What is a Makefile? How can you produce a Makefile for your project?

What is a Makefile? How can you produce a Makefile for your project?
C++ applications are generally composed of many source files, header files, and external libraries.Keeping track of all of the parts of such a application requires a mechanism that precisely specifies the input files involved, the tools needed to build, the intermediate targets and their dependencies, and the final executable target.

The most widely used utility for handling the job of building a project is make.

make reads the details of the project specifications and the instructions for the compiler from a Makefile.

With Qt, it is not necessary to write Makefiles. Qt provides a tool called qmake to generate Makefiles.

Depending on the development environment, developers may use variants of make, such as mingw32-make, gmake, or unsermake ,nmake in MS Dev Studio.

QT widgets

This example shows how to create parent and child widgets.
We'll keep it simple and use just a single parent and a lone child.

#include 
 #include 
 #include 
 #include 

 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);

     QWidget window;
     window.resize(200, 120);

     QPushButton quit("Quit", &window);
     quit.setFont(QFont("Times", 18, QFont::Bold));
     quit.setGeometry(10, 40, 180, 40);
     QObject::connect(&quit, SIGNAL(clicked()), &app, SLOT(quit()));

     window.show();
     return app.exec();
 }

Line by Line Walkthrough

#include 

We add an include of to get the base widget class we'll use.

QWidget window;

Here we simply create a plain widget object. The QWidget class is the base class of all user interface objects. The widget is the atom of the user interface: It receives mouse, keyboard and other events from the window system, and paints a representation of itself on the screen. A widget is clipped by its parent and by the widgets in front of it.
A widget that isn't embedded in a parent widget, like this particular widget, is called a window. Usually, windows have their own window frame and taskbar entry, provided by the window system. A widget without a parent widget is always an independent window. Its initial position on the screen is controlled by the window system.

window.resize(200, 120);

We set the window's width to 200 pixels and its height to 120 pixels.

QPushButton quit("Quit", &window);

A child is born. This QPushButton is created with a parent widget (window). A child widget is always displayed within its parent's area. When displayed, it is clipped by its parent's bounds. By default, it is rooted at the top-left corner of its parent, at position (0, 0).

quit.setGeometry(10, 40, 180, 40);

The QWidget::setGeometry() function takes four arguments: The first two arguments are the x and y coordinates of the button's top-left corner. The coordinates are relative to the parent widget. The last two arguments are the button's width and height. The result is a button that extends from position (10, 40) to position (190, 80).

window.show();

When a parent widget is shown, it will call show for all its children (except those that were explicitly hidden using QWidget::hide()).

Running the Application

The button no longer fills the entire window. Instead, it stays at position (10, 40) within the window and with a size of (180, 40), because of the QWidget::setGeometry() call.