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author Chris Cannam
date Wed, 07 Sep 2016 10:40:32 +0100
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Chris@19 1 <html lang="en">
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Chris@19 3 <title>Wisdom Generic Export/Import from Fortran - FFTW 3.3.4</title>
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Chris@19 48 <a name="Wisdom-Generic-Export%2fImport-from-Fortran"></a>
Chris@19 49 <a name="Wisdom-Generic-Export_002fImport-from-Fortran"></a>
Chris@19 50 <p>
Chris@19 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>,
Chris@19 52 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>
Chris@19 53 <hr>
Chris@19 54 </div>
Chris@19 55
Chris@19 56 <h4 class="subsection">7.6.3 Wisdom Generic Export/Import from Fortran</h4>
Chris@19 57
Chris@19 58 <p>The most generic wisdom export/import functions allow you to provide
Chris@19 59 an arbitrary callback function to read/write one character at a time
Chris@19 60 in any way you want. However, your callback function must be written
Chris@19 61 in a special way, using the <code>bind(C)</code> attribute to be passed to a
Chris@19 62 C interface.
Chris@19 63
Chris@19 64 <p><a name="index-fftw_005fexport_005fwisdom-575"></a>In particular, to call the generic wisdom export function
Chris@19 65 <code>fftw_export_wisdom</code>, you would write a callback subroutine of the form:
Chris@19 66
Chris@19 67 <pre class="example"> subroutine my_write_char(c, p) bind(C)
Chris@19 68 use, intrinsic :: iso_c_binding
Chris@19 69 character(C_CHAR), value :: c
Chris@19 70 type(C_PTR), value :: p
Chris@19 71 <em>...write c...</em>
Chris@19 72 end subroutine my_write_char
Chris@19 73 </pre>
Chris@19 74 <p>Given such a subroutine (along with the corresponding interface definition), you could then export wisdom using:
Chris@19 75
Chris@19 76 <p><a name="index-c_005ffunloc-576"></a>
Chris@19 77 <pre class="example"> call fftw_export_wisdom(c_funloc(my_write_char), p)
Chris@19 78 </pre>
Chris@19 79 <p><a name="index-c_005floc-577"></a><a name="index-c_005ff_005fpointer-578"></a>The standard <code>c_funloc</code> intrinsic converts a Fortran
Chris@19 80 <code>bind(C)</code> subroutine into a C function pointer. The parameter
Chris@19 81 <code>p</code> is a <code>type(C_PTR)</code> to any arbitrary data that you want
Chris@19 82 to pass to <code>my_write_char</code> (or <code>C_NULL_PTR</code> if none). (Note
Chris@19 83 that you can get a C pointer to Fortran data using the intrinsic
Chris@19 84 <code>c_loc</code>, and convert it back to a Fortran pointer in
Chris@19 85 <code>my_write_char</code> using <code>c_f_pointer</code>.)
Chris@19 86
Chris@19 87 <p>Similarly, to use the generic <code>fftw_import_wisdom</code>, you would
Chris@19 88 define a callback function of the form:
Chris@19 89
Chris@19 90 <p><a name="index-fftw_005fimport_005fwisdom-579"></a>
Chris@19 91 <pre class="example"> integer(C_INT) function my_read_char(p) bind(C)
Chris@19 92 use, intrinsic :: iso_c_binding
Chris@19 93 type(C_PTR), value :: p
Chris@19 94 character :: c
Chris@19 95 <em>...read a character c...</em>
Chris@19 96 my_read_char = ichar(c, C_INT)
Chris@19 97 end function my_read_char
Chris@19 98
Chris@19 99 ....
Chris@19 100
Chris@19 101 integer(C_INT) :: ret
Chris@19 102 ret = fftw_import_wisdom(c_funloc(my_read_char), p)
Chris@19 103 if (ret .eq. 0) stop 'error importing wisdom'
Chris@19 104 </pre>
Chris@19 105 <p>Your function can return <code>-1</code> if the end of the input is reached.
Chris@19 106 Again, <code>p</code> is an arbitrary <code>type(C_PTR</code> that is passed
Chris@19 107 through to your function. <code>fftw_import_wisdom</code> returns <code>0</code>
Chris@19 108 if an error occurred and nonzero otherwise.
Chris@19 109
Chris@19 110 <!-- -->
Chris@19 111 </body></html>
Chris@19 112