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From: friesen@psivax.UUCP
Newsgroups: net.lang.c
Subject: Re: Failure of "long x(cp) char * cp; { return *((long *) cp); }" is a bug?
Message-ID: <1329@psivax.UUCP>
Date: Wed, 9-Jul-86 18:47:52 EDT
Article-I.D.: psivax.1329
Posted: Wed Jul  9 18:47:52 1986
Date-Received: Sat, 12-Jul-86 10:29:09 EDT
References: <6152@elsie.UUCP> <3783@reed.UUCP>
Reply-To: friesen@psivax.UUCP (Stanley Friesen)
Organization: Pacesetter Systems Inc., Sylmar, CA
Lines: 35

In article <3783@reed.UUCP> kab@reed.UUCP (Kent Black) writes:
> 
>Oh, am I in over my head. . .
>
>If a (char *) can reference any `byte' of memory, and a (long *) can
>can only reference, as example, even number word addresses, then to have
>the compiler correctly cast a char * to a long * would mean it rearranged
>your data for you.  In particular, an array of characters would have to
>be remade into an array of longs with the apropriate (high or low) byte
>holding the character.  Is this all wrong?

	Yes, the  purpose of the cast is to allow you to look at your
array of char(or whatever) *as if* it were an array of longs. It would
defeat the purpose of the cast if the compiler rearranged the memory
for you!
>
>But do you *really want* to cast a char pointer to a long pointer just
>to dereference and return the value?  The example seems to instead call
>for dereferencing the char * and casting the value as a long, e.g.,
>		return (long) *cp;
>  
	No, this does something completely different. This reads a
single byte from memory, *extends* it to a long and returns the
result. On the other hand 
		return *(long *)cp;

reads a long from memory and returns it. That is it sort of acts like
a union and allows you to look at the same piece of memory as having
different types.
-- 

				Sarima (Stanley Friesen)

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