單體模式的簡單實現C++

#include <iostream>using namespace std;class Singleton {public:    static Singleton *instance();    int getTmp() {        return iTmp;    }    void incTmp() {        ++iTmp;    }    void decTmp() {        --iTmp;    }protected:    Singleton():iTmp(12) {}private:    int iTmp;    static Singleton *_instance;};Singleton *Singleton::instance() {    if (_instance == NULL) {        _instance = new Singleton();    }    return _instance;}Singleton* Singleton::_instance = NULL;int main() {    Singleton *obj1 = Singleton::instance();    Singleton *obj2 = Singleton::instance();    cout << "obj1: " << obj1->getTmp() << endl;    cout << "obj2: " << obj2->getTmp() << endl;    obj1->incTmp();    cout << "obj2: " << obj2->getTmp() << endl;    obj2->decTmp();    cout << "obj1: " << obj1->getTmp() << endl;    return 0;}