Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!usc!apple!agate!eris.berkeley.edu!mwm
From: mwm@eris.berkeley.edu (Mike (I'll think of something yet) Meyer)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Lattice and externals
Message-ID: <1989Nov14.195151.15283@agate.berkeley.edu>
Date: 14 Nov 89 19:51:51 GMT
References: <704@crash.cts.com>
Sender: usenet@agate.berkeley.edu (USENET Administrator;;;;ZU44)
Reply-To: mwm@eris.berkeley.edu (Mike (I'll think of something yet) Meyer)
Organization: Missionaria Phonibalonica
Lines: 38

In article <704@crash.cts.com> wade@pnet01.cts.com (Wade Bickel) writes:
<  I'm using Lattice C and have declared a pointer with the same name in two
<seperate modules.  Neither has the "extern" keyword in front of it, and I'd
<like each to be local to its own module (soon almost all of my modules will
<need such a pointer, and I'd like to avoid naming confusion).
<  When I link the program blink barfs on a "symbol redefined" error.  Should
<this be happening?

The answer is "it depends." Some C compilers allow you to have
multiple definitions of a variable, which will get treated as one
declaration at compile time. This behavior is not required by ANSI,
but is mentioned as a common extension. Lattice doesn't support that
extension.

On the other hand, that behavior isn't what you want. You want the
scope of the variable to be restricted to the file it's in. This is
where the static keyword comes in. When applied to a definition
outside of any function, it causes the defined object to have file
scope. This applies to functions as well as variables, so that each
modules private functions and variables can be made invisible to
anything outside the file.

Making all functions and variables that don't need linkage outside the
file static is generally a good idea. Not only does it decrease name
space polution for other modules, those objects have the internal name
equivalence properties (31 significant characters, case-sensitive)
instead of the external name equivalence propreties (6 characters,
case-insensitive).

Final note: don't confuse static outside of a function, which controls
scope, with static inside of a function, which controls duration.

	<mike
--
Come rain, come hail, come sleet, come snow		Mike Meyer
You don't like to drive to slow				mwm@berkeley.edu
You're always in the passing lane			ucbvax!mwm
It's enough to drive me out of my brain			mwm@ucbjade.BITNET