FORTRAN parsing file with varying line formate - fortran

Question

I have only limited experience with FORTRAN and I need to parse files with a structure similar to this:
H s 13.010000 0.019685
1.962000 0.137977
0.444600 0.478148
s 0.122000 1.000000
p 0.727000 1.000000
***
He s 38.360000 0.023809
5.770000 0.154891
1.240000 0.469987
s 0.297600 1.000000
p 1.275000 1.000000
***
I need to search for the label (e.g. He) and then read the corresponding blocks into an array.
I know I can parse file by specifying the format each line is supposed to have, but here there are different formats possible.
In Python I would just split each line by the white spaces and deal with it depending on the number of columns. But how to approach this in FORTRAN?

Answer 1

You can read each line as a character string and then process it. If, as it seems, the format is fixed (element symbol in first two characters, orbital letter in sixth character, etc.), the following program could serve you as inspiration:
program elms
implicit none
integer, parameter :: MAX_LEN = 40
character(len=MAX_LEN) :: line_el, line
integer :: u
integer :: is
integer :: nlin
character(len=2) :: element = 'He'
integer, parameter :: MAX_LINES = 20
real, dimension(MAX_LINES) :: e, f
open(newunit=u, file='elms.dat', status='old', action='read')
main_loop: do
! Read line
read(u, '(a)', iostat=is) line_el
if (eof_iostat(is)) exit main_loop
! Check first two characters of the line vs. chemical element.
if (line_el(1:2) .eq. element) then
! This is the beginning of an element block
nlin = 0
line = line_el
do
if (line .ne. '') then
! Line is not empty or only spaces.
nlin = nlin + 1
if (line(6:6) .ne. ' ') then
! Line contains an orbital letter - process it.
end if
! Read the real values in the rest of the line
read(line(7:),*) e(nlin), f(nlin)
end if
! Read next line
read(u, '(a)', iostat=is) line
if (eof_iostat(is)) exit main_loop
if (line(1:2) .ne. ' ') then
! Finished processing element block.
exit main_loop
end if
end do
end if
end do main_loop
! Close file
close(u)
contains
logical function eof_iostat(istat)
! Returns true if the end of file has been reached
use, intrinsic :: iso_fortran_env, only: IOSTAT_END
implicit none
integer, intent(in) :: istat
select case (istat)
case (0) ! No error
eof_iostat = .false.
case (IOSTAT_END) ! End of file reached
eof_iostat = .true.
case default ! Error
STOP
end select
end function eof_iostat
end program
You will probably need to make the program a subroutine, make element an intent(in) dummy argument, process the orbital symbols, etc.
Note that, if possible, it would be easier to just read all the data from the file in one go, and then search for the relevant data in the memory (e.g., having an array with the chemical symbols).