Re: union and overstamping zero values

From:

Adrian Hawryluk <adrian.hawryluk-at-gmail.com@nospam.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 22 Mar 2007 16:47:33 CST

Message-ID:

<hsBMh.399$__3.35@edtnps90>

andrew_nuss@yahoo.com wrote:

Not portably. The NULL pointer need not to be represented
by a bit pattern that also represents the zero integer

If so, then why does this work?:

main {
    void* p = 0;
    if (p == 0)
        p = malloc(2000);
    if (p)
        free(p);
}

I have chosen to use zero with pointers rather than the #define NULL
according to some recommendation that I saw once upon a time.

This is because the compiler makes provisions for this since the
language does (I don't know specifically where, I just know it does).

A void * being assigned 0 (NULL) or used as a test (NULL = FALSE, else
TRUE) has long historical reasons and would break a lot of code if not
implemented as such. So NULL does not necessarily mean all bits 0, but
the compiler makes it appear to be so.

Adrian
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