【设计模式】单例模式

#include <iostream>
using namespace std;

class CObj
{
    private:
        CObj() { cout << "Instance a object" << endl; }
        
    public:
        virtual ~CObj() {cout << "CObj::~CObj" << endl;   if(! s_pObj) delete s_pObj;  s_pObj = 0; }

        static CObj* Instance() 
        {
            //double lock
            if(0 == s_pObj)
            {
                //thread synchronization begin
                if(0 == s_pObj)
                {
                    s_pObj = new CObj();
                }
                //thread synchronizatioin end
            }
            
            return s_pObj;
        }

        void Show() { cout << "CObj::Show()" << endl; }
    protected:
        static CObj* s_pObj;
};

CObj* CObj::s_pObj = 0;


int main()
{
    CObj* pObj = CObj::Instance();
    pObj->Show();
    delete pObj;
    pObj = 0;

    return 0;
}