Xref: utzoo comp.sys.ibm.pc:22384 comp.sys.intel:611
Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!iuvax!bobmon
From: bobmon@iuvax.cs.indiana.edu (RAMontante)
Newsgroups: comp.sys.ibm.pc,comp.sys.intel
Subject: Re: correct code for pointer subtraction
Message-ID: <15891@iuvax.cs.indiana.edu>
Date: 18 Dec 88 16:25:11 GMT
Reply-To: bobmon@iuvax.UUCP (RAMontante)
Organization: malkaryotic
Lines: 20

chasm@killer.DALLAS.TX.US (Charles Marslett) writes:
>
>	[...]	  And subtraction of
>pointers OUGHT TO BE portable (to reiterate my original statement, the
>Microsoft and Borland compilers are broken since they do not work "right").

I don't buy this; why do you say they don't work "right"?  Pointer
subtraction is only valid when the pointers are to the same array, and
TurboC (at least) is simply referencing off the DS register in small
memory models.  So the pointers may be restricted in range, but they
should give the correct number of ELEMENTS (not bytes, unless  the array
elements are byte-sized).

Note that the original code in this thread made the mistaken assumption
that its "diff()" function was dealing in pointers that were guaranteed
to refer to the same array; in fact, they were independent pointers
which happened, in the example call, to have received values based on a
common array in the caller program.

Perhaps this discussion ought to move to comp.lang.c.