WRITE statement

Question

My program works with a set of files (several millions). All the files were created earlier with some other code. Some of the files are empty, some have values; all of them have 'OLD' status. My program has to

1. open one of the files;
2. add some value to the END of THE FILE if the file contains numbers already or just put a first value if the file is empty;
3. close the file and go to another file processing.

Right now, if the file is non-empty, the program erase the file's previous content and just write a new value. I think, in order TO ADD a value to the end of existing non-empty file I need to use some clause in OPEN or WRITE statement in addition to the 'OLD' status. Which ones? Thank you.

Answer 1

It would be easier with a MWE, but nonetheless, what you could do is something like that, using the append keyword

open(unit=file_unit, file=filename, status='old', access='append')

You could try it on this simple example adapted from the Fortran Wikibook to see how it works

program write
  implicit none
  integer            :: i, j
  integer, parameter :: out_unit=10

  print*,"Enter two integers:"
  read (*,*) i, j

  open (unit=out_unit, file="results.txt", action="write", status="old", access="append")
  write (out_unit,*) "The product of",i," and",j
  write (out_unit,*) "is",i*j

  close (out_unit)
end program write