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Re: Null pointer check elimination
On Mon, Nov 14, 2005 at 11:56:16PM +0100, Gabriel Dos Reis wrote:
> "Michael N. Moran" <mike@mnmoran.org> writes:
> SEGFAULT is not a behaviour defined by the language. It is *just* one
> form of undefined behaviour. If you execute that function, it might
> reformat your harddrive and that woud be fine -- though I know of no
> compiler that does that on purpose. But, the point is that your
> program in erring in the outer space.
>
> | // dereference: access to object
> | // If a is null, then SEGFAULT
> | *a = 0;
>
> Again, that may or may not happen.
Some operating systems load a page of zeroes at address zero, so the
dereference of a null pointer has no visible effect; a different form
of undefined behavior. DYNIX/ptx did that by default, and I think
that HP-UX does it. I much prefer a segfault.
Janis