Xref: utzoo comp.lang.c:13890 comp.lang.c++:1902
Path: utzoo!attcan!uunet!lll-winken!arisia!quintus!ok
From: ok@quintus.uucp (Richard A. O'Keefe)
Newsgroups: comp.lang.c,comp.lang.c++
Subject: Re: Something new for C?
Keywords: offset of vars within structures
Message-ID: <646@quintus.UUCP>
Date: 8 Nov 88 08:41:25 GMT
References: <73@dsoft.UUCP>
Sender: news@quintus.UUCP
Reply-To: ok@quintus.UUCP (Richard A. O'Keefe)
Organization: Quintus Computer Systems, Inc.
Lines: 19

In article <73@dsoft.UUCP> root@dsoft.UUCP (Super user) writes:
>Maybe I've missed something in C, but One of the things I've never found a way
>to do and have always wanted, was a precompiler command to allow me to use
>the offset of an item into a structure. for example:

This is one fo the things that has been easy to do for a long time.
If you're using a UNIX(tm) system, you may already have a header file
/usr/include/struct.h, which defines

	fldoff(Structure_TAG, Field_Name)
	fldsiz(Structure_TAG, Field_Name)

Modulo parens:

	fldoff(Tag, Field) = ((int) &((struct Tag *)0)->Field)
	fldsiz(Tag, Field) = (sizeof ((struct Tag *)0)->Field)

This may give trouble on some 80*86 C compilers.  ANSI C will have
an "official" offsetof macro.  I couldn't find the file on a V.3 '386
system, but the macros worked fine.