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From: wsb@boise.Eng.Sun.COM (Walt Brainerd)
Newsgroups: comp.lang.fortran
Subject: Re: SAVEing FORTRAN variables
Summary: DATA entities are not saved
Message-ID: <8042@exodus.Eng.Sun.COM>
Date: 15 Feb 91 19:53:32 GMT
References: <1991Feb15.000230.18585@news.arc.nasa.gov> <1991Feb15.172635.17261@craycos.com>
Sender: news@exodus.Eng.Sun.COM
Lines: 46

In article <1991Feb15.172635.17261@craycos.com>, pmk@craycos.com (Peter Klausler) writes:
> In article <1991Feb15.000230.18585@news.arc.nasa.gov> chau@xenon.arc.nasa.gov writes:
> >I am looking for a tool which scans FORTRAN source code and identifies 
> >variables which should be saved.  
> >
> >This is a simple example of a FORTRAN source code that needs to scan
> >and insert a SAVE statement:
> >
> >      subroutine sub (val)
> >      integer val, i
> >      data i/10/
> >
> >   10 val = val * i
> >      i = i -1
> >      goto 10
> >      return
> >      end
> >
> >When subroutine sub is called the second time the value of i may not be the 
> >same.  Therefore, it needs to have a SAVE statement to make i become static.
> 
> Variables that are initially defined with a DATA statement are static, and
> don't need a SAVE statement.

This is not correct, in general, though it may be true for some
implementations.  The rules state (17-4, 45-53) that

"The execution of a RETURN statement or an END
statement within a subprogram causes all entities
within the subprogram to become undefined except for
the following:
    . . .
(b) Initially defined entities that have netiher been
    redefined nor become undefined
    . . ."

In the example, i gets redefined, so its value upon reentry
is up for grabs.   This was done purposely to allow implementations
to either save the old value or reinitialize upon reentry.
Thus the programmer must use a SAVE statement to be portable
if that is what is desired.
--
Walt Brainerd        Sun Microsystems, Inc.
wsb@eng.sun.com      MS MTV 5-40
                     Mountain View, CA 94043
                     415/336-5991