230 lines
16 KiB
HTML
230 lines
16 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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<title>nearbyint, nearbyintf, nearbyintl</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_numeric_math_nearbyint 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">nearbyint, nearbyintf, nearbyintl</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-numeric.html">numeric</a>‎ | <a href="c-numeric-math.html">math</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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<td>
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<div>定义于头文件 <code><math.h></code></div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl t-since-c99">
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<div><span class="mw-geshi c source-c"><span class="kw4">float</span> nearbyintf<span class="br0">(</span> <span class="kw4">float</span> arg <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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<tr class="t-dcl t-since-c99">
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<td>
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<div><span class="mw-geshi c source-c"><span class="kw4">double</span> nearbyint<span class="br0">(</span> <span class="kw4">double</span> arg <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-c99">
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<td>
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<div><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">double</span> nearbyintl<span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">double</span> arg <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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</tr>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><tgmath.h></code></div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl t-since-c99">
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<td>
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<div><span class="mw-geshi c source-c"><span class="co2">#define nearbyint( arg )</span></span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<div class="t-li1"><span class="t-li">1-3)</span> 以<a href="c-numeric-fenv-FE_round.html">当前舍入模式</a>，舍入浮点参数 <code>arg</code> 到浮点格式的整数值。</div>
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<div class="t-li1"><span class="t-li">4)</span> 泛型宏：若 <code>arg</code> 拥有 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 类型，则调用 <code>nearbyintl</code> 。否则，若 <code>arg</code> 拥有整数类型或 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">double</span></span></span> 类型，则调用 <code>nearbyint</code> 。否则调用 <code>nearbyintf</code> 。</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0.E5.80.BC">参数值</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>arg</td>
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<td>-</td>
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<td>浮点值</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>返回 <code>arg</code> 按照<a href="c-numeric-fenv-FE_round.html">当前舍入模式</a>的最接近整数值。</p>
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<h3><span class="mw-headline" id=".E9.94.99.E8.AF.AF.E5.A4.84.E7.90.86">错误处理</span></h3>
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<p>此函数不受制于任何指定于 <a href="c-numeric-math-math_errhandling.html">math_errhandling</a> 的错误。</p>
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<p>若实现支持 IEEE 浮点算术（ IEC 60559 ），则</p>
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<ul>
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<li>决不引发 <span class="t-lc"><a href="c-numeric-fenv-FE_exceptions.html">FE_INEXACT</a></span></li>
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<li>若 <code>arg</code> 为 ±∞ ，则返回不修改的参数</li>
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<li>若 <code>arg</code> 为 ±0 ，则返回不修改的参数</li>
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<li>若 <code>arg</code> 为 NaN ，则返回 NaN</li>
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</ul>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p><code>nearbyint</code> 和 <span class="t-lc"><a href="c-numeric-math-rint.html">rint</a></span> 之间仅有的区别是 <code>nearbyint</code> 决不引发 <span class="t-lc"><a href="c-numeric-fenv-FE_exceptions.html">FE_INEXACT</a></span> 。</p>
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<p>所有标准浮点格式中，最大可表示浮点值都是整数，故 <code>nearbyint</code> 自身决不溢出；然而存储结果于整数对象时，结果可能溢出任何整数类型（包含 <span class="t-lc"><a href="c-types-integer.html">intmax_t</a></span> ）。</p>
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<p>若当前舍入模式为 <span class="t-lc"><a href="c-numeric-fenv-FE_round.html">FE_TONEAREST</a></span> ，则此函数在中点情况向偶数舍入（同 <span class="t-lc"><a href="c-numeric-math-rint.html">rint</a></span> ，但不同于 <span class="t-lc"><a href="c-numeric-math-round.html">round</a></span> ）。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="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 <fenv.h></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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<span class="co2">#pragma STDC FENV_ACCESS ON</span>
