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cannam@127:Dealing with FFTW’s C string export/import is a bit more painful. In
cannam@127: particular, the fftw_export_wisdom_to_string function requires
cannam@127: you to deal with a dynamically allocated C string. To get its length,
cannam@127: you must define an interface to the C strlen function, and to
cannam@127: deallocate it you must define an interface to C free:
cannam@127:
use, intrinsic :: iso_c_binding cannam@127: interface cannam@127: integer(C_INT) function strlen(s) bind(C, name='strlen') cannam@127: import cannam@127: type(C_PTR), value :: s cannam@127: end function strlen cannam@127: subroutine free(p) bind(C, name='free') cannam@127: import cannam@127: type(C_PTR), value :: p cannam@127: end subroutine free cannam@127: end interface cannam@127:
Given these definitions, you can then export wisdom to a Fortran cannam@127: character array: cannam@127:
cannam@127:character(C_CHAR), pointer :: s(:) cannam@127: integer(C_SIZE_T) :: slen cannam@127: type(C_PTR) :: p cannam@127: p = fftw_export_wisdom_to_string() cannam@127: if (.not. c_associated(p)) stop 'error exporting wisdom' cannam@127: slen = strlen(p) cannam@127: call c_f_pointer(p, s, [slen+1]) cannam@127: ... cannam@127: call free(p) cannam@127:
Note that slen is the length of the C string, but the length of
cannam@127: the array is slen+1 because it includes the terminating null
cannam@127: character. (You can omit the ‘+1’ if you don’t want Fortran to
cannam@127: know about the null character.) The standard c_associated function
cannam@127: checks whether p is a null pointer, which is returned by
cannam@127: fftw_export_wisdom_to_string if there was an error.
cannam@127:
To import wisdom from a string, use
cannam@127: fftw_import_wisdom_from_string as usual; note that the argument
cannam@127: of this function must be a character(C_CHAR) that is terminated
cannam@127: by the C_NULL_CHAR character, like the s array above.
cannam@127: