How to open an external file while a FORTRAN program is running - file-io

Question

I have a FORTRAN code which performs a numerical integration. All the computed data are written in an external file (data.out). Here is a simple sketch of the code
OPEN(UNIT=10,FILE='data.out')
DO i=1,n
........
WRITE(10,'(7(E22.16,1x))')a,b,c,d,e,f,g
........
ENDDO
CLOSE(10)
The program keeps running for long time (about 1.5 h) until the numerical integration is finished. During the execution I would like to see the results in the .out file. However, when I try to open the .out file while the .exe is running I get the following message:
"The document data.out is used by another application and cannot be accessed." So, is there a way to open the .out file during the execution? It is important for me to observe the output values (they are not only seven as in the above example) so, it is not convenient to send them in screen output (is reduces significantly the speed of the code).
Many thanks in advance.
* EDIT *
This is another scenario quite similar to the above mentioned case. Here, the integration routine reads the initial conditions from an input file and writes the outputs to another external file. Below I present the corresponding skeleton of the code
OPEN(UNIT=10,FILE='input.par',STATUS='UNKNOWN')
2 READ(10,*,END=1) x_0,y_0
! INTEGRATION LOOP
DO i=1,n
........
ENDDO
OPEN(UNIT=12,FILE='data.out')
WRITE(12,'(7(E22.16,1x))')a,b,c,d,e,f,g
GOTO 2
1 CLOSE(10)
CLOSE(12)
So, the routine opens UNIT 10 reads the initial conditions, performs the integration and at the end of the integration it writes the outputs to UNIT 12. Then, it takes another set of initial conditions and repeat the same procedure until it there is no more initial conditions in UNIT 10. Again, I want to be able to open and monitor UNIT 12. I tried your approach but it does not work properly at this case. I can open UNIT 12 any time I want but the routine does not write all the outputs there. In fact, it writes only the outputs of the last set of initial conditions. Any ideas? I strongly believe that a minor modification to your approach could do the job.

Answer 1

Alternative to printing out the result to the screen, you could just close your file after each write operation and reopen it in the next integration cycle to append the new data to it.
program test
implicit none
integer :: ii
! Create emtpy file
open(10, file='data.out', status='REPLACE', action='WRITE')
close(10)
do ii = 1, 100
!...
! Reopen file, append new information and close it again.
open(10, file='data.out', status='OLD', action='WRITE', position='APPEND')
write(10,'(7(E23.16,1x))') 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0
close(10)
end do
end program test
EDIT: THe main idea is, that before you start any kind of looping, you create an empty file by the first open statement:
open(10, file='data.out', status='REPLACE', action='WRITE')
close(10)
Then, inside the loop you just append to that file, to make sure you do not replace content already being there:
open(10, file='data.out', status='OLD', action='WRITE', position='APPEND')
write(10,'(7(E23.16,1x))') 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0
close(10)
Please note the differences in the arguments passed to the open statement.

Answer 2

The logical way to do this would be to echo the output to the terminal. By default, this is unit 6. So I would change your output to:
WRITE(6,'(7(E22.16,1x))')a,b,c,d,e,f,g
WRITE(10,'(7(E22.16,1x))')a,b,c,d,e,f,g
Try it and see. It may even work.