Re: Bug story

[fjh@cs.mu.oz.au (Fergus Henderson)]

"Samuel T. Harris" <sam_harris@hso.link.com> writes:

>Dave Sparks wrote:
>> 
>> Let me try to summarise the argument to date: it was asserted that
>> a code fragment like { A + 1; } (where the value of the expression
>> is discarded) can be optimised out because the code has no effect;

And indeed this is true, unless `A' was declared `volatile'.
(I presume by the syntax you are talking about C and/or C++.)

>A similar problem involves programming EGA cards.

And again, the solution is similar -- declare the video memory `volatile'.

>Personally,
>this was a common problem for me in the 80's as Ada compilers
>on PC's got better and better.

The solution in Ada is basically the same as in C/C++, with slightly
different syntax: `pragma Volatile' rather than `volatile'.

Well, that's true in Ada 95, at least.  I don't know off-hand
whether `pragma Volatile' was present in Ada 83.  Perhaps someone
from comp.lang.ada can tell us.

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