What Is Signals and Slots in C++?

Signals and slots is a mechanism for communication between objects which makes it easy to implement the observer pattern while avoiding boilerplate code.

In GUI programming, when we change one widget, we often want another widget to be notified. More generally, we want objects of any kind to be able to communicate with one another.

The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks.

Signals and slots are used for communication between objects. The signal is emitted by the object that has something to share, and the slot is executed by the object that receives the signal.

Signals and slots can be used for communication between any number of objects. They’re especially useful for communication between objects that are not part of the same hierarchy.

One way to think of signals and slots is as a means of inter-object communication (IOC). With signals and slots, objects can communicate with each other without needing to know anything about each other, except for the type of message they want to send or receive. This is similar to how we use events in GUI programming, where one object emits an event (e.g.

, a button being clicked) and another object receives and handles that event (e.g., displaying a message on screen).

In Qt, signals and slots are used for communication between objects which makes it easy to implement the observer pattern while avoiding boilerplate code. Signals and slots can be used for communication between any number of objects.

With signals and slots, objects can communicate with each other without needing to know anything about each other, making it easy to implement loosely coupled systems.