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From: khb%chiba@Sun.COM (Keith Bierman - SPD Advanced Languages)
Newsgroups: comp.lang.fortran
Subject: Re: Position in file after open?
Message-ID: <126396@sun.Eng.Sun.COM>
Date: 16 Oct 89 17:50:16 GMT
References: <1162@atha.AthabascaU.CA> <50500152@uxe.cso.uiuc.edu>
Sender: news@sun.Eng.Sun.COM
Reply-To: khb@sun.UUCP (Keith Bierman - SPD Advanced Languages)
Organization: Sun Microsystems, Mountain View
Lines: 52

In article <50500152@uxe.cso.uiuc.edu> mcdonald@uxe.cso.uiuc.edu writes:
>
>/* Written  2:19 pm  Oct 14, 1989 by lyndon@cs.AthabascaU.CA in uxe.cso.uiuc.edu:comp.lang.fortran */
>/* ---------- "Position in file after open?" ---------- */
>Can someone enlighten me as to what the ANSI F77 spec has to say
>about where a file pointer sits immediately after an open?

As is moderately well known, this is a "feature" of the '77 standard.
While it is "obvious" that a freshly opened file should be positioned
at the start, there is a legend that at least one popular compiler
positions to the end of file just to prove to customers how bad the
standard is ...

>
>
>         OPEN(UNIT = 9,FILE = 'ALREADYEXISTS', STATUS = 'UNKNOWN')
>         REWIND(9)
>
>Is "unknown" a standard contruct or not? If so, should this always

Unknown is perfectly standard ... but it doesn't address the
positioning question at all. The f8x standard does.

         OPEN(UNIT = 9,FILE = 'ALREADYEXISTS', STATUS = 'UNKNOWN',
&	      POSITION = pos)

where pos is a character expression which ignoring trailing blanks and
converting any lower-case letters to upper-case, has the value ASIS,
REWIND, or APPEND.

The default (in F8x as currently drafted) is to open a file to its
start. While this is what nearly everyuser ever asked wants ... it has
the _potential_ of breaking some outlandish program which was never
ported to another machine (as most vendors learned that users really
don't like to have to follow every open with a rewind ... and consider
such behavior a bug) 

...  >begin writing at the begiining of file,
overwriting anything alreay >there?  > >IF not legal, is there any
legal way to overwrite a file besides >attempting to open it for read,
and if there closing it with a >delete specifier, themn opening a new
file for write? That appears >to be the only way to do it in an
oddball Fortran compiler I have >(MicroWay NDPC for the 386).  > >Doug
McDonald

I don't understand the MicroWay problem ... doesn't the
open/rewind/write work on that system ? If not, (a) file a bug report,
(b) open, close (status=delete), open ?
Keith H. Bierman    |*My thoughts are my own. !! kbierman@sun.com
It's Not My Fault   |	MTS --Only my work belongs to Sun* 
I Voted for Bill &  | Advanced Languages/Floating Point Group            
Opus                | "When the going gets Weird .. the Weird turn PRO"