任何人都可以为我提供 C++ 中的单例示例吗?

2021-12-22 00:00:00 design-patterns singleton c++

我用以下方式编写了一个单例 C++:

I write a singleton c++ in the follow way:

class A {
    private:
        static A* m_pA;
        A();
        virtual ~A();

    public:
        static A* GetInstance();
        static void FreeInstance();

        void WORK1();
        void WORK2();
        void WORK3();
    }
}

A* A::GetInstance() {
    if (m_pA == NULL)
        m_pA = new A();
    return m_pA;
}

A::~A() {
    FreeInstance()  // Can I write this? are there any potential error?
}

void A::FreeInstance() {
    delete m_pA;
    m_pA = NULL;
}

谢谢！Evan Teran 和 sep61.myopenid.com 的回答是正确的，而且非常好！我的方法是错误的，我希望任何编写这样代码的人都可以避免我的愚蠢错误.

Thanks! Evan Teran and sep61.myopenid.com 's answer is right, and really good! My way is wrong, I wish any one writting such code can avoid my silly mistake.

我的项目中的单例A有一个智能指针向量，另一个线程也可以编辑这个向量，所以当应用程序关闭时，即使我添加了很多CMutex，它也会变得不稳定.多线程错误 + 单例错误浪费了我 1 天时间.

//-----------------------------------------------------------一个新的单例，如果您认为以下示例有问题，欢迎您

My singleton A in my project has a vector of smart pointer, and another thread can also edit this vector, so when the application is closing, it always become unstable even I add lots of CMutex. Multithread error + singleton error wasted me 1 day.

//----------------------------------------------------------- A new singleton, you are welcome to edit if you think there is any problem in the following sample:

class A {
    private:
        static A* m_pA;
        explicit A();
        void A(const A& a);
        void A(A &a);
        const A& operator=(const A& a);
        virtual ~A();

    public:
        static A* GetInstance();
        static void FreeInstance();

        void WORK1();
        void WORK2();
        void WORK3();
    }
}

A* A::GetInstance() {
    if (m_pA == NULL){
        static A self;
        m_pA = &self;
    }
    return m_pA;
}

A::~A() {
}

推荐答案

您可以使用像这样的静态对象来避免删除它:

You can avoid needing to delete it by using a static object like this:

if(m_pA == 0) {
    static A static_instance;
    m_pA = &static_instance;
}

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