Qt6 Connect Signal to Lambda Function - c++

Question

I'm using a DataRouter class to handle communication with a QSerialPort (and then communicate the results elsewhere). The connected device sends a status package every second or so, and I would like to read it without polling the device. I tried directly using QSerialPort's waitForReadyRead function, but no matter how long I set the wait time, it always timed out. Looking here and here I saw signals can be connected to Lambda functions. Now I'm trying to connect QSerialPort's readyRead signal to a Lambda which calls my on_dataRecieved function but I get the error C2665:"QObject::connect: none of the 3 overloads could convert all of the argument types. Below is an example of what I have:
DataRouter.h
template<class SerialPort>
class DataRouter
{
public:
DataRouter ();
private slots:
on_dataRecieved();
private:
shared_ptr<SerialPort> m_port;
};
DataRouter.cpp
template<class SerialPort>
DataRouter<SerialPort>::DataRouter()
{
m_port = std::make_shared<SerialPort>()
QObject::connect(m_port, &QSerialPort::readyRead, this, [=](){this->on_dataRecieved();})
}
template<class SerialPort>
void DataRouter<SerialPort>::on_dataRecieved()
{
//Do stuff
}

Answer 1

If your "target" is not QObject you need to use the following overload of connect. The problem is that, you are trying to use non-QObject as "context" to determine the lifetime of the connection and that's not possible. To mitigate it you will need to release the connection somehow on DataRouter's destruction; one way is to store what connect() will have returned and call disconnect on it later on.
As for the signal coming from a smart pointer, have you tried this:
connect(m_port->get(), &QSerialPort::readyRead, &DataRouter::on_dataRecieved);

Answer 2

Your m_port is not entity of QSerialPort class, that's why you don't have QSerialPort::readyRead that can be emitted from it. template<class SerialPort> doesn't do what you what, it is just name of templated parameter.
You probably wanted something like this:
DataRouter.h
class DataRouter : QObject
{
public:
DataRouter ();
private slots:
on_dataRecieved();
private:
QSerialPort* m_port;
};
DataRouter.cpp
DataRouter::DataRouter()
{
m_port = new QSerialPort(this);
connect(m_port, &QSerialPort::readyRead, this, &DataRouter::on_dataRecieved);
// or connect(m_port, &QSerialPort::readyRead, this, [this](){this->on_dataRecieved();});
}
void DataRouter::on_dataRecieved()
{
//Do stuff
}
You don't have to wrap Qt classes in smart pointers as long, as you provide parent class for them. Memory freed when parent is destructed.