MySingletonMap* MySM1 = SingletonMap<MySingletonMap>::GetInstance(1);

#include <iostream>
#include <map>
#include <list>using namespace std;// 使用 map 存放单类实例的基类
template <class T, typename K = int>
class SingletonMap{
public:// 先从 map 中根据 key 查找实例，如果没有就创建实例static T* GetInstance(K key){// 根据 key 查找实例typename map<K, T*>::iterator iter = GetMap().find(key);// 如果找到，就返回if (iter != GetMap().end()){return iter->second;}// 否则创建新的实例// 此处会进到构造函数 SingletonMap(K key) 里面，将实例插入 map 和 list 中return new T(key);}// 返回实例列表static list<T*>& GetAllInstances(){static list<T*> List;return List;}// 删除全部实例static void DeleteAllInstances() {list<T*>& List = GetAllInstances();list<T*>::iterator v;// 遍历 list 内的实例for(v = List.begin(); v != List.end();){cout << "Delete Instance " << ((T*)(*v))->getKey() << endl;delete *v;          // 删除该项对应的实例v = List.erase(v);  // 从 list 中删除该项
        }}// 获得 keyK getKey() const {return m_Key;}protected:SingletonMap(K key): m_Key(key){pair<const K, T*> Elem(key, (T*)this);  // 创建 pairGetMap().insert(Elem);                  // 将 pair 插入 mapGetAllInstances().push_back((T*)this);  // 将自身插入 list
    }private:static map<K, T*>& GetMap(){static map<K, T*> Map;                  // 此处生成静态 mapreturn Map;}K m_Key;                                    // key
};// 继承自 SingletonMap 的子类
class MySingletonMap: public SingletonMap<MySingletonMap>{
private:friend class SingletonMap<MySingletonMap>;  // 将 SingletonMap 设为 friend class
MySingletonMap(int key): SingletonMap<MySingletonMap>(key){}virtual ~MySingletonMap(){}
};int main(int argc, char* argv[])
{MySingletonMap* MySM1 = SingletonMap<MySingletonMap>::GetInstance(1); // 创建新实例cout << "Number of instances = " << MySingletonMap::GetAllInstances().size() << endl; // 返回1
MySingletonMap* MySM2 = SingletonMap<MySingletonMap>::GetInstance(2); // 创建新实例cout << "Number of instances = " << MySingletonMap::GetAllInstances().size() << endl; // 返回2
MySingletonMap* MySM3 = SingletonMap<MySingletonMap>::GetInstance(2); // 得到实例 MySM2cout << "Number of instances = " << MySingletonMap::GetAllInstances().size() << endl; // 返回2if (MySM2 == MySM3) {cout << "MySM2 == MySM3" << endl;   // 因为二者相等，所以打印 MySM2 == MySM3} else {cout << "MySM2 != MySM3" << endl;}MySingletonMap::DeleteAllInstances();   // 删除全部实例
getchar();return 0;
}

Number of instances = 1
Number of instances = 2
Number of instances = 2
MySM2 == MySM3
Delete Instance 1
Delete Instance 2