Re: GNU C keyword volatile, GNU compiler/optimizer and instruction re-ordering

Nick Maclaren <nmm1@cus.cam.ac.uk> wrote:
>Unfortunately, volatile is a complete mess.


I think this statement is overly pessimistic. I disagree entirely
with this assessment of volatile. I think it is clear what it means,
and it is useful. I think the C++ standard clarifies some points for
users that might not otherwise know what it means. I think it would
be possible to write down exactly what it means and add this to the
language standards, but such an undertaking absolutely must be done by
people that know what it means. The C++ standard almost got into
serious trouble trying to refine and fix volatile. Unfortunately all
the right people to do this weren't available to do the right job.
Fortunately disaster was averted.


>To a first approximation, the handling of volatile is implementation
>dependent


The C++ standard I think does a better job than the older C standard.
Newer C standards I think show improvement as well. Are they perfect,
no, much more could be written, more things be made clear.


>but there is no guarantee that the next one will do the same thing.


Again, this is misleading at best and just flat wrong at worse.


If people want better answers than these for their volatile question,
come over to the gcc list and ask them.
[I find that the main use of volatile is as a portable way to write
fundamentally unportable code like device drivers. -John]

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