[Interest] How to make the QString "10" behind "9" in QMap's key order

[jack ma]

Thanks all of you, seems that std::sort + QCollator is a good way

2018-01-07 18:47 GMT+08:00 Konstantin Tokarev <annulen at yandex.ru>:

>
>
> > Hi,
> >
> > you need a "lessThan"-function, tailored for your needs. An
> > example from me is this:
> >
> > bool Person::lessThanFamilyFirst(QSharedPointer<Person>
> > p1, QSharedPointer<Person>
> > p2)
> >
> > {
> >
> > return (QString::localeAwareCompare(p1->familyName(),p2->
> familyName())<0)
> >
> > || (( p1->familyName() == p2->familyName())
> >
> > && (QString::localeAwareCompare(p1->firstName(),p2->firstName())<0));
> >
> > }
> >
> > Now you can pass this as a functor to a sort method like this:
> >
> > std::stable_sort(pupils.begin(), pupils.end(),
> Person::lessThanFamilyFirst);
>
> FWIW, if this is not a list displayed in UI, or other place where
> preserving order of
> equal elements matters, you should consider std::sort
>
> >
> > Please notice, that there are no () when calling the lessThan functor.
>
> Original question was dealing with QMap. While sorted vector-like
> container can replace
> map (there is even convenience wrapper flat_map in Boost, which allows to
> work with
> sorted array just like it was a "true" map), it doesn't always fit, e.g.
> inserts in such
> "flat map" are very expensive.
>
> So, you can just replace QMap with std::map and pass your comparator, e.g.
>
> auto comparator = [](const QString &a, const QString &b) -> bool {
>     // Your comparison function here
> };
> std::map<QString, QGraphicsItem *, decltype(comparator)> myMap(comparator);
>
> See [1] for more examples.
>
> Yet another approach is to use your own type as a key of QMap instead of
> QString,
> and create desired operator< for it. This has a downside that your access
> to internal
> QString will be more complicated, and you'll have to invent different key
> type each time
> you want to change comparator.
>
> And, last but not least: you probably want to know *how* to write
> comparator for your
> particular sorting order. You can do this with QCollator, see [2].
>
> [1] http://en.cppreference.com/w/cpp/container/map/map
> [2] https://forum.qt.io/topic/68910/natural-sort-using-qcollator/2
>
> >
> > HTH
> > Sebastian
> >
> > Am 07.01.2018 um 09:01 schrieb jack ma:
> >
> >> Hi,
> >>
> >> there is a QMap<QString,QGraphicsItem *> type, then
> >> insert values with：
> >>
> >> type.insert("U1",nullptr),
> >>
> >> type.insert("U2",nullptr),
> >>
> >> …………
> >>
> >> type.insert("U9",nullptr),
> >>
> >> type.insert("U10",nullptr),
> >>
> >> I want get the values follow the order of U1, U2 ... U10，
> >> but the default order is U1, U10 ,……U9
> >>
> >> I know this is a common string sorting problem, but I do
> >> not know how to solve it well.
> >>
> >> Any suggestions are very grateful !
> >>
> >> Thanks.
> >>
> >> _______________________________________________
> >> Interest mailing list
> >> Interest at qt-project.org
> >> http://lists.qt-project.org/mailman/listinfo/interest
> >
> > --
> > http://www.classintouch.de - Tablet-Software für Lehrer
> --
> Regards,
> Konstantin
> _______________________________________________
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