JSON-Fortran 5.1
JSON-Fortran 5.1 is out. There are several new features in this release. I added a get_path() routine that can be used to return the path of a variable in a JSON structure. This can be used along with the traverse() routine to do something pseudointeresting: convert a JSON file into a Fortran namelist file. Why would anyone want to do that, you ask? Who knows. Consider the following example:
program why
use json_module
implicit none
type(json_core) :: json
type(json_value), pointer :: p
integer :: iunit !! file unit
open (newunit=iunit, file='data.nml', status='REPLACE')
write (iunit, '(A)') '&DATA'
call json%initialize()
call json%parse(file='data.json', p=p)
call json%traverse(p, print_json_variable)
write (iunit, '(A)') '/'
close (iunit)
contains
subroutine print_json_variable(json, p, finished)
!! A `traverse` routine for printing out all
!! the variables in a JSON structure.
implicit none
class(json_core), intent(inout) :: json
type(json_value), pointer, intent(in) :: p
logical(json_LK), intent(out) :: finished
character(kind=json_CK, len=:), allocatable :: path
character(kind=json_CK, len=:), allocatable :: value
logical(json_LK) :: found
type(json_value), pointer :: child
integer(json_IK) :: var_type
call json%get_child(p, child)
finished = .false.
!only print the leafs:
if (.not. associated(child)) then
!fortran-style:
call json%get_path(p, path, found, &
use_alt_array_tokens=.true., &
path_sep=json_CK_'%')
if (found) then
call json%info(p, var_type=var_type)
select case (var_type)
case (json_array, json_object)
!an empty array or object
!don't print anything
return
case (json_string)
! note: strings are returned escaped
! without quotes
call json%get(p, value)
value = '"'//value//'"'
case default
! get the value as a string
! [assumes strict_type_checking=false]
call json%get(p, value)
end select
!check for errors:
if (json%failed()) then
finished = .true.
else
write (iunit, '(A)') &
path//json_CK_' = '//value//','
end if
else
finished = .true.
end if
end if
end subroutine print_json_variable
end program why
Here, we are simply traversing the entire JSON structure, and printing out the paths of the leaf nodes using a namelist-style syntax. For the example JSON file:
{
"t": 0.0,
"x": [1.0, 2.0, 3.0],
"m": 2000.0,
"name": "foo"
}
This program will produce the following namelist file:
&DATA
t = 0.0E+0,
x(1) = 0.1E+1,
x(2) = 0.2E+1,
x(3) = 0.3E+1,
m = 0.2E+4,
name = "foo",
/
Which could be read using the following Fortran program:
program namelist_test
use iso_fortran_env, only: wp => real64
implicit none
real(wp) :: t,m,x(3)
integer :: iunit,istat
character(len=10) :: name
! define the namelist:
namelist /DATA/ t,x,m,name
! read the namelist:
open(newunit=iunit,file='data.nml',status='OLD')
read(unit=iunit,nml=DATA,iostat=istat)
close(unit=iunit)
end program namelist_test
There is also a new minification option for printing a JSON structure with no extra whitespace. For example:
{"t":0.0E+0,"x":[0.1E+1,0.2E+1,0.3E+1],"m":0.2E+4,"name":"foo"}
See also
- f90nml -- A Python module for parsing Fortran namelist files