Is #define NULL 0L ok?

[Mark Callow]

The situation as succintly as I can put it is:

1)	The C language definition (K&R) says that the *symbol* '0' may be
	used to represent a null pointer.

2)  	The compiler therefore has to identify places where '0' is being
	used as a null pointer (for example by identfying assignments to
	or comparisons with pointers) and it has to *replace it with* the
	actual value of a null pointer for the particular machine and the
	data type being pointed to.

3)	Given that there is no requirement (and no way) to inform the compiler
	of the types (or number) of arguments to an external function the
	compiler can't know that some argument to your function is a pointer.

	In the case of
	
		func( 0 );
		
	therefore,  the compiler can't intuit whether '0' is being used as a
	null pointer or in its more common usage as the symbol for the
	arithmetic value 0.

4)	The compiler assumes the more common usage so if the argument to
	*func* is actually a pointer you *must* give an explicit cast to
	the correct type of pointer.  For example you must say

		func( (char *)0 );
-- 
>From the Tardis of Mark Callow
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