Fortran read text file - fortran

Question

I have a file that writes like this
N
1000
NNODES
3
TURB_INT
0.20000
U_MEAN
30
TYPE_GP
dav
L
120
WIND_TURB
NODE_1 NODE_2 NODE_3
0.90139 -1.02858 0.03962
-2.56887 -1.59726 -0.82062
-0.58745 0.72129 -1.90712
-4.46302 -2.49995 -5.45345
-4.10550 -5.50565 -7.77285
-6.18588 -6.34998 -5.95054
I am really struggling to understand how to read it.
Finally what I need the most is reading the NODES records into variable WT(i,:), hence I could use a DO loop.
Here is what I have:
! open inputfile, ID=100
open(unit=100, file=inputfile, recl=fileln, status='old', iostat=iost)
print *, iost
print *, fileln
if (iost .ne. 0) then
print *, 'Error opening file'
print *, erromsg
else
print *, 'File opened correctly'
print *, erromsg
end if
! Trying to read what's written in file.
read(unit=100, *) N
print *, N
read(unit=100, *) Nval
print *, Nval
I was trying to see how reading is done line by line. I can read variable N, but right at second reading (line 2) I have "severe(24): END OF FILE during read".
Please could you advise me?
Thanks

Answer 1

I think you should read up on the proper flags for your open statement.
The keyword recl is used for direct access files. It means that every record has the same length, so if you need the 64th record, the program knows immediately where that record is.
If your file has a record length, I can't see it. As I said in my comment, I have the strong suspicion that fileln is the length of the file in bytes (you didn't say). So in your first read, the first record would be read, which is the entirety of the file, and then parsed into the variable N -- which can only take a single integer, everything else is then discarded.
And then it tries to read the next fileln bytes after the end of the file, which results in an 'end of file' error.
In your case, I would add the action="READ" and form="FORMATTED" keywords in the file open statement. And I always find it useful to not only look for the error code, but also the error message iomsg.
For what it's worth, here's my suggestion on how to read the file:
program readfile
implicit none
integer :: u ! File handle
integer :: ios
character(len=100) :: iom, line
integer :: N, NNodes, U_Mean, L
real :: Turb_Int
character(len=20) :: Type_GP
real, allocatable :: node_values(:)
character(len=10), allocatable :: node_names(:)
character(len=*), parameter :: inputfile = 'data.txt'
! newunit, instead of unit, creates a new unique
! file unit number. You could also set u to 100
! and then use unit=u
open(newunit=u, file=inputfile, action='READ', &
status='OLD', form='FORMATTED', iostat=ios, &
iomsg=iom)
if (ios /= 0) then
print *, "Error opening file:"
print *, iom
stop 1
end if
! Read the header. I'm always reading 'line' when
! I expect there to be just the next keyword
! in the line. You might want to check for that
read(u, *) line ! Hopefully 'N'
read(u, *) N
read(u, *) line ! Hopefully "NNODES"
read(u, *) NNodes
! I assume that NNODES stands for the number
! of columns later in the file.
! So here I'm also allocating the arrays.
allocate(node_values(NNodes))
allocate(node_names(NNodes))
read(u, *) line ! Hopefully TURB_INT
read(u, *) Turb_Int
read(u, *) line ! Hopefully U_MEN
read(u, *) U_Mean
read(u, *) line ! Hopefully TYPE_GP
read(u, *) Type_GP
read(u, *) line ! Hopefully L
read(u, *) L
read(u, *) line ! Hopefully WIND_TURB
read(u, *) node_names
! Just print out what we got from the header so far to see
! everyting's right
write(*, '(A, I0)') "N = ", N
write(*, '(A, I0)') "NNodes = ", NNodes
write(*, '(A, F5.1)') "Turb_Int = ", Turb_Int
write(*, '(A, I0)') "U_Mean = ", U_Mean
write(*, '(A, A)') "Type_GP = ", trim(Type_GP)
write(*, '(A, I0)') "L = ", L
write(*, '(A, *(A))') node_names
! Now read the data itself. In this case I'm just reading it
! line by line, print it out, and forget it again
! until the end of the file.
data_loop : do
read(u, *, iostat=ios, iomsg=iom) node_values
if (ios /= 0) exit data_loop
print *, node_values
end do data_loop
end program readfile