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Current fftw source
author Chris Cannam
date Tue, 18 Oct 2016 13:40:26 +0100
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Chris@42 3 <!-- This manual is for FFTW
Chris@42 4 (version 3.3.5, 30 July 2016).
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Chris@42 6 Copyright (C) 2003 Matteo Frigo.
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Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: Wisdom String Export/Import from Fortran</title>
Chris@42 26
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Chris@42 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@42 36 <link href="Accessing-the-wisdom-API-from-Fortran.html#Accessing-the-wisdom-API-from-Fortran" rel="up" title="Accessing the wisdom API from Fortran">
Chris@42 37 <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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Chris@42 72 <a name="Wisdom-String-Export_002fImport-from-Fortran"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 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>
Chris@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="Wisdom-String-Export_002fImport-from-Fortran-1"></a>
Chris@42 79 <h4 class="subsection">7.6.2 Wisdom String Export/Import from Fortran</h4>
Chris@42 80
Chris@42 81 <a name="index-fftw_005fexport_005fwisdom_005fto_005fstring-1"></a>
Chris@42 82 <p>Dealing with FFTW&rsquo;s C string export/import is a bit more painful. In
Chris@42 83 particular, the <code>fftw_export_wisdom_to_string</code> function requires
Chris@42 84 you to deal with a dynamically allocated C string. To get its length,
Chris@42 85 you must define an interface to the C <code>strlen</code> function, and to
Chris@42 86 deallocate it you must define an interface to C <code>free</code>:
Chris@42 87 </p>
Chris@42 88 <div class="example">
Chris@42 89 <pre class="example"> use, intrinsic :: iso_c_binding
Chris@42 90 interface
Chris@42 91 integer(C_INT) function strlen(s) bind(C, name='strlen')
Chris@42 92 import
Chris@42 93 type(C_PTR), value :: s
Chris@42 94 end function strlen
Chris@42 95 subroutine free(p) bind(C, name='free')
Chris@42 96 import
Chris@42 97 type(C_PTR), value :: p
Chris@42 98 end subroutine free
Chris@42 99 end interface
Chris@42 100 </pre></div>
Chris@42 101
Chris@42 102 <p>Given these definitions, you can then export wisdom to a Fortran
Chris@42 103 character array:
Chris@42 104 </p>
Chris@42 105 <div class="example">
Chris@42 106 <pre class="example"> character(C_CHAR), pointer :: s(:)
Chris@42 107 integer(C_SIZE_T) :: slen
Chris@42 108 type(C_PTR) :: p
Chris@42 109 p = fftw_export_wisdom_to_string()
Chris@42 110 if (.not. c_associated(p)) stop 'error exporting wisdom'
Chris@42 111 slen = strlen(p)
Chris@42 112 call c_f_pointer(p, s, [slen+1])
Chris@42 113 ...
Chris@42 114 call free(p)
Chris@42 115 </pre></div>
Chris@42 116 <a name="index-c_005fassociated"></a>
Chris@42 117 <a name="index-c_005ff_005fpointer-3"></a>
Chris@42 118
Chris@42 119 <p>Note that <code>slen</code> is the length of the C string, but the length of
Chris@42 120 the array is <code>slen+1</code> because it includes the terminating null
Chris@42 121 character. (You can omit the &lsquo;<samp>+1</samp>&rsquo; if you don&rsquo;t want Fortran to
Chris@42 122 know about the null character.) The standard <code>c_associated</code> function
Chris@42 123 checks whether <code>p</code> is a null pointer, which is returned by
Chris@42 124 <code>fftw_export_wisdom_to_string</code> if there was an error.
Chris@42 125 </p>
Chris@42 126 <a name="index-fftw_005fimport_005fwisdom_005ffrom_005fstring-1"></a>
Chris@42 127 <p>To import wisdom from a string, use
Chris@42 128 <code>fftw_import_wisdom_from_string</code> as usual; note that the argument
Chris@42 129 of this function must be a <code>character(C_CHAR)</code> that is terminated
Chris@42 130 by the <code>C_NULL_CHAR</code> character, like the <code>s</code> array above.
Chris@42 131 </p>
Chris@42 132
Chris@42 133
Chris@42 134
Chris@42 135 </body>
Chris@42 136 </html>