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C ++ Singleton设计模式

design-pattern

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?


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2020-07-30

共1个答案

小编典典

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

2020-07-30

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