int _tmain(int argc, _TCHAR* argv[]) { //知识点:注意区分指针类型(编译时确定)和对象类型(运行时确定). 总之,非虚方法是根据指针类型来调用,虚方法是根据对象类型来调用 //指针类型(CBase) 对象类型(CDerived()) //CBase *pBase = new CDerived(); CBase base; cout << "sizeof(base):" << sizeof(base) << endl; // 4 cout << sizeof(long long) << endl; //base.Test(); CDerived derived; cout << "sizeof(derived):" << sizeof(derived) << endl; derived.name(); derived.derived_print(); CBase* p = &derived; //隐式向上强制转换 //当一个derived class object被交出去当作一个base class object时, //它原本所以“成为一个derived class object”的所有特征,都会被切除(slicing)掉,只留下内部一个base class object。 //以by reference的方式传递参数,有另一个优点:可避免所谓的“切割(slicing)问题”。引用是除指针外另一个可以产生多态效果的手段。 Test1(derived);//Output from CBase! 出现切割 Test2(derived);//Output from CDerived! Test3(p); //Output from CDerived! cout << "打印指针自身内存地址:" << &p << endl; cout << "打印指针指向内存地址:" << (int *)p << endl; p->show(); //p->range();//编译错误.“range”: 不是“CBase”的成员 CDerived* derived2 = (CDerived *)&base; //显式向下强制转换 derived2->range();//调用派生类独有的方法,不安全操作(如果方法内有访问CDerived独有的成员变量,用到this指针就会出问题) CDerived* derived3 = dynamic_cast<CDerived*>(&base);//用dynamic_cast来转换类型可以检查转换是否安全成功,失败返回空指针 if (derived3) { cout<< "derived3 dynamic_cast successful !!" <<endl; derived3->range(); } else { cout<< "derived3 dynamic_cast failed !!" <<endl; } CDerived* derived4 = dynamic_cast<CDerived*>(p); if (derived4) { cout<< "derived4 dynamic_cast successful !!" <<endl; derived4->range(); } else { cout<< "derived4 dynamic_cast failed !!" <<endl; } derived2->Test();//Output from CBase (根据对象类型来判断) CBase *pBase = new CDerived(); /*虚析构: 如果一个类用作基类,我们通常需要virtual来修饰它的析构函数,这点很重要。 如果基类的析构函数不是虚析构,当我们用delete来释放基类指针(它其实指向的是派生类的对象实例)占用的内存的时候, 只有基类的析构函数被调用,而派生类的析构函数不会被调用,这就可能引起内存泄露。如果基类的析构函数是虚析构, 那么在delete基类指针时,继承树上的析构函数会被自低向上依次调用,即最底层派生类的析构函数会被首先调用, 然后一层一层向上直到该指针声明的类型。*/ delete pBase; Person *person = new Person(); person->showAge(); person->show1(); printf("%d\n", Person::date); Children *children = new Children(); printf("%d\n", Children::date); children->show1(); Person *person1 = children; //show2()没有使用virtual关键字,程序将根据引用或者指针类型选择方法。忠告:绝对不要重新定义继承而来的非虚拟函数 person1->show2(); //Person::show2() Children* children2 = (Children*)person;//显式向下强制转换 children2->show2(); //Children::show2() 发现转型之后还是可以调用Children的函数的,因为编译的时函数内存地址已经确定,如果函数里面需要用到this指针调用到成员变量就不安全 Person *person2 = new Children(); //person2->show4(); person2并不能调用show4(),只能调用Person类方法; person2->hide(); //children->hide(); //Person的hide()函数给隐藏了,不能调用 children->hide(1); //子类在外部调用父类方法!!!!好奇怪的语法 Children child; child.Person::show2(); Children *pChild = new Children(); pChild->Person::show2(); //测试覆盖 person1->testOverride(10); person2->testOverride(10); children->testOverride(10); system("Pause"); return 0; }