🚀 go-pugleaf

jaf3@motel6.cec.wustl.edu (Stephen W. Gevers) writes:

>Andy J Robb <AJRobb@pavilion.co.uk> wrote:
>:Ron Forrester <rjf@infograph.com> wrote:
>:...
>:>Of course, upon further examination we found that g++ is complaining
>:>because NULL is defined as ((void *)0). Defining NULL as (0) makes the
>:>warning go away.
[...]
>:It is madness if ANSI C++ allows implict casting of an integral value
>:of a different size (zero) to a pointer but NOT ((void*)0).
>
>The reason that you cannot implicitly cast (void*) 0 to a null pointer
>is because it would be a type hole (one that C currently allows):

If that is the reason, then it is a bogus reason.
Allowing `(void *)0' to be implicitly converted to a null
pointer does not create any type holes.

>#define	NULL ((void *) 0)
>
>char	*ptr = NULL;	// means char *ptr = ((void *) 0);

There is no type hole here.
The code simply assigns a null pointer to `ptr'.
What's the problem?

>what makes this different from
>
>long	l;
>void	*x = &l;
>char	*p = x;

The difference is that a null pointer can be safely converted
to any type, whereas that property doesn't hold of pointers in
general.

-- 
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fjh@cs.mu.oz.au              |   according to a new system of measuring wealth
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