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<a name="Wisdom-String-Export_002fImport-from-Fortran"></a>
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Next: <a href="Wisdom-Generic-Export_002fImport-from-Fortran.html#Wisdom-Generic-Export_002fImport-from-Fortran" accesskey="n" rel="next">Wisdom Generic Export/Import from Fortran</a>, Previous: <a href="Wisdom-File-Export_002fImport-from-Fortran.html#Wisdom-File-Export_002fImport-from-Fortran" accesskey="p" rel="prev">Wisdom File Export/Import from Fortran</a>, Up: <a href="Accessing-the-wisdom-API-from-Fortran.html#Accessing-the-wisdom-API-from-Fortran" accesskey="u" rel="up">Accessing the wisdom API from Fortran</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Wisdom-String-Export_002fImport-from-Fortran-1"></a>
<h4 class="subsection">7.6.2 Wisdom String Export/Import from Fortran</h4>

<a name="index-fftw_005fexport_005fwisdom_005fto_005fstring-1"></a>
<p>Dealing with FFTW&rsquo;s C string export/import is a bit more painful.  In
particular, the <code>fftw_export_wisdom_to_string</code> function requires
you to deal with a dynamically allocated C string.  To get its length,
you must define an interface to the C <code>strlen</code> function, and to
deallocate it you must define an interface to C <code>free</code>:
</p>
<div class="example">
<pre class="example">  use, intrinsic :: iso_c_binding
  interface
    integer(C_INT) function strlen(s) bind(C, name='strlen')
      import
      type(C_PTR), value :: s
    end function strlen
    subroutine free(p) bind(C, name='free')
      import
      type(C_PTR), value :: p
    end subroutine free
  end interface
</pre></div>

<p>Given these definitions, you can then export wisdom to a Fortran
character array:
</p>
<div class="example">
<pre class="example">  character(C_CHAR), pointer :: s(:)
  integer(C_SIZE_T) :: slen
  type(C_PTR) :: p
  p = fftw_export_wisdom_to_string()
  if (.not. c_associated(p)) stop 'error exporting wisdom'
  slen = strlen(p)
  call c_f_pointer(p, s, [slen+1])
  ...
  call free(p)
</pre></div>
<a name="index-c_005fassociated"></a>
<a name="index-c_005ff_005fpointer-3"></a>

<p>Note that <code>slen</code> is the length of the C string, but the length of
the array is <code>slen+1</code> because it includes the terminating null
character.  (You can omit the &lsquo;<samp>+1</samp>&rsquo; if you don&rsquo;t want Fortran to
know about the null character.) The standard <code>c_associated</code> function
checks whether <code>p</code> is a null pointer, which is returned by
<code>fftw_export_wisdom_to_string</code> if there was an error.
</p>
<a name="index-fftw_005fimport_005fwisdom_005ffrom_005fstring-1"></a>
<p>To import wisdom from a string, use
<code>fftw_import_wisdom_from_string</code> as usual; note that the argument
of this function must be a <code>character(C_CHAR)</code> that is terminated
by the <code>C_NULL_CHAR</code> character, like the <code>s</code> array above.
</p>


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author	Chris Cannam <cannam@all-day-breakfast.com>
date	Mon, 02 Mar 2020 14:03:47 +0000
parents	7867fa7e1b6b
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