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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c++
Subject: Re: What is the data structure of a NULL?
Date: Tue, 31 Dec 2019 11:11:17 -0800
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Chris Vine <chris@cvine--nospam--.freeserve.co.uk> writes:
[...]
> You have a point so far as concerns, say, memset'ing structs of
> trivial type to all-bits-zero where those structs contain pointers
> which you want to be NULL (should your code actually do that).  But you

null, not NULL.

> are completely wrong in your example above.  'array' will be a null
> pointer constant if calloc fails, and the test for falsity will work
> correctly irrespective of whether the null pointer constant is
> signalled by all-bits-zero.

'array' will be a null pointer, not a null pointer constant.

A *null pointer constant* is a source code construct (and NULL is a
macro that expands to a null pointer constant).  A *null pointer* is a
value that can exist at run time.

It's probably OK in most cases to use the term "NULL" to refer to a null
pointer value, but in this case the distinction is a large part of what
we're talking about, so I suggest being a bit more pedantic than usual.

> You have something wrong with your mental image of this.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
    [Note updated email address]
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */