dynamic_cast

#include <typeinfo>

using std::bad_cast;



#include <iostream>

using std::cout; using std::endl;



struct A { virtual ~A() { } };

struct B : virtual public A { /* . . . */ };

struct C : public B { /* . . . */ };

struct D : public B, virtual public A { /* . . . */ };



void exercises() {

    A *pa = new C;

    if (B *pb = dynamic_cast< B* >(pa))

         cout << "cast from C to B* ok" << endl;

    else

         cout << "cast from C to B* not ok" << endl;

    B *pb = new B;

    if (C *pc = dynamic_cast< C* >(pb))

         cout << "cast from B to C* ok" << endl;

    else

         cout << "cast from B to C* not ok" << endl;



    A *pc = new C;

    if (B *pb = dynamic_cast< B* >(pc))

         cout << "cast C to B* ok" << endl;

    else

         cout << "cast C to B* not ok" << endl;



    A *pd = new D;

    if (B *pb = dynamic_cast< B* >(pd))

         cout << "cast D to B* ok" << endl;

    else

         cout << "cast D to B* not ok" << endl;

}



struct Base {

   virtual ~Base() {};

};



struct Derived: public Base { };



void cast_to_ref(const Base &b)

{

    try {

        const Derived &d = dynamic_cast<const Derived&>(b);

    cout<<"success"<<endl;

    // use the Derived object to which b referred

    } catch (bad_cast) {

        cout << "called f with an object that is not a Derived" << endl;

    }

}



int main()

{

    Base *bp; 

    bp = new Derived;  // bp actually points to a Derived object

    if (Derived *dp = dynamic_cast<Derived*>(bp)) 

    {

        // use the Derived object to which dp points

    } else {  // bp points at a Base object

        // use the Base object to which bp points

    }



    exercises();

    

    cast_to_ref(*bp);

    cast_to_ref(Base());

}

j结果如下：

cast from C to B* ok

cast from B to C* not ok

cast C to B* ok

cast D to B* ok

success

called f with an object that is not a Derived