Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!samsung!umich!yale!husc6!cmcl2!lanl!jlg
From: jlg@lanl.gov (Jim Giles)
Newsgroups: comp.lang.fortran
Subject: Re: Fortran 77 Style Guide
Message-ID: <59134@lanl.gov>
Date: 4 Aug 90 02:24:17 GMT
References: <348@ccrwest.UUCP>
Organization: Los Alamos Natl Lab, Los Alamos, N.M.
Lines: 39

From article <348@ccrwest.UUCP>, by desj@ccrwest.UUCP (David desJardins):
> In article <59012@lanl.gov> jlg@lanl.gov (Jim Giles) writes:
>>[...]  Anyway, _wherever_ you
>>do it, you _should_ initialize _all_ common data.
> 
>    I find it hard to believe that you really mean this (especially as
> you are writing from LANL).  On Crays at least, and probably on a lot
> of other machines, initialized storage is included, byte for byte, in
> the executable (a.out) file.  In fact, if any item in the common block
> is initialized, the whole block is included.

Yes, I know.  It's one of the things that I've been asked to look
into.  I do local site analysis on SEGLDR, the loader on UNICOS.
Still, I don't see why you don't want the arrays initialized.  There
_are_ ohter mechanisms that DATA syayements you know.  For example,
there is a SEGLDR directive that is _supposed_ to initialize all memory
that isn't otherwise initialized to a number you can supply at load time -
uninitialized data are still compressed out of the executable and the
initialization is done by the startup routine (unfortunately, it's not
implemented yet - another thing to "look into" - which means _I_ probably
have to fix it.)

> [...]                   If the initialization is not necessary for the
> functioning of the program, it seems likely to mislead the reader, who
> will probably think that the initialized value has some particular
> purpose.

It _does_ have a purpose.  It is to prevent accidental use of meaningless
data.  I initialize stuff to NANs or (on the Cray) to infinity.  Integers
are a bit harder.  Still, I want accidental use of meaningless data to
stand out as clearly as possible.

> [...]      And, as noted above, it is probably better to initialize
> large arrays in code rather than with DATA statements anyway.

Yes, that's a way too.  (It is, in fact what the SEGLDR directive is
supposed to do.)  Like I say, you should _always_ initialize your data.

J. Giles