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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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72 <a name="Wisdom-Generic-Export_002fImport-from-Fortran"></a>
73 <div class="header">
74 <p>
75 Previous: <a href="Wisdom-String-Export_002fImport-from-Fortran.html#Wisdom-String-Export_002fImport-from-Fortran" accesskey="p" rel="prev">Wisdom String 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>
76 </div>
77 <hr>
78 <a name="Wisdom-Generic-Export_002fImport-from-Fortran-1"></a>
79 <h4 class="subsection">7.6.3 Wisdom Generic Export/Import from Fortran</h4>
80
81 <p>The most generic wisdom export/import functions allow you to provide
82 an arbitrary callback function to read/write one character at a time
83 in any way you want. However, your callback function must be written
84 in a special way, using the <code>bind(C)</code> attribute to be passed to a
85 C interface.
86 </p>
87 <a name="index-fftw_005fexport_005fwisdom-1"></a>
88 <p>In particular, to call the generic wisdom export function
89 <code>fftw_export_wisdom</code>, you would write a callback subroutine of the form:
90 </p>
91 <div class="example">
92 <pre class="example"> subroutine my_write_char(c, p) bind(C)
93 use, intrinsic :: iso_c_binding
94 character(C_CHAR), value :: c
95 type(C_PTR), value :: p
96 <em>...write c...</em>
97 end subroutine my_write_char
98 </pre></div>
99
100 <p>Given such a subroutine (along with the corresponding interface definition), you could then export wisdom using:
101 </p>
102 <a name="index-c_005ffunloc"></a>
103 <div class="example">
104 <pre class="example"> call fftw_export_wisdom(c_funloc(my_write_char), p)
105 </pre></div>
106
107 <a name="index-c_005floc"></a>
108 <a name="index-c_005ff_005fpointer-4"></a>
109 <p>The standard <code>c_funloc</code> intrinsic converts a Fortran
110 <code>bind(C)</code> subroutine into a C function pointer. The parameter
111 <code>p</code> is a <code>type(C_PTR)</code> to any arbitrary data that you want
112 to pass to <code>my_write_char</code> (or <code>C_NULL_PTR</code> if none). (Note
113 that you can get a C pointer to Fortran data using the intrinsic
114 <code>c_loc</code>, and convert it back to a Fortran pointer in
115 <code>my_write_char</code> using <code>c_f_pointer</code>.)
116 </p>
117 <p>Similarly, to use the generic <code>fftw_import_wisdom</code>, you would
118 define a callback function of the form:
119 </p>
120 <a name="index-fftw_005fimport_005fwisdom-1"></a>
121 <div class="example">
122 <pre class="example"> integer(C_INT) function my_read_char(p) bind(C)
123 use, intrinsic :: iso_c_binding
124 type(C_PTR), value :: p
125 character :: c
126 <em>...read a character c...</em>
127 my_read_char = ichar(c, C_INT)
128 end function my_read_char
129
130 ....
131
132 integer(C_INT) :: ret
133 ret = fftw_import_wisdom(c_funloc(my_read_char), p)
134 if (ret .eq. 0) stop 'error importing wisdom'
135 </pre></div>
136
137 <p>Your function can return <code>-1</code> if the end of the input is reached.
138 Again, <code>p</code> is an arbitrary <code>type(C_PTR</code> that is passed
139 through to your function. <code>fftw_import_wisdom</code> returns <code>0</code>
140 if an error occurred and nonzero otherwise.
141 </p>
142 <hr>
143 <div class="header">
144 <p>
145 Previous: <a href="Wisdom-String-Export_002fImport-from-Fortran.html#Wisdom-String-Export_002fImport-from-Fortran" accesskey="p" rel="prev">Wisdom String 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>
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