doubt in virtual funtion

[sridhard2406]

Hi All,
I am new to c++, please find my program below and my doubt as mentioned below.

#include <iostream>
using namespace std;
 
class base
{
    public:
        virtual void Show(void)
        {
            cout << "base:Show" << endl;
            return ;
        }
        void Test(base obj)
        {
            obj.Show();
        }
};
class derived:public base
{
    public:
        void Show(void)
        {
            cout << "derived:Show" << endl;
            return ;
        }
};
int main(int argc, char **argv)
{
    derived d1;
    derived d2;
    d1.Test(d2);
    return 0;
}
 
 

When I call this d1.Test(d2) , its always refers baseclass show funtion( ).Why its refering always base class member funtion. please let me know, what is referring in the backend!

[Banfa]

The parameter of test has type base. That is it passes an object. What actually happens is the base copy constructor is called to construct a new base object from the derived object d2 that is passed. Inside test since obj has type base it calls base::Show.

I suspect you intended to pass a reference to base into test, base& then when you call test it will pass a base reference to d2 but when you call Show it will call derived::Show because the object is actually a derived object even though it is a base reference.