator_22_22s.html"><span class="t-lines"><span>operator""s</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>表示秒的 <span class="t-lc"><a href="cpp-chrono-duration.html">std::chrono::duration</a></span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-chrono-operator_22_22ms.html"><span class="t-lines"><span>operator""ms</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>表示毫秒的 <span class="t-lc"><a href="cpp-chrono-duration.html">std::chrono::duration</a></span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-chrono-operator_22_22us.html"><span class="t-lines"><span>operator""us</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>表示微秒的 <span class="t-lc"><a href="cpp-chrono-duration.html">std::chrono::duration</a></span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-chrono-operator_22_22ns.html"><span class="t-lines"><span>operator""ns</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>表示纳秒的 <span class="t-lc"><a href="cpp-chrono-duration.html">std::chrono::duration</a></span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-chrono-operator_22_22y.html"><span class="t-lines"><span>operator""y</span></span></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>表示特定年的 <span class="t-lc">std::chrono::year</span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-chrono-operator_22_22d.html"><span class="t-lines"><span>operator""d</span></span></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>表示月内日期的 <span class="t-lc">std::chrono::day</span> 字面量<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc-header">
|
|
<td colspan="2">
|
|
<div>定义于内联命名空间 <code>std::literals::string_literals</code></div>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-string-basic_string-operator_22_22s.html"><span class="t-lines"><span>operator""s</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>转换字符数组字面量为 <code>basic_string</code><br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc-header">
|
|
<td colspan="2">
|
|
<div>定义于内联命名空间 <code>std::literals::string_view_literals</code></div>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-string-basic_string_view-operator_22_22sv.html"><span class="t-lines"><span>operator""sv</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>创建一个字符数组字面量的字符串视图<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
|
|
<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>
|
|
<table class="dsctable" style="font-size:0.8em">
|
|
<tr>
|
|
<th>DR</th>
|
|
<th>应用于</th>
|
|
<th>出版时的行为</th>
|
|
<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://wg21.cmeerw.net/cwg/issue1473">CWG 1473</a></td>
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<td>C++11</td>
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<td>字面量运算符声明中曾要求 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">""</span></span></span> 与 <span class="t-spar">用户定义后缀</span> 间的空格</td>
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<td>不再强制要求</td>
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