[GeekBand]|[GeekBand] C++面向对象高级编程-2 [GeekBand]C++面向对象高级编程

对象模型（Object Model）
C++对象的内容分为数据成员（class data members）与成员函数（class member functions），其中数据成员又可分为静态数据成员、非静态数据成员两类，成员函数又可分为静态函数、非静态函数与虚函数三类。
存在虚函数的类对象里连续存放着虚函数表指针（Vptr）与静态数据成员，Vptr 指向虚函数表（Vtbl），Vtbl 存放于其他区域，而Vtbl里连续存放着此类对象的所有虚函数的地址。

class Base {private: int i; double d; public: virtual f( ) {} virtual g( ) {}};

【[GeekBand]|[GeekBand] C++面向对象高级编程-2】可以通过如下代码验证虚函数的相关机制：
定义一种函数指针类型 Fun：

typedef void(*Fun)(void);

定义Base类的对象 b：

Base b;

虚函数表指针（Vptr）的地址：(int*)(&b)；
虚函数表（Vtbl）的地址：*((int*)(&b)) ；
第一个虚函数 f( ) 的地址：(int*)*(int*)(&b) + 0，或：(int*)(*(int*)(&b)) + 0；
第二个虚函数 g( ) 的地址: (int*)*(int*)(&b) + 1，或：(int*)(*(int*)(&b)) + 1；
将第一个虚函数的地址转化为Fun类型的函数指针：(Fun)*((int*)*(int*)(&b) + 0)。
验证程序如下：

// ObjectModel.cpp #include #include using namespace std; class Fruit{ int no = 1; double weight = 0.1; char key = 'k'; public: Fruit(int _no, double _weight, char _key): no(_no), weight(_weight), key(_key) { cout << "Calling Fruit(int, double, char)..." << endl; } Fruit() { cout << "Calling Fruit()..." << endl; } void print() {} virtual void process(){ cout << "Fruit::process()" << endl; } virtual ~Fruit() { cout << "Calling ~Fruit()..." << endl; } }; class Apple: public Fruit{ int size = 2; char type = 't'; public: Apple(int _no, double _weight, char _key, int _size, char _type) : Fruit(_no, _weight, _key), size(_size), type(_type) { cout << "Calling Apple(int, double, char, int, char)..." << endl; } Apple() { cout << "Calling Apple()..." << endl; } void save() {} virtual void process(){ cout << "Apple::process()" << endl; } virtual ~Apple() { cout << "Calling ~Apple()..." << endl; } }; void* myAlloc(size_t size) { return malloc(size); } void myFree(void* ptr) { return free(ptr); }inline void* operator new(size_t size) { cout << "global new()... \n"; return myAlloc(size); } inline void operator delete(void* ptr) { cout << "global delete()... \n"; myFree(ptr); }int main() { cout << "---------------------------------------------------" << endl; cout << "size of int: " << sizeof(int) << ", " << "size of double: " << sizeof(double) << ", " << "size of char: " << sizeof(char) << endl; cout << "size of Fruit: " << sizeof(Fruit) << endl; cout << "size of Apple: " << sizeof(Apple) << endl; Fruit fr; Apple ap; cout << "Address of Vptr in fr: " << (int*)(&fr) << endl; cout << "Address of Vptr in ap: " << (int*)(&ap) << endl; cout << "Address of Vtbl in fr: " << *((int*)(&fr)) << endl; cout << "Address of Vtbl in ap: " << *((int*)(&ap)) << endl; cout << "Address of Vfunc of fr: " << (int*)(*((int*)(&fr))) << endl; cout << "Address of Vfunc of ap: " << (int*)(*((int*)(&ap))) << endl; typedef void(*Fun)(void); Fun pFun = NULL; pFun = (Fun)*((int*)(*((int*)(&fr)))); pFun(); pFun = (Fun)*((int*)(*((int*)(&ap)))); pFun(); cout << endl << endl; cout << "------Display Data Member of Fruit Object fr: " << endl; cout << "Address of no: " << (int*)(&fr) + 1 << endl; cout << "no = " <<*((int*)(&fr) + 1) << endl; cout << "Address of weight: " << (double*)((int*)(&fr) + 2) << endl; cout << "weight = " << *((double*)((int*)(&fr) + 2)) << endl; cout << "Address of key: " << (int*)(((double*)((int*)(&fr) + 2)) + 1) << endl; cout << "key = " << (char)*(int*)(((double*)((int*)(&fr) + 2)) + 1)<< endl; cout << "------Display Data Member of Apple Object ap: " << endl; cout << "Address of no: " << (int*)(&ap) + 1 << endl; cout << "no = " <<*((int*)(&ap) + 1) << endl; cout << "Address of weight: " << (double*)((int*)(&ap) + 2) << endl; cout << "weight = " << *((double*)((int*)(&ap) + 2)) << endl; cout << "Address of key: " << (int*)(((double*)((int*)(&ap) + 2)) + 1) << endl; cout << "key = " << (char)*(int*)(((double*)((int*)(&ap) + 2)) + 1)<< endl; cout << "Address of size: " << (int*)(((double*)((int*)(&ap) + 2)) + 1) + 1 << endl; cout << "size = " << *((int*)(((double*)((int*)(&ap) + 2)) + 1) + 1) << endl; cout << "Address of type: " << (int*)(((double*)((int*)(&ap) + 2)) + 1) + 2<< endl; cout << "type = " << (char)*((int*)(((double*)((int*)(&ap) + 2)) + 1) + 2) << endl; cout << "----------------------------------------------------" << endl; Fruit fru = Fruit(4, 3.5, 'l'); Apple app = Apple(6, 4.7, 'm', 2, 'u'); cout << "----------------------------------------------------" << endl; Apple* pApp = new Apple(); delete pApp; cout << "----------------------------------------------------" << endl; return 0; }

以GNU GCC Complier进行测试，运行结果如下图：