RTTI (Run-time type information) in C++

　　In C++, RTTI (Run-time type information) is available only for the classes which have at least one virtual function.

　　For example, dynamic_cast uses RTTI and following program fails with error “cannot dynamic_cast `b’ (of type `class B*’) to type `class D*’ (source type is not polymorphic) ” because there is no virtual function in the base class B.

#include<iostream>

using namespace std;

class B 
{ 
};
class D: public B 
{
};

int main()
{
    B *b = new D;
    D *d = dynamic_cast<D*>(b);
    if(d != NULL)
    {
        cout<<"works";
    }
    else
    {
        cout<<"cannot cast B* to D*";
    }
    getchar();
    return 0;
}

　　Adding a virtual function to the base class B makes it working.

#include<iostream>

using namespace std;

class B 
{ 
public:
    virtual void fun()
    {
    }
};
class D: public B 
{
};

int main()
{
    B *b = new D;
    D *d = dynamic_cast<D*>(b);
    if(d != NULL)
    {
        cout<<"works";
    }
    else
    {
        cout<<"cannot cast B* to D*";
    }
    getchar();
    return 0;
}

　　

　　Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

　　转载请注明：http://www.cnblogs.com/iloveyouforever/

　　2013-11-26　　21:13:16