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From: steve@taumet.com (Stephen Clamage)
Newsgroups: comp.lang.c++
Subject: Re: undesired optimiztion (was C++ coding standards)
Message-ID: <422@taumet.com>
Date: 27 Aug 90 17:29:52 GMT
References: <883@zinn.MV.COM> <280@paradim.UUCP>
Organization: Taumetric Corporation, San Diego
Lines: 26

jean@paradim.UUCP (Jean Pierre LeJacq) writes:

|In article <883@zinn.MV.COM>, mjv@objects.mv.com (Michael J. Vilot) writes:
|> ...
|> The Timer object `t' is only active in the inner block.  Of course, the
|> object is apparently never used, so I may get into trouble with those
|> building aggressively-optimizing compilers. ...

|C++ uses the keyword volatile to provide a hint to the compiler
|to avoid aggresive optimization involving an object. Since it is
|only a hint, I'm not sure how portable a solution this would be.

E&S section 3.5:
	"A named local object may not be destroyed before the end
	of its block nor may a local named object of a class with
	a constructor or a destructor with side effects be
	eliminated even if it appears to be unused."

So a correct compiler, even an agressively-optimizing one, may not
omit (or move) the constructor/destructor Mike Vilot mentions.

As Jean Pierre mentions, "volatile" is not guaranteed to do what you want,
as its semantics are explicitly implementation-dependent (section 7.1.6).
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com