Difference between revisions of "Interview Preparation C++ Virtual, Polymorphism and Abstract class"

/* Base class */
class printer {
    public :
        // Pure virtual
        // Abstract class, or an interface
        void pixel()
        {
            puts("printer pixel()");
        }
        void draw_image() {
            // Some complicated algorithm that uses our method ()
            printf("draw_image() is using : ");
            pixel();
        }
};

/* A printer model class inheriting base class */
class model_a : public printer {
    public :
        void pixel() {
            puts("model-a pixel (very sharp)");
        }
};

int main(void)
{
    setvbuf(stdout, 0, _IONBF, 0);
    setvbuf(stdin, 0, _IONBF, 0);

    /* Let's go over simple stuff */
    model_a a;
    a.pixel(); /* Prints "printer pixel" */

    printer p;
    p.pixel(); /* Prints "model-a pixel" */

    /* Let's use a pointer of type "printer" */
    printer *ptr = NULL;
    ptr = &a;
    ptr->pixel(); /* Prints "printer pixel" */
    ptr = &p;
    ptr->pixel(); /* Prints "printer pixel" */

    return 0;
}

void main(void)
{
    /* Let's use a pointer of type "printer" */
    printer *ptr = NULL;
    ptr = &a;
    ptr->print_pixel(); /* Prints "model-a pixel" */
    ptr = &p;
    ptr->print_pixel(); /* Prints "printer pixel" */

    /* Now, model-a's pixel method will be called because the "virtual" is
     * basically an instruction that says :
     * "Here is the function, but if a parent has the same function defined,
     *  then I will call the parent's method instead of the base class method"
     */
}