I have a class with Qtimer, if I dont create it as new it does not works...

[tonnot]

I dont know very well what is happen....

I have a class with some utilities, one of them is a cronometer.

W_qtutil *w_qt=new W_qtutil();
 w_qt->time_start_crono(ui->my_label);

W_qtutil *w_qt=new W_qtutil();
 w_qt->time_start_crono(ui->my_label);

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This works .

But this one does not :

W_qtutil w_qt;
 w_qt.time_start_crono(ui->my_label);

W_qtutil w_qt;
 w_qt.time_start_crono(ui->my_label);

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void W_qtutil::time_start_crono(QWidget *indicador) {
    m_timer = new QTimer();
    m_timer->setInterval(1000);
    QObject::connect(m_timer, SIGNAL(timeout()), this, SLOT(time_update_crono()));
    m_timer->start();
}

void W_qtutil::time_start_crono(QWidget *indicador) {
    m_timer = new QTimer();
    m_timer->setInterval(1000);
    QObject::connect(m_timer, SIGNAL(timeout()), this, SLOT(time_update_crono()));
    m_timer->start();
}

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(m_timer is public, and declared at .h section)

Any idea ?

[agarny]

In the case that doesn't work, I would imagine that the reason is that w_qt gets out of scope before your timer has time to emit its timeout signal.

[tonnot]

Thanks
So, If I use the *var = new ... it means that my object are going to live outside of the method where it was created?

[mcosta]

Sorry, but you need to study about C++ and only later about Qt.

You have to know about stack variables and heap variables.

[agarny]

Thanks
So, If I use the *var = new ... it means that my object are going to live outside of the method where it was created?

Yes, and unless you free it, it will become what we call a memory leak (i.e. the kind of thing that should be avoided at all costs). Please note that Qt widget classes may be instantiated by providing a parent to the widget. So, unless you don't provide a parent, the widget object will be automatically freed when its parent is deleted.

[tonnot]

Thanks agarny.
And I can be sure that an object that has parent is destroyed when the parent die ? Or have I to delete it ?

[agarny]

If you were to check the source code (on line 1643), you would realise that this is exactly what it does...

[ChrisW67]

Thanks agarny.
And I can be sure that an object that has parent is destroyed when the parent die ? Or have I to delete it ?

If a heap-allocated QObject (QTimer is one) has a parent QObject then it will be deleted when the parent is deleted. You can still delete the child manually if you want. A QObject without a parent is like any other C++ object with regard to lifetime: scoped if allocated on the stack, or until deleted if on the heap.