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From: ds@juniper09.cray.com (David Sielaff)
Newsgroups: comp.lang.c
Subject: Re: Expressions in initializers
Message-ID: <205653.3418@timbuk.cray.com>
Date: 5 Mar 91 03:38:34 GMT
References: <17270@crdgw1.crd.ge.com> <760@ajpo.sei.cmu.edu> <1991Mar4.144939.8311@ux1.cso.uiuc.edu> <17294@crdgw1.crd.ge.com> <10592@dog.ee.lbl.gov>
Organization: Cray Research, Inc., Eagan, MN
Lines: 36

In article <10592@dog.ee.lbl.gov> torek@elf.ee.lbl.gov (Chris Torek) writes:
>In article <17294@crdgw1.crd.ge.com> volpe@camelback.crd.ge.com
>(Christopher R Volpe) writes:
>>"The square root of two" can be evaluated at compile time, but "sqrt(2.0)"
>>is an invocation of a function. How is the compiler supposed to know
>>what sqrt is? I could have in another file:
>>
>>double sqrt(double x)
>>{
>>  return x - 1.0;
>>}
>
>Not in ANSI C (at least, not if you `#include <math.h>'; I am not sure
>about the case where you do not include the standard header).  Compilers
>can of course define their own languages and allow
>
>	static double root2 = sqrt(2.0);
>
>but someone writing ANSI C should assume neither this nor that writing
>
>	double sqrt(double x) { return x - 1.0; }
>
>will work.
>-- 
>In-Real-Life: Chris Torek, Lawrence Berkeley Lab EE div (+1 415 486 5427)
>Berkeley, CA		Domain:	torek@ee.lbl.gov

According to ANSI C, it is not necessary to `#include <math.h>' to have
this effect.  Identifiers such as `sqrt' are always reserved as
identifiers with external linkage.  Thus you could define a new `sqrt'
as a static function in a compilation unit, but if `sqrt' ends up with
external linkage, the compiler can assume that it means the library
function.

Dave Sielaff
Cray Research