175 lines
17 KiB
HTML
175 lines
17 KiB
HTML
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<title>std::nearbyint, std::nearbyintf, std::nearbyintl</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_math_nearbyint 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>nearbyint, <span style="font-size:0.7em; line-height:130%">std::</span>nearbyintf, <span style="font-size:0.7em; line-height:130%">std::</span>nearbyintl</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-numeric.html">numeric</a>‎ | <a href="cpp-numeric-math.html">math</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-cmath.html"><cmath></a></code></div>
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<td></td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span> nearbyint <span class="br0">(</span> <span class="kw4">float</span> arg <span class="br0">)</span><span class="sy4">;</span><br />
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<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-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><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>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span> nearbyint <span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">double</span> arg <span class="br0">)</span><span class="sy4">;</span><br />
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<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>(3)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span> nearbyint <span class="br0">(</span> IntegralType arg <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 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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<div class="t-li1"><span class="t-li">1-3)</span> 以<a href="cpp-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> 接受任何<a href="cpp-types-is_integral.html">整数类型</a>参数的重载集或函数模板。等价于 <span class="t-v">(2)</span> （将参数转型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</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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<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="cpp-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 <span class="t-lc"><a href="cpp-numeric-math-math_errhandling.html">math_errhandling</a></span> 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="cpp-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>std::nearbyint</code> 和 <span class="t-lc">rint</span> 之间仅有的区别是 <code>std::nearbyint</code> 决不引发 <span class="t-lc"><a href="cpp-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>std::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="cpp-types-integer.html">std::intmax_t</a></span> ）。</p>
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<p>若当前舍入模式为 <span class="t-lc"><a href="cpp-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">rint</span> ，但不同于 <span class="t-lc">round</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="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 <cfenv></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="co2">#pragma STDC FENV_ACCESS ON</span>
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<a href="cpp-numeric-fenv-feround.html"><span class="kw1455">std::<span class="me2">fesetround</span></span></a><span class="br0">(</span><a href="cpp-numeric-fenv-FE_round.html"><span class="kw1467">FE_TONEAREST</span></a><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">"rounding to nearest: <span class="es1">\n</span>"</span>
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<span class="sy1"><<</span> <span class="st0">"nearbyint(+2.3) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="nu16">2.3</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nearbyint(+2.5) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="nu16">2.5</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nearbyint(+3.5) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="nu16">3.5</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"nearbyint(-2.3) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="sy2">-</span><span class="nu16">2.3</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nearbyint(-2.5) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="sy2">-</span><span class="nu16">2.5</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nearbyint(-3.5) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="sy2">-</span><span class="nu16">3.5</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-numeric-fenv-feround.html"><span class="kw1455">std::<span class="me2">fesetround</span></span></a><span class="br0">(</span><a href="cpp-numeric-fenv-FE_round.html"><span class="kw1466">FE_DOWNWARD</span></a><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">"rounding down:<span class="es1">\n</span>"</span>
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<span class="sy1"><<</span> <span class="st0">"nearbyint(+2.3) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="nu16">2.3</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nearbyint(+2.5) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="nu16">2.5</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nearbyint(+3.5) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="nu16">3.5</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"nearbyint(-2.3) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="sy2">-</span><span class="nu16">2.3</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nearbyint(-2.5) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="sy2">-</span><span class="nu16">2.5</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" nearbyint(-3.5) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="sy2">-</span><span class="nu16">3.5</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-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"nearbyint(-0.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="sy2">-</span><span class="nu16">0.0</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"nearbyint(-Inf) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">nearbyint</span><span class="br0">(</span><span class="sy2">-</span><a href="cpp-numeric-math-INFINITY.html"><span class="kw1376">INFINITY</span></a><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></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 nearbyint(+2.5) = 2 nearbyint(+3.5) = 4
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nearbyint(-2.3) = -2 nearbyint(-2.5) = -2 nearbyint(-3.5) = -4
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rounding down:
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nearbyint(+2.3) = 2 nearbyint(+2.5) = 2 nearbyint(+3.5) = 3
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nearbyint(-2.3) = -3 nearbyint(-2.5) = -3 nearbyint(-3.5) = -4
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nearbyint(-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=".E5.8F.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-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-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>使用当前舍入模式的最接近整数<br />
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若结果有别则有异常<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="cpp-numeric-math-round.html"><span class="t-lines"><span>round</span><span>roundf</span><span>roundl</span><span>lround</span><span>lroundf</span><span>lroundl</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-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>最接近整数，中间情况下向远离零舍入<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-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-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>获取或设置舍入方向<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 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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