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From: thomas@utah-gr.UUCP (Spencer W. Thomas)
Newsgroups: net.lang.c
Subject: Re: Casting Question
Message-ID: <1655@utah-gr.UUCP>
Date: Fri, 17-Jan-86 18:09:50 EST
Article-I.D.: utah-gr.1655
Posted: Fri Jan 17 18:09:50 1986
Date-Received: Sun, 19-Jan-86 05:00:17 EST
References: <162@butler.UUCP>
Reply-To: thomas@utah-gr.UUCP (Spencer W. Thomas)
Organization: Univ of Utah CS Dept
Lines: 22

In article <162@butler.UUCP> chinn@butler.UUCP (David Chinn) writes:
>Inst    *pc;            /* program counter during execution */
>			/* pc is declared to be a pointer to an Inst;
>	.	           or, a pointer to a pointer to a function  */

>        	pc = *((Inst **)(savepc+2));     /* next stmt */
>                     ^^^^^^^^^^^^^^^^^^^^^^
>                      So what is this for?
What appears to be happening here is that the location savepc+2 is a
POINTER to a location containing the desired pc value.  Certainly
(in this case) removing the cast will not affect the code (you are still
dereferencing savepc+2, and the value there is still a pointer), but the
types on the left and right of the assignment DO NOT MATCH!  If you run
lint over the code, it will complain.  The right hand side of the
assignment will be an Inst, while the left side is an Inst *.  The cast
keeps the types right.


-- 
=Spencer   ({ihnp4,decvax}!utah-cs!thomas, thomas@utah-cs.ARPA)
	"Ask not what your kernel can do for you, but rather what you
	 can do for you kernel!"