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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.std.c
Subject: Re: so how do I do it? (was Re: call to revolt)
Message-ID: <16561@smoke.brl.mil>
Date: 27 Jun 91 20:20:01 GMT
References: <rabson.677868220@physics.ubc.ca> <m0jspJY-0001ieC@shiva.reed.edu> <1991Jun27.115736.18417@tkou02.enet.dec.com>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 17

In article <1991Jun27.115736.18417@tkou02.enet.dec.com> diamond@jit533.enet@tkou02.enet.dec.com (Norman Diamond) writes:
>>and then (struct foo *)p->c  or (struct foo *)p->u
>This is legal.

Actually, no.  ((struct foo *)p)->c is the way to write this.
You want to cast the pointer, not the char member.

>>this is nonportable, as to my understanding, as struct arrangements are not
>>guaranteed.
>Huh?  Oh, you mean that the buffer was laid out by some other entity
>than your C program.

I don't know exactly what he meant (could have been any of several things),
but the problems are:  (1) there might be padding between the struct members
and (2) the representation, especially of the unsigned member, may not agree
with the C implementation's.  The first problem is easy; the second one is
harder.