NULL pointer

[Alexis Dimitriadis]

> 	#define NULL	((char *) 0)
> 
> rather than arithmetic zero. This would make it work on machines which use a
> non-zero null pointer. I have tried doing this in a number of programs to
> examine the effect on lint and/or the generated code, and have yet to find a
> case where it caused a problem (although it did reveal a few genuine bugs in
> "working code").

What exactly did you try?  Defining NULL this way generates _compiler_
errors whenever you use NULL in a context that requires anything other
than a char pointer, e.g. a comparison.  The only case when it _fixes_
things is when NULL is a function argument, and the draft standard will
provide for function argument coercion, as well.  Example:

#include <stdio.h>
#undef NULL
#define NULL ((char *)0)
main()
{
	if (fopen("foo", "w") == NULL)
		;
}
% cc t.c
"t.c", line 8: warning: illegal pointer combination

--Alexis Dimitriadis
-- 
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