The new versus the old way to use connect

So signals and slots are very safe by default, and in an automatic way. But for the sender to call the receiver, it needs a pointer to it, and you as a user, don’t need to worry at all about the receiver being destroyed and becoming invalid (that is done automatically by the library), so you very rarely need to call QObject::disconnect. If the sender object is destroyed, it obviously can not emit any signal because it is a member function of its class. This has a very subtle advantage over a typical mechanism used in standard C or C++ 11 like callbacks with function pointers and lambda functions wrapped in std::function, and is subtle only because is so nice we often forget about it when we have used signals and slots for a while. Now to the main point that I want you to notice here. That could be a typical statement from a “Hello World” tutorial, where a button is created and shown, and when it’s pressed the whole window closes and the application terminates.

Qt creator signal slot editor