Re: [Boost-users] null_ptr?

From: Robert Dailey (rcdailey_at_[hidden])
Date: 2008-01-02 18:09:21

I can't really agree or disagree, as my information comes from an article I
read a long time ago. It stated that the portable way to assign NULL to a
pointer is to first cast it to the type of the lvalue. At the very least I
would expect (out of pessimism) SOME compiler in the world today to throw a
warning when it sees this:

class foo {};
foo* myfoo = 0;

However, I haven't personally tried this. In all honesty I don't see any
reason why the compiler would ever need to complain about this since I don't
foresee any problems with assigning an integral constant of 0 to pointer
types, or even using them during comparisons. However I guess if you guys
say that it is portable, I suppose I should just save myself some executable
size and avoid the use of nullptr. At this point the only real use I see in
a nullptr class/struct is for readability.

Where in the standard does it state that assigning an integral constant to a
pointer type is legal? Perhaps there is some more generic rule in the
standard to which this concept applies.

On Jan 2, 2008 4:17 PM, Scott McMurray <me22.ca+boost_at_[hidden]> wrote:

> On 02/01/2008, Robert Dailey <rcdailey_at_[hidden]> wrote:
> > They are unrelated types.
> >
>
> But 0 is a compile-time integral constant with value 0, and is
> therefore implicitly convertible to any null pointer.  Why do you
> think the comparison is any less portable than the initialization?
>
> And the reinterpret_cast is actually less portable, since it assumes
> that the null pointer is represented by a null bit sequence.  The
> correct way to cast 0 to a null pointer is through static_cast (or
> boost::implicit_cast).
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