单例实现c++

#include <iostream>
using namespace std;

class Singleton
{
public:
    static Singleton *GetInstance()
    {
        if (m_Instance == NULL)
        {
            m_Instance = new Singleton();
            cout<<"get Singleton instance success"<<endl;
        }
        return m_Instance;
    }

private:
    Singleton(){cout<<"Singleton construction"<<endl;}
    static Singleton *m_Instance;

    // This is important
    class GC // 垃圾回收类
    {
    public:
        GC()
        {
            cout<<"GC construction"<<endl;
        }
        ~GC()
        {
            cout<<"GC destruction"<<endl;
            // We can destory all the resouce here, eg:db connector, file handle and so on
            if (m_Instance != NULL)
            {
                delete m_Instance;
                m_Instance = NULL;
                cout<<"Singleton destruction"<<endl;
                system("pause");//不暂停程序会自动退出，看不清输出信息
            }
        }
    };
    static GC gc;  //垃圾回收类的静态成员

};

Singleton *Singleton::m_Instance = NULL;
Singleton::GC Singleton::gc; //类的静态成员需要类外部初始化，这一点很重要，否则程序运行连GC的构造都不会进入，何谈自动析构
int main(int argc, char *argv[])
{
    Singleton *singletonObj = Singleton::GetInstance();
    return 0;
}

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