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From: jac@paul.rutgers.edu (J. A. Chandross)
Newsgroups: comp.compilers
Subject: Layout of Structs
Keywords: symbol tables, offsets, psects, real-time monitor
Message-ID: <3992@ima.ima.isc.com>
Date: 28 May 89 02:06:27 GMT
References: <3979@ima.ima.isc.com>
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Reply-To: jac@paul.rutgers.edu (J. A. Chandross)
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stein@pixelpump.osc.edu (Rick 'Transputer' Stein)
> I have some questions about how a compiler constructs a symbol table.
> [questions on structure layout deleted]

Our erstwhile moderator replies:
> C compilers have the right to lay out structures any way they see fit,
> unless the ANSI committee changed the rules.

I quote, without permission, from The Bible, page 196, First Edition:

"Within a structure, the objects declared have addresses which increase 
as their declarations are read lef-to-right.  Each non-field member of 
a structure begins on an addressing boundry appropriate to its type; 
therefore, there may be unnamed holes in a structure.  Field members 
are packed into machine integers; they do not straddle words.  A field 
which does not fit into the space remaining in a word is put into the 
next word....."

It is a Good Thing [tm] that structures are laid out in this way.  As
a hardware type, I often need to write device drivers.  Being able to 
impose a structure onto a hardware memory map is a very useful thing, 
indeed.

Jonathan A. Chandross
Internet: jac@paul.rutgers.edu
UUCP: rutgers!paul.rutgers.edu!jac
[I hope I'm not the erstwhile moderator yet, but stand corrected.  -John]
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