单例（C）

根据 Wiki ：在软件工程中，单例模式是一种设计模式，它将类的实例化限制为一个对象。

这需要创建一个对象来协调整个系统的操作。

class Singleton
{
    // Private constructor so it can not be arbitrarily created.
    Singleton()
    {}
    // Disable the copy and move
    Singleton(Singleton const&)            = delete;
    Singleton& operator=(Singleton const&) = delete;
  public:

    // Get the only instance
    static Singleton& instance()
    {
        // Use static member.
        // Lazily created on first call to instance in thread safe way (after C++ 11)
        // Guaranteed to be correctly destroyed on normal application exit.
        static Singleton _instance;

        // Return a reference to the static member.
        return _instance;
    }
};