RE: [avr-gcc-list] Question about gcc preprocessing and port/pin assignments

[Dave Hylands]

Hi wbounce,

> I do not know the inner working of gcc but I disagree with your
> statement 
> "The only thing that the language promises is that all side 
> effects from
> the expression are completed before the next statement is executed."
> 
> In your example 
> a = (b = 3) + 4;
> Order of operation requires the following
> Assign 3 to b (because of the ())
> Return 3 from that
> Add 4 
> Then assign result (7) to a
> 
> 
> C DOES have order of operation and operations on the same level are
> supposed to be processed left to right.

This is the classic misunderstanding between precedence and order of
evaluation.

In the statement:

        x = f() + g() * h();

We know that the result of f will be added to the product of g times h.
What we don't know is the order that f, g, and h will be called.

In the example I showed, a = ( b = 3 ) + 4; we know that a will be
assigned 7 and b will be assigned 3. We don't know the order that these
assignments will take place in.

It's a similar thing with function calls. We might know the order that
the arguments are pushed on the stack, but we don't know the order that
they will be evaluated in.

--
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/