get_unit.f90 Source File

subroutine get_unit ( iunit )
  
    !*****************************************************************************80
    !
    !! GET_UNIT returns a free FORTRAN unit number.
    !
    !  Discussion:
    !
    !    A "free" FORTRAN unit number is avalue between 1 and 99 which
    !    is not currently associated with an I/O device.  A free FORTRAN unit
    !    number is needed in order to open a file with the OPEN command.
    !
    !    If IUNIT = 0, then no free FORTRAN unit could be found, although
    !    all 99 units were checked (except for units 5, 6 and 9, which
    !    are commonly reserved for console I/O).
    !
    !    Otherwise, IUNIT is a value between 1 and 99, representing a
    !    free FORTRAN unit.  Note that GET_UNIT assumes that units 5 and 6
    !    are special, and will never return those values.
    !
    !  Licensing:
    !
    !    This code is distributed under the GNU LGPL license.
    !
    !  Modified:
    !
    !    18 September 2005
    !
    !  Author:
    !
    !    John Burkardt
    !
    !  Parameters:
    !
    !    Output, integer ( kind = 4 ) IUNIT, the free unit number.
    !
      implicit none
    
      integer ( kind = 4 ) i
      integer ( kind = 4 ) ios
      integer ( kind = 4 ) iunit
      logical lopen
    
      iunit = 0
    
      do i = 1, 99
    
        if ( i /= 5 .and. i /= 6 .and. i /= 9 ) then
    
          inquire ( unit = i, opened = lopen, iostat = ios )
    
          if ( ios == 0 ) then
            if ( .not. lopen ) then
              iunit = i
              return
            end if
          end if
    
        end if
    
      end do
    
      return
end