Path: utzoo!utgpu!jarvis.csri.toronto.edu!dgp.toronto.edu!flaps
Newsgroups: comp.std.c
From: flaps@dgp.toronto.edu (Alan J Rosenthal)
Subject: observability
Message-ID: <1989Sep6.183349.2866@jarvis.csri.toronto.edu>
References: <1237@gmdzi.UUCP> <10885@smoke.BRL.MIL> <242@ssp1.idca.tds.philips.nl> <10937@smoke.BRL.MIL> <1989Sep6.160709.4890@light.uucp>
Date: 6 Sep 89 22:33:49 GMT

bvs@light.uucp (Bakul Shah) writes:
>I have some questions about `observable behavior'.  How does this
>concept interact with `volatile' variables? with debuggers? with
>shared memory?

Debuggers and shared memory are not specified in the ansi C standard.
That is, there does not exist behaviour of debuggers or of shared memory
that violate the standard.

Many people claim that "volatile" is meaningless since it is not observable.

>Is a program with *no* output of any kind observable?

Yes, you can observe that it produced no output, a different observation from
observing it producing some output.  However, the ansi C standard probably
doesn't prevent "int main() { return(0); }" from outputting, as a concession to
verbose environments.  So there might not exist standard-violating behaviour
for the execution of a program which produces no output.

ajr