C++ tidbit - virtual functions and default arguments

Virtual functions are bound dynamically where as default arguments are bound statically

class Base {
    public:
        virtual void func( int x = 10 ) { 
            _x = x;
            std::cout << _x;
        };

   private:
        int _x;
};

class Derived: public Base {
    public:
        virtual void func( int x = 20 ) { 
            _x = x; 
            std::cout << _x; 
        };

   private:
        int _x;
};

int main()
{
    Base *b = new Base();
    std::cout << "Default Value in Base: ";
    b->func();
    std::cout << std::endl;

    Base *d = new Derived();
    std::cout << "Default Value in Derived: ";
    d->func();
    std::cout << std::endl;

    return 0;
}

Output:

Default Value in Base: 10
Default Value in Derived: 10

Default arguments of virtual methods in the base gets statically bound (in our case Base::func() ), hence never override the default values in derived virtual methods, doing so might confuse us with derived object's default behavior.