How can I put this qt program into one source code file - c++

Question

I want to have this code in one file, but can't figure out how to. I know it might not be good practice to do so but I am trying to learn qt, and would find it easier to understand the information if it were in one file.
This is the main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MainWindow mainWindow;
mainWindow.showMaximized();
return app.exec();
}
This is the mainwindow.cpp
#include "mainwindow.h"
#include <QCoreApplication>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
// Create the button, make "this" the parent
m_button = new QPushButton("My Button", this);
// set size and location of the button
m_button->setGeometry(QRect(QPoint(100, 100),
QSize(200, 50)));
// Connect button signal to appropriate slot
connect(m_button, SIGNAL(released()), this, SLOT(handleButton()));
}
void MainWindow::handleButton()
{
// change the text
m_button->setText("Example");
// resize button
m_button->resize(100,100);
}
this is the mainwindow.h
#define MAINWINDOW_H
#include <QMainWindow>
#include <QPushButton>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
private slots:
void handleButton();
private:
QPushButton *m_button;
};

Answer 1

By just copying everything in one file.
#include <QApplication>
#include <QMainWindow>
#include <QPushButton>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
private slots:
void handleButton();
private:
QPushButton *m_button;
};
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
// Create the button, make "this" the parent
m_button = new QPushButton("My Button", this);
// set size and location of the button
m_button->setGeometry(QRect(QPoint(100, 100),
QSize(200, 50)));
// Connect button signal to appropriate slot
connect(m_button, SIGNAL(released()), this, SLOT(handleButton()));
}
void MainWindow::handleButton()
{
// change the text
m_button->setText("Example");
// resize button
m_button->resize(100,100);
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MainWindow mainWindow;
mainWindow.showMaximized();
return app.exec();
}

Answer 2

It is usually not a good idea to define new classes in same file as your main. Generally you want new classes each in their own file or you would want to put several related classes together in a seperate file. There are a tonne of resources you can google related to best practices for this. I'd suggest you spend some time reading.
But since you asked... below is how you would do it for your example. If you do not define your class above the main, the compiler will complain because it won't know what a "MainWindow" is.
#include <QApplication>
#include <QMainWindow>
#include <QPushButton>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
private slots:
void handleButton();
private:
QPushButton *m_button;
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MainWindow mainWindow;
mainWindow.showMaximized();
return app.exec();
}
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
// Create the button, make "this" the parent
m_button = new QPushButton("My Button", this);
// set size and location of the button
m_button->setGeometry(QRect(QPoint(100, 100),
QSize(200, 50)));
// Connect button signal to appropriate slot
connect(m_button, SIGNAL(released()), this, SLOT(handleButton()));
}
void MainWindow::handleButton()
{
// change the text
m_button->setText("Example");
// resize button
m_button->resize(100,100);
}

Answer 3

#include essentially takes the contents of whatever file you choose and copy/pastes it at that location. The compiler then starts at the top of the file and works its way down to the bottom.
Knowing that, you should be able to just copy-paste the contents of the files in the order they are included.
mainwindow.h
mainwindow.cpp
main.cpp

Answer 4

The short answer is don't do this, you should define a class in its own header file and #include it to the main when you want to run it in the main. This allows you to reuse the class as you see fit throughout the program, its one of the tenets of Object Oriented programming, reusable code. For example
class A
{
public:
A();
~A();
void somePublicMethod();
private:
void somePrivateMethod();
};
If you include that class in your main when you compile that class to object code(assuming you know about implementing that class in a .cpp file) then when all the object files are linked to create the program the linker basically makes one big file with all the object code included in file to be fully compiled. I suggest you read up more on compiling and linking, essentially it boils down to three phases, preprocessing, compiling and linking. Learn more about Object Oriented programming and read up why it's a bad idea to just shove them all into one file. Every class should be in its own self contained .h file(unless its a tightly coupled class) so you can include them as you see fit. Hope this helps, have fun with Qt :)