Why does Eclipse's Photran require 'call flush(6)' after 'write' to prevent buffering to std out?

Question

I'm using Classic Eclipse 4.2.2 with the Photran plugin and cygwin's gfortran compiler on a Windows 7 Professional machine. If I remove 'call flush(6)' below, the program does not write to console until AFTER reading from std in:

program mult1
implicit none

integer :: i,j,k

!
!
! This program just multiplies two integers
! together.
!
!

write(*,*) 'Enter i,j: '
call flush(6)
read(*,*)i,j

k = i*j

write(*,*) 'The product is ', k
stop
end program mult1

Any thoughts or fixes?

Answer 1

I resolved the issue by preventing ALL buffering. This is not the perfect solution (it would be nice to buffer some outputs and not others), but it solves my problem---namely, not having to call flush(6) every time I write(,).

To prevent all buffering with gfortran (NOTE: It is compiler specific),

1. Include the environment variable: GFORTRAN_UNBUFFERED_ALL
2. And assign it the value: 1

In the event that you are USING PHOTRAN (the eclipse plug-in for Fortran), you will have to do the following:

1. Navigate in overhead bar to Run>Run Configurations
2. In the left pane, choose your project in the drop down menu Fortran Local Application> Your Project
3. In the right pane, select the "Environment Tab"
4. Click "New" and add the variable and value listed above.