Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!ncar!gatech!udel!mmdf
From: ns@csd.cri.dk (Nick Sandru)
Newsgroups: comp.os.minix
Subject: NULL
Message-ID: <57140@nigel.ee.udel.edu>
Date: 25 Jun 91 11:51:53 GMT
Sender: mmdf@ee.udel.edu
Lines: 36

Exerpt from FAQ posting in comp.lang.c:

---
Section 1. Null Pointers

[...]

3.   What is NULL and how is it #defined?

A:   As a matter of style, many people prefer not to have unadorned 0's
     scattered throughout their programs.  For this reason, the
     preprocessor macro NULL is #defined (by <stdio.h> or <stddef.h>),
     with value 0 (or (void *)0, about which more later).  A programmer
     who wishes to make explicit the distinction between 0 the integer
     and 0 the null pointer can then use NULL whenever a null pointer is
     required.  This is a stylistic convention only; the preprocessor
     turns NULL back to 0 which is then recognized by the compiler (in
     pointer contexts) as before.  In particular, a cast may still be
     necessary before NULL (as before 0) in a function call argument.
     (The table under question 2 above applies for NULL as well as 0.)

     NULL should _only_ be used for pointers; see question 8.

     References: K&R I Sec. 5.4 pp. 97-8; K&R II Sec. 5.4 p. 102; H&S
     Sec. 13.1 p. 283; ANSI Sec. 4.1.5 p. 99, Sec. 3.2.2.3 p. 38,
     Rationale Sec. 4.1.5 p. 74.

---

I will post the whole article if there is interest for it.


Nick Sandru

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