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Add FFTW3
author Chris Cannam <cannam@all-day-breakfast.com>
date Wed, 20 Mar 2013 15:35:50 +0000
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3 <title>Wisdom String Export/Import from Fortran - FFTW 3.3.3</title>
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49 <a name="Wisdom-String-Export%2fImport-from-Fortran"></a>
50 <a name="Wisdom-String-Export_002fImport-from-Fortran"></a>
51 <p>
52 Next:&nbsp;<a rel="next" accesskey="n" href="Wisdom-Generic-Export_002fImport-from-Fortran.html#Wisdom-Generic-Export_002fImport-from-Fortran">Wisdom Generic Export/Import from Fortran</a>,
53 Previous:&nbsp;<a rel="previous" accesskey="p" href="Wisdom-File-Export_002fImport-from-Fortran.html#Wisdom-File-Export_002fImport-from-Fortran">Wisdom File Export/Import from Fortran</a>,
54 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>
55 <hr>
56 </div>
57
58 <h4 class="subsection">7.6.2 Wisdom String Export/Import from Fortran</h4>
59
60 <p><a name="index-fftw_005fexport_005fwisdom_005fto_005fstring-568"></a>Dealing with FFTW's C string export/import is a bit more painful. In
61 particular, the <code>fftw_export_wisdom_to_string</code> function requires
62 you to deal with a dynamically allocated C string. To get its length,
63 you must define an interface to the C <code>strlen</code> function, and to
64 deallocate it you must define an interface to C <code>free</code>:
65
66 <pre class="example"> use, intrinsic :: iso_c_binding
67 interface
68 integer(C_INT) function strlen(s) bind(C, name='strlen')
69 import
70 type(C_PTR), value :: s
71 end function strlen
72 subroutine free(p) bind(C, name='free')
73 import
74 type(C_PTR), value :: p
75 end subroutine free
76 end interface
77 </pre>
78 <p>Given these definitions, you can then export wisdom to a Fortran
79 character array:
80
81 <pre class="example"> character(C_CHAR), pointer :: s(:)
82 integer(C_SIZE_T) :: slen
83 type(C_PTR) :: p
84 p = fftw_export_wisdom_to_string()
85 if (.not. c_associated(p)) stop 'error exporting wisdom'
86 slen = strlen(p)
87 call c_f_pointer(p, s, [slen+1])
88 ...
89 call free(p)
90 </pre>
91 <p><a name="index-c_005fassociated-569"></a><a name="index-c_005ff_005fpointer-570"></a>
92 Note that <code>slen</code> is the length of the C string, but the length of
93 the array is <code>slen+1</code> because it includes the terminating null
94 character. (You can omit the &lsquo;<samp><span class="samp">+1</span></samp>&rsquo; if you don't want Fortran to
95 know about the null character.) The standard <code>c_associated</code> function
96 checks whether <code>p</code> is a null pointer, which is returned by
97 <code>fftw_export_wisdom_to_string</code> if there was an error.
98
99 <p><a name="index-fftw_005fimport_005fwisdom_005ffrom_005fstring-571"></a>To import wisdom from a string, use
100 <code>fftw_import_wisdom_from_string</code> as usual; note that the argument
101 of this function must be a <code>character(C_CHAR)</code> that is terminated
102 by the <code>C_NULL_CHAR</code> character, like the <code>s</code> array above.
103
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