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author Chris Cannam <cannam@all-day-breakfast.com>
date Wed, 20 Mar 2013 15:35:50 +0000
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+<html lang="en">
+<head>
+<title>Wisdom Generic Export/Import from Fortran - FFTW 3.3.3</title>
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+<link rel="up" href="Accessing-the-wisdom-API-from-Fortran.html#Accessing-the-wisdom-API-from-Fortran" title="Accessing the wisdom API from Fortran">
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+Copyright (C) 2003 Matteo Frigo.
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+<div class="node">
+<a name="Wisdom-Generic-Export%2fImport-from-Fortran"></a>
+<a name="Wisdom-Generic-Export_002fImport-from-Fortran"></a>
+<p>
+Previous:&nbsp;<a rel="previous" accesskey="p" href="Wisdom-String-Export_002fImport-from-Fortran.html#Wisdom-String-Export_002fImport-from-Fortran">Wisdom String Export/Import from Fortran</a>,
+Up:&nbsp;<a rel="up" accesskey="u" href="Accessing-the-wisdom-API-from-Fortran.html#Accessing-the-wisdom-API-from-Fortran">Accessing the wisdom API from Fortran</a>
+<hr>
+</div>
+
+<h4 class="subsection">7.6.3 Wisdom Generic Export/Import from Fortran</h4>
+
+<p>The most generic wisdom export/import functions allow you to provide
+an arbitrary callback function to read/write one character at a time
+in any way you want.  However, your callback function must be written
+in a special way, using the <code>bind(C)</code> attribute to be passed to a
+C interface.
+
+   <p><a name="index-fftw_005fexport_005fwisdom-572"></a>In particular, to call the generic wisdom export function
+<code>fftw_export_wisdom</code>, you would write a callback subroutine of the form:
+
+<pre class="example">       subroutine my_write_char(c, p) bind(C)
+         use, intrinsic :: iso_c_binding
+         character(C_CHAR), value :: c
+         type(C_PTR), value :: p
+         <em>...write c...</em>
+       end subroutine my_write_char
+</pre>
+   <p>Given such a subroutine (along with the corresponding interface definition), you could then export wisdom using:
+
+   <p><a name="index-c_005ffunloc-573"></a>
+<pre class="example">       call fftw_export_wisdom(c_funloc(my_write_char), p)
+</pre>
+   <p><a name="index-c_005floc-574"></a><a name="index-c_005ff_005fpointer-575"></a>The standard <code>c_funloc</code> intrinsic converts a Fortran
+<code>bind(C)</code> subroutine into a C function pointer.  The parameter
+<code>p</code> is a <code>type(C_PTR)</code> to any arbitrary data that you want
+to pass to <code>my_write_char</code> (or <code>C_NULL_PTR</code> if none).  (Note
+that you can get a C pointer to Fortran data using the intrinsic
+<code>c_loc</code>, and convert it back to a Fortran pointer in
+<code>my_write_char</code> using <code>c_f_pointer</code>.)
+
+   <p>Similarly, to use the generic <code>fftw_import_wisdom</code>, you would
+define a callback function of the form:
+
+   <p><a name="index-fftw_005fimport_005fwisdom-576"></a>
+<pre class="example">       integer(C_INT) function my_read_char(p) bind(C)
+         use, intrinsic :: iso_c_binding
+         type(C_PTR), value :: p
+         character :: c
+         <em>...read a character c...</em>
+         my_read_char = ichar(c, C_INT)
+       end function my_read_char
+     
+       ....
+     
+       integer(C_INT) :: ret
+       ret = fftw_import_wisdom(c_funloc(my_read_char), p)
+       if (ret .eq. 0) stop 'error importing wisdom'
+</pre>
+   <p>Your function can return <code>-1</code> if the end of the input is reached. 
+Again, <code>p</code> is an arbitrary <code>type(C_PTR</code> that is passed
+through to your function.  <code>fftw_import_wisdom</code> returns <code>0</code>
+if an error occurred and nonzero otherwise.
+
+<!--  -->
+   </body></html>
+