what to do during long calculation?

[Raccoon29]

I am not sure about details of Qt4, but in Qt3 was quite easy.
You have to inherit a your class from QThread and there override the virtual function run() that is called by the QThread start()method.
An example could be:

class MyThread : public QThread
{
   private:
      . . .
   public:
      // constructor
      virtual void run();   //inside this you execute your calculate(int)
      . . .
}

class MyThread : public QThread
{
   private:
      . . .
   public:
      // constructor
      virtual void run();   //inside this you execute your calculate(int)
      . . .
}

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for more details that sure you need, refer to http://doc.trolltech.com/4.3/qthread.html

Anyway, calculate from thread is a bit more complicated and could be a risk, since unxpected terminations could crash your program. Complicated because you have to manage the thread result to send it to your application, with some wrappers.
So I suggest you to well study the thread guide.

Greetings