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<a href="c-numeric-fenv-feround.html"><span class="kw723">fesetround</span></a><span class="br0">(</span><a href="c-numeric-fenv-FE_round.html"><span class="kw735">FE_TONEAREST</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"rounding to nearest:<span class="es1">\n</span>nearbyint(+2.3) = %+.1f "</span>, nearbyint<span class="br0">(</span><span class="nu16">2.3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(+2.5) = %+.1f "</span>, nearbyint<span class="br0">(</span><span class="nu16">2.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(+3.5) = %+.1f<span class="es1">\n</span>"</span>, nearbyint<span class="br0">(</span><span class="nu16">3.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(-2.3) = %+.1f "</span>, nearbyint<span class="br0">(</span><span class="sy2">-</span><span class="nu16">2.3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(-2.5) = %+.1f "</span>, nearbyint<span class="br0">(</span><span class="sy2">-</span><span class="nu16">2.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(-3.5) = %+.1f<span class="es1">\n</span>"</span>, nearbyint<span class="br0">(</span><span class="sy2">-</span><span class="nu16">3.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-numeric-fenv-feround.html"><span class="kw723">fesetround</span></a><span class="br0">(</span><a href="c-numeric-fenv-FE_round.html"><span class="kw734">FE_DOWNWARD</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"rounding down: <span class="es1">\n</span>nearbyint(+2.3) = %+.1f "</span>, nearbyint<span class="br0">(</span><span class="nu16">2.3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(+2.5) = %+.1f "</span>, nearbyint<span class="br0">(</span><span class="nu16">2.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(+3.5) = %+.1f<span class="es1">\n</span>"</span>, nearbyint<span class="br0">(</span><span class="nu16">3.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(-2.3) = %+.1f "</span>, nearbyint<span class="br0">(</span><span class="sy2">-</span><span class="nu16">2.3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(-2.5) = %+.1f "</span>, nearbyint<span class="br0">(</span><span class="sy2">-</span><span class="nu16">2.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(-3.5) = %+.1f<span class="es1">\n</span>"</span>, nearbyint<span class="br0">(</span><span class="sy2">-</span><span class="nu16">3.5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(-0.0) = %+.1f<span class="es1">\n</span>"</span>, nearbyint<span class="br0">(</span><span class="sy2">-</span><span class="nu16">0.0</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"nearbyint(-Inf) = %+.1f<span class="es1">\n</span>"</span>, nearbyint<span class="br0">(</span><span class="sy2">-</span>INFINITY<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>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">rounding to nearest:
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nearbyint(+2.3) = +2.0 nearbyint(+2.5) = +2.0 nearbyint(+3.5) = +4.0
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nearbyint(-2.3) = -2.0 nearbyint(-2.5) = -2.0 nearbyint(-3.5) = -4.0
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rounding down:
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nearbyint(+2.3) = +2.0 nearbyint(+2.5) = +2.0 nearbyint(+3.5) = +3.0
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nearbyint(-2.3) = -3.0 nearbyint(-2.5) = -3.0 nearbyint(-3.5) = -4.0
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nearbyint(-0.0) = -0.0
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nearbyint(-Inf) = -inf</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>7.12.9.3 The nearbyint functions (p: 251-252)</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>7.25 Type-generic math <tgmath.h> (p: 373-375)</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>F.10.6.3 The nearbyint functions (p: 526)</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>7.12.9.3 The nearbyint functions (p: 232)</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>7.22 Type-generic math <tgmath.h> (p: 335-337)</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>F.9.6.3 The nearbyint functions (p: 463)</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-numeric-math-rint.html"><span class="t-lines"><span>rint</span><span>rintf</span><span>rintl</span><span>lrint</span><span>lrintf</span><span>lrintl</span><span>llrint</span><span>llrintf</span><span>llrintl</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><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><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>使用当前舍入模式取整到整数，若结果有误则产生异常<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-round.html"><span class="t-lines"><span>round</span><span>roundf</span><span>roundl</span><span>lround</span><span>lroundf</span><span>lround</span><span>llround</span><span>llroundf</span><span>llroundl</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><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><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>取整到最接近的整数，在相邻整数正中间时取远离零的数<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-fenv-feround.html"><span class="t-lines"><span>fegetround</span><span>fesetround</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></div>
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</div>
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</td>
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<td>获得或设置数字的舍入方向<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>
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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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