205 lines
11 KiB
HTML
205 lines
11 KiB
HTML
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<title>std::bad_optional_access</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_optional_bad_optional_access 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>bad_optional_access</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-optional.html">optional</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-optional.html"><optional></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> bad_optional_access<span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>定义 <span class="t-lc"><a href="cpp-utility-optional-value.html">std::optional::value</a></span> 在访问不含值的 <code>optional</code> 对象时所抛出的异常对象类型。</p>
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<div class="noresize" style="height: 40px; width: 283px;"><map name="ImageMap_1_1379215822" id="ImageMap_1_1379215822">
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<area href="cpp-error-exception.html" shape="rect" coords="5,4,107,36" alt="cpp/error/exception" /></map><img alt="std-bad optional access-inheritance-lwg2806.svg" src="std-bad_optional_access-inheritance-lwg2806.svg" width="283" height="40" usemap="#ImageMap_1_1379215822" /></div>
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<p><span style="font-size:0.7em; line-height:130%">继承图</span></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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<div><span class="t-lines"><span>(构造函数)</span></span></div>
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</td>
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<td>构造新的 <code>bad_optional_access</code> 对象<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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<td>替换 <code>bad_optional_access</code> 对象<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>what</span></span></div>
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<td>返回解释字符串<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::bad_optional_access::bad_optional_access"><span style="font-size:0.7em; line-height:130%">std::bad_optional_access::</span>bad_optional_access</span></h2>
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<div><span class="mw-geshi cpp source-cpp">bad_optional_access<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><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-cxx17">(C++17 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">bad_optional_access<span class="br0">(</span> <span class="kw4">const</span> bad_optional_access<span class="sy3">&</span> other <span class="br0">)</span> <span class="kw1">noexcept</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-cxx17">(C++17 起)</span></td>
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<td></td>
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<p>构造新的拥有实现定义的空终止字节字符串的 <code>bad_optional_access</code> 对象，字符串能通过 <a href="cpp-error-exception-what.html"><tt>what()</tt></a> 访问。</p>
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<div class="t-li1"><span class="t-li">1)</span> 默认构造函数。</div>
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<div class="t-li1"><span class="t-li">2)</span> 复制构造函数。若 <code>*this</code> 与 <code>other</code> 均拥有动态类型 <code>std::bad_optional_access</code> 则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-string-byte-strcmp.html"><span class="kw1145">std::<span class="me2">strcmp</span></span></a><span class="br0">(</span>what<span class="br0">(</span><span class="br0">)</span>, other.<span class="me1">what</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span></span></span> 。</div>
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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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<td>other</td>
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<td>-</td>
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<td>要复制的另一异常对象</td>
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<h2><span class="mw-headline" id="std::bad_optional_access::operator.3D"><span style="font-size:0.7em; line-height:130%">std::bad_optional_access::</span>operator=</span></h2>
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<div><span class="mw-geshi cpp source-cpp">bad_optional_access<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span> <span class="kw4">const</span> bad_optional_access<span class="sy3">&</span> other <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>以 <code>other</code> 的内容赋值。若 <code>*this</code> 与 <code>other</code> 均拥有动态类型 <code>std::bad_optional_access</code> 则赋值后 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-string-byte-strcmp.html"><span class="kw1145">std::<span class="me2">strcmp</span></span></a><span class="br0">(</span>what<span class="br0">(</span><span class="br0">)</span>, other.<span class="me1">what</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0_2">参数</span></h3>
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<table class="t-par-begin">
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<td>other</td>
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<td>-</td>
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<td>用以赋值的另一异常对象</td>
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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><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span></p>
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<h2><span class="mw-headline" id="std::bad_optional_access::what"><span style="font-size:0.7em; line-height:130%">std::bad_optional_access::</span>what</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">virtual</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> what<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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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<tr class="t-dcl-sep">
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<td></td>
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<p>返回解释字符串。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0_3">参数</span></h3>
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<p>（无）</p>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC_2">返回值</span></h3>
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<p>指向有解释信息的空终止字符串的指针。该字符串适合转换并显示为 <span class="t-lc"><a href="cpp-string-basic_string.html">std::wstring</a></span> 。保证该指针至少到获得它来源的异常对象被销毁，或在该异常对象上调用非 const 成员函数（例如复制赋值运算符）为止合法。</p>
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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>允许但不要求实现覆写 <code>what()</code> 。</p>
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<h2><span class="mw-headline" id=".E7.BB.A7.E6.89.BF.E8.87.AA_std::exception">继承自 <a href="cpp-error-exception.html"><span style="font-size:0.7em; line-height:130%">std::</span>exception</a></span></h2>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0_2">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><a href="cpp-error-exception-~exception.html"><span class="t-lines"><span>(析构函数)</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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<td>析构该异常对象<br />
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<span class="t-mark">(<code>std::exception</code> 的虚公开成员函数)</span></td>
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<div><a href="cpp-error-exception-what.html"><span class="t-lines"><span>what</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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<td>返回解释性字符串<br />
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<span class="t-mark">(<code>std::exception</code> 的虚公开成员函数)</span></td>
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