How to write Fortran Output as CSV file?

Question

Can any one tell me, how can I write my output of Fortran program in CSV format? So I can open the CSV file in Excel for plotting data.

Answer 1

I'd also recommend the csv_file module from FLIBS. Fortran is well equipped to read csv files, but not so much to write them. With the csv_file module, you put

    use csv_file

at the beginning of your function/subroutine and then call it with:

    call csv_write(unit, value, advance)

where unit = the file unit number, value = the array or scalar value you want to write, and advance = .true. or .false. depending on whether you want to advance to the next line or not.

Sample program:

  program write_csv

    use csv_file

    implicit none

    integer :: a(3), b(2)

    open(unit=1,file='test.txt',status='unknown')

    a = (/1,2,3/)
    b = (/4,5/)

    call csv_write(1,a,.true.)
    call csv_write(1,b,.true.)

  end program

output:

1,2,3

4,5

if you instead just want to use the write command, I think you have to do it like this:

    write(1,'(I1,A,I1,A,I1)') a(1),',',a(2),',',a(3)
    write(1,'(I1,A,I1)') b(1),',',b(2)

which is very convoluted and requires you to know the maximum number of digits your values will have.

I'd strongly suggest using the csv_file module. It's certainly saved me many hours of frustration.