9. Implementing singletons

class Singleton {
public:
    static Singleton* get_singleton();
    //...

protected:
    Singleton();

private:
    static Singleton* m_ptr;
};// class Singleton

Singleton* Singleton::m_ptr = NULL;

Singleton* Singleton::get_singleton()
{
    if ( m_ptr == NULL )
        m_ptr = new Singleton;
    return m_ptr;
}

Singleton details:

• Constructor is protected to prevent multiple instances.

• Lazy creation avoids two problems with initialization:

  1. Unknown order of get_singleton( ) calls

  2. Might need some run-time information for proper initialization.

What if we also need to control deallocation?