Jonas Maebe wrote:
On 13 Sep 2006, at 19:39, Vinzent Höfler wrote:
In FPC, nil = pointer(0) on all currently supported platforms, but in
principle it could be anything.
I'm making enemies now,
Where?
but:
If the NIL pointer is represented by another value (like 0xFFFFF780 or
such) on a given target platform, the integer conversion from a
_compile-time_ constant 0 literal should still lead to a NIL
representation.
I don't see why, except for compatibility with code built on wrong
assumptions.
For C language interfacing, I'd say.
Basically that would be the same behaviour as what the C-standard
guarantees.
Does it guarantee that (void*)(0) == NULL?
Yes. It's about the only guarantee it gives regarding the "null pointer
constant":
--- 8< ---
ISO/IEC 9899:1999 (E) - 6.3.2.3 Pointers
[...]
3 An integer constant expression with the value 0, or such an expression
cast to type void *, is called a null pointer constant[55] If a null
pointer constant is converted to a pointer type, the resulting pointer,
called a null pointer, is guaranteed to compare unequal to a pointer to
any object or function.
4 Conversion of a null pointer to another pointer type yields a null
pointer of that type.
Any two null pointers shall compare equal.
5 An integer may be converted to any pointer type. Except as previously
specified, the result is implementation-defined, might not be correctly
aligned, might not point to an entity of the referenced type, and might
be a trap representation.
[...]
[55] The macro NULL is defined in <stddef.h> (and other headers) as a
null pointer constant; see 7.17.
--- 8< ---
Vinzent.
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