127 lines
6.5 KiB
HTML
127 lines
6.5 KiB
HTML
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<title>_Complex_I</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_numeric_complex_Complex_I skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading">_Complex_I</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-complex.html">complex</a></span></div>
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<div>定义于头文件 <code><complex.h></code></div>
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<div><span class="mw-geshi c source-c"><span class="co2">#define _Complex_I /* unspecified */</span></span></div>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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<p><code>_Complex_I</code> 宏展开成类型 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">const</span> <span class="kw4">float</span> _Complex</span></span> 的值,其值为虚数单位。</p>
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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>可在 <span class="t-lc">I</span> 非法时,譬如程序已取消定义它时使用此宏。</p>
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<p>不同于 <span class="t-lc"><a href="c-numeric-complex-Imaginary_I.html">_Imaginary_I</a></span> 及 <span class="t-lc"><a href="c-numeric-complex-CMPLX.html">CMPLX</a></span> 不同,用此宏构造复数会失去虚数组分的零的符号位。</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 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 <complex.h></span>
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<span class="co2">#undef I</span>
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<span class="co2">#define J _Complex_I // 可用于重定义 I</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="co1">// 可用于构建复数</span>
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<span class="kw4">double</span> <a href="c-numeric-complex-complex.html"><span class="kw743">complex</span></a> z <span class="sy1">=</span> <span class="nu16">1.0</span> <span class="sy2">+</span> <span class="nu16">2.0</span> <span class="sy2">*</span> _Complex_I<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">"1.0 + 2.0 * _Complex_I = %.1f%+.1fi<span class="es1">\n</span>"</span>, <a href="c-numeric-complex-creal.html"><span class="kw753">creal</span></a><span class="br0">(</span>z<span class="br0">)</span>, <a href="c-numeric-complex-cimag.html"><span class="kw750">cimag</span></a><span class="br0">(</span>z<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 零的符号不会被保留</span>
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<span class="kw4">double</span> <a href="c-numeric-complex-complex.html"><span class="kw743">complex</span></a> z2 <span class="sy1">=</span> <span class="nu16">0.0</span> <span class="sy2">+</span> <span class="sy2">-</span><span class="nu16">0.0</span> <span class="sy2">*</span> _Complex_I<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">"0.0 + -0.0 * _Complex_I = %.1f%+.1fi<span class="es1">\n</span>"</span>, <a href="c-numeric-complex-creal.html"><span class="kw753">creal</span></a><span class="br0">(</span>z2<span class="br0">)</span>, <a href="c-numeric-complex-cimag.html"><span class="kw750">cimag</span></a><span class="br0">(</span>z2<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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<p>可能的输出:</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">1.0 + 2.0 * _Complex_I = 1.0+2.0i
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0.0 + -0.0 * _Complex_I = 0.0+0.0i</pre></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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<li>7.3.1/4 _Complex_I (p: 188)</li>
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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>7.3.1/2 _Complex_I (p: 170)</li>
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</ul>
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</dd>
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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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<div class="t-dsc-member-div">
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<div><a href="c-numeric-complex-Imaginary_I.html"><span class="t-lines"><span>_Imaginary_I</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></div>
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</td>
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<td>虚数单位常量 i<br />
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<span class="t-mark">(宏常量)</span></td>
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<div><a href="c-numeric-complex-I.html"><span class="t-lines"><span>I</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></div>
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</div>
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</td>
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<td>复数或虚数单位常量 i<br />
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<span class="t-mark">(宏常量)</span></td>
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</table>
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</div>
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