Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!uunet!snorkelwacker.mit.edu!bloom-picayune.mit.edu!news
From: jfc@athena.mit.edu (John F Carr)
Newsgroups: comp.lang.c
Subject: offsetof
Message-ID: <1991Mar4.182846.6386@athena.mit.edu>
Date: 4 Mar 91 18:28:46 GMT
Sender: news@athena.mit.edu (News system)
Organization: Massachusetts Institute of Technology
Lines: 23


Two questions about offsetof.

1. Is the following legal?

	struct foo { struct bar { int b;} a;};
	offsetof (struct foo, a.b);

The X toolkit source code assumes that offsetof (struct foo, a.b) is legal.
The compiler I use disagrees.  I think it is right, but I'm not sure.

2. On how many compilers does the following trick to emulate offsetof not work:
	(int)&((struct foo*)0)->member

How many of those do not provide an offsetof macro?

(I know of only one compiler which doesn't like the version using a NULL
pointer (Metaware High C 1.4r for the IBM RT), and that compiler provides
an offsetof macro).

 
--
    John Carr (jfc@athena.mit.edu)