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Current fftw source
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 18 Oct 2016 13:40:26 +0100
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cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
cannam@127 5
cannam@127 6 Copyright (C) 2003 Matteo Frigo.
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cannam@127 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: Wisdom String Export/Import from Fortran</title>
cannam@127 26
cannam@127 27 <meta name="description" content="FFTW 3.3.5: Wisdom String Export/Import from Fortran">
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cannam@127 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">
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cannam@127 72 <a name="Wisdom-String-Export_002fImport-from-Fortran"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 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>
cannam@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="Wisdom-String-Export_002fImport-from-Fortran-1"></a>
cannam@127 79 <h4 class="subsection">7.6.2 Wisdom String Export/Import from Fortran</h4>
cannam@127 80
cannam@127 81 <a name="index-fftw_005fexport_005fwisdom_005fto_005fstring-1"></a>
cannam@127 82 <p>Dealing with FFTW&rsquo;s C string export/import is a bit more painful. In
cannam@127 83 particular, the <code>fftw_export_wisdom_to_string</code> function requires
cannam@127 84 you to deal with a dynamically allocated C string. To get its length,
cannam@127 85 you must define an interface to the C <code>strlen</code> function, and to
cannam@127 86 deallocate it you must define an interface to C <code>free</code>:
cannam@127 87 </p>
cannam@127 88 <div class="example">
cannam@127 89 <pre class="example"> use, intrinsic :: iso_c_binding
cannam@127 90 interface
cannam@127 91 integer(C_INT) function strlen(s) bind(C, name='strlen')
cannam@127 92 import
cannam@127 93 type(C_PTR), value :: s
cannam@127 94 end function strlen
cannam@127 95 subroutine free(p) bind(C, name='free')
cannam@127 96 import
cannam@127 97 type(C_PTR), value :: p
cannam@127 98 end subroutine free
cannam@127 99 end interface
cannam@127 100 </pre></div>
cannam@127 101
cannam@127 102 <p>Given these definitions, you can then export wisdom to a Fortran
cannam@127 103 character array:
cannam@127 104 </p>
cannam@127 105 <div class="example">
cannam@127 106 <pre class="example"> character(C_CHAR), pointer :: s(:)
cannam@127 107 integer(C_SIZE_T) :: slen
cannam@127 108 type(C_PTR) :: p
cannam@127 109 p = fftw_export_wisdom_to_string()
cannam@127 110 if (.not. c_associated(p)) stop 'error exporting wisdom'
cannam@127 111 slen = strlen(p)
cannam@127 112 call c_f_pointer(p, s, [slen+1])
cannam@127 113 ...
cannam@127 114 call free(p)
cannam@127 115 </pre></div>
cannam@127 116 <a name="index-c_005fassociated"></a>
cannam@127 117 <a name="index-c_005ff_005fpointer-3"></a>
cannam@127 118
cannam@127 119 <p>Note that <code>slen</code> is the length of the C string, but the length of
cannam@127 120 the array is <code>slen+1</code> because it includes the terminating null
cannam@127 121 character. (You can omit the &lsquo;<samp>+1</samp>&rsquo; if you don&rsquo;t want Fortran to
cannam@127 122 know about the null character.) The standard <code>c_associated</code> function
cannam@127 123 checks whether <code>p</code> is a null pointer, which is returned by
cannam@127 124 <code>fftw_export_wisdom_to_string</code> if there was an error.
cannam@127 125 </p>
cannam@127 126 <a name="index-fftw_005fimport_005fwisdom_005ffrom_005fstring-1"></a>
cannam@127 127 <p>To import wisdom from a string, use
cannam@127 128 <code>fftw_import_wisdom_from_string</code> as usual; note that the argument
cannam@127 129 of this function must be a <code>character(C_CHAR)</code> that is terminated
cannam@127 130 by the <code>C_NULL_CHAR</code> character, like the <code>s</code> array above.
cannam@127 131 </p>
cannam@127 132
cannam@127 133
cannam@127 134
cannam@127 135 </body>
cannam@127 136 </html>