【设计模式】单例模式

单例模式(Singleton)

保证一个类只有一个实例，并提供一个访问它的全局访问点。

 

关键在于要有

1、一个私有的构造函数

2、一个公有的析构函数  

3、一个生成实例的接口

4、线程安全

 

Talk is cheap, show me the code.

 

#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;
}

 

 

 运行结果

 

---------------------------------华丽的分割线-----------------------------------------------------------

另一种单例模式的写法

  1 
  2 #include <iostream>
  3 using namespace std;
  4 
  5 class CSingleton
  6 {
  7 public:
  8     static  CSingleton& Instance()
  9     {
 10         static CSingleton singleton;
 11         return singleton;
 12     }
 13 
 14     virtual ~CSingleton() { cout << endl << "CSingleton::~CSingletion" << endl; }
 15     void Show() { cout << endl << "This is CSingleton::Show() " << endl; }
 16 
 17 protected:
 18     CSingleton() { cout << endl << "CSingleton::CSingleton" << endl; }
 19 
 20 };
 21 
 22 int main()
 23 {
 24     CSingleton& singleton = CSingleton::Instance();
 25     singleton.Show();
 26 
 27     CSingleton& singleton2 = CSingleton::Instance();
 28     singleton.Show();
 29 
 30     return 0;
 31 }

执行结果