c++类型转换之dynamic_cast

dynamic_cast仅用于对象的指针和引用，它确保类型转换记过是一个完全合法的请求类对象。

因此，dynamic_cast在转换一个类到一个其基类的时候，总是成功：

    class CBase{ };  
    class CDerived:public CBase{ };  
    CBase b; CBase* pb;  
    CDerived d; CDerived* pd;  
    pb = dynamic_cast
  
   (&d);    // ok:derived-to-base  
    pd = dynamic_cast
   
    (&b); // wrong:base-to-derived 
   
  

在此程序片段中的第二个转换会产生一个编译错误，因为在dynamic_cast中基类到继承类转换是不允许的，除非基类是多态的。

那下面例子只要在基类中添加一个虚函数，基类就支持多态了：

class CBase
{
public:
	virtual void test(){};
};
class CDerived:public CBase
{
};

int main()
{
	CBase *b= new CDerived();
	CBase *pb;
	CDerived d;
	CDerived* pd;
	pb = dynamic_cast
  
   (&d);
	pd = dynamic_cast
   
    (b); } 
   
  

class Animal   {public: virtual ~Animal(){};   int m1; };
class Creature {public: virtual ~Creature(){}; int m2; };

class Bird:public Animal, public Creature { };


int main()
{
         Bird *bird = new Bird;
        Creature *creature = dynamic_cast
   
    (bird);//case 1
        Animal *animal = dynamic_cast
    
     (creature);//case 2 Creature *creature1 = new Creature; Animal *animal1 = dynamic_cast
     
      (creature1);//case 3这个也能正常执行，我就很奇怪了，谁能告诉我？ }