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author Chris Cannam
date Wed, 20 Mar 2013 15:35:50 +0000
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3 <title>Wisdom Generic Export/Import from Fortran - FFTW 3.3.3</title>
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48 <a name="Wisdom-Generic-Export%2fImport-from-Fortran"></a>
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50 <p>
51 Previous:&nbsp;<a rel="previous" accesskey="p" href="Wisdom-String-Export_002fImport-from-Fortran.html#Wisdom-String-Export_002fImport-from-Fortran">Wisdom String Export/Import from Fortran</a>,
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54 </div>
55
56 <h4 class="subsection">7.6.3 Wisdom Generic Export/Import from Fortran</h4>
57
58 <p>The most generic wisdom export/import functions allow you to provide
59 an arbitrary callback function to read/write one character at a time
60 in any way you want. However, your callback function must be written
61 in a special way, using the <code>bind(C)</code> attribute to be passed to a
62 C interface.
63
64 <p><a name="index-fftw_005fexport_005fwisdom-572"></a>In particular, to call the generic wisdom export function
65 <code>fftw_export_wisdom</code>, you would write a callback subroutine of the form:
66
67 <pre class="example"> subroutine my_write_char(c, p) bind(C)
68 use, intrinsic :: iso_c_binding
69 character(C_CHAR), value :: c
70 type(C_PTR), value :: p
71 <em>...write c...</em>
72 end subroutine my_write_char
73 </pre>
74 <p>Given such a subroutine (along with the corresponding interface definition), you could then export wisdom using:
75
76 <p><a name="index-c_005ffunloc-573"></a>
77 <pre class="example"> call fftw_export_wisdom(c_funloc(my_write_char), p)
78 </pre>
79 <p><a name="index-c_005floc-574"></a><a name="index-c_005ff_005fpointer-575"></a>The standard <code>c_funloc</code> intrinsic converts a Fortran
80 <code>bind(C)</code> subroutine into a C function pointer. The parameter
81 <code>p</code> is a <code>type(C_PTR)</code> to any arbitrary data that you want
82 to pass to <code>my_write_char</code> (or <code>C_NULL_PTR</code> if none). (Note
83 that you can get a C pointer to Fortran data using the intrinsic
84 <code>c_loc</code>, and convert it back to a Fortran pointer in
85 <code>my_write_char</code> using <code>c_f_pointer</code>.)
86
87 <p>Similarly, to use the generic <code>fftw_import_wisdom</code>, you would
88 define a callback function of the form:
89
90 <p><a name="index-fftw_005fimport_005fwisdom-576"></a>
91 <pre class="example"> integer(C_INT) function my_read_char(p) bind(C)
92 use, intrinsic :: iso_c_binding
93 type(C_PTR), value :: p
94 character :: c
95 <em>...read a character c...</em>
96 my_read_char = ichar(c, C_INT)
97 end function my_read_char
98
99 ....
100
101 integer(C_INT) :: ret
102 ret = fftw_import_wisdom(c_funloc(my_read_char), p)
103 if (ret .eq. 0) stop 'error importing wisdom'
104 </pre>
105 <p>Your function can return <code>-1</code> if the end of the input is reached.
106 Again, <code>p</code> is an arbitrary <code>type(C_PTR</code> that is passed
107 through to your function. <code>fftw_import_wisdom</code> returns <code>0</code>
108 if an error occurred and nonzero otherwise.
109
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