From: "John M. Aldrich" <fighteer AT cs DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: assigning the correct adress?
Date: Tue, 17 Feb 1998 18:43:02 -0500
Organization: Two pounds of chaos and a pinch of salt.
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Donnie Roos wrote:
> 
> In my program i have a variable of word size (unsigned short)
> and two pointers which point to the two bytes of this word.
> 
> word TMP;
> byte *ptr_TMP_l, *ptr_TMP_h;
> 
> In my code i try to assign it in the following way.
> It needs a cast to increase the adress by 1 byte instead of a word.
> 
> ptr_TMP_l = & (byte) reg_TMP;
> ptr_TMP_h = & (byte) reg_TMP + 1;
> 
> When compiling my source from RHIDE (default options) i get the
> message: invalid lvalue in unary `&'

Of course this won't work.  It is logically impossible to take the
address of the result of a typecast; the value this represents does not
exist in any form that would be useful to your program.  What you need
to do is figure out the address first and then typecast it to the proper
pointer type, as shown below:

ptr_TMP_l = (byte *) (&reg_TMP);
ptr_TMP_h = ( (byte *) (&reg_TMP) ) + 1;

I've added parentheses for clarity, but the order of operations doesn't
require them.

Hope this helps.

-- 
John M. Aldrich, aka Fighteer I <fighteer AT cs DOT com>  UIN# 7406319

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