Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!necntc!ima!haddock!karl
From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Does extern "const" allocate storage?
Message-ID: <3287@haddock.ISC.COM>
Date: 1 Apr 88 19:54:33 GMT
References: <7712@apple.Apple.Com> <3034@haddock.ISC.COM> <613@mcrware.UUCP> <3117@haddock.ISC.COM> <3938@chinet.UUCP> <3241@haddock.ISC.COM> <4381@chinet.UUCP>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 21

In article <4381@chinet.UUCP> dag@chinet.UUCP (Daniel A. Glasser) writes:
>---- begin file 1 -----
>  const int x = 5;
>  int foo() { return x; }
>---- begin file 2 -----
>  extern const int x;
>  extern int foo();
>  int fie() { return x == foo(); }
>---- end example -----
>Maybe the compiler is at liberty to substitute the value 5 for the use of x
>in the function foo [but it isn't allowed to omit the storage entirely].

I think we're in agreement now.  What I claim is that (a) the substitution is
valid if the compiler knows the value, and (b) if *all* possible references
are so optimized, then the compiler need not allocate the space.  This is
normally possible only if the object has non-external linkage.

Actually, it's theoretically possible even in your example, if the compiler is
willing to do cross-file optimization.  (It would also have to "know" that no
library routines depend on x.)

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint