Xref: utzoo comp.lang.c:14096 comp.lang.c++:1985
Path: utzoo!utgpu!watmath!rbutterworth
From: rbutterworth@watmath.waterloo.edu (Ray Butterworth)
Newsgroups: comp.lang.c,comp.lang.c++
Subject: Re: offsetof (was: Re: Something new for C?)
Keywords: offset of vars within structures
Message-ID: <22164@watmath.waterloo.edu>
Date: 15 Nov 88 16:29:01 GMT
References: <73@dsoft.UUCP> <481@njsmu.UUCP> <26740@ucbvax.BERKELEY.EDU>
Organization: U of Waterloo, Ontario
Lines: 22

In article <26740@ucbvax.BERKELEY.EDU>, jas@ernie.Berkeley.EDU (Jim Shankland) writes:
> On such machines, you must have an instance of the structure:
> struct mumble foo;
> int mem_offset = (char *)(&foo.member) - (char *)(&foo);
> Sigh.  The things you have to put up with in the portability trenches.


The same argument applies for the alignof macro:

#define alignof(type) /* assumes double is max aligned */ \
    ( (char*)&(((struct {double _d; char _c; type _t;}*)0)->_t) \
    - (char*)&(((struct {double _d; char _c; type _t;}*)0)->_c) )

which is equally non-portable,
but for some reason the Committee chose not to make this macro
part of the Standard even though alignof() seems to be more useful
(to me at least) than offsetof().


> This is about the 10,000th reason that we need ANSI C *now*.
And this is one more reason why "ANSI C now" still isn't good enough.