C ++ Singleton设计模式

Question

最近，我碰到了C ++的Singleton设计模式的实现/实现。它看起来像这样（我从现实生活的示例中采用了它）：

// a lot of methods are omitted here
class Singleton
{
   public:
       static Singleton* getInstance( );
       ~Singleton( );
   private:
       Singleton( );
       static Singleton* instance;
};

从该声明中，我可以推断出实例字段是在堆上初始化的。这意味着存在内存分配。对我来说，完全不清楚的是何时确切地将要释放内存？还是有错误和内存泄漏？似乎实现中存在问题。

我的主要问题是，如何以正确的方式实施它？

Answer 1

在2008年，我提供了Singleton设计模式的C ++ 98实现，该模式是延迟评估，保证销毁，技术上不是线程安全的。

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
};

Dobbs博士：C ++和双重检查锁定的风险：第一部分