Let's define our own NULL II

[Mark Stevans]

So far, most responders to the article I posted on Wednesday have not addressed
my question.  I am not asking about what is a legal definition of NULL.  I am
asking whether one should define NULL in a product-wide header file *just* so
that people won't have to include <stdio.h> if they only need a definition of
"NULL" in a module.

Perhaps I am partially at fault: to avoid prejudicing responses one way or
the other, I gave the question without presenting any guiding arguments for
either side.  Here are some arguments to start us off on the right track (my
personal opinion should now become obvious):

Pros:
	Assuming you don't need to use the standard I/O library in a module,
	compilation will be slightly faster if you could leave out "stdio.h"
	and still have "NULL" defined.

	You should never include something you don't need, so if you are not
	actually using the standard I/O library in a module, you shouldn't
	have to include it.

Cons:
	For reasons of portability and style, you should never create your own
	copies or versions of system-dependent constants unless the system
	header definition is incorrect or otherwise unusable.  I know that
	some say NULL is system-dependent, while some say it is not.  Ignore
	this one item if you favor the latter, but please *do not* mutate my
	posting into an argument about various definitions of NULL.

	Like it or not, <stdio.h> actually contains two completely separate
	things: it defines the structures and declares the external variables
	of the standard I/O library, *and* it defines "NULL".  So if you need
	either one, you should include <stdio.h>.  It contains no definitions
	(as opposed to declarations), so including it will never increase the
	size of your compiled code (except possibly a few words of debugging
	symbol space in the object file).  Thus, including it never does any
	harm.

	The fraction of a second you save in compile time by not including
	<stdio.h> is insignificant.  Even if you think you will not need the
	standard I/O library in some particular module, you or some later
	maintainer might someday insert an error message or debugging
	statement like "fprintf(stderr, ...)" or open a file with "fopen",
	and it will fail to compile until you edit the file to re-include
	<stdio.h>, thus wasting far more programmer and compilation time in
	one fell swoop than you previously saved by not including it.  In
	general, this falls completely in the category of
	"micro-optimizations", where one puts emphasis on optimizing tiny
	details while overlooking the big picture.

A personal message to Guy Harris at Sun: I'd love to see your analysis of
this -- I encountered this idea first at a company I will not name -- the
one we both worked at as of the beginning of 1984 (though I was at their main
facility).

						Mark "The Shark" Stevans