Book Image

Mastering Qt 5

By : Guillaume Lazar, Robin Penea
Book Image

Mastering Qt 5

By: Guillaume Lazar, Robin Penea

Overview of this book

Qt 5.7 is an application development framework that provides a great user experience and develops full-capability applications with Qt Widgets, QML, and even Qt 3D. This book will address challenges in successfully developing cross-platform applications with the Qt framework. Cross-platform development needs a well-organized project. Using this book, you will have a better understanding of the Qt framework and the tools to resolve serious issues such as linking, debugging, and multithreading. Your journey will start with the new Qt 5 features. Then you will explore different platforms and learn to tame them. Every chapter along the way is a logical step that you must take to master Qt. The journey will end in an application that has been tested and is ready to be shipped.
Table of Contents (20 chapters)
Mastering Qt 5
Credits
About the Authors
About the Reviewer
www.PacktPub.com
Preface

Transforming SysInfo into a singleton


Promises are made to be kept: we will now transform the SysInfo class into a singleton. C++ offers many ways to implement the singleton design pattern. We will explain one of them here. Open the SysInfo.h file and make the following changes:

class SysInfo 
{ 
public: 
    static SysInfo& instance(); 
    virtual ~SysInfo(); 
 
    virtual void init() = 0; 
    virtual double cpuLoadAverage() = 0; 
    virtual double memoryUsed() = 0; 
 
protected: 
    explicit SysInfo(); 
 
private: 
    SysInfo(const SysInfo& rhs); 
    SysInfo& operator=(const SysInfo& rhs); 
}; 

The singleton must guarantee that there will be only one instance of the class and that this instance will be easily accessible from a single access point.

So the first thing to do is to change the visibility of the constructor to protected. This way, only this class and the child classes will be allowed to call the constructor.

Since only one instance of the object must exist...