An Ubiquitous C bug

[Zev Sero]

Peter = hpa at casbah.acns.nwu.edu (Peter Anvin) 

Peter> Should NULL be all ones?  Performance issues aside, such a
Peter> machine would only need to subtract one when converting an int
Peter> to a pointer, and add one the other way.  In constant
Peter> expressions, such as when using the macro NULL, that can of
Peter> course be done at compile time. 

It would have to be done only at compile time.  Fragments such as:
  int x = 0;
  char *p = (char *)x;
*should* point at location zero if that is a valid address on this
machine, and dereferencing it should give you whatever is at that
address.  *Only* constant expressions evaluating to zero (such as the
macro NULL) represent the null pointer, and these are determined
at compile time.
--
	                                Zev Sero  -  zvs at bby.oz.au
This I say unto you, be not sexist pigs.
		-  The prophetess, Morgori Oestrydingh  (S.Tepper)