What is int &volatile r; [Was: What is int &const r;]

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2 total messages Started by Tom Ngo Thu, 18 Apr 1991 02:42

#1021

Author: Tom Ngo
Date: Thu, 18 Apr 1991 02:42

20 lines
940 bytes

I wrote:

>Here's an interesting C++ statement.  What does it mean?
>    int &const r;
>Hopefully your answer is that it is illegal and/or meaningless.  If

Harald Fuchs replied:

Fuchs> A reference is always constant, so "int&const r" is just a more
Fuchs> verbose alternative to "int& r". Why bother with explicitly
Fuchs> disallowing redundancies?

OK, I can accept that.  But what is "int &volatile r"?

--Tom
--
  Tom Ngo
  ngo@harvard.harvard.edu
  617/495-1768 lab number, leave message

Re: What is int &volatile r; [Was: What is int &const r;]

#1037

Author: Mike Banahan
Date: Mon, 22 Apr 1991 18:48

20 lines
1604 bytes

... what is "int & volatile .. " ...

A good question to ask! A volatile reference to (exactly what doesn't matter)
- if we were talking about C, and using a pointer, then it would mean that
the value of the pointer was subject to unpredictable external change
which cannot be discovered by simply reading the program; this is intended
to allow for interrupts and concurrency to be implemented.

Since a reference is not modifiable by the program (it's const), the utility
of having a volatile one is severely questionable, but undoubtedly capable
of implementation. One could imagine a globally-visible reference which
is somehow updated by an interrupt routine to refer to various different
objects at run-time. This makes me want to throw up, but that's what it
mean by analogy with pointer types. If one of my guys did that with a reference,
I daren't put in writing what I would want to do with him/her.

Mike Banahan
-- 
Mike Banahan, Founder Director, The Instruction Set Ltd.
mikeb@inset.co.uk

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