Re: Avoiding "assignment from incompatible pointer type" warning

["Claudio Bley" <bley at cs dot uni-magdeburg dot de>]

>>>>> "Florian" == Florian Weimer <fw@deneb.enyo.de> writes:

    Florian> "Claudio Bley" <bley@cs.uni-magdeburg.de> writes:
    >> >> What do you consider legal and why wouldn't it be?
    >> 
    Florian> Casting a pointer from float to int can result in
    Florian> undefined behavior on some implementations.
    >>  I can't see why. Can you elaborate on that?

    Florian> Well, it's all in the standard, although it's a bit
    Florian> scattered.

    >> I mean, casting on the machine code level does just nothing -
    >> it's just "syntactic sugar" to convince the compiler to be
    >> quiet.

    Florian> It's not.  In C, pointers are NOT machine addresses.
    Florian> Pointers are an abstract concept, and often, something
    Florian> which would work if they were machine addresses, fails
    Florian> miserably.  For example, even if two pointers compare
    Florian> equal (because they point to the same object), it's
    Florian> possible that an operation on one of the two is
    Florian> undefined, while it is defined for the other one.

    >> I think casting from one pointer type to another does no harm
    >> at all. Am I wrong?

    Florian> Yes, you are, I'm afraid.

I'm afraid too! ;-) Really. I'm using C for quite a while now, read a
few books but I never realized that. I was thinking that a cast just
meant "pretend these bits have a different type, and treat them
accordingly". Also, as Mathew Moore mentioned, I was not thinking
about alignment issues. 

Regards.
-- 
Claudio Bley                                 ASCII ribbon campaign (")
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