C++ c# 分别实现单件模式

C#
1)

public sealed class Singleton
{
    static Singleton instance = null;
    private Singleton()
    {
    }
    public static Singleton Instance
    {
        get
        {
            if (instance == null)
            {
                instance = new Singleton();
            }
            return instance;
        }
    }
}

2) 线程安全

public sealed class Singleton
{
    static Singleton instance = null;
    static readonly object lockObj = new object();
    private Singleton()
    {
    }
    public static Singleton Instance
    {
        get
        {
            lock (lockObj)
            {
                if (instance == null)
                {
                    instance = new Singleton();
                }
            }
            return instance;
        }
    }
}

C++:

1)

class Singleton
{
public:
   static Singleton * Instance()
   {
        if( 0== _instance)
        {
            _instance = new Singleton;
        }
        return _instance;
   }

protected:
    Singleton(){}
    virtual ~Singleton(void){}
    static Singleton* _instance;
};

2) 利用智能指针进行垃圾回收

class Singleton
{
    public:
        ~Singleton(){}

    static Singleton* Instance()
    {
        if(!pInstance.get())
        {
        pInstance = std::auto_ptr<Singleton>(new Singleton());
        }
        return pInstance.get();
    }
    protected:  
        Singleton(){}
    private:
        static std::auto_ptr<Singleton> pInstance;
 };

3） 线程安全