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From: andrew@teletron.UUCP (Andrew Scott)
Newsgroups: comp.lang.c
Subject: pointer cast question
Message-ID: <100@teletron.UUCP>
Date: Tue, 15-Sep-87 15:57:00 EDT
Article-I.D.: teletron.100
Posted: Tue Sep 15 15:57:00 1987
Date-Received: Sun, 20-Sep-87 03:00:35 EDT
Organization: TeleTronic Communications Ltd., Edmonton, Alta.
Lines: 16
Keywords: pointer  cast  alignment

I am curious as to why pointer casts behave the way they do.  Specifically,
casting from a pointer to one type to a pointer to another type may cause
address exceptions if the alignment requirements of the two types differ
(as described in section 14.4 of K&R).  Thus, it is the programmer's
responsibility to insure that the pointers involved in such expressions
point to valid addresses after the cast.

Why is this the case?  It seems to me that the cast should produce code
which aligns the pointer to a proper alignment boundary if necessary.  The
compiler should hide such a machine dependant thing from the programmer.
What is the purpose of such a cast (other than to make lint happy) if not
to convert a valid data value of one type to a valid data type of another?

Does anybody have any answers?

	Andrew