Re: question about nullptr

James Kuyper <jameskuyper@alumni.caltech.edu> writes:

On 7/6/24 4:23 PM, Chris M. Thomasson wrote:

On 7/6/2024 7:04 AM, Scott Lurndal wrote:

...

Whereas I spent 6 years programming on an architecture[*] where a
null pointer was represented in hardware by the value 0xc0eeeeee.  I
always
use the NULL macro in both C and C++ code.

 
Where:
 
void* x = 0;
 
Should be x = 0xc0eeeeee, right?

>
No, 0 is a null pointer constant. The C standard requires that when a
null pointer constant is converted to a pointer value, it must be
converted to a null pointer of that type. The result will be that the
representation of 'x' after such an assignment would be 0xc0eeeeee.
>
Whether or not an integer value of 0xc0eeeeee can be converted to a
pointer type, and what that pointer's value would be after the
conversion is up to the implementation.
>
Note that even after x acquires that representation, it's still required
to compare equal to 0. For the purposes of the comparison, the null
pointer constant gets converted to a null pointer of the appropriate
type. All null pointers, regardless of representation (the C standard
allows there to be multiple ways of representing null pointers) must
compare equal.

Furthermore, `void* x = 0xc0eeeeee;` is a constraint violation.  There
is no implicit conversion from integers to pointers other than the
special case of a null pointer constant, which 0xc0eeeeee is not.

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */