Cast to derived class?

Hi all,

lately I had a problem where I wanted to cast a basic class to a
derived type, which did not introduce any new members and did not
change any stuff with dynamically allocated memory. I just wanted to
add some methods to the class.

So my question is:
Is it valid C++ to create a basic class and to cast it to a derived
one the way I did in my example below? The example works fine for
MinGW, but I'm not sure if this is ABI dependent.

Example code:

<code>

#include <stdio.h>

class Basic {

public:
    Basic(int a, int b) {
        a_ = a;
        b_ = b;
    };

    int getA() {
        return a_;
    };
    int getB() {
        return b_;
    };

private:
    int a_, b_;
};

class Derived : Basic {

public:
    Derived(int a, int b) : Basic(a, b) {}
    ;

    int multiply() {
        return getA() * getB();
    };
};

int main() {
    Basic *basic = new Basic(2, 4);

    Derived *derived = (Derived *)basic;
    printf("%d * %d = %d\n", basic->getA(), basic->getB(), derived-


    delete basic;

    return 0;
}

</code>