Question

Why are we using * character when we are creating button but we aren’t adding it to app instance?

#include <QApplication>
#include <QPushButton>

int main(int argc,char *argv[])
{
    QApplication app(argc,argv);
    QPushButton *button = new QPushButton("Button Text");
    QObject::connect(button,SIGNAL(clicked()),&app,SLOT(quit()));
    button->show();
    return app.exec();
}

When should we use *, &, ., ->?

Answer 1

new returns a pointer, hence the * is used here to define button as a pointer-to-QPushButton, The & is used to reference (get the address of) app, which is then passed to connect.

button->show(); 

is equivalent to:

(*button).show(); 

This is all basic C (except new) and C++ covered in any introductory book.