X</code> type code.
</p>
<p>Because some Fortran compilers do not support
<code>C_LONG_DOUBLE_COMPLEX</code>, the <code>fftwl_</code> declarations are
segregated into a separate interface file <code>fftw3l.f03</code>, which you
should include <em>in addition</em> to <code>fftw3.f03</code> (which declares
precision-independent &lsquo;<samp>FFTW_</samp>&rsquo; constants):
</p>
<span id="index-iso_005fc_005fbinding-2"></span>
<div class="example">
<pre class="example">  use, intrinsic :: iso_c_binding 
  inclu