202 lines
11 KiB
HTML
202 lines
11 KiB
HTML
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<title>std::abs(int), std::labs, std::llabs, std::imaxabs</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_math_abs 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>abs<span style="font-size:0.7em; line-height:130%">(int)</span>, <span style="font-size:0.7em; line-height:130%">std::</span>labs, <span style="font-size:0.7em; line-height:130%">std::</span>llabs, <span style="font-size:0.7em; line-height:130%">std::</span>imaxabs</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 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><a href="cpp-header-cstdlib.html"><cstdlib></a></code></div>
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<td></td>
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<td></td>
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<tr class="t-dsc-header">
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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">int</span> abs<span class="br0">(</span> <span class="kw4">int</span> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> abs<span class="br0">(</span> <span class="kw4">long</span> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> abs<span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">long</span> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div>定义于头文件 <code><a href="cpp-header-cstdlib.html"><cstdlib></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">long</span> labs<span class="br0">(</span> <span class="kw4">long</span> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> llabs<span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">long</span> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div>定义于头文件 <code><a href="cpp-header-cinttypes.html"><cinttypes></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-types-integer.html"><span class="kw118">std::<span class="me2">intmax_t</span></span></a> abs<span class="br0">(</span> <a href="cpp-types-integer.html"><span class="kw118">std::<span class="me2">intmax_t</span></span></a> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></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"><a href="cpp-types-integer.html"><span class="kw118">std::<span class="me2">intmax_t</span></span></a> imaxabs<span class="br0">(</span> <a href="cpp-types-integer.html"><span class="kw118">std::<span class="me2">intmax_t</span></span></a> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>计算整数的绝对值。若结果不能以返回类型表示则行为未定义。</p>
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<p>若以不能由<a href="cpp-language-implicit_conversion.html#.E6.95.B4.E5.9E.8B.E6.8F.90.E5.8D.87">整型提升</a>转换成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span> 的无符号整型参数调用 <code>std::abs</code> ，则程序为谬构。</p>
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<table class="t-rev-begin">
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<p><code><cinttypes></code> 中提供 <code>std::abs</code> 对 <code>std::intmax_t</code> 的重载，当且仅当 <code>std::intmax_t</code> 为扩展整数类型。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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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>n</td>
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<td>-</td>
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<td>整数值</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>若可表示，则为 <code>n</code> 的绝对值（即 <code>|n|</code> ）。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>补码系统中，最负值的绝对值在范围外，例如对于 32 位补码类型 int ， INT_MIN 是 -2147483648 ，但本应有的结果 2147483648 大于 INT_MAX ，即 2147483647 。</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 <cstdlib></span>
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<span class="co2">#include <climits></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="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"abs(+3) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">abs</span><span class="br0">(</span><span class="nu0">3</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">"abs(-3) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">abs</span><span class="br0">(</span><span class="sy2">-</span><span class="nu0">3</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">// std::cout << abs(INT_MIN); // 补码系统上是未定义行为</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">abs(+3) = 3
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abs(-3) = 3</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2192">LWG 2192</a></td>
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<td>C++98</td>
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<td><code>std::abs</code> 的重载不一致地声明于二个头文件</td>
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<td>在两个头文件中都声明这些重载</td>
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</tr>
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</table>
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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>
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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-complex-abs.html"><span class="t-lines"><span>abs<span class="t-dsc-small">(std::complex)</span></span></span></a></div>
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</div>
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</td>
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<td>返回复数的模<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-valarray-abs.html"><span class="t-lines"><span>abs<span class="t-dsc-small">(std::valarray)</span></span></span></a></div>
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</div>
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</td>
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<td>应用函数 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">abs</span></span></span> 到 valarray 的每个元素<br />
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<span class="t-mark">(函数模板)</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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