// Created by Ketan Lalcheta // Created by Ketan Lalcheta // https://www.sololearn.com/Discuss/2680650/how-to-release-memory-singleton #include #include using namespace std; class Singleton { public: static weak_ptr getInstance(); static void deleteInstance(); void dislpay(); Singleton(const Singleton&) = delete; Singleton& operator= (const Singleton&) = delete; friend void deleteSingleton(Singleton* singleton); private: Singleton() = default; ~Singleton() { cout << "Destructor called\n"; } static shared_ptr pSingleton; static bool deleted; }; shared_ptr Singleton::pSingleton; bool Singleton::deleted = false; // Friend function to use private destructor void deleteSingleton(Singleton* ptr) { delete ptr; } weak_ptr Singleton::getInstance() { if (!deleted) { if (!pSingleton) { cout << " Memory allocated\n"; pSingleton = shared_ptr(new Singleton, deleteSingleton); // I could not use make_shared() because the constructor is private } else { cout << " Memory reused\n"; } } return pSingleton; } void Singleton::deleteInstance() { pSingleton.reset(); deleted = true; } void Singleton::dislpay() { cout << "Hi" << endl; } int main() { auto pObj1 = Singleton::getInstance(); pObj1.lock()->dislpay(); auto pObj2 = Singleton::getInstance(); pObj2.lock()->dislpay(); Singleton::deleteInstance(); // will only delete the instance if there are no more references made by lock() if (auto pObj3 = Singleton::getInstance(); !pObj3.expired()) pObj3.lock()->dislpay(); else cout << "Singleton already deleted\n"; return 0; }

Singleton_5Default with smart pointers