Unbuffered output in mixed C / Fortran programs

[Steve Kargl]

On Wed, Oct 15, 2008 at 05:20:46PM +0200, Georg Denk wrote:
> Hello Tobias!
> 
> Tobias Burnus wrote:
> > Try FLUSH. The following uses a Fortran 2003 feature:
> > 
> >       SUBROUTINE FORTRAN_OUTPUT
> >       USE ISO_FORTRAN_ENV   !!! make OUTPUT_UNIT available
> >       WRITE(*,*) 'HELLO WORLD, FORTRAN (should be 1st)'
> >       FLUSH(OUTPUT_UNIT)  !!! FLUSH standard out (stdout)
> >       RETURN
> >       END
> > 
> > Besides OUTPUT_UNIT, you can use INPUT_UNIT and ERROR_UNIT or any
> > numerical unit such as "FLUSH(99)".
> > 
> > In C one can use, e.g.,  fflush(FILE *stream) to do the same there; e.g.
> > "fflush(stdout);"
> 
> Thanks for this hint. To be honest, I was aware of flush, and it might be
> a solution for this simple test case. But for the real thing, there are so
> many output statements that it is more or less impossible to add
> some flush to all of them. That's the reason for the setvbuf call in
> the C part which is similar to adding a "flush" after each printf.
> 

Since you're already doing mix language program, you can
use the ISO C binding mechanism to call putenv at the
start of main to set GFORTRAN_UNBUFFERED_PRECONNECTED.
It would look something like

   program main
     use iso_c_binding
     ! other declarations
     ! ....
     ! first executed statement
     call putenv("GFORTRAN_UNBUFFERED_PRECONNECTED=y")
     ! rest of program
   end program main

PS: I wrote the above off the top of head, you'll need to check
    the actual syntax.
-- 
Steve