Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uwm.edu!cs.utexas.edu!uunet!xstor!iverson
From: iverson@xstor.UUCP (Tim Iverson)
Newsgroups: comp.std.c++
Subject: Re: Packing, Ordering, and Rearranging
Message-ID: <198@xstor.UUCP>
Date: 20 Aug 90 22:59:29 GMT
References: <1030@lupine.NCD.COM> <56637@microsoft.UUCP> <195@xstor.UUCP> <1233@lupine.NCD.COM>
Reply-To: iverson@xstor.UUCP (Tim Iverson)
Organization: Storage Dimensions, Inc.
Lines: 22

In article <1233@lupine.NCD.COM> rfg@NCD.COM (Ron Guilmette) writes:
>In article <195@xstor.UUCP> iverson@xstor.UUCP (Tim Iverson) writes:
><If the language had constructs for specifying such things as packing and
><ordering (bit, word, etc.), it could deal transparently with structures
><created outside of its own venue and should result in code that is
><both cleaner and more portable.
>
>You can definitely specify what you want the exact layout of a struct to be
>in C and have it be obeyed and have it be portable.

I don't know what kind of C you're using, but in both K&R and ANSI C, the
structs are definitely not WYSIWIG - the compiler is allowed to insert any
number bytes between fields for the sake of padding.  This makes the struct
wholely non-portable; i.e., two programs with the same struct are not
guaranteed to interpret the data in the struct in the same way.  BTW,
almost all of the compiler vendors realize this and provide some way to
"pack" a struct (e.g. #pragma pack()).

>Ron Guilmette  - Internet: rfg@ncd.com      uucp: ...uunet!lupine!rfg

- Tim Iverson
  uunet!xstor!iverson