When you click on the Build button, what exactly is Qt Creator doing? How does Qt handle the compilation of the different platforms with a single .pro file? What does the Q_OBJECT macro imply exactly? We will dig into each of these questions in the following sections. Our example case will be the SysInfo application we just completed, and we will study what Qt is doing under the hood.

We can start this study by digging into the .pro file. It is the main entry point in compiling any Qt project. Basically, a .pro file is a qmake project file describing the sources and headers used by the project. It is a platform-agnostic definition of a Makefile. First, we can cover the different qmake keywords used in the ch02-sysinfo application:

#------------------------------------------------- 
# 
# Project created by QtCreator 2016-03-24T16:25:01 
# 
#------------------------------------------------- 
QT += core gui charts 
CONFIG += C++14 
 
greaterThan(QT_MAJOR_VERSION, 4): QT...