XL Fortran Enterprise Edition for AIX : User's Guide - IBM

If you have applications in which Fortran routines work with routines in other
languages or in which a Fortran process works with other processes on the
same data file, the data written by Fortran routines may not be seen
immediately by other parties (and vice versa), because of the buffering. Also, a
Fortran READ statement may read more data than it needs into the I/O buffer
and cause the input operation performed by a routine in other languages or
another process that is supposed to read the next data item to fail. In these
cases, you can use the buffering run-time option to disable the buffering in the
XL Fortran run-time library. As a result, a READ statement will read in exactly
the data it needs from a file and the data written by a WRITE statement will
be flushed out to the file system at the completion of the statement.
Note: I/O buffering is always enabled for files on sequential access devices
(such as pipes, terminals, sockets, and tape drives). The setting of the
buffering option has no effect on these types of files.
If you disable I/O buffering for a logical unit, you do not need to call the
Fortran service routine flush_ to flush the contents of the I/O buffer for that
logical unit.
The suboptions for buffering are as follows:
enable
disable_preconn
disable_all
The Fortran run-time library maintains an I/O
buffer for each connected logical unit. The
current read-write file pointers that the
run-time library maintains might not be
synchronized with the read-write pointers of
the corresponding files in the file system.
The Fortran run-time library does not maintain
an I/O buffer for each preconnected logical
unit (0, 5, and 6). However, it does maintain
I/O buffers for all other connected logical
units. The current read-write file pointers that
the run-time library maintains for the
preconnected units are the same as the
read-write pointers of the corresponding files
in the file system.
The Fortran run-time library does not maintain
I/O buffers for any logical units. You should
not specify the buffering=disable_all option
with Fortran programs that perform
asynchronous I/O.
In the following example, Fortran and C routines read a data file through
redirected standard input. First, the main Fortran program reads one integer.
Then, the C routine reads one integer. Finally, the main Fortran program reads
another integer.
Fortran main program:
integer(4) p1,p2,p3
print *,’Reading p1 in Fortran...’
read(5,*) p1
call c_func(p2)
print *,’Reading p3 in Fortran...’
read(5,*) p3
print *,’p1 p2 p3 Read: ’,p1,p2,p3
end
52 XL Fortran Enterprise Edition for AIX : User’s Guide