151 lines
13 KiB
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151 lines
13 KiB
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<title>std::fdim, std::fdimf, std::fdiml</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>fdim, <span style="font-size:0.7em; line-height:130%">std::</span>fdimf, <span style="font-size:0.7em; line-height:130%">std::</span>fdiml</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> fdim <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> fdimf<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>
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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> fdim <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> fdim <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> fdiml<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 fdim <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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<tr class="t-dcl-sep">
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<td></td>
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<div class="t-li1"><span class="t-li">1-3)</span> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">x</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">y</span></span> 间的正差，即若 <span class="t-c"><span class="mw-geshi cpp source-cpp">x<span class="sy1">></span>y</span></span> 则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">x<span class="sy2">-</span>y</span></span> ，否则（若 <span class="t-c"><span class="mw-geshi cpp source-cpp">x≤y</span></span> ）返回 +0 。</div>
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<div class="t-li1"><span class="t-li">4)</span> 任何 1-3) 所不覆盖的<a href="cpp-types-is_arithmetic.html">算术类型</a>参数组合的重载集或函数模板。若任何参数拥有<a href="cpp-types-is_integral.html">整数类型</a>，则将它转型为 <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>x, y</td>
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<td>-</td>
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<td>浮点或<a href="cpp-types-is_integral.html">整数类型</a>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>若成功，则返回 x 与 y 间的正差。</p>
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<p>若出现上溢所致的值域错误，则返回 <code>+HUGE_VAL</code> 、 <code>+HUGE_VALF</code> 或 <code>+HUGE_VALL</code> 。</p>
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<p>若出现下溢所致的值域错误，则返回（舍入后的）正确结果。</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>报告 <span class="t-lc"><a href="cpp-numeric-math-math_errhandling.html">math_errhandling</a></span> 中指定的错误。</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>若任一参数为 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>等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-numeric-math-fmax.html"><span class="kw1315">std::<span class="me2">fmax</span></span></a><span class="br0">(</span>x<span class="sy2">-</span>y, <span class="nu0">0</span><span class="br0">)</span></span></span> ，除了 NaN 处理要求。</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 <cfenv></span>
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<span class="co2">#pragma STDC FENV_ACCESS ON</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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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"fdim(4, 1) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fdim</span><span class="br0">(</span><span class="nu0">4</span>, <span class="nu0">1</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" fdim(1, 4) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fdim</span><span class="br0">(</span><span class="nu0">1</span>, <span class="nu0">4</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">"fdim(4,-1) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fdim</span><span class="br0">(</span><span class="nu0">4</span>, <span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" fdim(1,-4) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fdim</span><span class="br0">(</span><span class="nu0">1</span>, <span class="sy2">-</span><span class="nu0">4</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="co1">// 错误处理</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="cpp-numeric-fenv-feclearexcept.html"><span class="kw1449">std::<span class="me2">feclearexcept</span></span></a><span class="br0">(</span><a href="cpp-numeric-fenv-FE_exceptions.html"><span class="kw1460">FE_ALL_EXCEPT</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">"fdim(1e308, -1e308) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fdim</span><span class="br0">(</span><span class="nu19">1e308</span>, <span class="sy2">-</span><span class="nu19">1e308</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="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="kw862">ERANGE</span></a><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">" errno == ERANGE: "</span> <span class="sy1"><<</span> <a href="cpp-string-byte-strerror.html"><span class="kw1161">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="kw1">if</span> <span class="br0">(</span><a href="cpp-numeric-fenv-fetestexcept.html"><span class="kw1450">std::<span class="me2">fetestexcept</span></span></a><span class="br0">(</span><a href="cpp-numeric-fenv-FE_exceptions.html"><span class="kw1464">FE_OVERFLOW</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">" FE_OVERFLOW raised<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">fdim(4, 1) = 3 fdim(1, 4) = 0
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fdim(4,-1) = 5 fdim(1,-4) = 5
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fdim(1e308, -1e308) = inf
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errno == ERANGE: Numerical result out of range
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FE_OVERFLOW raised</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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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-math-abs.html"><span class="t-lines"><span>abs<span class="t-dsc-small">(int)</span></span><span>labs</span><span>llabs</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></div>
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</div>
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<td>计算整数值的绝对值（ <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 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-fmax.html"><span class="t-lines"><span>fmax</span><span>fmaxf</span><span>fmaxl</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></div>
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</div>
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</td>
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<td>两个浮点值的较大者<br />
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<span class="t-mark">(函数)</span></td>
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</div>
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<div class="visualClear"></div>
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