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From: firth@sei.cmu.edu (Robert Firth)
Newsgroups: comp.lang.fortran
Subject: Re: Semantics of local variables
Message-ID: <3669@aw.sei.cmu.edu>
Date: 4 Jan 88 14:12:53 GMT
References: <2617@killer.UUCP>
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Organization: Carnegie-Mellon University, SEI, Pgh, Pa
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Keywords: semantics local variables DATA

In article <2617@killer.UUCP> richardh@killer.UUCP (Richard Hargrove) writes:
>A quick question for serious FORTRAN user's: do the semantics of initializing
>a local variable in a DATA statement force the variable to have static 
>scope? That is, can you generally count on the variable retaining its value
>across calls to the subroutine in which it's defined? I know this is the case
>for some compilers, but can you count on it generally? F77 and no, I don't 
>have a copy of the standard.

The quick answer: No.

You'll find it in ANSI X3.9-1978 para 17.3 (6)

	"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 neither been redefined
	     nor become undefined

	 ...
	"

In other words, if you haven't yet assigned to the variable, it will retain
its initial value (as given in the DATA statement); if you have assigned to
it (or caused it to become undefined in any of the many ways allowed by
Fortran), then it is NOT guaranteed to retain any value between invocations
of the subprogram.

As you say, most compilers will let you get away with this, since they make
the variables static.  However, there are other legitimate implementations.
If you want to follow the standard, don't ever assume more than it guarantees.