Can I create a slot without creating a class? - c++

Question

Just a simple prog to illustrate the issue in a larger one. What I am trying to do is to create a function for signal/slot connection without using any classes. I am new to OOP and don't want to have to do with classes at the moment. So, I am creating a function before the main function and hope this will work... but it doesn't. The prog can be compiled and executed, but I get a notification: Object::connect: No such slot QTextEdit::onClicked(). I anticipate the issue can very easily be solved as it is rather a mistake of expression than of understanding, so thanks in advance for your help! :)
#include <QtGui>
#include <QtCore>
void onClicked (QTextEdit text, QString a)
{
text.setText(a);
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QWidget mw;
mw.setWindowTitle("Main Window");
mw.resize(400, 400);
mw.show();
QLabel label ("Enter something:", &mw);
label.setAlignment(Qt::AlignHCenter);
label.show();
QLineEdit line (&mw);
line.show();
QString a = line.text();
QTextEdit text (&mw);
text.show();
QPushButton btn ("Convert", &mw);
QObject::connect(
&btn,
SIGNAL(clicked()),
&text,
SLOT(onClicked()));
btn.show();
QVBoxLayout layout_mw;
layout_mw.addWidget(&label);
layout_mw.addWidget(&line);
layout_mw.addWidget(&btn);
layout_mw.addWidget(&text);
mw.setLayout(&layout_mw);
return app.exec();
}

Answer 1

well,it is true that slots are only available in QObjects BUT you can for sure connect signals to lambdas too :)
so, in this case you can uses the helpful lambda and omit the custom function
void onClicked (QTextEdit text, QString a) :
like
QObject::connect(&btn, &QPushButton::clicked,
[](QTextEdit te, QString s){qDebug() << "am in...";});

Answer 2

You can read in the Qt documentation that:
All classes that inherit from QObject or one of its subclasses (e.g.,
QWidget) can contain signals and slots.
So you can not define slots in main.cpp. You have two options. Either define a class derived from QObject and add your slot there or use Qt 5.* and connect your signal to a lambda using the new syntax for connections.