如何正确的在C++中实现单例SingleTone模式

class S
{
    public:
        static S& getInstance()
        {
            static S    instance; // Guaranteed to be destroyed.
                                  // Instantiated on first use.
            return instance;
        }
    private:
        S() {}                    // Constructor? (the {} brackets) are needed here.

        // C++ 03
        // ========
        // Don't forget to declare these two. You want to make sure they
        // are inaccessible(especially from outside), otherwise, you may accidentally get copies of
        // your singleton appearing.
        S(S const&);              // Don't Implement
        void operator=(S const&); // Don't implement

        // C++ 11
        // =======
        // We can use the better technique of deleting the methods
        // we don't want.
    public:
        S(S const&)               = delete;
        void operator=(S const&)  = delete;

        // Note: Scott Meyers mentions in his Effective Modern
        //       C++ book, that deleted functions should generally
        //       be public as it results in better error messages
        //       due to the compilers behavior to check accessibility
        //       before deleted status
};
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单例模式保证该类始终只有一个实例对象，以表现唯一资源的设计（不可拷贝）。
需要注意2点：

1. 提供GetInstance接口用于获取实例，实例在类内部作为static成员存在，在首次调用GetInstance构造对象；
2. 禁止用户构造和析构对象；

参考：How do you implement the Singleton design pattern?