class B
{
public:
    B();

    QVector<int> mVector;
    void setVector()
    {
        mVector.resize(10);
        qDebug() << "size: " << mVector.size();
        for(int i = 0; i < 10; i++) {
            mVector.push_back(i);
        }
        qDebug() << "vector:" << mVector;
    }
};

B testingB;
qDebug() << testingB.mVector.size();
testingB.setVector();
qDebug() << testingB.mVector;
qDebug() << testingB.mVector.size();

0
size:  10
vector: QVector(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
QVector(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
20