Article View: comp.std.c
Article #5220Pointer comparison question
From: Jeffrey_J_Vanepps
Date: Sat, 23 Jul 1988 23:14
Date: Sat, 23 Jul 1988 23:14
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K&R says that you can't reliably compare pointers to one another unless
they both point into the same array. But later they do just that in a
storage allocator. Is this a real discrepancy or am I hallucinating?
I found this because I had to replace the malloc/free functions of
Microsoft C 5.0. Free() does not join adjacent free blocks to form
larger free blocks, and we were suffering fragmentation. Implementing
K&R's malloc/free required casting pointers to (unsigned long) so
they could be compared (it saw some of the pointers as negative when
addresses got up into the 7Fxx:xxxx range).
^^^^^^^^^
that's right, ugly segmented address space.
Anyway, I just wondered about the apparent self-contradiction, and if
there was a better way to do this.
Jeff Van Epps
Jeffrey_J_Vanepps@cup.portal.com
P.S. My sympathy to anyone who is forced to work with either DOS or
segmented architectures.
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!water!watmath!clyde!bellcore!decvax!decwrl!sun!pitstop!sundc!seismo!uunet!portal!cup.portal.com!Jeffrey_J_Vanepps From: Jeffrey_J_Vanepps@cup.portal.com Newsgroups: comp.std.c Subject: Pointer comparison question Message-ID: <7613@cup.portal.com> Date: 23 Jul 88 23:14:05 GMT References: <1608@dataio.Data-IO.COM> <469@m3.mfci.UUCP> <513@proxftl.UUCP> Distribution: na Organization: The Portal System (TM) Lines: 23 XPortal-User-Id: 1.1001.4153