139 lines
11 KiB
HTML
139 lines
11 KiB
HTML
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<title>std::copysign, std::copysignf, std::copysignl</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_math_copysign 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>copysign, <span style="font-size:0.7em; line-height:130%">std::</span>copysignf, <span style="font-size:0.7em; line-height:130%">std::</span>copysignl</h1>
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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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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span> copysign <span class="br0">(</span> <span class="kw4">float</span> x, <span class="kw4">float</span> y <span class="br0">)</span><span class="sy4">;</span><br />
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<span class="kw4">float</span> copysignf<span class="br0">(</span> <span class="kw4">float</span> x, <span class="kw4">float</span> y <span class="br0">)</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-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span> copysign <span class="br0">(</span> <span class="kw4">double</span> x, <span class="kw4">double</span> y <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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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span> copysign <span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">double</span> x, <span class="kw4">long</span> <span class="kw4">double</span> y <span class="br0">)</span><span class="sy4">;</span><br />
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<span class="kw4">long</span> <span class="kw4">double</span> copysignl<span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">double</span> x, <span class="kw4">long</span> <span class="kw4">double</span> y <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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<div><span class="mw-geshi cpp source-cpp">Promoted copysign <span class="br0">(</span> Arithmetic1 x, Arithmetic2 y <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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<div class="t-li1"><span class="t-li">1-3)</span> 以 <code>x</code> 的模和 <code>y</code> 的符号组成浮点值。</div>
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<div class="t-li1"><span class="t-li">4)</span> 重载集或函数模板，用于所有 <span class="t-v">(1-3)</span> 所不覆盖的算术类型参数组合。若任何参数拥有<a href="cpp-types-is_integral.html">整数类型</a>，则将它转型到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 。若任何参数为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> ，则返回类型 <code>Promoted</code> 亦为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> ， 否则返回类型始终是 <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>x, y</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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<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>若无错误发生，则返回以 <code>x</code> 的模与 <code>y</code> 的符号组成的浮点值。</p>
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<p>若 <code>x</code> 为 NaN ，则返回带 <code>y</code> 符号的 NaN 。</p>
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<p>若 <code>y</code> 为 -0 ，则仅若实现支持与算术运算一致的有符号零，结果才为负。</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>返回值是准确的（决不引发 <span class="t-lc"><a href="cpp-numeric-fenv-FE_exceptions.html">FE_INEXACT</a></span> ）且独立于当前<a href="cpp-numeric-fenv-FE_round.html">舍入模式</a>。</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::copysign</code> 是操作 NaN 值符号的唯一可移植方式（ <span class="t-lc">signbit</span> 亦可用于检验 NaN 的符号）</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="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="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"copysign(1.0,+2.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">copysign</span><span class="br0">(</span><span class="nu16">1.0</span>,<span class="sy2">+</span><span class="nu16">2.0</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">"copysign(1.0,-2.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">copysign</span><span class="br0">(</span><span class="nu16">1.0</span>,<span class="sy2">-</span><span class="nu16">2.0</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">"copysign(inf,-2.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">copysign</span><span class="br0">(</span><a href="cpp-numeric-math-INFINITY.html"><span class="kw1376">INFINITY</span></a>,<span class="sy2">-</span><span class="nu16">2.0</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">"copysign(NaN,-2.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">copysign</span><span class="br0">(</span><a href="cpp-numeric-math-NAN.html"><span class="kw1377">NAN</span></a>,<span class="sy2">-</span><span class="nu16">2.0</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></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">copysign(1.0,+2.0) = 1
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copysign(1.0,-2.0) = -1
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copysign(inf,-2.0) = -inf
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copysign(NaN,-2.0) = -nan</pre></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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-math-fabs.html"><span class="t-lines"><span>abs<span class="t-dsc-small">(float)</span></span><span>fabs</span><span>fabsf</span><span>fabsl</span></span></a></div>
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<div><span class="t-lines"><span></span><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>浮点值的绝对值（ <span class="mjax" style="display:none">\(\small{|x|}\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">|x|</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-numeric-math-signbit.html"><span class="t-lines"><span>signbit</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></div>
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</div>
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</td>
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<td>检查给定数是否为负<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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