TITLE: Portability and comparing null pointers

PROBLEM: ???

 ... the constructs 
       if (p)
 and
       if (!p)
 checks for NULL and non-NULL respectively.  Is this portable to *all*
 platforms?


RESPONSE: nh@cbnewsg.cb.att.com (nicholas.hounsome)

It is NOT portable for C.
It is portable for C++ which is the group that you have posted to -
did you mean to?


RESPONSE: steve@taumet.com (Steve Clamage), 26 Jan 93

Just to reduce confusion, Hounsome's comments are not correct.
Tony Hansen posted the best answer to this question.

Both C and C++ guarantee that any pointer which compares equal to a
null pointer constant is a null pointer, and any null pointer compares
equal to a null pointer constant.  Finally, any null pointer compares
equal to any other null pointer when suitably cast.

In C++, a literal zero is most appropriate for use as a null pointer
constant.  In any event, for both C and C++, use the NULL macro which is
supplied in the standard header files in preference to writing your own
macro.