Associativity -- what is it?

[The Beach Bum]

In article <234 at mccc.UUCP> pjh at mccc.UUCP (Peter J. Holsberg) writes:

[ one explaination down, twenty five more to go ;-) ]

>Well, that still leaves me confused.  If i has the value 7, it is 7 that
>is added to 3, so it seems to be that the ++ *is* deferred until later. 
>Also, ++ has higher precedence than +, so why is the incrementation
>delayed until after the current value of i is used?
> 
>I think we're getting close, though.  :-)  Thanks for the help.
>-- 
>Peter Holsberg                  UUCP: {rutgers!}princeton!mccc!pjh

This comes from a discussion which I believe was given in the document
explaining the implementation of the portable C compiler.

Consider ++ in it's two forms as a short-hand notation (don't believe
it's true, just consider it.  Flames to /dev/null) for:

pre-fix:	++ X	->	(X = X + 1)
post-fix:	X ++	->	((X = X + 1), X - 1)

So, the increment gets done, but, the value you get has been `adjusted'
if you will.

Try this:
		x = 5;
		printf ("3 * x ++ = %d\n", 3 * x ++);
		printf ("now x = %d\n", x);

You should get 15 and 4.  I suspect you expected 18 or 16 or something
like that.

[ I believe the context was that the compiler generated the trees using
  the long-hand, and then hoped to optimize to using increment instructions
  later. ]

- John.
-- 
John F. Haugh II                  SNAIL:  HECI Exploration Co. Inc.
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