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From: bothner@sevenlayer.cs.wisc.edu (Per Bothner)
Newsgroups: comp.lang.c++
Subject: Re: C++ coding standards (Comment needed)
Keywords: standard,variables
Message-ID: <11190@spool.cs.wisc.edu>
Date: 7 Sep 90 19:59:19 GMT
References: <56642@microsoft.UUCP> <41673@think.Think.COM> <56953@microsoft.UUCP> <2675@dataio.Data-IO.COM> <57167@microsoft.UUCP>
Sender: news@spool.cs.wisc.edu
Reply-To: bothner@sevenlayer.cs.wisc.edu (Per Bothner)
Organization: University of Wisconsin--Madison
Lines: 24

jimad@microsoft.UUCP (Jim ADCOCK) writes:
>|	func()
>|	{	{ int i; .... }
>|		{ int j; .... }
>|	}
>|
>|i and j's live ranges do not overlap, so they can (and do with some
>|compilers) share the same storage location.
>
>Yes, but C++ defines that destruction of named objects be on exit from
>scope [with few exceptions], thus greatly restricting a compilers from
>performing these optimizations on other than primitives.

Huh? "On exit from scope" means "at the end of the block"
in this case, so there is no problem allocating i and j
to the same location, even if their class(es) have destructors.

Construction and destruction must by definition delimit an
object's live range. Two variables in the same function,
but defined in non-intersection blocks do not have overlapping
live ranges. And can therefore share storage locations.
-- 
	--Per Bothner
bothner@cs.wisc.edu Computer Sciences Dept, U. of Wisconsin-Madison