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From: john@anasazi.UUCP
Newsgroups: net.unix,net.unix-wizards,net.arch,net.lang.c
Subject: (Really addressing inside struct)Re: get size of malloc'd object
Message-ID: <403@anasazi.UUCP>
Date: Sat, 5-Jul-86 13:03:15 EDT
Article-I.D.: anasazi.403
Posted: Sat Jul  5 13:03:15 1986
Date-Received: Fri, 11-Jul-86 05:57:37 EDT
References: <165@daisy.UUCP> <334@valid.UUCP> <2206@peora.UUCP>
Reply-To: john@anasazi.UUCP (John Moore)
Organization: Anasazi, Phoenix Az.
Lines: 42
Xref: watmath net.unix:8559 net.unix-wizards:18769 net.arch:3662 net.lang.c:9798

A related problem that we have found with C alignment is this:
We have a structure with a number of structures contained within it. 
Because of linked list processing, we have a pointer to one of the
structures within, and we want to derive a pointer to the top of
the structure without LINT complaining, and in a truly portable way.
How can this be done? Many things have been tried without success
here at Anasazi. Example:

struct links {
   struct links *forward;
   struct links *backward;
};

struct foo {
   char bar;
   struct links snake;
   struct whocares junk;
   struct links lizard;
};

struct links *reptile;

Assume that reptile points to the lizard structure of a "foo" structure.
What construct allows one to do the following:

struct foo *iwish = (mystery function of reptile);

Example of a wrong solution:
struct foo *iwish = (struct foo *)((char *)reptile + (char *)0->lizard);

Any help would be appreciated.

-- 
John Moore (NJ7E)
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(602) 861-7607 (day or evening)
7525 Clearwater Pkwy, Paradise Valley, AZ, 85253 (Home Address)

The opinions expressed here are obviously not mine, so they must be
someone else's.