[Qt-interest] Question about bitfields

[Atlant Schmidt]

All:

> You need to know which end to start from.  Especially if you
> are getting a bucket of bits from another machine and you
> cannot guarantee it has the same byte order as your machine.

  Right.

  Within a single application on a single machine, byte-
  ordering with bitfields (and other issues around how
  structs are packed) is no problem. But the moment you
  move bitfield data to another machine (via a file or
  or via a network), you may have byte-ordering problems.

  Given that it's pretty loosely specified how structs
  can be packed, you even need to be careful how things
  are packed *ON THE SAME MACHINE* if you've used more
  than one compiler or linker. It's entirely possible that
  a given compiler might blow a bitfield out to use an
  complete byte (or more!) for each individual bit if
  the compiler thinks that's an optimum implementation
  for your chosen speed/size trade-offs.

                           Atlant


-----Original Message-----
From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Dan White
Sent: Friday, July 16, 2010 11:13 AM
To: pritam ghanghas
Cc: Qt Mailing List
Subject: Re: [Qt-interest] Question about bitfields

You need to know which end to start from.  Especially if you are getting a bucket of bits from another machine and you cannot guarantee it has the same byte order as your machine.

"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
Bill Waterson (Calvin & Hobbes)

----- Pritam Ghanghas <pritam_ghanghas at infosys.com> wrote:
> Why would there be any Byte Ordering issue while using C/C++ bit fields?
>
>
> On Fri, 2010-07-16 at 18:55 +0530, Dan White wrote:
> > Wow ! Thanks for that. I had not considered that.
> >
> > Is there anything available that covers byte-order ?
> >
> > "Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
> > Bill Waterson (Calvin & Hobbes)
> >
> > ----- Atlant Schmidt <aschmidt at dekaresearch.com> wrote:
> > > Dan:
> > >
> > > > Are there any Qt classes that deal with bitfields ?
> > > > Or do I have to do it in plain old vanilla C ?
> > >
> > >   (As a way of helping us better understand your question,)
> > >   what "value added" are you looking for beyond what is
> > >   provided in the basic C/C++ language?
> > >
> > >   For example, "byte-order independence"?
> > >
> > >                           Atlant
> > >
> > > -----Original Message-----
> > > From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Dan White
> > > Sent: Friday, July 16, 2010 8:49 AM
> > > To: Qt Mailing List
> > > Subject: [Qt-interest] Question about bitfields
> > >
> > > Are there any Qt classes that deal with bitfields ?  Or do I have to do it in plain old vanilla C ?
> > >
> > > I searched documentation and mailing lists and did not find anything.
> > >
> > > "Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
> > > Bill Waterson (Calvin & Hobbes)
> > >
> > > _______________________________________________
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