123 lines
8.1 KiB
HTML
123 lines
8.1 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>errno</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_error_errno 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">errno</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-error.html">error</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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<div>定义于头文件 <code><a href="cpp-header-cerrno.html"><cerrno></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="co2">#define errno /*implementation-defined*/</span></span></div>
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<p><code>errno</code> 是用于错误指示的预处理器宏。它展开成一个<span class="t-rev-inl t-until-cxx11"><span>静态</span> <span><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></span></span><span class="t-rev-inl t-since-cxx11"><span>线程局域</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> 类型可修改左值。</p>
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<p>数个标准库函数通过写入正整数到 <code>errno</code> 指示错误。 <code>errno</code> 的值被典型地设置为作为列于 <code><cerrno></code> 的,以字母 <code>E</code> 起始,后随大写字母或数字的宏常量。</p>
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<p>程序启动时 <code>errno</code> 的值为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ,而且尽管不管在错误发生与否时,允许写入正整数到 <code>errno</code> ,库函数决不会存储 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 于 <code>errno</code> 。</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 <iostream></span>
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<span class="co2">#include <cmath></span>
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<span class="co2">#include <cerrno></span>
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<span class="co2">#include <cstring></span>
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<span class="co2">#include <clocale></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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<span class="kw4">double</span> not_a_number <span class="sy1">=</span> <a href="cpp-numeric-math-log.html"><span class="kw1323">std::<span class="me2">log</span></span></a><span class="br0">(</span><span class="sy2">-</span><span class="nu16">1.0</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span><span class="kw2">errno</span> <span class="sy1">==</span> <a href="cpp-error-errno_macros.html"><span class="kw809">EDOM</span></a><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"log(-1) failed: "</span> <span class="sy1"><<</span> <a href="cpp-string-byte-strerror.html"><span class="kw1160">std::<span class="me2">strerror</span></span></a><span class="br0">(</span><span class="kw2">errno</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-locale-setlocale.html"><span class="kw1989">std::<span class="me2">setlocale</span></span></a><span class="br0">(</span>LC_MESSAGES, <span class="st0">"de_DE.utf8"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Or, in German, "</span> <span class="sy1"><<</span> <a href="cpp-string-byte-strerror.html"><span class="kw1160">std::<span class="me2">strerror</span></span></a><span class="br0">(</span><span class="kw2">errno</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>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出:</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">log(-1) failed: Numerical argument out of domain
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Or, in German, Das numerische Argument ist ausserhalb des Definitionsbereiches</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue310">LWG 310</a></td>
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<td>C++98</td>
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<td>未指明 errno 是宏还是有外部链接的标识符</td>
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<td>errno 必须是宏</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-error-errno_macros.html"><span class="t-lines"><span>E2BIG, EACCES, ..., EXDEV</span></span></a></div>
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</div>
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</td>
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<td>兼容标准 POSIX 的错误条件的宏<br />
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<span class="t-mark">(宏常量)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-c-perror.html"><span class="t-lines"><span>perror</span></span></a></div>
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</div>
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</td>
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<td>显示对应当前错误的字符串于 <span class="t-lc"><a href="cpp-io-c.html">stderr</a></span><br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-byte-strerror.html"><span class="t-lines"><span>strerror</span></span></a></div>
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</div>
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</td>
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<td>返回给定错误码的文本版本<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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