#include <iostream> using namespace std; class CBasic { public:      virtual int test(){return 0;} // 一定要是 virtual }; class CDerived : public CBasic { public:      virtual int test(){    return 1;} }; int main() {      CBasic        cBasic;      CDerived    cDerived;      CBasic * pB1 = new CBasic;      CBasic * pB2 = new CDerived;      //dynamic cast failed, so pD1 is null.      CDerived * pD1 = dynamic_cast<CDerived * > (pB1);         //dynamic cast succeeded, so pD2 points to  CDerived object                                              CDerived * pD2 = dynamic_cast<CDerived * > (pB2);         //dynamci cast failed, so throw an exception.             //    CDerived & rD1 = dynamic_cast<CDerived &> (*pB1);    //dynamic cast succeeded, so rD2 references to CDerived object.      CDerived & rD2 = dynamic_cast<CDerived &> (*pB2);         return 0; }