Segmentation fault on accessing virtual function of base class by base class pointer

Code:

---

#include<iostream>
using namespace std;
class A
{
        public:
        virtual void s()
        {
                cout<<"I am in A"<<endl;
        }
};
class B:public A
{
        public:
        void s()
        {
                cout<<"I am in B"<<endl;
        }
};
int main()
{
        A *o;
        o->s();                                  //Problem
        B ob;
        o=&ob;
        o->s();
        return 0;
}

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Though that virtual function is accessible if I call it inside derived class' s(); using scope resolution, i.e.:

Code:

---

void s()
        {
                A::s();
                cout<<"I am in B"<<endl;
        }

---

Why can't I call base class (A's) virtual function by base class pointer?

'o' is not pointing to anything (well, technically it's pointing to an undefined location)

isn't o pointing to location of s() of base location?

Quote:

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Originally Posted by gaurav#

isn't o pointing to location of s() of base location?

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No, you have to initialise it to point to an object. E.g.

Code:

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        A foo;
        A *o = &foo;

        o->s();

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Sorry, that was real basic I've missed!!! :(