singleton模式

#include <iostream>

using namespace std;

class Singleton
{

public:
    static Singleton* Instance();
    void setValue(int val) { value = val; }
    int getValue() { return value; }
protected:
    Singleton() {}
private:
    static Singleton *_instance;
    int value;

};

Singleton* Singleton::_instance = NULL;

Singleton* Singleton::Instance()
{
    if (_instance == NULL)
    {
         _instance = new Singleton();
    }

    return _instance;
}

void main()
{
 Singleton *a = Singleton::Instance();
 Singleton *b = Singleton::Instance();

 a->setValue(10);
 cout << b->getValue() << endl;
}