How to delete the last n items in a QSet

[odelaune]

Hi,
I use a QSet of QObject* such as QSet<QObject*> m_set

To add new item in the QSet, I do m_set.insert(new QObject);

I also want to delete item in the QSet depending on its size. So I have a function like this:

while(m_set.size() > number)
        m_set.erase(std::prev(m_set.constEnd()));

but I get a crash when I try to remove items from the QSet. What is wrong?

[Christian Ehrlicher]

QSet::erase(QSet::begin())
But you're using a wrong container for your task. Maybe take a look at QList or even better QCache.

[Christian Ehrlicher]

Since QSet is unordered there is no 'last' . But this was already told you on stackoverflow iirc.

[odelaune]

@Christian-Ehrlicher
I understand there is no last element, so how should I use QSet::erase?

If my QSet contains 3 items, I would like to keep only 1 of them (any of them). How could I do that?

[Christian Ehrlicher]

QSet::erase(QSet::begin())
But you're using a wrong container for your task. Maybe take a look at QList or even better QCache.

[odelaune]

@Christian-Ehrlicher

Thanks, it works with

while(m_set.size() > number)
        m_set.erase(m_set.constBegin());