203 lines
12 KiB
HTML
203 lines
12 KiB
HTML
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<title>errno</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_error_errno skin-cppreference2 action-view cpp-navbar">
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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="c.html">c</a>‎ | <a href="c-error.html">error</a></span></div>
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<div>定义于头文件 <code><errno.h></code></div>
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<td></td>
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<div><span class="mw-geshi c source-c"><span class="co2">#define errno /*implementation-defined*/</span></span></div>
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<p><code>errno</code> 是一个预处理器宏（见后述），展开成<span class="t-rev-inl t-since-c11"><span>线程局域的</span> <span><span class="t-mark-rev t-since-c11">(C11 起)</span></span></span> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span> 类型可修改左值。一些标准库函数通过写入正整数到 <code>errno</code> 指定错误。通常，会将 <code>errno</code> 的值设置为错误码之一。错误码作为以字母 <code>E</code> 后随大写字母或数字开始的宏常量，列于 <code><errno.h></code> 。</p>
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<p><code>errno</code> 的值在程序启动时为 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> ，而且无论是否出现错误，都允许库函数将正整数写入 <code>errno</code> ，不过库函数决不会将 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> 存储于 <code>errno</code> 。</p>
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<p>库函数 <span class="t-lc"><a href="c-io-perror.html">perror</a></span> 和 <span class="t-lc"><a href="c-string-byte-strerror.html">strerror</a></span> 能用于获得对应当前 <code>errno</code> 值的错误条件的文本描述。</p>
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<p>注解： C11 前， C 标准有矛盾的要求，称 <code>errno</code> 是宏但<i>亦</i>称“不指明 <code>errno</code> 是宏还是声明带外部链接的标识符”。 C11 修正了此错误，要求必须定义它为宏（参阅 WG14 <a rel="nofollow" class="external text" href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1338.htm">N1338</a> ）。</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="c source-c">
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<pre class="de1"><span class="co2">#include <stdio.h></span>
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<span class="co2">#include <math.h></span>
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<span class="co2">#include <errno.h></span>
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<span class="kw4">void</span> show_errno<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>err_info <span class="sy1">=</span> <span class="st0">"unknown error"</span><span class="sy4">;</span>
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<span class="kw1">switch</span> <span class="br0">(</span><span class="kw2">errno</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">case</span> <a href="c-error-errno_macros.html"><span class="kw425">EDOM</span></a><span class="sy4">:</span>
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err_info <span class="sy1">=</span> <span class="st0">"domain error"</span><span class="sy4">;</span>
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<span class="kw1">break</span><span class="sy4">;</span>
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<span class="kw1">case</span> <a href="c-error-errno_macros.html"><span class="kw431">EILSEQ</span></a><span class="sy4">:</span>
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err_info <span class="sy1">=</span> <span class="st0">"illegal sequence"</span><span class="sy4">;</span>
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<span class="kw1">break</span><span class="sy4">;</span>
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<span class="kw1">case</span> <a href="c-error-errno_macros.html"><span class="kw477">ERANGE</span></a><span class="sy4">:</span>
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err_info <span class="sy1">=</span> <span class="st0">"pole or range error"</span><span class="sy4">;</span>
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<span class="kw1">break</span><span class="sy4">;</span>
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<span class="kw1">case</span> <span class="nu0">0</span><span class="sy4">:</span>
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err_info <span class="sy1">=</span> <span class="st0">"no error"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<a href="c-io-fputs.html"><span class="kw831">fputs</span></a><span class="br0">(</span>err_info, <a href="c-io.html"><span class="kw886">stdout</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-puts.html"><span class="kw835">puts</span></a><span class="br0">(</span><span class="st0">" occurred"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="c-io-fputs.html"><span class="kw831">fputs</span></a><span class="br0">(</span><span class="st0">"MATH_ERRNO is "</span>, <a href="c-io.html"><span class="kw886">stdout</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-puts.html"><span class="kw835">puts</span></a><span class="br0">(</span>math_errhandling <span class="sy3">&</span> MATH_ERRNO <span class="sy4">?</span> <span class="st0">"set"</span> <span class="sy4">:</span> <span class="st0">"not set"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw2">errno</span> <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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<span class="nu16">1.0</span><span class="sy2">/</span><span class="nu16">0.0</span><span class="sy4">;</span>
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show_errno<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw2">errno</span> <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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<a href="c-numeric-math-acos.html"><span class="kw672">acos</span></a><span class="br0">(</span><span class="sy2">+</span><span class="nu16">1.1</span><span class="br0">)</span><span class="sy4">;</span>
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show_errno<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw2">errno</span> <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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<a href="c-numeric-math-log.html"><span class="kw659">log</span></a><span class="br0">(</span><span class="nu16">0.0</span><span class="br0">)</span><span class="sy4">;</span>
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show_errno<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw2">errno</span> <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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<a href="c-numeric-math-sin.html"><span class="kw668">sin</span></a><span class="br0">(</span><span class="nu16">0.0</span><span class="br0">)</span><span class="sy4">;</span>
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show_errno<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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</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">MATH_ERRNO is set
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no error occurred
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domain error occurred
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pole or range error occurred
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no error occurred</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准（ISO/IEC 9899:2011）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.5 Errors <errno.h> (p: 205)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>K.3.1.3 Use of errno (p: 584)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>K.3.2 Errors <errno.h> (p: 585)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准（ISO/IEC 9899:1999）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.5 Errors <errno.h> (p: 186)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c89">
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<ul>
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<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>4.1.3 Errors <errno.h></li>
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</ul>
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</dd>
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</dl>
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</div>
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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="c-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>标准 POSIX 兼容的错误条件宏<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="c-io-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到 <span class="t-lc"><a href="c-io.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="c-string-byte-strerror.html"><span class="t-lines"><span>strerror</span><span>strerror_s</span><span>strerrorlen_s</span></span></a></div>
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<div><span class="t-lines"><span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></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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<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="c-numeric-math-math_errhandling.html"><span class="t-lines"><span>math_errhandling</span><span>MATH_ERRNO</span><span>MATH_ERREXCEPT</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div>
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</div>
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</td>
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<td>定义用于常用数学函数的错误处理机制<br />
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<span class="t-mark">(宏常量)</span></td>
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</tr>
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</table>
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</div>
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</div>
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</div>
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<div class="visualClear"></div>
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</div>
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</body>
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