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Path: utzoo!mnetor!seismo!vrdxhq!dgis!bms-at!stuart
From: stuart@bms-at.UUCP (Stuart D. Gathman)
Newsgroups: comp.lang.c
Subject: Re: structure element offsets
Message-ID: <292@bms-at.UUCP>
Date: Tue, 25-Nov-86 21:17:48 EST
Article-I.D.: bms-at.292
Posted: Tue Nov 25 21:17:48 1986
Date-Received: Wed, 26-Nov-86 03:40:37 EST
References: <1096@spice.cs.cmu.edu>
Organization: Business Management Systems, Inc., Fairfax, VA
Lines: 26
Keywords: structure, offset
Summary: Structure offsets and other goodies

In article <1096@spice.cs.cmu.edu>, bader@spice.cs.cmu.edu (Miles Bader) writes:
> Is there any way of finding the offset of a structure element from
> the beginning of a structure in a portable AND efficient way?  I have

--------spos.h---------------------------
/*
  structure info macros
  spos	- member offset
  sposa	- array member offset (since &array often illegal)
  slen	- member size
  smp	- convert pointer to member to pointer to enclosing structure
  smpa	- smp for array member

  NOTE - these macros assume sizeof(char) == 1.  If the nerds win and
  we have to do it, this file needs to be fixed.

  This file can also be tweaked for stupid compilers that like to evaluate
  constants at run time.
*/
#define spos(s,m)	((char *)&((struct s *)0)->m - (char *)0)
#define sposa(s,m)	((char *)((struct s *)0)->m - (char *)0)
#define slen(s,m)	(sizeof((struct s *)0)->m)
#define smp(s,m,p)	((struct s *)(p-&((struct s *)0)->m))
#define smpa(s,m,p)	((struct s *)(p-((struct s *)0)->m))
-- 
Stuart D. Gathman	<..!seismo!dgis!bms-at!stuart>