Getting started with Qt development is rather easy. As with other C++ development discussed earlier, all tools and libraries are native in the Debian / Ubuntu repositories. The following packages should take care of the basic setup:

apt-get install gcc g++ gdb cmake make build-essential qtcreator qt5-default qtdeclarative5-dev qt5-doc qt5-doc-html qtbase5-doc-html qtbase5-examples

Once installed, this small "Hello World" example, inspired by this tutorial but updated for Qt 5, will verify that everything is setup correctly.

Notice that it is important that this file has the extension .cpp, e.g. helloworld.cpp.

#include <QtWidgets/QApplication>
#include <QtWidgets/QPushButton>


int main( int argc, char **argv ) {
  QApplication a( argc, argv );

  QPushButton hello( "Hello world!", 0 );
  hello.resize( 100, 30 );

  hello.show();
  return a.exec();
}

Once this file is in place, a Qt .pro project must be generated. (This should only be executed once, to generate the file).

qmake -project

It will create a file based on the name of the current directory, with the extension .pro. Edit the file to include the following two lines:

QT += core gui
QT += widgets

If backwards compatibility with older Qt versions is a concern, change the last line to:

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

Now, the application can be compiled and linked into a binary:

qmake && make && ./helloworld

It should generate a Makefile, make or compile the source code, and start the binary. If everything works out, a new application window with a small button like below will appear.