What is an event loop in Qt?

Question

I have understood the following regarding QApplication's exec function:

QApplication exec starts the main event loop. It launches the GUI. It processes the signals and calls appropriate slots on receiving them. It waits until exit is called and returns the value which was set in exit.

Now, when we say event loop, does it mean that there is some while loop running in the internal code of Qt, and in that while loop the method of handling signals and slots is written?

Solution

Now, when we say event loop, does it mean that there is some while loop running in the internal code of Qt, and in that while loop the method of handling signals and slots is written?

In a sense, yes. Most software these days sits and waits for events -- user input, network traffic, timer events, sensors, etc. -- and responds accordingly.

This is not specific to Qt. It's a common design pattern you'll find everywhere from Windows to Android to Arduino.

Comments

[Omid CompSCI]

Event loop means that your code is continuously running, think about it as being refreshed every time, so changes will be seen and made continuously based off your cases you have.

[thuga]

Directly connected slots don't go to the event queue, only queued connections.

[Andre]

This was really helpful to me, have a look link

[Kuba hasn't forgotten Monica]

Note that the event loop has nothing to do with the concept of signals and slots per se. It is used as an implementation detail in delivering slot/functor calls in queued connections or across threads in automatic connections.