(ref.doc)kanze 200194

Newsgroups: comp.std.c++
From: [email protected] (James Kanze)
Subject: Re: Plum&Saks Pointer Advice
Date: 20 Jan 1994 16:55:36 GMT

In article <[email protected]> [email protected] (Sharon
Barton) writes:

|> Can anyone tell me why Thomas Plum and Donald Saks recommend using
|> 0 to initialize pointers instead of NULL in their C++ Programming
|> Guidelines book?  This isn't consistent with ANSI C.  Isn't C++
|> based on ANSI C?

Here we go again:-(.

Historically, a number of early C++ compilers (well, at least one)
were really just front-ends for the C compiler.  In addition, since
the commercial market was not worth the effort, the simple solution of
just enrobing the standard C header files in extern "C" { ... } was
adapted.

In C, NULL may be legally defined as '(void*)0', and some systems
actually do this.  This works well in C, since a void* can be assigned
to any type of pointer.  On the other hand, C++ does not allow an
implicit cast *from* void*, and this lead to the fact that you could
not assign NULL to a pointer (nor compare a pointer to NULL, nor...).

Today, there is a significant commercial market for C++; if the header
files for C++ define NULL as '(void*)0', then a complaint to your
vendor is in order.  In fact, I know of no current implementation
where this is the case.  So there is no *technical* reason not to use
NULL.

The question of style remains.  I have many years of C experience, and
in all of the companies, the house style was to use NULL.  I find that
information is missing when 0 is used; the type system is being
abused.  In fact, until the last big discussion of this on the net, I
was convinced that without the obslete technical reason, only a hacker
would use 0.  In that discussion, however, it became clear that
several people for whom I have great respect, and who are definitly
software engineers and not hackers (Paul Lucas and Pete Becker come to
mind) preferred 0 to NULL, even while recognizing that the technical
imperative was no longer valid.  As a result, I am forced to consider
this a question of style.  (But I still think my style is better:-).)