dyncast2.cpp

来自「本课程主要介绍面向对象程序设计的方法和c++语言的基本概念。以c++语言中的面向」· C++ 代码 · 共 48 行

//dyncast2.cpp
//tests dynamic casts
//RTTI must be enabled in compiler
#include <iostream>
#include <typeinfo>            //for dynamic_cast
using namespace std;
////////////////////////////////////////////////////////////////
class Base
   {
   protected:
      int ba;
   public:
      Base() : ba(0)
         {  }
      Base(int b) : ba(b)
         {  }     
      virtual void vertFunc()  //needed for dynamic_cast
         {  }
      void show()
         { cout << "Base: ba=" << ba << endl; }
   };
////////////////////////////////////////////////////////////////
class Derv : public Base
   {
   private:
      int da;
   public:
      Derv(int b, int d) : da(d)
         { ba = b; }
      void show()
         { cout << "Derv: ba=" << ba << ", da=" << da << endl; }
   };
////////////////////////////////////////////////////////////////
int main()
   {
   Base* pBase = new Base(10);          //pointer to Base
   Derv* pDerv = new Derv(21, 22);      //pointer to Derv

   //derived-to-base: upcast -- points to Base subobject of Derv
   pBase = dynamic_cast<Base*>(pDerv);
   pBase->show();                       //"Base: ba=21"

   pBase = new Derv(31, 32);            //normal
   //base-to-derived: downcast -- (pBase must point to a Derv)
   pDerv = dynamic_cast<Derv*>(pBase);
   pDerv->show();                       //"Derv: ba=31, da=32"
   return 0;
   }