《Inside the C++ Object Model》关于基类与派生类的Tips

近来阅读《Inside the C++ Object Model》,里边讲到，在C++中多态只存于public class体系中，且只有通过pointer和reference来间接处理。

#include <iostream>using std::cout;using std::endl;class Base{public:virtual void printf(void){cout<< "Base printf"<< endl;}};class Derv : public Base{public:virtual void printf(void){cout<< "Derv printf"<< endl;}};int main(int argc, char** argv){Base* pBase = new Base();Derv* pDerv = new Derv();pBase = pDerv;pBase->printf();cout<<"-------------------------"<< endl;Base* pBase2 = new Derv();pBase2->printf();cout<<"-------------------------"<< endl;Base base;Derv derv;base = derv;base.printf();cout<<"-------------------------"<< endl;Derv derv2;Base &base2 = derv2;base2.printf();getchar();return 0;}

结果如下：

 可见对象base并未调用派生类中的printf()函数，而是继续使用基类的函数。

 不知在哪见过，调用printf()函数时，指向它的this指针属于谁，那么就调用谁的printf()；具体内容待找到后补上。

 例子：

 

#include <iostream>using std::cout;using std::endl;class Base{public:Base(): m_nData(1){}virtual void printf(void){cout<< m_nData<< endl;}private:int m_nData;};class Derv : public Base{public:Derv() : m_nData(2){}virtual void printf(void){cout<< m_nData<< endl;}private:int m_nData;};int main(int argc, char** argv){Base* pBase = new Base();Derv* pDerv = new Derv();pBase = pDerv;pBase->printf();cout<<"-------------------------"<< endl;Base* pBase2 = new Derv();pBase2->printf();cout<<"-------------------------"<< endl;Base base;Derv derv;base = derv;base.printf();cout<<"-------------------------"<< endl;Derv derv2;Base &base2 = derv2;base2.printf();getchar();return 0;}

结果如下：