Can't output to QTextEdit - c++

Question

My program should:
collect some input from QLineEdits;
convert it into QStrings;
add it to some QStrings which are constant;
output the whole stuff in a QTextEdit when a button is clicked.
Below is the simplified model of the program. It can be compiled; I get no errors; however, it doesn't do what I need. It just fails to output and I have really no idea why. I've struggled too hard to get it show no errors and now I've run out of ideas. Can anybody help me please?
#include <QtGui>
#include <QtCore>
class MyObject : public QObject
{
Q_OBJECT
public:
QTextEdit text;
QString c;
public slots:
void onClicked() {
text.setText(c);
}
};
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();
QString b = "This line is to be added";
QString c = a+b;
QTextEdit text (&mw);
text.show();
QPushButton btn ("Convert", &mw);
MyObject obj;
QObject::connect(
&btn,
SIGNAL(clicked()),
&obj,
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();
}
#include "sample.moc"

Answer 1

According to the code you provide it seems that you do not know that:
Qt works asynchronously, for example the value of a that you get is before the window is displayed, what value will it have? Well, it will have an empty string, so at what moment should I ask for the text? right in the slot that is called when the button is pressed.
Variables with the same name do not imply that they are the same, for example you have 2 QTextEdit with the name of text, these are different objects.
So as you realize the objects (widgets) must have the same scope to be able to interact with each other, so I will create a class that inherits from QWidget and that has the other elements as attributes.
#include <QtGui>
#include <QtCore>
class Widget: public QWidget
{
Q_OBJECT
public:
Widget(QWidget *parent=nullptr):
QWidget(parent)
{
QVBoxLayout *layout = new QVBoxLayout(this);
layout->addWidget(&label);
layout->addWidget(&line);
layout->addWidget(&button);
layout->addWidget(&textedit);
label.setText("Enter something:");
label.setAlignment(Qt::AlignHCenter);
button.setText("Convert");
connect(&button, SIGNAL(clicked()), this, SLOT(onClicked()));
}
private slots:
void onClicked(){
QString a = line.text();
QString b = "This line is to be added";
QString c = a+b;
textedit.setText(c); // or textedit.append(c);
}
private:
QLabel label;
QLineEdit line;
QPushButton button;
QTextEdit textedit;
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
Widget w;
w.show();
return app.exec();
}
#include "sample.moc"