[Qgis-developer] Qt5 rounding issue spotted in the wild

[Mathieu Pellerin]

Denis,

There's an additional way to mitigate this:
1/ requesting Qt devs to apply the patch fixing this issue (
http://code.qt.io/cgit/qt/qtbase.git/patch/src/corelib/tools/qlocale.h?id=726fed0d67013cbfac7921d3d4613ca83406fb0f
) onto Qt 5.6, which after all is a LTS version;
2/ requesting distributions - such as Ubuntu and Fedora - to apply the
patch onto the packages maintained and offered through their repositories.

Regarding #2, I've filed such a request earlier today:
https://bugs.launchpad.net/ubuntu/+source/qtbase-opensource-src/+bug/1620173

It's a shame we can't override the QVariant conversion to QString with some
code of our own to patch the issue on Qt5 < 5.7.

Math

On Mon, Sep 5, 2016 at 12:23 PM, Denis Rouzaud <denis.rouzaud at gmail.com>
wrote:

> Hi Mathieu,
>
> For reference, here is the Qt issue
> https://bugreports.qt.io/browse/QTBUG-47192
>
> It's the conversion from QVariant to QString which is broken.
>
> There are several ways to deal with this:
> * fix this for some versions of Qt (no idea how)
> * require Qt 5.7+
> * ship like this with a warning notice
>
> The discussion already arised and the latter seems to be prefered:
> https://lists.osgeo.org/pipermail/qgis-developer/2016-August/044127.html
>
> Denis
>
>
>
> On 09/05/2016 04:39 AM, Mathieu Pellerin wrote:
>
> Greetings,
>
> While testing QGIS compiled against Qt5 5.6.1 (the version that will be
> offered in Ubuntu's next release in a month or so), I ran into a rounding
> issue, whereas the round() expression engine function simply fails to round
> values to the stated number of decimals.
>
> As seen in this screenshot[1], using this expression "round( 0.972743...,
> 2 )" to round the double value to two decimals returns 0.96999999999997.
>
> Nyall says the issue has been fixed in Qt5 5.7. For Qt5 < 5.7, is there a
> contingency plan for this problem? Could we get distributions to include a
> fix in their 5.6.x packages (if that’s possible)?
>
> Math
>
> [1] http://i.imgur.com/7v2Z24Z.png
>
>
>
> _______________________________________________
> Qgis-developer mailing listQgis-developer at lists.osgeo.org
> List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20160905/c1488c23/attachment.html>