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From: bruce@seismo.gps.caltech.edu (Bruce Worden)
Newsgroups: comp.lang.c
Subject: Re: ** help...
Summary: pad those pups out
Message-ID: <1990Aug30.191533.20589@laguna.ccsf.caltech.edu>
Date: 30 Aug 90 19:15:33 GMT
References: <2409@dsacg2.dsac.dla.mil> <1884@jura.tcom.stc.co.uk> <11245@crdgw1.crd.ge.com> <1912@islay.tcom.stc.co.uk>
Sender: bruce@seismo.gps.caltech.edu (Bruce Worden)
Organization: California Institute of Technology, CA
Lines: 44

In article <1912@islay.tcom.stc.co.uk> rmj@htc1.UUCP (Rhodri James) writes:
[material deleted]
>The crux of the potential health hazard comes with the definition of
>sizeof, which K&R2 says (section 6.3) gives a size_t result equal to the
>size of the specified object or type in bytes. Nothing here guarentees
>that the *end* of the object will be such that another object straight
>after it in memory (which is what the multiplication implies) will be
>correctly aligned. Many structs would give appropriately odd lengths;
>I'm sure you don't need examples.

Actually, examples would be nice, since I don't see what you mean. 
On a machine requiring alignment:

struct thingy {
	char a;
	}

sizeof(struct thingy) is 1.

struct thingy {
	int i;	/* four byte ints */
	}

sizeof(struct thingy) is 4.

struct thingy {
	int i;
	char a;
	}

sizeof(struct thingy) is 8.  The structure is padded to insure that 
alignment is maintained.

> ... Can anyone
>quote chapter and verse invalidating this argument (please)?

I don't know what the standard says about the issue (if anything), but it 
is difficult to imagine a serious vendor shipping a system that required 
more than single byte alignment and in which the structure in the last 
example was size 5.  It is not so much a question of the standard, but, 
rather, one of functionality. 
--------------------------------------------------------------------------
C. Bruce Worden                            bruce@seismo.gps.caltech.edu
252-21 Seismological Laboratory, Caltech, Pasadena, CA 91125