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<h3 class="section">8.5 Wisdom of Fortran?</h3>
<p>In this section, we discuss how one can import/export FFTW wisdom
(saved plans) to/from a Fortran program; we assume that the reader is
already familiar with wisdom, as described in <a href="Words-of-Wisdom_002dSaving-Plans.html#Words-of-Wisdom_002dSaving-Plans">Words of Wisdom-Saving Plans</a>.
<p><a name="index-portability-598"></a>The basic problem is that is difficult to (portably) pass files and
strings between Fortran and C, so we cannot provide a direct Fortran
equivalent to the <code>fftw_export_wisdom_to_file</code>, etcetera,
functions. Fortran interfaces <em>are</em> provided for the functions
that do not take file/string arguments, however:
<code>dfftw_import_system_wisdom</code>, <code>dfftw_import_wisdom</code>,
<code>dfftw_export_wisdom</code>, and <code>dfftw_forget_wisdom</code>.
<a name="index-dfftw_005fimport_005fsystem_005fwisdom-599"></a><a name="index-dfftw_005fimport_005fwisdom-600"></a><a name="index-dfftw_005fexport_005fwisdom-601"></a><a name="index-dfftw_005fforget_005fwisdom-602"></a>
<p>So, for example, to import the system-wide wisdom, you would do:
<pre class="example"> integer isuccess
call dfftw_import_system_wisdom(isuccess)
</pre>
<p>As usual, the C return value is turned into a first parameter;
<code>isuccess</code> is non-zero on success and zero on failure (e.g. if
there is no system wisdom installed).
<p>If you want to import/export wisdom from/to an arbitrary file or
elsewhere, you can employ the generic <code>dfftw_import_wisdom</code> and
<code>dfftw_export_wisdom</code> functions, for which you must supply a
subroutine to read/write one character at a time. The FFTW package
contains an example file <code>doc/f77_wisdom.f</code> demonstrating how to
implement <code>import_wisdom_from_file</code> and
<code>export_wisdom_to_file</code> subroutines in this way. (These routines
cannot be compiled into the FFTW library itself, lest all FFTW-using
programs be required to link with the Fortran I/O library.)
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