Weird behavior in QList.erase

[jefftee]

Does the following accomplish what you want?

vectorOutput = vectorFirst;
 
QVectorIterator<Data*> itOutput(vectorOutput);
QVectorIterator<Data*> itSecond(vectorSecond);
 
while (itOutput.hasNext())
{
    Data *d1 = itOutput.next();
    vectorSecond.toFront();
    while (itSecond.hasNext())
    {
        Data *d2 = itSecond.next();
        if (d1->x == d2->x && d1->y == d2->y)
        {
            vectorDeleted.push_back(d1);
            vectorOutput.removeOne(d1);
        }
    }
}

vectorOutput = vectorFirst;

QVectorIterator<Data*> itOutput(vectorOutput);
QVectorIterator<Data*> itSecond(vectorSecond);

while (itOutput.hasNext())
{
    Data *d1 = itOutput.next();
    vectorSecond.toFront();
    while (itSecond.hasNext())
    {
        Data *d2 = itSecond.next();
        if (d1->x == d2->x && d1->y == d2->y)
        {
            vectorDeleted.push_back(d1);
            vectorOutput.removeOne(d1);
        }
    }
}

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[d_stranz]

erase() returns the iterator pointing to the next element.

But the trick to this is you have to continuously evaluate container.end() as part of the for() loop termination condition. You can't assign it to a variable prior to entering the for() loop, because the value it holds will become invalid as soon as the container content changes (either through insertion or erasure). In other words, this will not work:

QVector<Data *>::iterator it;
QVector<Data *>::iterator eIt = container.end();
for (it = container.begin(); it != eIt; /* no ++ here */) {
    if (condition) {
        it = container.erase(it);
    }else {
        // only increment if no delete happened
        ++it;
    }
}

QVector<Data *>::iterator it;
QVector<Data *>::iterator eIt = container.end();
for (it = container.begin(); it != eIt; /* no ++ here */) {
    if (condition) {
        it = container.erase(it);
    }else {
        // only increment if no delete happened
        ++it;
    }
}

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