145 lines
7.3 KiB
HTML
145 lines
7.3 KiB
HTML
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<title>_Imaginary_I</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_numeric_complex_Imaginary_I skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading">_Imaginary_I</h1>
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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 _Imaginary_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>_Imaginary_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> _Imaginary</span></span> 的值，其值为虚数单位。</p>
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<p>同 C 中的纯虚数支持，仅若支持虚数才定义此宏。</p>
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<td>推荐编译器定义 <span class="t-c"><span class="mw-geshi c source-c">__STDC_IEC_559_COMPLEX__</span></span> ，但并不强制要求其支持虚数。 POSIX 推荐检查是否定义宏 <span class="t-c"><span class="mw-geshi c source-c">_Imaginary_I</span></span> 以鉴别是否支持虚数。</td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span><br />
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<span class="t-mark-rev t-until-c11">(C11 前)</span></td>
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<p>若定义 <span class="t-c"><span class="mw-geshi c source-c">__STDC_IEC_559_COMPLEX__</span></span> ，则支持虚数。</p>
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<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
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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>此宏允许从其实部和虚部精确地构成复数，例如用 <span class="t-c"><span class="mw-geshi c source-c"><span class="br0">(</span><span class="kw4">double</span> <a href="c-numeric-complex-complex.html"><span class="kw743">complex</span></a><span class="br0">)</span><span class="br0">(</span><span class="br0">(</span><span class="kw4">double</span><span class="br0">)</span>x <span class="sy2">+</span> _Imaginary_I <span class="sy2">*</span> <span class="br0">(</span><span class="kw4">double</span><span class="br0">)</span>y<span class="br0">)</span></span></span> 。此模式在 C11 中作为 <span class="t-c"><span class="mw-geshi c source-c"><a href="c-numeric-complex-CMPLX.html"><span class="kw747">CMPLX</span></a></span></span> 标准化。注意若使用了 <span class="t-c"><span class="mw-geshi c source-c"><a href="c-numeric-complex-Complex_I.html"><span class="kw744">_Complex_I</span></a></span></span> ，则允许此表达式在虚数位置将负零转变成正零。</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="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="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="kw4">double</span> <a href="c-numeric-complex-complex.html"><span class="kw743">complex</span></a> z <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> _Imaginary_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">"z = %.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="br0">}</span></pre></div>
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<p>输出：</p>
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<div class="text source-text">
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<pre class="de1">z = 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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<li>C11 标准（ISO/IEC 9899:2011）：</li>
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<li>7.3.1/5 _Imaginary_I (p: 188)</li>
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</dd>
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<li>G.6/1 _Imaginary_I (p: 537)</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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<li>C99 标准（ISO/IEC 9899:1999）：</li>
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<li>7.3.1/3 _Imaginary_I (p: 170)</li>
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<li>G.6/1 _Imaginary_I (p: 472)</li>
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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><a href="c-numeric-complex-Complex_I.html"><span class="t-lines"><span>_Complex_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>复数单位常量 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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<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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