QTimer singleShot or delete

tjudg

Is there a difference between calling a singleShot timer and a regular timer with delete after? Is one way better than the other?
For example:

void MainWindow::on_pushButton_clicked()
{
   timer = new QTimer();
   timer->start(5000);
   connect(timer,SIGNAL(timeout()),this,SLOT(timerDone()));
}
void MainWindow::timerDone()
{
   delete timer;
   qDebug()<<"timer done";
}

void MainWindow::on_pushButton_clicked()
{
   QTimer *timer = new QTimer();
   timer->start(5000);
   timer->setSingleShot(true);
   connect(timer,SIGNAL(timeout()),this,SLOT(timerDone()));
}
void MainWindow::timerDone()
{
   qDebug()<<"timer done";
}

SGaist

Hi,

In the second case you wrote you have a memory leak. Setting single shot to true means that the timer will timeout only once after a call to start. not that it will be deleted after that.

Chris Kawa

The first one has a bug. If main window is destroyed before the timer times out you have a memory leak.

The second one also has a bug. You never delete the timer so you have a memory leak.

If you just want a single shot just use the static method and don't bother with manual resource management:

void MainWindow::on_pushButton_clicked()
{
    QTimer::singleShot(5000, this, SLOT(timerDone()));
}
void MainWindow::timerDone()
{
   qDebug()<<"timer done";
}