[SOLVED]Execute function at a specific time

[Mr.FreakyJo]

How do I call a function at a specific time?
For example I want to execute function launch() on 18/02/2012 15:35:01 .

[koahnig]

If you want to do it through Qt you may want to have a look to "QTimer":http://developer.qt.nokia.com/doc/qt-4.8/qtimer.html

[Mr-Merlin]

Hi,

You could inherit from QTime and poll the current time in the object. When it reaches the time you want, emit a signal.

Hope that helps ;O)

[Mr.FreakyJo]

I was thinking of using QTimer this way:
Create a QTimer object that emits a signal every second.
When the signal is emited I remove a seconds from some sort of Countdown timer that when reaches 0 launch the function that I want.I think that this way is consuming too much resources that's why I asked help :),maybe someone knows a better way.My knowledge in QT is not too good but I learn fast.
Sorry for my bad english.

[Mr-Merlin]

There's also QDateTime which is probably better than QTime, as it provides AM/PM too.
So you could do something like this: -

@
class QActOnDateTime : public QDateTime
{
Q_OBJECT
private:

     int timerID;
     QDateTime checkTime;

     void Init()
     {
         timerId = startTimer(1000);  // start a timer at 1 second intervals
     }

     void timerEvent(QTimerEvent* evt)
     {
         if(evt->timerId() == timerID)
         {
             if(currentDateTime() >= checkTime)
             {
                   // call function due to elapsed time
                   DoSomething();
             }
         }
     }

};
@

[tobias.hunger]

The simplistic "Count down some timer every second" is going to fail when you loose/gain an hour due to daylight saving time.

Why not get the current QDateTime every minute and only use a QTimer for the last couple of seconds (if you need that kind of resolution)? The fewer wakeups your application triggers the less power your computer is going to consume.

[Mr.FreakyJo]

How about this:
@QDateTime now = QDateTime::currentDateTime();
QDateTime timeoftheaction;
QTimer *timer=new QTimer;
connect(timer, SIGNAL(timeout()),object,SLOT(action);
timer->start(now.secsTo(timeoftheaction)*1000);@
Isn't this aproach better?

[tobias.hunger]

It is... once you managed to abolish daylight saving time and had your user sign a contract stating that he will never set the clock.

[giesbert]

If you assume, the user changes the clock, you can forget that stuff without "polling via timer".
I would convert both times to UTC, to be sure DST is in calculation.

[Mr.FreakyJo]

I'll read the current time from a server and then I'll convert it to UTC.Thank you for your help.