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From: hansm@cs.kun.nl (Hans Mulder)
Newsgroups: comp.lang.c
Subject: Re: Expressions in initializers
Message-ID: <2842@wn1.sci.kun.nl>
Date: 7 Mar 91 22:34:31 GMT
References: <1991Mar4.144939.8311@ux1.cso.uiuc.edu> <1032@caslon.cs.arizona.edu> <3599.27d3ca8a@iccgcc.decnet.ab.com>
Sender: root@sci.kun.nl
Organization: University of Nijmegen, The Netherlands
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In article <3599.27d3ca8a@iccgcc.decnet.ab.com> browns@iccgcc.decnet.ab.com (Stan Brown) writes:
>So a conforming compiler is free to consider sqrt(2.0) to be a
>compile-time constant.

Nope.  The ANSI standard gives an exhaustive list of operators that
can appear in a "constant expression" as required in an aggregate
initialiser and function calls are not on the list.

Consequently,

	struct silly { double d; } foo = { sqrt(2.0) };

is illegal.  This has nothing to do with the question of whether the
optimiser is allowed to replace

	foo.d = sqrt(2.0);
by
	foo.d = 1.4142135623730950488;


Also missing from the list is the array subscript operator, thus

	struct silly { char ch; } foo = { "hello"[3] };

is illegal, the fact that "hello"[3] == 'l' notwithstanding.


Have a nice day,

Hans Mulder	hansm@cs.kun.nl