1：什么是多态？ 多态就是多种形态。 满足构成多态的条件：必须有虚函数的重写（函数名，参数，返回值均相同，协变除外） 父类的指针或引用调用虚函数 多态跟类型无关而和对象有关，如果不构成多态则与类型有关 父类必须为虚函数，子类可以是也可以不是，构造函数不能为虚函数。
class A { public: virtual void func()//父类必须为虚函数 { cout << "A::func()" << endl; } protected: int _a; }; class B:public A { public: virtual void func() { cout << "B::func()" << endl; } protected: int _b; }; //void f(A* a) void f(A& a)//父类的指针或引用调用虚函数 { a.func(); } int main() { A a; B b; f(a); f(b); A* p1 = &a; p1->func(); p1 = &b; p1->func(); system("pause"); return 0; }如果A中没有virtual，则以上都调用父类
2：多态的对象模型–单继承&多继承？ 虚函数表是通过一块连续内存来存储虚函数的地址。解决了继承，虚函数（重写）的问题，指明了实际调用虚函数的问题。
#include<iostream> using namespace std; typedef void(*V_FUNC)(); class A { public: virtual void func1() { cout << "A::func1()" << endl; } virtual void func2() { cout << "A::func2()" << endl; } protected: int a; }; class B:public A { public: virtual void func1() { cout << "B::func1()" << endl; } virtual void func3() { cout << "B::func3()" << endl; } virtual void func4() { cout << "B::func4()" << endl; } protected: int b; }; void PrintVtable(int vtable)//打印虚表 { int *vfArray = (int*)vtable; printf("vtable:0x%p\n", vfArray); for (size_t i = 0; vfArray[i] != 0; ++i)//虚表以0结束 { printf("vfunc[%d]:0x%p->", i, vfArray[i]); V_FUNC f = (V_FUNC)vfArray[i]; f(); } cout << endl; } int main() { A a; B b; PrintVtable(*((int*)&a)); PrintVtable(*((int*)&b)); system("pause"); return 0; }由于编译器的优化，在监视窗口中关于B调用的虚函数并不能显示完全，所以需要我们自己写一个打印虚表的函数 以上是单继承的模型 多继承中子集将虚函数存放在第一个继承的虚函数表中
#include<iostream> using namespace std; typedef void(*V_FUNC)(); class A { public: virtual void func1() { cout << "A::func1()" << endl; } virtual void func2() { cout << "A::func2()" << endl; } protected: int a; }; class B { public: virtual void func1() { cout << "B::func1()" << endl; } virtual void func3() { cout << "B::func3()" << endl; } protected: int b; }; class C:public A,public B { public: virtual void func1() { cout << "C::func1()" << endl; } virtual void func3() { cout << "C::func3()" << endl; } virtual void func4() { cout << "C::func4()" << endl; } protected: int c; }; void PrintVtable(int vtable) { int *vfArray = (int*)vtable; printf("vtable:0x%p\n", vfArray); for (size_t i = 0; vfArray[i] != 0; ++i) { printf("vfunc[%d]:0x%p->", i, vfArray[i]); V_FUNC f = (V_FUNC)vfArray[i]; f(); } cout << endl; } int main() { C c; PrintVtable(*((int*)&c));//A的虚表 PrintVtable(*(int*)((char*)&c + sizeof(A)));//B的虚表在A的虚表之后，相差sizeof（A） system("pause"); return 0; }如func1（），A和C中都有，则进行虚函数重定义 3：多态的对象模型–菱形继承和菱形虚拟继承？
#include<iostream> using namespace std; typedef void(*V_FUNC)(); class A { public: virtual void func1() { cout << "A::func1()" << endl; } virtual void func2() { cout << "A::func2()" << endl; } protected: int a; }; class B:public A { public: virtual void func1() { cout << "B::func1()" << endl; } virtual void func3() { cout << "B::func3()" << endl; } protected: int b; }; class C:public A { public: virtual void func1() { cout << "C::func1()" << endl; } virtual void func4() { cout << "C::func4()" << endl; } protected: int c; }; class D :public B, public C { public: virtual void func5() { cout << "D::func5()" << endl; } protected: int d; }; void PrintVtable(int vtable) { int *vfArray = (int*)vtable; printf("vtable:0x%p\n", vfArray); for (size_t i = 0; vfArray[i] != 0; ++i) { printf("vfunc[%d]:0x%p->", i, vfArray[i]); V_FUNC f = (V_FUNC)vfArray[i]; f(); } cout << endl; } int main() { D d; PrintVtable(*((int*)&d)); PrintVtable(*(int*)((char*)&d + sizeof(B))); system("pause"); return 0; }菱形虚拟继承
class A { public: virtual void func1() { cout << "A::func1()" << endl; } virtual void func2() { cout << "A::func2()" << endl; } public: int _a; }; class B : virtual public A { public: virtual void func1() { cout << "B::func1()" << endl; } virtual void func3() { cout << "B::func3()" << endl; } public: int _b; }; class C : virtual public A { virtual void func1() { cout << "C::func1()" << endl; } virtual void func3() { cout << "C::func3()" << endl; } public: int _c; }; class D : public B, public C { virtual void func1() { cout << "D::func1()" << endl; } virtual void func4() { cout << "D::func4()" << endl; } public: int _d; };菱形虚拟继承（B，C共用A的虚表，各自有独立的虚表）
