(C question) (s - out.s) + func(&out) -> ?

[Lennart Sorensen]

On Thu, Oct 31, 2013 at 11:40:20AM -0400, D. Hugh Redelmeier wrote:
> | From: William Park <opengeometry-FFYn/CNdgSA at public.gmane.org>
> 
> | Question for C expert...  Given the following
> 
> The order of operation is well-defined in C: operator precedence.
> 
> That says nothing about the order of evaluation of operands, only
> about how they are combined.
> 
> Your code has a race condition and is undefined by the C standard.

Functions calls are evaluated before addition/subtraction.  That's in
the standard.  Since the function modifies the parameter, the value
changes before the addition work is done.

Relying on the order variables are read into registers in a given C
statement is generally a bad idea.  Just don't do it.  Don't use and
modify a value in the same statement either.  The outcome is often
undefined so that the compiler is free to do whatever is most efficient.

-- 
Len Sorensen
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