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From: dricejb@drilex.UUCP (Craig Jackson drilex1)
Newsgroups: comp.lang.fortran
Subject: Re: Position in file after open?
Message-ID: <5443@drilex.UUCP>
Date: 16 Oct 89 12:47:07 GMT
References: <1162@atha.AthabascaU.CA> <1989Oct14.233757.8471@esegue.segue.boston.ma.us>
Reply-To: dricejb@drilex.UUCP (Craig Jackson drilex1)
Organization: DRI/McGraw-Hill, Lexington, MA
Lines: 39

In article <1989Oct14.233757.8471@esegue.segue.boston.ma.us> johnl@esegue.segue.boston.ma.us (John R. Levine) writes:
>In article <1162@atha.AthabascaU.CA> lyndon@cs.AthabascaU.CA (Lyndon Nerenberg) writes:
>>Can someone enlighten me as to what the ANSI F77 spec has to say
>>about where a file pointer sits immediately after an open?
>
>It doesn't say anything (and I just reread the section on OPEN for the
>zillionth time, just to be sure.)  A standard conforming processor could
>position the file at the beginning, at the end, or at the 17th record.  It
>could pick a different position every time.  If you think this is stupid,
>then you understand the essence of F77 file processing.

I believe that the standard is silent on this point so that things like
JCL's DISP=MOD are allowed to have their correct semantics.   In JCL, if
you say DISP=NEW on an output file, a new file is created.  If you say
DISP=MOD, an old file is appended to.  All of this happens outside the
actual Fortran program.

These things are useful in a batch environment if you don't want a lot of file
positioning  code in your application.

>My impression is that there was a lot of arguing in the F77 committee
>among vendors with real file systems, vendors with no file systems, and
>vendors like IBM which were somewhere in between.  They ended up with a
>compromise that is full of features that are so vague as to be useless.
>I hope F8x is better, I await my copy of the standard eagerly.

I think that F8x does address this subject somewhat better, but I think
that there are still provisions which allow external positioning for
the batch people.

>-- 
>John R. Levine, Segue Software, POB 349, Cambridge MA 02238, +1 617 864 9650
>johnl@esegue.segue.boston.ma.us, {ima|lotus|spdcc}!esegue!johnl


-- 
Craig Jackson
dricejb@drilex.dri.mgh.com
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