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Current fftw source
author Chris Cannam
date Tue, 18 Oct 2016 13:40:26 +0100
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+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<!-- This manual is for FFTW
+(version 3.3.5, 30 July 2016).
+
+Copyright (C) 2003 Matteo Frigo.
+
+Copyright (C) 2003 Massachusetts Institute of Technology.
+
+Permission is granted to make and distribute verbatim copies of this
+manual provided the copyright notice and this permission notice are
+preserved on all copies.
+
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the
+entire resulting derived work is distributed under the terms of a
+permission notice identical to this one.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation
+approved by the Free Software Foundation. -->
+<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
+<head>
+<title>FFTW 3.3.5: Wisdom String Export/Import from Fortran</title>
+
+<meta name="description" content="FFTW 3.3.5: Wisdom String Export/Import from Fortran">
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+<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
+<link href="Accessing-the-wisdom-API-from-Fortran.html#Accessing-the-wisdom-API-from-Fortran" rel="up" title="Accessing the wisdom API from Fortran">
+<link href="Wisdom-Generic-Export_002fImport-from-Fortran.html#Wisdom-Generic-Export_002fImport-from-Fortran" rel="next" title="Wisdom Generic Export/Import from Fortran">
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+<a name="Wisdom-String-Export_002fImport-from-Fortran"></a>
+<div class="header">
+<p>
+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>
+</div>
+<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>
+
+
+
+</body>
+</html>