Alain <aze### [at] qwertyorg> wrote:
> >>     while (x[i] = y[i--]) ;

> Nothing undefined here.

> It's a simple loop that compare the array x[] and y[] untill it find a 
> value that is different.
> You get the value of x[i] and see if it's the same as the value of y[i] 
> then you decrement i by one.
> On exit, i will point to the value preceding the first different value.

  The compiler is free to decrement 'i' before it evaluates 'x[i]' or
after it. Hence you might get 'x[i]' as it was before the decrement, or
after. (The only thing that is guaranteed is that 'y[i]' is evaluated
before 'i' is decremented.) That's why it's undefined behavior.

-- 
                                                          - Warp

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