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From: ray@rogue.llnl.gov (Ray, Scott)
Newsgroups: comp.lang.fortran
Subject: COMMON and SAVE statements
Message-ID: <65861@lll-winken.LLNL.GOV>
Date: 3 Aug 90 09:05:43 GMT
Sender: usenet@lll-winken.LLNL.GOV
Reply-To: ray@rogue.llnl.gov
Organization: Lawrence Livermore National Laboratory-Engineering
Lines: 28

I have been taught that it is good programming practice to use SAVE
statements in conjunction with labeled COMMON blocks to insure that the
variables in COMMON get saved when exiting a program module.  Apparently,
the FORTRAN 77 standard makes no such guarantee unless the SAVE statement
is used.  Thus, when writing my own codes I religiously stick in the
SAVE statement.  However, I work with a lot of hand-me-down codes
written by other people who take no such precautions and have never
encountered any problems that could be traced to the COMMON variables
being lost due to the lack of a SAVE statement.  So, two questions
come to mind:

1. Are there any quasi-FORTRAN 77 compliant compilers on machines in
   widespread use in the 1990's where COMMON variables can actually
   become undefined when a program module is exited and a SAVE statement
   has not been used?  In other words, is the SAVE statement really
   necessary in practice (ignoring the standard)?  If so, on which
   machines and under what conditions?

2. What could possibly be the motivation for the standard allowing
   variables in COMMON to be become undefined without a SAVE statement?
   I can't think of a case where this would be desirable behavior.
   Hence why isn't it built into the COMMON framework?

Note that I am restricting these questions to variables in COMMON.  Using
a SAVE with local variables is a much more understandable issue.

					Scott Ray
					ray@icdc.llnl.gov