单例模式Singleton(线程不安全)

#include <iostream>

class TestClass
{
public:
    TestClass()
        :x(0)
    {
    }
    ~TestClass(){}
    void Inc() { x++;}
    void Show(){ std::cout << "x = " << x << std::endl;}

private:
    int x;
};

template <typename T>
class Singleton
{
public:
    static T* getPointer()
    {
        if(m_instance != 0)
        {
            return reinterpret_cast<T*>(m_instance);
        }

        T* instance = new T();

        m_instance = reinterpret_cast<void*>(instance);

        return instance;
    }

    static T & instance()
    {
        return *getPointer();
    }

    static void release()
    {
        if(m_instance)
        {
            delete m_instance;
            m_instance = NULL;
        }
    }

private:
    static void* m_instance;
};

template<typename T>
void* Singleton<T>::m_instance = 0;

int main()
{
    for(int i = 0; i < 10; ++i)
    {
        Singleton<TestClass>::instance().Inc();
        Singleton<TestClass>::instance().Show();
    }

    Singleton<TestClass>::release();

    system("pause");

    return 0;
}

程序运行结果:

x = 1
x = 2
x = 3
x = 4
x = 5
x = 6
x = 7
x = 8
x = 9
x = 10