devdocs/c/numeric%2Fcomplex%2Fimaginary_i.html


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    <h1 id="firstHeading" class="firstHeading">_Imaginary_I</h1>            <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code>&lt;complex.h&gt;</code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">#define _Imaginary_I /* unspecified */</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr>  </table> <p>The <code>_Imaginary_I</code> macro expands to a value of type <code>const float _Imaginary</code> with the value of the imaginary unit.</p>
<p>As with any pure imaginary number support in C, this macro is only defined if the imaginary numbers are supported.</p>
<table class="t-rev-begin"> <tr class="t-rev t-since-c99 t-until-c11">
<td> <p>A compiler that defines <code>__STDC_IEC_559_COMPLEX__</code> is not required to support imaginary numbers. POSIX recommends checking if the macro <code>_Imaginary_I</code> is defined to identify imaginary number support.</p>
</td> <td>
<span class="t-mark-rev t-since-c99">(since C99)</span><br><span class="t-mark-rev t-until-c11">(until C11)</span>
</td>
</tr> <tr class="t-rev t-since-c11">
<td> <p>Imaginary numbers are supported if <code>__STDC_IEC_559_COMPLEX__</code> is defined.</p>
</td> <td><span class="t-mark-rev t-since-c11">(since C11)</span></td>
</tr> </table>  <h3 id="Notes"> Notes</h3> <p>This macro allows for the precise way to assemble a complex number from its real and imaginary components, e.g. with <code><span class="br0">(</span><span class="kw4">double</span> <a href="http://en.cppreference.com/w/c/numeric/complex/complex"><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></code>. This pattern was standardized in C11 as the macro <code><a href="http://en.cppreference.com/w/c/numeric/complex/CMPLX"><span class="kw747">CMPLX</span></a></code>. Note that if <code><a href="http://en.cppreference.com/w/c/numeric/complex/Complex_I"><span class="kw744">_Complex_I</span></a></code> is used instead, this expression is allowed to convert negative zero to positive zero in the imaginary position.</p>
<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include &lt;stdio.h&gt;
#include &lt;complex.h&gt;
#include &lt;math.h&gt;
 
int main(void)
{
    double complex z1 = 0.0 + INFINITY * _Imaginary_I;
    printf("z1 = %.1f%+.1fi\n", creal(z1), cimag(z1));
 
    double complex z2 = 0.0 + INFINITY * _Complex_I;
    printf("z2 = %.1f%+.1fi\n", creal(z2), cimag(z2));
}</pre></div> <p>Output:</p>
<div class="text source-text"><pre data-language="c">z1 = 0.0+Infi 
z2 = NaN+Infi</pre></div> </div> <h3 id="References"> References</h3>  <ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul>
<li> 7.3.1/5 _Imaginary_I (p: 188) </li>
<li> G.6/1 _Imaginary_I (p: 537) </li>
</ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul>
<li> 7.3.1/3 _Imaginary_I (p: 170) </li>
<li> G.6/1 _Imaginary_I (p: 472) </li>
</ul>
</ul>        <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="complex_i" title="c/numeric/complex/Complex I"> <span class="t-lines"><span>_Complex_I</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> the complex unit constant i <br> <span class="t-mark">(macro constant)</span>  </td>
</tr> <tr class="t-dsc"> <td> <div><a href="i" title="c/numeric/complex/I"> <span class="t-lines"><span>I</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> the complex or imaginary unit constant i <br> <span class="t-mark">(macro constant)</span>  </td>
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