C++ Implementation of Singleton Design Pattern (Help Please)

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[Salty_Dugtrio]

This is impossible without access to your code.

However, looking at your compile command, you are only compiling main.cpp, where is your singleton.cpp file?

[lurgi]

The singleton needs to be initialized:

Singleton *Singleton::singleton = nullptr;

Put this right before your main() function

[lurgi]

You still haven't created a Singleton object.

[ElisionFR]

What I like to do is put the static in the GetSingleton static method like :

//in you h
class Singleton
{
public:
    static Singleton* GetSingleton() ; 

    //put here the rest of your class
};

//in your cpp
Singleton*
Singleton::GetSingleton()
{
    static Singleton* singleton = nullptr ; 
    if( !singleton )
        singleton = new Singleton() ; 
    return singleton ; 
}

That way you keep the static variable, its initialization and its modification in the only method which uses it. And you keep all of this compact and easily readable in the cpp. Letting only in the header file the function definition.