Virtual Functions

Consider the following:

#include <iostream>

using namespace std;

class A
{
public:
    virtual void func1( int a ){ cout<<"A::func1"; }
    virtual void func2( int i=20  ){ cout<<i; }
};

class B: public A
{
public:
    void func1( float a ){ cout<<"B::func1"; }
    void func2( int i=40 ){ cout<<i; }
};

int main(int argc, char* argv[])
{
    A* pb=new B;
    pb->func1(1);
    pb->func2();
    return 0;
}

Can you guess the output for the same?

pb->func1(1) => A::func1!! This is so, because, B::func1 hides( as a result of overloading) A::func1, rather then override it. And in C++, overload resolution is done on the static type, as it is done at compile time.

pb->func2() => 20!! This is so because, although B::func2 is called, the compiler picks up the default value from the base class. So, default values should be the same down the class hierarchy.

As an aside, the C++ standard states that built in conversions have more priority then user defined conversions.

Source: http://www.gotw.ca/gotw/005.htm