Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mailrus!cornell!uw-beaver!blake!keffer
From: keffer@blake.acs.washington.edu (Thomas Keffer)
Newsgroups: comp.lang.c++
Subject: ?-tion on sizeof classes
Keywords: sizeof structure boundaries
Message-ID: <2425@blake.acs.washington.edu>
Date: 16 Jun 89 03:10:40 GMT
Reply-To: keffer@ocean.washington.edu
Organization: University of Washington, Seattle
Lines: 28

On p. 54 of The Bible BS says

	"It is not possible to compute the size of an
	object of a structure type simply as the sum of its
	members.  The reason for this is that many machines
	require [certain objects to] be allocated on
	architecture - dependent boundaries."

Aside from this cavaet, is there any other reason why the size of an
object might not be the sum of its members?  Suppose I was willing
to check for the alignment problem.  Could I then be assured that
the whole is the sum of its parts, or will there ever be a "hidden"
member, put in there by the compiler?

The reason I ask is that it would sure be nice if I could assume
	sizeof(Complex) == 2*sizeof(double)
because this is what a LOT of FORTRAN routines assume.  FFT
routines, for example, routinely treat an N point complex vector as
a 2N real vector.  

-tk

---
 Dr. Thomas Keffer          | Internet: keffer@sperm.ocean.washington.edu
 School of Oceanography     | BITNET:   keffer%sperm.ocean.washington.edu@UWAVM
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