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Add null config files
author Chris Cannam <cannam@all-day-breakfast.com>
date Mon, 02 Mar 2020 14:03:47 +0000
parents 89f5e221ed7b
children
rev   line source
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cannam@95 3 <title>Wisdom String Export/Import from Fortran - FFTW 3.3.3</title>
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cannam@95 12 <!--
cannam@95 13 This manual is for FFTW
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cannam@95 49 <a name="Wisdom-String-Export%2fImport-from-Fortran"></a>
cannam@95 50 <a name="Wisdom-String-Export_002fImport-from-Fortran"></a>
cannam@95 51 <p>
cannam@95 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>,
cannam@95 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>,
cannam@95 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>
cannam@95 55 <hr>
cannam@95 56 </div>
cannam@95 57
cannam@95 58 <h4 class="subsection">7.6.2 Wisdom String Export/Import from Fortran</h4>
cannam@95 59
cannam@95 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
cannam@95 61 particular, the <code>fftw_export_wisdom_to_string</code> function requires
cannam@95 62 you to deal with a dynamically allocated C string. To get its length,
cannam@95 63 you must define an interface to the C <code>strlen</code> function, and to
cannam@95 64 deallocate it you must define an interface to C <code>free</code>:
cannam@95 65
cannam@95 66 <pre class="example"> use, intrinsic :: iso_c_binding
cannam@95 67 interface
cannam@95 68 integer(C_INT) function strlen(s) bind(C, name='strlen')
cannam@95 69 import
cannam@95 70 type(C_PTR), value :: s
cannam@95 71 end function strlen
cannam@95 72 subroutine free(p) bind(C, name='free')
cannam@95 73 import
cannam@95 74 type(C_PTR), value :: p
cannam@95 75 end subroutine free
cannam@95 76 end interface
cannam@95 77 </pre>
cannam@95 78 <p>Given these definitions, you can then export wisdom to a Fortran
cannam@95 79 character array:
cannam@95 80
cannam@95 81 <pre class="example"> character(C_CHAR), pointer :: s(:)
cannam@95 82 integer(C_SIZE_T) :: slen
cannam@95 83 type(C_PTR) :: p
cannam@95 84 p = fftw_export_wisdom_to_string()
cannam@95 85 if (.not. c_associated(p)) stop 'error exporting wisdom'
cannam@95 86 slen = strlen(p)
cannam@95 87 call c_f_pointer(p, s, [slen+1])
cannam@95 88 ...
cannam@95 89 call free(p)
cannam@95 90 </pre>
cannam@95 91 <p><a name="index-c_005fassociated-569"></a><a name="index-c_005ff_005fpointer-570"></a>
cannam@95 92 Note that <code>slen</code> is the length of the C string, but the length of
cannam@95 93 the array is <code>slen+1</code> because it includes the terminating null
cannam@95 94 character. (You can omit the &lsquo;<samp><span class="samp">+1</span></samp>&rsquo; if you don't want Fortran to
cannam@95 95 know about the null character.) The standard <code>c_associated</code> function
cannam@95 96 checks whether <code>p</code> is a null pointer, which is returned by
cannam@95 97 <code>fftw_export_wisdom_to_string</code> if there was an error.
cannam@95 98
cannam@95 99 <p><a name="index-fftw_005fimport_005fwisdom_005ffrom_005fstring-571"></a>To import wisdom from a string, use
cannam@95 100 <code>fftw_import_wisdom_from_string</code> as usual; note that the argument
cannam@95 101 of this function must be a <code>character(C_CHAR)</code> that is terminated
cannam@95 102 by the <code>C_NULL_CHAR</code> character, like the <code>s</code> array above.
cannam@95 103
cannam@95 104 <!-- =========> -->
cannam@95 105 </body></html>
cannam@95 106