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<!-- This manual is for FFTW
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(version 3.3.10, 10 December 2020).
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Copyright (C) 2003 Matteo Frigo.
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Copyright (C) 2003 Massachusetts Institute of Technology.
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Permission is granted to make and distribute verbatim copies of this
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manual provided the copyright notice and this permission notice are
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preserved on all copies.
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided that the
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entire resulting derived work is distributed under the terms of a
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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<title>Wisdom Generic Export/Import from Fortran (FFTW 3.3.10)</title>
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Accessing-the-wisdom-API-from-Fortran.html" rel="up" title="Accessing the wisdom API from Fortran">
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</head>
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<span id="Wisdom-Generic-Export_002fImport-from-Fortran"></span><div class="header">
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<p>
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Previous: <a href="Wisdom-String-Export_002fImport-from-Fortran.html" accesskey="p" rel="prev">Wisdom String Export/Import from Fortran</a>, Up: <a href="Accessing-the-wisdom-API-from-Fortran.html" accesskey="u" rel="up">Accessing the wisdom API from Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<span id="Wisdom-Generic-Export_002fImport-from-Fortran-1"></span><h4 class="subsection">7.6.3 Wisdom Generic Export/Import from Fortran</h4>
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<p>The most generic wisdom export/import functions allow you to provide
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an arbitrary callback function to read/write one character at a time
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in any way you want. However, your callback function must be written
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in a special way, using the <code>bind(C)</code> attribute to be passed to a
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C interface.
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</p>
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<span id="index-fftw_005fexport_005fwisdom-1"></span>
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<p>In particular, to call the generic wisdom export function
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<code>fftw_export_wisdom</code>, you would write a callback subroutine of the form:
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</p>
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<div class="example">
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<pre class="example"> subroutine my_write_char(c, p) bind(C)
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use, intrinsic :: iso_c_binding
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character(C_CHAR), value :: c
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type(C_PTR), value :: p
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<em>...write c...</em>
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end subroutine my_write_char
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</pre></div>
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<p>Given such a subroutine (along with the corresponding interface definition), you could then export wisdom using:
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</p>
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<span id="index-c_005ffunloc"></span>
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<div class="example">
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<pre class="example"> call fftw_export_wisdom(c_funloc(my_write_char), p)
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</pre></div>
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<span id="index-c_005floc"></span>
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<span id="index-c_005ff_005fpointer-4"></span>
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<p>The standard <code>c_funloc</code> intrinsic converts a Fortran
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<code>bind(C)</code> subroutine into a C function pointer. The parameter
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<code>p</code> is a <code>type(C_PTR)</code> to any arbitrary data that you want
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to pass to <code>my_write_char</code> (or <code>C_NULL_PTR</code> if none). (Note
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that you can get a C pointer to Fortran data using the intrinsic
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<code>c_loc</code>, and convert it back to a Fortran pointer in
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<code>my_write_char</code> using <code>c_f_pointer</code>.)
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</p>
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<p>Similarly, to use the generic <code>fftw_import_wisdom</code>, you would
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define a callback function of the form:
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</p>
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<span id="index-fftw_005fimport_005fwisdom-1"></span>
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<div class="example">
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<pre class="example"> integer(C_INT) function my_read_char(p) bind(C)
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use, intrinsic :: iso_c_binding
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type(C_PTR), value :: p
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character :: c
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<em>...read a character c...</em>
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my_read_char = ichar(c, C_INT)
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end function my_read_char
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....
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integer(C_INT) :: ret
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ret = fftw_import_wisdom(c_funloc(my_read_char), p)
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if (ret .eq. 0) stop 'error importing wisdom'
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</pre></div>
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<p>Your function can return <code>-1</code> if the end of the input is reached.
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Again, <code>p</code> is an arbitrary <code>type(C_PTR</code> that is passed
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through to your function. <code>fftw_import_wisdom</code> returns <code>0</code>
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if an error occurred and nonzero otherwise.
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</p>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="Wisdom-String-Export_002fImport-from-Fortran.html" accesskey="p" rel="prev">Wisdom String Export/Import from Fortran</a>, Up: <a href="Accessing-the-wisdom-API-from-Fortran.html" accesskey="u" rel="up">Accessing the wisdom API from Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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