fftw3: Wisdom Generic Export/Import from Fortran
7.6.3 Wisdom Generic Export/Import from Fortran
-----------------------------------------------
The most generic wisdom export/import functions allow you to provide an
arbitrary callback function to read/write one character at a time in any
way you want. However, your callback function must be written in a
special way, using the 'bind(C)' attribute to be passed to a C
interface.
In particular, to call the generic wisdom export function
'fftw_export_wisdom', you would write a callback subroutine of the form:
subroutine my_write_char(c, p) bind(C)
use, intrinsic :: iso_c_binding
character(C_CHAR), value :: c
type(C_PTR), value :: p
_...write c..._
end subroutine my_write_char
Given such a subroutine (along with the corresponding interface
definition), you could then export wisdom using:
call fftw_export_wisdom(c_funloc(my_write_char), p)
The standard 'c_funloc' intrinsic converts a Fortran 'bind(C)'
subroutine into a C function pointer. The parameter 'p' is a
'type(C_PTR)' to any arbitrary data that you want to pass to
'my_write_char' (or 'C_NULL_PTR' if none). (Note that you can get a C
pointer to Fortran data using the intrinsic 'c_loc', and convert it back
to a Fortran pointer in 'my_write_char' using 'c_f_pointer'.)
Similarly, to use the generic 'fftw_import_wisdom', you would define
a callback function of the form:
integer(C_INT) function my_read_char(p) bind(C)
use, intrinsic :: iso_c_binding
type(C_PTR), value :: p
character :: c
_...read a character c..._
my_read_char = ichar(c, C_INT)
end function my_read_char
....
integer(C_INT) :: ret
ret = fftw_import_wisdom(c_funloc(my_read_char), p)
if (ret .eq. 0) stop 'error importing wisdom'
Your function can return '-1' if the end of the input is reached.
Again, 'p' is an arbitrary 'type(C_PTR' that is passed through to your
function. 'fftw_import_wisdom' returns '0' if an error occurred and
nonzero otherwise.
Info Catalog
fftw3: Wisdom String Export/Import from Fortran
fftw3: Accessing the wisdom API from Fortran