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<h2 class="chapter">8 Calling FFTW from Legacy Fortran</h2>
<p><a name="index-Fortran-interface-577"></a>
This chapter describes the interface to FFTW callable by Fortran code
in older compilers not supporting the Fortran 2003 C interoperability
features (see <a href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran">Calling FFTW from Modern Fortran</a>). This interface
has the major disadvantage that it is not type-checked, so if you
mistake the argument types or ordering then your program will not have
any compiler errors, and will likely crash at runtime. So, greater
care is needed. Also, technically interfacing older Fortran versions
to C is nonstandard, but in practice we have found that the techniques
used in this chapter have worked with all known Fortran compilers for
many years.
<p>The legacy Fortran interface differs from the C interface only in the
prefix (‘<samp><span class="samp">dfftw_</span></samp>’ instead of ‘<samp><span class="samp">fftw_</span></samp>’ in double precision) and
a few other minor details. This Fortran interface is included in the
FFTW libraries by default, unless a Fortran compiler isn't found on
your system or <code>--disable-fortran</code> is included in the
<code>configure</code> flags. We assume here that the reader is already
familiar with the usage of FFTW in C, as described elsewhere in this
manual.
<p>The MPI parallel interface to FFTW is <em>not</em> currently available
to legacy Fortran.
<ul class="menu">
<li><a accesskey="1" href="Fortran_002dinterface-routines.html#Fortran_002dinterface-routines">Fortran-interface routines</a>
<li><a accesskey="2" href="FFTW-Constants-in-Fortran.html#FFTW-Constants-in-Fortran">FFTW Constants in Fortran</a>
<li><a accesskey="3" href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran">FFTW Execution in Fortran</a>
<li><a accesskey="4" href="Fortran-Examples.html#Fortran-Examples">Fortran Examples</a>
<li><a accesskey="5" href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f">Wisdom of Fortran?</a>
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