Slots in C++


Slots are member functions that can be used in C++ to invoke methods. When called directly, slots follow the usual C++ rules. They can also be called through the signal-slot connection, where a signal from one class will cause a private slot to be invoked in another class. They can also be declared as virtual.


QObject::connect() creates a connection between a sender and a receiver object. It returns a handle for the connection, which can be used to connect and disconnect. QObject::connect() is similar to QSignal: it creates a signal connection, and returns a handle for it. If the signal connection is already in place, QObject::connect() will do nothing, and the current pointer in this-> memberPtrToObjX_ is connected to the signal.


The SIGNAL slot in Qt makes object-to-object communication easy. It helps to avoid boilerplate code and simplifies the observer pattern.

SLOT macros

SLOT macros are useful for defining a lexical environment for variables and slots. For instance, a macro can set the value of a slot by using the slot name. When a macro uses this lexical environment, it will translate the appearance of the slot name as a variable into a call to the slot-value function.


When you use a signal, you can pass a single argument or an array of multiple arguments. Then, when the signal is received, the signal emits a valueChanged() signal. Similarly, when a value changes in a slot, it emits a setValue() signal. There are two types of slots: protected slots and private slots. A protected slot is used in a class’s interface and implementation. A private slot is used when a tight connection is needed.

Emit line

The emit line slot emits an identifier. The identifier must be the same as the signal. If it is different, the slot is not recognized.


In C#, you can use the m_value of slot to access data within a table. This is useful in many different contexts. For example, you can use the slot to copy an object from one table to another. You can also use the slot to emit a signal whenever its value changes.