Re: Any pointer to Byte Alignment & Structure Padding?

[Steve Graegert <graegerts@gmail.com>]

On 8/2/05, Amit Dang <amit_dang@intersolutions.stpn.soft.net> wrote:
> Hi Glynn,
>    You are very right in saying that "there is no need for structures to
> have same layout on different platform" until structures are being written
> directly to the file system. But many time there is a requirement that the
> data file can be moved across platforms.

Reading and writing binary files in a portable way is not possible as
is.  Unless it is absolutely necessary to read/write binary data you
should always prefer a portable solution like XML and its derivatives.

An easy way to improve portability of binary files is to prepend a
header that contains enough information to discover byte ordering,
floating-point format, etc.  That makes it easy enough to write simple
tools that are able to read/write binary data.

All other techniques used for binary data are quite complex and rely
on other (quasi-)standards like XDR (invented by Sun and used for NFS
and RPC), CCITT X.409 or ASN.1.  They can be seen as a meta-languages
that specify the data representation for particular file formats.
 
> ----- Original Message -----
> From: "Glynn Clements" <glynn@gclements.plus.com>
> To: "Amit Dang" <amit_dang@intersolutions.stpn.soft.net>
> Cc: <linux-c-programming@vger.kernel.org>
> Sent: Tuesday, August 02, 2005 4:24 PM
> Subject: Re: Any pointer to Byte Alignment & Structure Padding?
> 
> 
> >
> > Amit Dang wrote:
> >
> > > Thanks Steve. So what is the best way of laying down a structure
> definition
> > > to over come cross platform issues?
> > > I read about introducing some explicit padding in the structure to take
> care
> > > for cross platform issues but for that I suppose one should have
> information
> > > about byte alignment & structure padding on all targeted platforms. Is
> that
> > > true or there is some generic way of doing that? (Apart from using
> compiler
> > > option to remove any padding )
> >
> > Structure layout has nothing to do with portability. There's no reason
> > why a structure needs to have the same layout on different platforms.
> > In most situations, you don't need to know anything about how the
> > structure is laid out; you just reference the fields.
> >
> > --
> > Glynn Clements <glynn@gclements.plus.com>
> > -
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