[Development] JSON 64 bit int

Marc Mutz marc.mutz at kdab.com
Wed Feb 11 16:11:24 CET 2015

On Wednesday 11 February 2015 14:04:59 Bo Thorsen wrote:
> Den 11-02-2015 kl. 13:27 skrev Giuseppe D'Angelo:
> > On 11 February 2015 at 12:12, Bo Thorsen <bo at vikingsoft.eu> wrote:
> >> It's so easy to say we just follow the standard. But I have two current
> >> projects where my customers say they send me a 64 bit database ID in a
> >> JSON value. Converting those through a double might work, but can you
> >> guarantee this?
> > 
> > No, because IEEE754 64-bit floating point numbers can't represent all
> > 64 bit integers... the right solution, from a JSON point of view, is
> > not sending a number but a string.
> Exactly, that's why I wrote "might". You don't know if the number you
> get is correct or not.
> But we can't get the string from {"i":1}. You get an empty string if you
> do toString on the i value.
> And that's the problem. People have web APIs that return uint64 as a
> number and I need to get that number. ATM the only way is to read it
> from the full QByteArray. If the toString would never fail and give me
> the contents or I can get the bytes from it or add the extra type
> reading functions - all three would work. The current meagre API is
> pretty much the only way that doesn't.

If Qt produces 64-bit integers in its JSON output, then the next bug report 
will (probably rightfully) be that Qt's JSON output cannot be read by some 
JavaScript library X.

That said, if in doubt, follow Postel's Law.

Marc Mutz <marc.mutz at kdab.com> | Senior Software Engineer
KDAB (Deutschland) GmbH & Co.KG, a KDAB Group Company
www.kdab.com || Germany +49-30-521325470 || Sweden (HQ) +46-563-540090
KDAB - Qt Experts - Platform-Independent Software Solutions

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