virtual functions

gistfile1.txt

#include <iostream>

class A {
    public:
        virtual double f () = 0 ;
        double g() { return f() ; } 
} ;

class B : public A {
    public:
        double f() { return 1 ; }
} ;

int main(int argc, char *argv[])
{
    B b ;
    std::cout << b.g() << std::endl ;
    return 0;
}