Re: Incrementing volatiles?

[Andreas Schwab <schwab at issan dot informatik dot uni-dortmund dot de>]

Carlo Wood <carlo@runaway.xs4all.nl> writes:

|> Can someone explain to me what exactly the definition
|> of 'volatile' is? :)

>From the C9x draft:

       6.5.3  Type qualifiers

       [#6] An object  that  has  volatile-qualified  type  may  be
       modified in ways unknown to the implementation or have other
       unknown side effects.  Therefore any expression referring to
       such  an object shall be evaluated strictly according to the
       rules of the abstract  machine,  as  described  in  5.1.2.3.
       Furthermore,  at  every sequence point the value last stored
       in the object  shall  agree  with  that  prescribed  by  the
       abstract  machine, except as modified by the unknown factors
       mentioned previously.99  What constitutes an  access  to  an
       object  that  has volatile-qualified type is implementation-
       defined.

Footnote:

       99. A volatile declaration may be used to describe an object
           corresponding to a memory-mapped input/output port or an
           object  accessed  by  an   asynchronously   interrupting
           function.   Actions  on objects so declared shall not be
           ``optimized out''  by  an  implementation  or  reordered
           except   as   permitted  by  the  rules  for  evaluating
           expressions.

-- 
Andreas Schwab                                      "And now for something
schwab@issan.informatik.uni-dortmund.de              completely different"
schwab@gnu.org