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FAST Protocol
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Re: Empy String and "\0" actual lenght
David Rosenborg / Pantor Engineering AB
20 Mar 2009 8:22AM ET The delta value for an *optional* string field will use a *nullable* signed integer to convey the subtraction length. A non-negative nullable integer is increased by one when encoding, and conversely decreased when decoding. That operation is independent of the excess-1 coding used for the subtraction length itself.
/David
> Many thanks for your prompt reply. For the best of my knowledge,
> positive subtraction lengths have not to be adjusted for the excess-1
> encoding. So 1 is the value in the stream, without any manipulations.
>
> W.r.t. FAST specification, if I had received a subtraction length = -1,
> it would have been correct (because after excess-1 encoding I would have
> got subtraction length=0).
>
> So could the error be on the SWX stream (forgetting the minus)?
>
>
> P.S. In your opinion what's the lenght of the string "\0"? Is it 0
> or is it 1?
>
> Thanks in advance.
>
>
>
> > How an empty string is represented within a particular implementation
> > is not specified by the FAST specification. However, it should of
> > course have the length 0.
> >
> > If the subtraction length is 1 and the base value is the empty string,
> > then this is indeed an error.
> >
> > When you get the subtraction length 1, is this after you've adjusted
> > it for the excess-1 coding used for nullable string deltas? Otherwise
> > that could explain the problem you're facing.
> >
> > /David
> >
> >
> > > Hi, I'm trying to decode the SWX FAST stream, and in particular an
> > > optional ASCII string attribute (named RandomisedInterval) with
> > > delta operator and no initial value (default base value 'Empty
> > > String' is used). Let suppose we have an undefined dictionary
> > > previous value (i.e. the 'Empty String' should be used as previous
> > > value) and we read from the stream an ASCII String Delta made by a
> > > Substraction Length = 1 followed by an ASCII String that in that
> > > case corresponds to the whole RandomisedInterval string "00:02:00".
> > >
> > > The problem I'm facing with is quite simple: since I consider the
> > > 'Empty String' (the default base value) as a string with lenght=0, a
> > > Substraction Length = 1 (meaning to remove 1 character from the back
> > > of base value) makes my application to report the error [ERR D7].
> > >
> > > I would like to undertand if I'm making a mistake calculating the
> > > actual length of the 'Empty String' or if the right behaviour is
> > > actually to report the error.
> > >
> > >
> > > Furthermore, since I also consider the string "\0" as it had
> > > length=0, I think a similar problem could arise in any case I have a
> > > dictionary previous value = 'Empty String' or "\0".
> > >
> > > Many thanks in advance.
Re: Empy String and "\0" actual lenght
David Rosenborg / Pantor Engineering AB 20 Mar 2009 8:22AM ET
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