可繼承的模板類單件模式

#include <iostream>

using namespace std;

template<class T>
class Singleton
{
public:
 static T* CreateInstance();
 static void Release();
protected:
 Singleton(){}
 virtual ~Singleton(){}
private:
 Singleton(const Singleton&){}
 Singleton& operator=(const Singleton&){}
private:
 static T* m_pT;
};

template<class T>
T* Singleton<T>::m_pT = NULL;

template<class T>
T* Singleton<T>::CreateInstance()
{
 if (m_pT == NULL)
 {
  m_pT = new T;
 }
 return m_pT;
}

template<class T>
void Singleton<T>::Release()
{
 if (m_pT != NULL)
 {
  delete m_pT;
  m_pT = NULL;
 }
}

class PA : public Singleton<PA>
{
 friend class Singleton<PA>;
private:
 PA(){}
 virtual ~PA(){}
};

int main()
{
 PA* q = PA::CreateInstance();
 PA* p = Singleton<PA>::CreateInstance();
 PA::Release();
 return 0;
}