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5.4 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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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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into another language, under the above conditions for modified versions,
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except that this permission notice may be stated in a translation
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approved by the Free Software Foundation. -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>Wisdom String Export/Import from Fortran (FFTW 3.3.10)</title>
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<meta name="description" content="Wisdom String Export/Import from Fortran (FFTW 3.3.10)">
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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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<link href="Wisdom-Generic-Export_002fImport-from-Fortran.html" rel="next" title="Wisdom Generic Export/Import from Fortran">
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</head>
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<body lang="en">
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<span id="Wisdom-String-Export_002fImport-from-Fortran"></span><div class="header">
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<p>
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Next: <a href="Wisdom-Generic-Export_002fImport-from-Fortran.html" accesskey="n" rel="next">Wisdom Generic Export/Import from Fortran</a>, Previous: <a href="Wisdom-File-Export_002fImport-from-Fortran.html" accesskey="p" rel="prev">Wisdom File 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-String-Export_002fImport-from-Fortran-1"></span><h4 class="subsection">7.6.2 Wisdom String Export/Import from Fortran</h4>
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<span id="index-fftw_005fexport_005fwisdom_005fto_005fstring-1"></span>
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<p>Dealing with FFTW’s C string export/import is a bit more painful. In
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particular, the <code>fftw_export_wisdom_to_string</code> function requires
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you to deal with a dynamically allocated C string. To get its length,
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you must define an interface to the C <code>strlen</code> function, and to
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deallocate it you must define an interface to C <code>free</code>:
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</p>
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<div class="example">
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<pre class="example"> use, intrinsic :: iso_c_binding
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interface
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integer(C_INT) function strlen(s) bind(C, name='strlen')
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import
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type(C_PTR), value :: s
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end function strlen
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subroutine free(p) bind(C, name='free')
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import
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type(C_PTR), value :: p
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end subroutine free
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end interface
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</pre></div>
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<p>Given these definitions, you can then export wisdom to a Fortran
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character array:
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</p>
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<div class="example">
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<pre class="example"> character(C_CHAR), pointer :: s(:)
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integer(C_SIZE_T) :: slen
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type(C_PTR) :: p
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p = fftw_export_wisdom_to_string()
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if (.not. c_associated(p)) stop 'error exporting wisdom'
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slen = strlen(p)
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call c_f_pointer(p, s, [slen+1])
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...
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call free(p)
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</pre></div>
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<span id="index-c_005fassociated"></span>
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<span id="index-c_005ff_005fpointer-3"></span>
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<p>Note that <code>slen</code> is the length of the C string, but the length of
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the array is <code>slen+1</code> because it includes the terminating null
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character. (You can omit the ‘<samp>+1</samp>’ if you don’t want Fortran to
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know about the null character.) The standard <code>c_associated</code> function
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checks whether <code>p</code> is a null pointer, which is returned by
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<code>fftw_export_wisdom_to_string</code> if there was an error.
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</p>
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<span id="index-fftw_005fimport_005fwisdom_005ffrom_005fstring-1"></span>
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<p>To import wisdom from a string, use
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<code>fftw_import_wisdom_from_string</code> as usual; note that the argument
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of this function must be a <code>character(C_CHAR)</code> that is terminated
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by the <code>C_NULL_CHAR</code> character, like the <code>s</code> array above.
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</p>
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</body>
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</html>
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