单例模式

#include <iostream>

class SingleTone
{
private:
    int m_iProp;

public:
    static SingleTone& GetInstance()
    {
        static SingleTone instance;
        return(instance);
    }

    void SetProp(int val)
    {
        m_iProp = val;
    }

    int GetProp() const
    {
        return (m_iProp);
    }

private:
    SingleTone() : m_iProp(0)
    {
    }
    // SingleTone instance = SingleTone::GetInstance() is not allowed;
    // SingleTone& instanceRef = SingleTone::GetInstance() is correct.
    SingleTone(const SingleTone&);
};

class MonoState
{
private:
    static MonoState*  s_pInstance;

private:
    int m_iProp;

public:
    static MonoState& GetInstance()
    {
        if(0 == s_pInstance)
            s_pInstance = new MonoState;
        return(*s_pInstance);
    }

public:
    void SetProp(int val)
    {
        m_iProp = val;
    }

    int GetProp() const
    {
        return(m_iProp);
    }

private:
    MonoState() : m_iProp(0)
    {
    }

    MonoState(const MonoState&);
};

MonoState* MonoState::s_pInstance = 0;


int main(int argc, char* argv[])
{
    SingleTone& firstInstance = SingleTone::GetInstance();
    firstInstance.SetProp(10);
    std::cout << "firstInstance: " << firstInstance.GetProp() << std::endl;

    SingleTone& secondInstance = SingleTone::GetInstance();
    std::cout << "secondInstance: " << secondInstance.GetProp() << std::endl;


    MonoState& firstMonostate = MonoState::GetInstance();
    firstMonostate.SetProp(10);
    std::cout << "firstMonostate: " << firstMonostate.GetProp() << std::endl;

    MonoState& secondMonostate = MonoState::GetInstance();
    std::cout << "secondMonostate: " << secondMonostate.GetProp() << std::endl;

    return(0);
}