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From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: sizeof a struc field
Message-ID: <11338@smoke.BRL.MIL>
Date: 19 Oct 89 10:07:51 GMT
References: <7710@microsoft.UUCP> <11086@smoke.BRL.MIL> <131@dtoa3.dt.navy.mil> <11316@smoke.BRL.MIL> <1234@crdos1.crd.ge.COM>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 23

In article <1234@crdos1.crd.ge.COM> davidsen@crdos1.UUCP (bill davidsen) writes:
>What the original poster wanted was the size of a field within a struct.
>He proposed using:
>	sizeof(((struct mytype *)0)->field)
>which involves using a null values pointer. The value of this under pcc
>compilers is the size of the field within a struct mytype. You interpret
>the standard to forbid this.

No, what I say is that the Standard does not require that it work
as the programmer seems to expect it to.  That's not the same thing.
A conforming implementation is free to make it work if it so chooses.
It is also free to not make it work.

>Do you also interpret the standard to forbid:
>	int fieldlen = sizeof(head->a);

Of course not.  It does forbid
	int fieldlen = sizeof(((struct mytype*)0)->a).

As I keep telling you, it is NOT an issue about sizeof!
It's an issue about ->.
So long as you persist in trying to determine this by reading the
sizeof specs in the Standard, you'll never understand what I'm saying.