#include <iostream>
using namespace std;

template<typename Type>
class AutoRelease
{
    typedef void (Type::* pFunc)(void);
public:
    AutoRelease(Type* p, pFunc pfunc)
        :m_class(p), m_pFunc(pfunc)
    {}
    ~AutoRelease()
    {
        cout<< "release memory"<<endl;
        (m_class->*m_pFunc)();
    }
private:
    Type* m_class;
    pFunc m_pFunc;
};

class TestClass
{
public:
    TestClass(){cout<<"TestClass()"<<endl;}
    void release()
    {
        cout<<"release()"<<endl;
        delete ptr;
        ptr = NULL;
    }
    void excute(void)
    {
        AutoRelease<TestClass> autoR(this, &TestClass::release);
        cout<<"excute()"<<endl;
        this->testMem();
    }
    void testMem(void)
    {
        if(NULL == ptr)
        {
            cout<< "ptr is NULL" <<endl;
        }
        else
        {
            cout << "ptr is not NULL" <<endl;
        }
    }
    void testInt()
    {
        cout<<this->tempVal<<endl;
    }
    static TestClass* getInstance();
    int tempVal;
private:
    static TestClass* ptr;    
};

TestClass* TestClass::ptr = NULL;
TestClass* TestClass::getInstance()
{
    if(NULL == ptr)
    {
        ptr = new TestClass;
    }
    return ptr;
}

int main(void)
{
    TestClass* p = TestClass::getInstance();
    p->excute();
    p->testMem();
    cout << (NULL==p)<< endl;
    p->excute();
    p->testMem();
    delete p;

    TestClass* p1 =new TestClass;
    p1->tempVal = 100;
    delete p1;
    delete p1;
    /* 
     把p1=NULL 的注释打开和关闭，运行对比下。
     可以参考 深入探究C++对象模型 中“成员函数调用” 解释
    */
    //p1 = NULL;
    p1->testMem();
    
    p1->testInt(); //思考：为什么delete之后还可以执行？ NULL 还可以调用成员函数？
    p1->testInt();
    p1->testInt();
    return 0;
}